Background. Accurate acetabular cup positioning is considered to be essential to prevent postoperative dislocation and improve the long-term outcome of total hip arthroplasty (THA). Recently various devices such as navigation systems and patient-specific guides have been used to ensure the accuracy of acetabular cup positioning. Objectives. The present study evaluated the usefulness of CT-based three-dimensional THA preoperative planning for acetabular cup positioning. Methods. This study included 120 hips aged mean 68.3 years, who underwent primary THA using CT-based THA preoperative planning software ZedHip® (LEXI, Tokyo Japan) and postoperative CT imaging (Fig.1). The surgical approach adopted the modified Watson-Jones approach in the lateral decubitus position and Trident HA acetabular cups were used for all cases. Preoperatively the optimum cup size and position in the acetabular were decided using the ZedHip® software, taking into consideration femoral anteversion and to achieve the maximum range of motion in dynamic motion simulation. Radiographic inclination (RI) was selected in the range between 40°∼45° and radiographic anteversion (RA) in the range between 5°∼25°. Three-dimensional planning images of the cup positioning were obtained from the ZedHip® software, and the distances between the edge of the implant and anatomical landmarks such as the edge of the anterior or superior acetabular wall were measured on the three-dimensional images and recorded (Fig.2). Intraoperatively, the RI and RA were confirmed by reference to these distances and the acetabular cup was inserted. Relative positional information of the implant was extracted from postoperative CT imaging using the ZedHip® software and used to reproduce the position of the implant on preoperative CT imaging with the software image matching function. The difference between the preoperative planning and the actual implant position was measured to assess the accuracy of acetabular cup positioning using the ZedHip® software. Results. Actual cup size corresponded with that of preoperative planning in 95% of cases (114 hips). Postoperative mean RI was 42.3° ± 4.2° (95% confidence interval (CI), 41.5° ∼ 43.0°) and mean RA was 16.1° ± 5.9° (95%CI, 15.0° ∼ 17.1°). Deviation from the target RI was 4.2° ± 3.7° (95%CI, 3.5° ∼ 4.9°) and deviation from the target RA was 4.0° ± 3.6° (95%CI, 3.4° ∼ 4.7°). Overall 116 hips (96.7%) were within the RI safe zone (30° ∼ 50°) and 108 hips (90.0%) were within the RA safe zone (5° ∼ 25°), and 105 hips (87.5%) were within both the RI and RA safe zones (Fig.3). Mean cup shift from preoperative planning was 0.0mm ± 3.0mm to the cranial side in the cranio-caudal direction, 2.1mm ± 3.0mm to the anterior side in the antero-posterior direction, and 1.7mm ± 2.1mm to the lateral side in the medio-lateral direction. Conclusion. The accuracy of acetabular cup positioning using our method of CT-based three-dimensional THA preoperative planning was slightly inferior to reported values for CT-based navigation, but obviously superior to those without navigation and similar to those with portable navigation. CT-based three-dimensional THA preoperative planning is effective for acetabular cup positioning, and has better cost performance than expensive CT-based navigation. For any figures or tables, please contact the authors directly

INTRODUCTION. Additive manufacturing (3D printing) is used to create porous surfaces that promote bone ingrowth in an effort to improve initial stability and optimize long-term biological fixation. The acetabular cup that was studied is manufactured with titanium alloy powder via electron beam melting. Electron beam melting integrates the porous and solid substrate rather than sintering a porous coating to a solid surface. The 3D-printed acetabular cup's high surface coefficient of friction (up to 1.2), combined with its geometry, creates a predictable press-fit in the acetabulum, improving initial mechanical stability and ultimately leading to reproducible biologic fixation. The objective of this study was to evaluate the early clinical outcomes and implant fixation of this 3D-printed acetabular cup in total hip arthroplasty (THA). METHODS. Four hundred twenty-eight subjects from 8 US and international research sites underwent primary THA with the 3D-printed acetabular cup. All sites received IRB approval prior to conducting the study, and all participants signed the informed consent. Screw usage and number used during surgery were used as a surrogate measurement for initial implant fixation. Clinical performance outcomes included pre- and post-operative Harris Hip Scores (HHS) and Oxford Hip Scores (OHS), patient satisfaction, and revision assessment. 215 patients had a minimum 1-year post-operative follow-up visit. Student t-tests were used to identify significant mean differences (p<0.05). RESULTS. Acetabular screws were used in 206 of 428 cases (48.1%); 85.9% used 1 screw, 12.6% used 2 screws, and 1.5% used 3 screws. For patients with a 1-year post-operative visit, the HHS improved by 49.8 points to 91.9 from 42.1, and the OHS improved by 27.7 points to 44.4 from16.7. Patient satisfaction scores at the 1-year post-operative visit were 9.7±0.7 (n=94). There was no significant difference between genders with regard to BMI, the 1-year post-operative HHS, OHS, or patient satisfaction scores. However, the males were significantly younger (59.8 vs. 62.9 years) and had significantly higher pre-operative HHS (45.7 vs. 37.9) and OHS scores (17.8 vs. 15.3). There were 9 revisions reported. DISCUSSION. For initial implant fixation, compared to a similar, non-3D-printed acetabular cup in the same product line, the 3D-printed cup used significantly fewer screws per case (n=1 for 85.9% cases vs. n=2 for 85.7% of cases) in a fewer percentage of cases (48.1% vs. 70.4%), suggesting greater initial stability and “scratch fit”. The 3D-printed acetabular cup also displayed positive early clinical results as evidenced by the pronounced improvement in clinical outcome scores from the pre-operative visit to the 1-year post-operative visit. These 1-year improvements are better than moderate clinically important improvements reported in the literature (40.1 points for HHS). Patient satisfaction scores were also excellent (9.7/10). There were nine revisions; however, four of these were due to patient falls and one was due to infection. SIGNIFICANCE. The 3D-printed acetabular cup evaluated in this study demonstrated improved implant fixation and positive early clinical outcomes for THA

The angle of acetabular inclination is an important measurement in total hip replacement (THR) procedures. Determining the acetabular component orientation intra-operatively remains a challenge. An increasing number of innovators have described techniques and devices to achieve it. This paper describes a mechanical inclinometer design to measure intra-operative acetabular cup inclination. Then, the mechanical device is tested to determine its accuracy. The aim was to design an inclinometer to measure inclination without existing instrumentation modification. The device was designed to meet the following criteria: 1. measure inclination with acceptable accuracy (+/− 5o); 2. easy to use intra-operatively (handling & visualization); 3. adaptable and useable with majority of instrumentation kits without modification; 4. sterilizable by all methods; 5. robust/reusable. The prototype device was drafted by computer aided design (CAD) software. Then a prototype was constructed using a 3D printer to establish the final format. The final device was CNC machined from SAE 304 stainless steel. The design uses an eccentrically weighted flywheel mounted on two W16002-2RS ball bearings pressed into symmetrical housing components. The weighted wheel is engraved with calibrated markings relative to its mass centre. Device functioning is dependent on gravity maintaining the weighted wheel in a fixed orientation while the housing can adapt to the calibration allowing for determining the corresponding measurement. The prototype device accuracy was compared to a digital device. A digital protractor was used to create an angle. The mechanical inclinometer (user blinded to digital reading) was used to determine the angle and compared to the digital reading. The accuracy of the device compared to the standard freehand technique was assessed using a saw bone pelvis fixed in a lateral decubitus position. 18 surgeons (6 expert, 6 intermediate, 6 novice) were asked to place an uncemented acetabular cup in a saw bone pelvis to a target of 40 degrees. First freehand then using the inclinometer. The inclination was determined using a custom-built inertial measurement unit with the user blinded to the result. Comparison between the mechanical and digital devices showed that the mechanical device had an average error of −0.2, a standard deviation of 1.5, and range −3.3 to 2.6. The average root mean square error was 1.1 with a standard deviation of 0.9. Comparison of the inclinometer to the freehand technique showed that with the freehand component placement 50% of the surgeons were outside the acceptable range of 35–45 degrees. The use of the inclinometer resulted all participants to achieve placement within the acceptable range. It was noted that expert surgeons were more accurate at achieving the target inclination when compared to less experienced surgeons. This work demonstrates that the design and initial testing of a mechanical inclinometer is suitable for use in determining the acetabular cup inclination in THR. Experimental testing showed that the device is accurate to within acceptable limits and reliably improved the accuracy of uncemented cup implantation in all surgeons

INTRODUCTION. Unlike current acetabular cups, this novel ceramic cup has a Ti/HA coating which removes the requirement for assembly into a metal shell which avoiding potential chipping/misalignment and reducing wall thickness [Figure 1]. This study examines the resistance of novel thin-walled, direct to bone fixation ceramic cups to critical impact loads. METHODS. Samples of the smallest (Ø46mm) and largest (Ø70mm) diameter ReCerf. TM. acetabular cups and corresponding femoral head implants were implanted into Sawbones foam blocks considered representative of pelvic cancellous bone. Two different positional configurations were tested and were considered worst case and the extremes of surgical compromise; P1 simulates the cup fully supported by the acetabulum with a high inclination angle (70°) and a vertical impaction axis (worst case loading near the cup rim) and. P2 simulates the cup implanted with a lower inclination (55°) but with the superior section unsupported by acetabulum bone [Figure 2]. For each size, three acetabular cups were tested in each position. The impact fixture was positioned within a drop weight rig above a bed of sand and ≈22mm of pork belly representative of soft tissues damping effect and the implant components aligned to achieve the defined impact point on the cup [Figure 2]. Lateral falls were tested on all available samples applying impact energy of 140J [1] and 3m/s impact velocity [2]. After the lateral fall test, each sample was tested under impact conditions equivalent to a frontal car crash considering a peak impact force of 5.7kN occurring 40ms from initial contact (able to produce acetabular fracture)[3]. RESULTS. None of the testing simulating a lateral fall produced fracture or any other damage to the ceramic acetabular cup. In 7 of the 12 tests, the impact force was sufficient to fracture the foam block representing the periprosthetic bone. The cups showed a good stability within the blocks, with a maximum recorded cup spinning angle relative to the acetabulum of 4.5˚. Subsequent testing simulating a car crash resulted in the fracture of two samples out of 12, one of the largest and one of the smallest ReCerf. TM. cups. In both instances, failure occurred very close to the inner edge. Of the remaining 10 samples no cup fractures were observed. All foam acetabulum blocks were severely damaged and 5 blocks fractured. The maximum recorded cup spinning angle following the car crash impact was 5.8˚. SIGNIFICANCE. Extreme testing scenarios presented here are not a regulatory requirement for manufacturers and have not previously been considered for ceramic acetabular components. Fracture is a possible failure mode of ceramics but this testing has proven that modern ceramics can withstand lateral falls and the large majority can withstand subsequent loading equivalent to head on car-crash; loading under which pelvic bone fracture and significant injury is far more likely to occur than implant fracture

Lewinnek's safe zone recommendation to minimise dislocations was a target of 5–25° for anteversion angle and 30–50° for inclination angle. Subsequently, it was demonstrated that mal-positioning of the acetabular cup can also lead to edge loading, liner fracture, and greater conventional polyethylene wear. The purpose of this study was to measure the effect of acetabular cup position on highly crosslinked polyethylene wear in total hip arthroplasty (THA) at long-term follow-up. We identified all patients that underwent primary THA with a minimum of 10 years follow-up using an institutional database in London, Ontario, Canada. Patients with a single implant design consisting of a 28 mm cobalt chromium head and highly crosslinked polyethylene liner (ram extruded, GUR 1050, 100 kGy gamma irradiated, remelted, ethylene oxide sterilised) were selected for inclusion. In total, 85 hips from 79 recruited patients were analysed. Patients underwent a supine radiostereometric analysis (RSA) exam in which the x-ray sources and detectors were positioned to obtain an anterior-posterior and cross-table lateral radiograph. Acetabular cup anteversion angle, inclination angle, and 3D penetration rate (including wear and creep) were measured from the stereo radiograph pairs. At a mean follow-up of 13 years (range, 10–17 years) the mean penetration rate was 0.059 mm/year (95% CI: 0.045 to 0.073 mm/year). Mean anteversion angle was 18.2° (range, −14 to 40°) and mean inclination angle was 43.6° (range, 27 to 61°). With respect to the Lewinnek safe zone, 67% hips met the target for anteversion angle, 77% met the target for inclination angle, and 51% met the target for both. There was no correlation between anteversion angle and penetration rate (r = −0.14, p = 0.72) or between inclination angle and penetration rate (r = 0.11, p = 0.35). There was also no difference (p = 0.07) in penetration rate between hips located within the Lewinnek safe zone for both anteversion angle and inclination angle (mean 0.057 mm/year, 95% CI: 0.036 to 0.079 mm/year) and those outside the safe zone (mean 0.062 mm/year, 95% CI: 0.042 to 0.083 mm/year). Acetabular cup position had no effect on the wear rate of highly crosslinked polyethylene at long-term follow-up. Although care should still be taken to correctly position the acetabular cup for stability, highly crosslinked polyethylene is a forgiving bearing material that can withstand a wide range of cup positions without negatively impacting longevity due to wear

Introduction. Proper acetabular cup placement is very important factor for successful clinical results in total hip arthroplasty (THA). Malposition of acetabular cup has been linked to increased rates of dislocation, impingement, pelvic osteolysis, cup migration, leg length discrepancy and polyethylene wear. Recently, some authors reported usefulness of navigation systems to set the acetabular cups with correct position. The purpose of this study is to evaluate the accuracy of acetabular cup placement in THA using computed tomography (CT)-based navigation system. Material and Methods. Subjects were 235 hip joints we performed primary THA using CT based navigation system (Stryker® Navigation System, Stryker Corporation, Kalamazoo, MI, USA) from 2008 to 2014 and could assess the implant position by postoperative CT images. Their average age was 65.1 years (range 35–88). In all cases, non-cemented acetabular cups were implanted. TriAD cups (Stryker®) were used in 31 hips, and Tritanium cups (Stryker®) were used in 15 hips, and Trident cups (Stryker®) were used in 189 hips. Registration in this navigation system used surface matching system. We designed cup implantation using preoperative CT images and 3-dimensional (3-D) templates. The planned position of acetabular cup was in principle 40 degrees of inclination and 20 degrees of anteversion. However, we adjusted the better position of the cups according to pelvic tilt and femoral neck anteversion. When we placed acetabular cups, the position, inclination and anteversion, were measured by navigation system. After surgery, the positions of the cups were measured using postoperative CT images, navigation software and 3-D templates. Postoperative position using CT images were adjusted according to preoperative pelvic plane. The discrepancies between intraoperative navigation data and postoperative CT images data were analyzed as accuracy of navigation system in cup placement. Results. No complications related to navigation procedures were encountered. There was no case with acetabular cup displacement obviously. The discrepancies between intraoperative data and postoperative data were an average difference of 1.6 degrees (SD, 1.4 degrees) for inclination and 2.1 degrees (SD, 1.7 degrees) for anteversion. Discussion and Conclusions. In THA, cup position is very important factor of postoperative long-term success. However, it is not easy to place the acetabular cup with proper position using conventional devices. CT-based navigation system was reported that it had many advantages than previous techniques in preoperative planning, setting the implants and analysis of postoperative data. But in registration with surface matching, learning-curve was pointed out and might be a problem for proper placement of implants. Therefore, we performed this study after some navigation THA cases. In the results of this study, the discrepancies between intraoperative and postoperative data were average 1.6 degrees for inclination and 2.1 degrees for anteversion. The accuracy of navigation system was good in inclination and anteversion of the cups, and there was no complication related it. CT-based navigation system is very useful device

Introduction: In vitro studies have shown that low clearance bearings have the potential to generate low wear. However, cementless acetabular cups are designed to be press fitted into the acetabulum, which could generate compressive stresses and non-uniform cup deformation during implantation. Deformation of the low clearance acetabular cups could also potentially lead to clamping or seizure of the joints and high frictional torque leading to implant failure. To obtain the benefit of low clearance and low wear, without compromising the tribological performance of the cup, a deflection compensation (DefCom) cup was designed. DefCom offers the benefits of low wear associated with low clearance components whilst reducing the risk of component seizure and high frictional torque due to component deformation. Aim: The study was conducted in order to evaluate the tribological performance of a DefCom acetabular cup. Materials and Methods: 50 mm diameter metal-on-metal DefCom hip resurfacing cups were used in this study. The components had an average clearance of 105±3 μm at the articulating sphere. Three of the cups were deformed plastically, along the ilial-ischeal column of the acetabulum. The degree of deformation was measured using the coordinate measuring machine, measuring the change in diameter of the cup in the direction of deformation. The cups were deformed on average by 65μm. The devices were tested in a ProSim hip wear Simulator for 5 million cycles. The lubricant was new born calf serum with 0.2% sodium azide diluted with de-ionised water to achieve protein concentration of 20 mg/ml. The flexion/extension was 30° and 15° with an internal/external rotation of ±10°. The force was Paul-type stance phase loading with a maximum load of 3 kN and a swing phase load of 0.3 kN, conducted at 1 Hz. Results: The DefCom and deformed DefCom components showed a similar bi-phasic wear pattern to that of the BHR devices. Showing a period of ‘running in’ wear up to 1 Mc and then a reduced wear rate during the steady state phase from 1 Mc onwards. The DefCom devices produced a wear rate of 0.24 mm3/Mc, whilst the deformed DefCom joints produced a wear rate of 0.48 mm3/Mc for the running-in phase. Steady state wear was achieved for all joints after 1 Mc. The average steady state wear (1.0–5.0 Mc) rate for the DefCom joints was 0.12 mm3/Mc, with 0.14 mm3/Mc for the deformed joints joint. The wear rate for the non-deformed DefCom device is lower than that generated by the BHR, which were 0.72 mm3/Mc and 0.18 mm3/Mc for the running-in and steady state wear, respectively. Conclusion: The study has shown that the DefCom acetabular cup has the potential to reduce the initial running-in wear by reducing the clearance at the contact area between the head and cup, whilst compensating for deformation that may occur during cup implantation

Dislocation after total hip arthroplasty (THA) remains a significant clinical problem. The acetabular cup position is one of the main factors in the incidence of dislocation after THA. We reviewed dislocation cases in 247 primary THA. Between 1997 and 2001, 247 patients underwent a primary THA procedure. The original diagnoses in these patients were as follows: osteoarthritis (OA, n = 190), osteonecrosis (ION, n=28), rheumatiod arthritis (RA, n=16), and rapidly destructive coxarthropathy (RDC, n=13). A posterolateral approach was used in all cases. We examined mainly the acetabular cup position (ante-version and inclination angle) using anteroposterior radiographs. Six dislocations (2.4%) occurred : three anterior dislocations and three posterior dislocations. Dislocation rate according to the original diagnoses were as follows, 2 dislocations in OA (1.1%), 2 dislocations in RA(12.5%), 2 dislocations in RDC(15.4%) and no dislocation in ION. All cases were treated with close reduction and no component revision was needed. On X-P measurement of setting the acetabular cup in all cases, the mean ante-version angle was 16.3617;6.8 degrees and inclination angle was 43.3& #61617;7.3 degrees. In comparison with these measurement values, there was no statistical difference between the dislocation groups and no-dislocation groups. The number of the cases within Lewinnek’s safe zone in acetabular cup was 178 (72%). The dislocation rate in these 178 cases was low (1.1%). Setting the acetabular cup in adequate position is one of the major factors avoiding dislocation after THA. We have been performimg computer - assisted THA since 2003. Computer - assisted surgery enables the acetabular cup position to be precisely planned before surgery and allows superior positioning during surgery

Introduction. Ultra-high molecular weight polyethylene (UHMWPE) is the sole polymeric material currently used for weight- bearing surfaces in total joint replacement. However, the wear of UHMWPE in knee and hip prostheses after total joint replacement is one of the major restriction factors on the longevity of these implants. In order to minimize the wear of UHMWPE and to improve the longevity of artificial joints, it is necessary to clarify the factors influencing the wear of UHMWPE. A number of studies have investigated the factors influencing the wear of UHMWPE acetabular cup liner in hip prosthesis. Most of these studies, however, have focused on the main articulating surfaces between the femoral head and the polyethylene liner. Materials and Methods. In a previous study (Cho et al., 2016), the generations of cold flow into the screw holes in the metal acetabular cup were observed on the backside of the retrieved UHMWPE acetabular cup liners as shown in Figure 1. We focused on the screw holes in the metal acetabular cup (Figure 2) as a factor influencing the wear behavior of polyethylene liner in hip prosthesis. In this study, computer simulations of the generation of cold flow into the screw holes were performed using the finite element method (FEM) in order to investigate the influence of the screw holes in the metal acetabular cup on the mechanical state and wear behavior of polyethylene liner in hip prosthesis. Results. An example of the results of the FEM simulations performed in this study is shown in Figure 3. In the region which the cold flow into the screw holes occurred, it was found that locally high contact stresses which exceed the yield stress of UHMWPE and considerable plastic strains were generated throughout the overall thickness between the backside and top surface of the polyethylene liners. On the contrary, in the case of the polyethylene liner combined with the metal acetabular cup without screw hole, although the regions of high contact stress and high plastic strain had a tendency to be limited around contact surface compared with those of the combination with screw holes, the values of contact stress and plastic strain were lower than the combination with screw holes. Discussion and Conclusions. The results of this study suggest that the cold flow generated by the existence of the screw holes in the metal acetabular cup of hip prosthesis reduces the wear resistance of the UHMWPE acetabular cup liner. It would appear that the cold flow into the screw holes contributes to structural weakening of the UHMWPE and reduction of the polyethylene thickness, thus increase of internal stresses and plastic strains in and around the regions of cold flow. Therefore, it is required that improvement of the screw holes in the metal acetabular cup and/or improvement of fixation method of the metal acetabular cup to a pelvis in order to enhance the wear resistance of the polyethylene liner. For any figures or tables, please contact authors directly

Purpose. Cementless cup with structural allograft is one of option for acetabular revision in the cases which has severe bone loss. This study was performed to verify that the structural allograft with cementless cup could be one of good options for revision of acetabular cup with severe bone defect and to verify that the allograft resorption affect the stability of cementless acetabular cup. Materials and Methods. We reviewed 25 cases of 25 patients who underwent acetabular cup rvision using cementless porous coated hemispherical cup with structural allograft from May 1992 to July 2011 July 2011. There were nine males and sixteen females with an average age of 50.0 years. The average follow-up period was 76.7(28∼212) months. The clinical evaluation was performed using Harris Hip Score(HHS) and UCLA activity score. Radiologically, the degree of resorption of grafted bone, incorporation of allograft bone with normal bone, osteolysis and cup loosening were evaluated. Results. Clinically, the average Harris hip score was improved from 54 preoperatively to 93.4 at the last follow-up. The average UCLA activity score was also improved from 4.3 preoperatively to 6.4 at the last follow-up. Radiologically, the incorporation of allograft was accomplished in 11.4 months and the resorption of grafted bone was noted in 3 cases(12%), but the allograft resorption had not progressed to moderate degree even in long term follow-up. There was no cup loosening and average survivor rate was 100% in 6 years. There was no infection, allograft nonunion, osteolysis. Conclusion. Cementless cup with structural allograft in acetabular cup reconstruction can provide excellent mi-term results in both clinical and radiological aspects. Structural allograft can provide strong mechanical support for the bone ingrowth of cementless cup. The clinical result of this study auggest that cementless cup with structural allograft can be a good option for acetabular cup revision with severe bone defect. Resorption of structural allograft rarely occurred, and the resorption of structural allograft does not affect stablility of cup even in long term follow-up

Acetabular cup placement in total hip replacement surgery is often difficult to assess, especially in the lateral position and using the posterior approach. On table control X-Rays are not always accessible, especially in the government sector. Conventional techniques and computer assisted surgery (CAS), are currently the two most popular methods for proper placement of the acetabular cup in Lewinnek's safe zone of orientation (anteversion 15°–10° and lateral inclination 40°±10°). We developed a simple way to get accurate cup placement using Smartphone technology. Methods:. A spirit level application was downloaded to the Smartphone. The acetabulum inclination was measured on the pre-operative X-Rays. The phone is placed in a sterile bag and then used intra-operatively, to measure and set our acetabular cup orientation to our pre-operative measurements. The inclination level was measured before and after final placement of the acetabular cup. This was compared to the acetabular cup inclination in our post-operative X-Rays. Results:. In our series of 50 cup placements we found high accuracy. The results show less than 5° deviation between our pre-, intra- and post-operative measurements. Conclusions:. Smartphone technology proves to be good alternative to conventional methods and CAS, to improve Acetabular Cup placement in Total Hip Arthroplasty

Background. Supine positioning during direct anterior approach total hip arthroplasty (DAA THA) facilitates use of fluoroscopy, which has been shown to improve acetabular component positioning on plane radiograph. This study aims to compare 2- dimensional intraoperative radiographic measurements of acetabular component position with RadLink to postoperative 3- dimensional SterEOS measurements. Methods. Intraoperative fluoroscopy and RadLink (El Segundo, CA) were used to measure acetabular cup position intraoperatively in 48 patients undergoing DAA THA. Cup position was measured on 6-week postoperative standing EOS images using 3D SterEOS software and compared to RadLink findings using Student's t-test. Safe-zone outliers were identified. We evaluated for measurement difference of > +/− 5 degrees. Results. RadLink acetabular cup abduction measurement (mean 43.0°) was not significantly different than 3D SterEOS in the anatomic plane (mean 42.6°, p = 0.50) or in the functional plane (mean 42.7°, p = 0.61) (Fig. 1–2). RadLink acetabular cup anteversion measurement (mean 17.9°) was significantly different than 3D SterEOS in both the anatomic plane (mean 20.6°, p = 0.022) and the functional plane (mean 21.2°, p = 0.002) (Fig. 3–4). RadLink identified two cups outside of the safe-zone. However, SterEOS identified 12 (anatomic plane) and 10 (functional plane) outside of the safe-zone (Fig. 5–7). In the functional plane, 58% of anteversion and 92% of abduction RadLink measurements were within +/− 5° of 3D SterEOS. Conclusion. Intraoperative fluoroscopic RadLink acetabular anteversion measurements are significantly different than 3D SterEOS measurements, while abduction measurements are similar. Significantly more acetabular cups are placed outside of the safe- zone when evaluated with 3D SterEOS versus RadLink

Introduction. Recent gains in knowledge reveal that the ideal acetabular cup position is in a narrower range than previously appreciated and that position is likely different based on femoral component anteversion. For that reason more accurate acetabular cup positioning techniques will be important for contemporary THA. It is well known that malalignment of the acetabular component in THA may result in dislocation, reduced range of motion or accelerated wear. Up to 8% of THA patients have cups malaligned in version by more than ±10° outside of the Lewinnek safe zone. This type of malalignment may result in dislocation of the femoral head and instability of the joint within the first year, requiring reoperation. Reported incidences of reoperation are 1-9% depending on surgical skills and technique. In addition, cup malalignment is becoming increasingly important as adoption of hard on hard bearings increases as the success of large head hard on hard bearings seems to be more sensitive to cup positioning. This study reports the accuracy of a haptic robotic system to ream the acetabulum and impact an acetabular cup compared to manual instrumentation. Methods. Six fresh frozen cadaveric acetabula were CT scanned and three-dimensional templating of the center of rotation, anteversion and inclination of the cup was determined pre-operatively. Half of the specimens were prepared with manual instrumentation while half were prepared with robotic guidance. Haptic and visual feedback were provided through robotics and an associated navigation system to guide reaming and impaction of the cup. The robot constrained the orientation and position of the instruments thus constraining the inclination, anteversion and center of rotation of the reamer, trial and the final cup. Post-operative CT's were used to determine the achieved cup placement and compared to the pre-operative plans. Results. In all cases, robotic guidance resulted in placement of the acetabular cup within ±3° of anteversion, ±3° of relative to the pre-op plan. The average absolute inclination error was 1.5±1.2° and the average absolute anteversion error 1.3±1.4°. Cup placement with robotic assistance was significantly more accurate and precise than with manual instrumentation. With manual instrumentation the errors were, on average, 4.2 times higher in inclination and 4.8 times higher in anteversion compared to robotic instrumentation. Conclusion. This haptic robotic system substantially improved the accuracy of acetabular reaming and placement of the final cup compared to traditional manual techniques. With greater knowledge of ideal acetabular cup position, highly accurate techniques may allow surgeons to decrease the risk of dislocation, promote durability and improve the ability to restore appropriate leg length and offset. Haptic robotics has proven to be safe and effective in both knee and hip surgery and provides the potential to redefine the “instrument set” used for orthopedic procedures

Introduction. Modern acetabular cups require a convenient bone stock for sufficient cup fixation. Thereby, fixation stability is influenced by the chosen interference fit of the acetabular cup, the cup surface structure, circularity of the reamed acetabulum and by the acetabular bone quality. The ideal implantation situation of the cup is commonly compromised by joint dysplasia and acetabular bone defects. The aim of the present experimental study was to characterise implant fixation of primary acetabular cups in case of definite acetabular cavity defects. Materials and Methods. For the experimental determination bone substitute blocks (100 × 100 × 50 mm) made of polymethacrylimide (PMI) foam with a density of 7 pcf were used. The created acetabular defect situations were derived from the defect classification according to Paprosky. The defect geometries in the PMI foam blocks were realised by a CNC drilling machine. Thereby the defects are described in the dorso-ventral direction by the angle α and in medio-lateral direction by the angle β (given as angle combination α/β) related to the centre of rotation of the reamed cavity. For the lever-out tests the defect types IIb and IIIa (each with different α and β angles) were considered and compared to the intact fixation situation. Therefore, a macrostructured titanium cup (Allofit, Zimmer GmbH, Wintherthur, Switzerland) with an outer diameter of 56 mm were displacement-controlled (v = 20 mm/min) pushed into the 2 mm diametric under reamed PMI-foam cavities. Three cups were inserted until the cup overhang pursuant to surgical technique was reached. Subsequently the cups were displacement-controlled (v = 20 mm/min) levered out via a rod which was screwed into the implant pole by perpendicular displacement (U. axial. ) of the rod in direction of the defect aperture. The lever-out moments were calculated by multiplying the first occurring force maximum (F. max. ) with the effective lever arm length (l. lever. ), whereby moments caused by the deadweight of the rod were considered. Primary stability was defined by the first maximum lever-out moment. Results. The calculated lever-out moments were in a range from 15.5 ± 1.4 Nm to 1.4 ± 0.5 Nm. Defects with a 90° dorso-ventral opening angle showed 57 ± 17% lower lever-out moments. Defects with a 120° dorso-ventral opening angle showed 80 ± 6% lower lever-out moments compared to the cup fixation into intact cavities. Moreover, medio-lateral angles greater than 20° reduced the lever-out moment by 79 ± 12% compared to the intact cavities. Conclusion. The determined lever-out moments underline the reduction of fixation stability of acetabular cup by loss of circumferential rim and absent of superior wall support of the acetabular bone. Thereby, the fixation stability is influenced by the degree of dorso-ventral and medio-lateral defect manifestation. Hence, the fixation stability depends on the cavity surface and in particular the surface of the bone-implant interface in the fixation zone of the acetabular cup Thus, dorso-ventral defect sizes with greater opening angle than 60° and medio-lateral defect sizes greater than 20° are critically for sufficient fixation of primary acetabular cup implants

INTRODUCTION. Poor acetabular cup orientation in total hip arthroplasty (THA) can cause dislocation and impingement, and lead to osteolysis (Little et al., 2009) and inflammatory soft tissue reactions (Haan et al., 2008). While the intrinsic accuracy of cup positioning in navigation is reported as low as 1° (Parratte et al., 2009), a large anterior pelvic tilt may lead to an offset of the same magnitude in the final cup anteversion (Wolf et al., 2005). The objectives of this study are to demonstrate feasibility of a new, non-invasive radiographic tool for accurate preoperative determination of a patient's specific pelvis angle, and intraoperative and postoperative assessment of the acetabular cup orientation with respect to boney landmarks. METHODS. The methodology stitches multiple radiographic views around the pelvis using a multi-planar radiography setup (Amiri et al., 2011) and reconstructs the reference boney landmarks and the acetabular cup in three dimensions using previously developed algorithms and software (Amiri et al., 2012). To validate the methodology, a Sawbone model of the pelvis and femur was implanted with a standard cementless metal-on-polyethylene THA, and was tracked and digitized by an Optotrak motion tracking system. Five radiographic views were acquired at the pubic tubercle (PT) and anterior-superior iliac spine (ASIS) levels (Views 1 to 5 in Fig 1). Imaging and analysis were repeated 10 times. Custom software (Joint 3D) was used to reconstruct the right and left PT and ASIS by fitting spheres to the corresponding pairs of images (Fig 1). The three-dimensional pose of the acetabular cup was reconstructed in the software by solving a back-projection equation of the elliptical shadow of the cup opening. Accuracies were measured as mean differences from the digitized references. A sample of the reconstructed graphical output for the anterior pelvic plane (APP) and the cup, in comparison to the digitized reference, is shown in Fig 2. Repeatability was estimated as standard deviation of the measures for the reconstructed locations of the boney landmarks and the APP (known as a standard reference plane for cup placement). RESULTS. Accuracy for the pelvis pose angles was <1.6°, with SD <0.8° (Fig 3). Pelvic tilt was the most accurate with accuracy of 0.1° and SD=0.4°. For the acetabular cup, accuracy was 2.5° or better, with SD <0.2°. Accuracies in the cup operative anteversion and inclination were 2.4° and 0.6°, with SD=0.4° and 0.9°, respectively. DISCUSSION. The measured accuracies were within an acceptable range, according to previous studies that recommended a 5° cut-off error for acetabular anteversion. The method shows accuracy and radiation dose advantages over current radiographic, fluoroscopic and computed tomography methods. These results suggest that the proposed method is feasible for assessing cup placement with reference to the functional and anatomical references. CONCLUSION. Use of this technique could improve acetabular cup placement and reduce the incidence of instability, wear and loosening, by providing tools to incorporate the individual's pelvic pose in preoperative planning of the surgery, and by serving as an accurate and reliable tool for intraoperative and postoperative assessment of the acetabular cup position

Introduction. Component positioning is of great importance in total hip arthroplasty (THA) and navigation systems can help guide surgeons in the optimal placement of the implants. We report on a newly developed navigation system which employs an inertial measurement unit (IMU) to measure acetabular cup inclination and anteversion. Aims. To assess the accuracy of the IMU when used for acetabular cup placement and compare this with an established optical navigation system (ONS). Methods. At the time of acetabular cup impaction, the IMU and ONS were separately mounted on the impactor handle. Cup inclination and anteversion as measured by each device were recorded. Post-operative CTs were acquired for all patients and used to determine the final cup position. Results. Data were recorded for a total of 100 patients undergoing THA; 51 had a direct anterior approach (DAA) and 49 had a posterior approach (PA). In the DAA group, the mean difference in IMU versus CT measured cup inclination was −0.7°(range −6 to 8º) compared with mean difference of ONS versus CT of −2° (range −8 to 5º). Mean difference in IMU versus CT measured anteversion was − 1.3° (range −10 to 10º) compared with a mean difference of −1.1° (range −23 to 20º) between ONS and CT. In the PA group, mean difference in IMU versus CT inclination was 1.3º (range −8 to 6º) compared with mean difference between ONS versus CT of 1.6° (range −5 to 7º). Mean difference in anteversion was 3.7° (range −7 to 16º) between IMU and CT and 7.3° (range −3 to 19º) between ONS and CT. Conclusion. The novel IMU can be used to accurately determine the position of the acetabular cup at the point of impaction, demonstrating comparable accuracy with an established navigation system in the direct anterior approach, and even greater accuracy in the posterior approach

Abstract. Objectives. The importance of cup position on the performance of total hip replacements (THR) has been demonstrated in in vitro hip simulator tests and clinically. However, how cup position changes during gait has not been considered and may affect failure scenarios. The aim of this study was to assess dynamic cup version using gait data. Methods. Pelvic movement data for walking for 39 unilateral THR patients was acquired (Leeds Biomedical Research Centre). Patient's elected walking speed was used to group patients into high- and low-functioning (mean speed, 1.36(SD 0.09)ms. −1. and 0.85(SD 0.08)ms. −1. respectively). A computational algorithm (Python3.7) was developed to calculate cup version during gait cycle. Inputs were pelvic angles and initial cup orientation (assumed to be 45° inclination and 7° version, anterior pelvic plane was parallel to radiological frontal plane). Outputs were cup version angles during a gait cycle (101 measurements/cycle). Minimum, maximum and average cup version during gait cycle were measured for each patient. Two-sample t-test (p=0.05) was used to compare groups. Results. Over a gait cycle the mean minimum, maximum and average version angles for the high-functioning group were −4.5(SD 4.4)°, 5.0(SD 4.3)°, 9.5(SD 4.0)° and for low-functioning group 2.0(SD 3.7)°, 6.2(SD 2.9)°, 8.1(SD 3.2)°. There were no significant differences for the minimum, maximum and average version angles between the two groups. Conclusions. The study shows that dynamic acetabular cup version changes substantially during gait and this must be considered clinically and in pre-clinical testing. There was no significant difference between the two groups; however, dynamic cup version was more negative in high-functioning compared to low-functioning patients. Further studies on a larger cohort are required to determine whether patients’ profiles can be stratified to provide enhanced inputs for pre-clinical THR testing. Declaration of Interest. (b) declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research reported:I declare that there is no conflict of interest that could be perceived as prejudicing the impartiality of the research project

Introduction. Aseptic loosening of the acetabular cup in total hip replacement (THR) remains a major problem. Current diagnostic imaging techniques are ineffective at detecting early loosening, especially for the acetabular component. The aim of this preliminary study was to assess the viability of using a vibration analysis technique to accurately detect acetabular component loosening. Methods. A simplified acetabular model was constructed using a Sawbones foam block into which an acetabular cup was fitted. Different levels of loosening were simulated by the interposition of thin layer of silicon between the acetabular component and the Sawbones block. This included a simulation of a secure (stable) fixation and various combinations of cup zone loosening. A constant amplitude sinusoidal excitation with a sweep range of 100–1500 Hz was used. Output vibration from the model was measured using an accelerometer and an ultrasound probe. Loosening was determined from output signal features such as the number and relative strength of the observed harmonic frequencies. Results. Both measurement methods were capable of measuring the output vibration. Preliminary findings show different patterns in the output signal spectra were visible when comparing the stable cup with the 1mm of simulated spherical loosening at driving frequencies 1050 Hz, 1100 Hz and 1150 Hz (p < 0.05) using the accelerometer, whereas for ultrasound at frequencies 950 Hz and 1350 Hz (p < 0.05). Conclusions. Experimental testing showed that vibration analysis could be used as a potential detection method for acetabular cup component loosening using either an accelerometer or ultrasound probe to detect the vibration. However, the capacity of ultrasound to overcome the attenuating effect of the surrounding soft tissues and its high signal to noise ratio suggest it has the best potential for clinical use

Acetabular cup orientation in hip arthroplasty is critical to prevent edge loading and impingement. Aerial alignment guides position the cup at a specified angle to the orthogonal planes, but only if the pelvis is in strict lateral-decubitus. Computer navigation can also be used to position the acetabular cup, but there are limitations associated with defining the pelvic reference plane. It can also be postulated that a fixed angle of inclination and anteversion is not suitable for every patient and every cup design. This paper describes the development and testing of instrumentation that allows patient specific acetabular cup placement without knowing the exact pelvic orientation. Stage 1 determines the cup position during a trial reduction. A Judd nail retractor is left in the pelvis during the trial reduction. A single-use laser pointer is attached to the top of this nail, is free to move and can be locked in position. The trial acetabular cup has a handle protruding at a fixed angle from the face of the cup. At the end of this handle is another single-use laser pointer that projects a laser beam parallel to the axis of the cup onto the wall/ceiling. Keeping the handle parallel to the medio-lateral axis to control inclination angle, the leg is moved through a range of motion (ROM). The anteversion of the trial cup is adjusted until a position is found where flexion extension ROM is possible without impingement and satisfactory abduction-adduction is achieved with stability. Once this position is found, the Judd nail laser (fixed to the pelvis) is adjusted until its projected point, on the wall/ceiling, coincides with that from the trial handle. The Judd nail laser is then fixed in position, the hip dislocated and trial components removed. Stage 2 aligns the definitive acetabular cup. The introducer has a laser pointer pointing parallel to its axis (away from the patient) and is attached to the definitive cup. The definitive cup is placed in the acetabulum and the introducer adjusted until its projected laser coincides with that from the Judd nail. The cup is then in the same orientation as determined during the trial reduction and can be impacted. To demonstrate the accuracy of the laser alignment method, the position of the definitive cup was compared to that of the trial cup in polyurethane foam models. With the laser points projected onto an object > 2m away, the accuracy was ±2°. To compare the laser guided instrumentation with the conventional aerial device, the ROM of the definitive cup was assessed in Sawbones resurfaced pelvis/femur models. The pelvis orientation was rotated by ±10° about the medio-lateral axis and the superio-inferior axis to investigate the effect of the pelvis being unknowingly out of lateral-decubitus. In the worst case of pelvis position, the aerial halved the required flexion and allowed double the required extension. The laser guided instrumentation maintained the physiological range of flexion/extension regardless of pelvis position and is therefore considered an improvement on current technology and a viable alternative to computer navigation

Positioning of the hip resurfacing is crucial for its long term survival and is critical in young patients for some reasons; manly increase the wear in the components and change the load distribution. THR have increased in the last years, mainly in young patients between 45 to 59 years old. The resurfacing solution is indicated for young patients with good bone quality. A long term solution is required for these patients to prevent hip revision. The resurfacing prosthesis Birmingham Hip Resurfacing (BHR) was analyzed in the present study by in vitro experimental studies. This gives indications for surgeons when placing the acetabular cup. One synthetic left model of composite femur (Sawbones®, model 3403), which replicates the cadaveric femur, and four composite pelvic bones (Sawbones®, model 3405), were used to fix the commercial models of Hip resurfacing (Birmingham model). The resurfacing size was chosen according to the head size of femurs with 48 mm head diameter and a cup with 58 mm. They were introduced by an experimented surgeon with instrumental of prosthesis. The cup is a press fit system and the hip component was cemented using bone cement Simplex, Stryker Corp. The acetabular cup was analyzed in 4 orientations; in anteverion with 15º and 20°; and in inclination 40 and 45°. Combinations of these were also considered. The experimental set-up was applied according to a system previously established by Ramos et al. (2013) in the anatomic position. The femur rotates distally and the Pelvic moves vertically as model changes, such that the same boundary conditions are satisfied. This system allows compensating motions of the acetabular cup orientation. A vertical load of 1700 N was applied on all cases, which have resulted in joint reaction force of 2.4 kN. The femur and iliac bone was instrumented with rosettes. 5 repetitions at each position were conducted. When the femur was instrumented with three rosettes in medial, anterior and posterior aspect, the maximum strain magnitude was observed in the medial aspect of femur with a minimum principal strain of −2070µε for 45° inclination and 20° of anterversion. The pubic region was found most critical region after instrumenting the Iliac bone with four rosettes, with a minimum principal strain around −2500µε (rosette 1), for the 45° inclination and 20° of anterversion. We have observed the great influence of the inclination on the strain distribution, changing its magnitude from compression to traction in different bone regions. The minimum principal strain is more critical in medial aspect of the femur and the influence of strain is about 7% when orientation and inclination change. The maximum influence was observed in the anterior aspect, where the anteversion presents a significant influence. The results show the interaction between inclination and anterversion in all aspects, being observed lower values in lower angles. The orientation of the acetabular cup significantly influences the strain distribution on the iliac surface. Besides, as anterversion increases, more strains are induced, mainly in the region of iliac body (rosette 3)

Objective. The purpose of this study was to investigate how rim poly locking scallop cutting depth could affect the rigidity of acetabular cup. Materials and Methods. (11) generic FEA models including (5) 50mm OD Ti6Al4VELI hemispherical acetabular shells with thicknesses of 3.0, 3.5, 4.0, 4.5 and 5.0mm, and (6) 4mm thick hemispherical shells with standard rim poly indexing scallops varied in cutting depths from inner diameter of the cup in 1.0, 1.5, 2.0, 2.5, 3.0 and 3.5mm. All cups were analyzed in ANSYS® Workbench™ FEA software with a loading condition of 2000N applied to the cup rim per V15 ISO/TC 150/SC 4 N. Verification was carried out by the physical test of a same generic Ti6Al4VELI 50mmOD and 5mm thick solid hemispherical shell under 2000N rim directed load. The cup deformation was compared with FEA results. The maximum deformation of FEA scalloped cups were compared with that of solid hemispherical cups with different shell thickness. Results. The average value for physical test was 0.265(0.282/0.268) mm. The FEA result of the same 50mm OD and 5mm thick shell was 0.2464mm representing a 7% difference. (Figure 1) FEA results for solid hemisphere cups and scalloped shells are shown in Figure 2 and Figure 3 respectively. Conclusion and Discussion. Cup deformation increased in the average of 40% for every 0.5mm shell thickness decrease from 5mm to 3mm for 50mm OD solid cup. The increase of rim scallop depth from 0 to 2.5mm was equivalent to a 0.5mm shell thickness reduction for 4mm thick 50mm OD cup. The higher deformation reading in physical test was likely caused by the accumulations of the fixture deformations. Intraoperative acetabular cup deformation is a clinical issue. It increases the risk of ceramic liner fracture when the liner is inserted in the out of round cup. The increase of shell thickness is a simple and effective way to reduce the cup deformation. However it also reduces the poly thickness and that puts the adverse effects to the poly wear property and poly rim fatigue strength. The common design of the indexing scallops in the rim of cup helps the rotational locking for the poly liner. But the drawbacks including the reduction of cup stiffness must be noticed. The shallower scallop design may be warranted to maximize the cup rigidity in a given cup thickness and maximize poly thickness in a given cup rigidity

Introduction. Robotic-assisted hip arthroplasty helps acetabular preparation and implantation with the assistance of a robotic arm. A computed tomography (CT)-based navigation system is also helpful for acetabular preparation and implantation, however, there is no report to compare these methods. The purpose of this study is to compare the acetabular cup position between the assistance of the robotic arm and the CT-based navigation system in total hip arthroplasty for patients with osteoarthritis secondary to developmental dysplasia of the hip. Methods. We studied 31 hips of 28 patients who underwent the robotic-assisted hip arthroplasty (MAKO group) between August 2018 and March 2019 and 119 hips of 112 patients who received THA under CT-based navigation (CT-navi group) between September 2015 and November 2018. The preoperative diagnosis of all patients was osteoarthritis secondary to developmental dysplasia of the hip. They received the same cementless cup (Trident, Stryker). Robotic-assisted hip arthroplasty were performed by four surgeons while THA under CT-based navigation were performed by single senior surgeon. Target angle was 40 degree of radiological cup inclination (RI) and 15 degree of radiological cup anteversion (RA) in all patients. Propensity score matching was used to match the patients by gender, age, weight, height, BMI, and surgical approach in the two groups and 30 patients in each group were included in this study. Postoperative cup position was assessed using postoperative anterior-posterior pelvic radiograph by the Lewinnek's methods. The differences between target and postoperative cup position were investigated. Results. The acetabular cup position of all cases in both Mako and CT-navi group within Lewinnek's safe zone (RI: 40±10 degree; RA: 15±10 degree) in group were within this zone. Three was no significant difference of RI between Mako and CT-navi group (40.0 ± 2.1 degree vs 39.7± 3.6 degree). RA was 15.0 ± 1.2 degree and 17.0 ± 1.9 degree in MAKO group and in CT-navi group, respectively, with significant difference (p<0.001). The differences of RA between target and postoperative angle were smaller in MAKO group than CT-navi group (0.60± 1.05 degree vs 2.34± 1.40 degree, p<0.001). The difference or RI in MAKO group was smaller than in CT-navi, however, there was no significance between them (1.67± 1.27 degree vs 2.39± 2.68 degree, p=0.197). Conclusions. Both the assistance of the robotic arm and the CT-based navigation system were helpful to achieve the acetabular cup implantation, however, MAKO system achieved more accurate acetabular cup implantation than CT-based navigation system in total hip arthroplasty for the patients with OA secondary to DDH. Longer follow-up is necessary to investigate the clinical outcome

Purposes. To compare the acetabular component size relative to the patient's native femoral head size between conventional THA (CTHA) approach and robotic-guided THA (RGTHA) to infer which of these techniques preserves more acetabular bone. Methods. Patients were included if they had primary osteoarthritis (OA) and underwent total hip replacement between June 2008 and March 2014. Patients were excluded if they had missing or rotated postoperative anteroposterior radiographs. RGTHA patients were matched to a control group of CTHA patients, in terms of pre-operative native femoral head size, age, gender, body mass index (BMI) and approach. Acetabular cup size relative to femoral head size was used as a surrogate for amount of bone resected. We compared the groups according to two measures describing acetabular cup diameter (c) in relation to femoral head diameter (f): (1) c-f, the difference between cup diameter and femoral head diameter and (2) (c-f)/f, the same difference as a fraction of femoral head diameter. Results. 57 matched pairs were included in each group. There were no significant differences between groups for demographic measures, femoral head diameter, or acetabular cup diameter (p>0.05). However, measures (1) and (2) did differ significantly between the groups, with lower values in the RGTHA group (p<0.02). Conclusion. Using acetabular cup size relative to femoral head size as an approximate surrogate measure of acetabular bone resection may suggest greater preservation of bone stock using RGTHA compared to CTHA. Further studies are needed to validate the relationship between acetabular cup size and bone loss in THA

Objectives. Porous metal surfaces have been a popular option for acetabular component fixation in total hip arthroplasty (THA). New THA component designs are introduced periodically with the expectation of better wear properties and survivorship. Since its approval for use in 2002 there have been few clinical outcome studies published on the Pinnacle acetabular cup system. We hypothesised that the hemispherical porous coated Pinnacle acetabular cup system with a range of cup options and bearing surfaces would give us predictably good fixation and survivorship at five years post implantation. Materials and Methods. A total of 1391 Pinnacle acetabular cups (De Puy, a Johnson & Johnson company, Warsaw IN) were implanted between the period March 2003 to August 2011 by four senior surgeons. There were a total of 29 patients requiring revision surgery. Of these revisions, 23 were excluded from the final analysis. Sixteen were for early infection requiring debridement of the hip joint and exchange of the modular liner and femoral head. Five patients sustained femoral peri-prosthetic fractures requiring further surgery with retention of the acetabular component in all cases. Of the remaining 8 revision cases, only 6 had more than two years follow-up. All patients had pre and post-operative Harris hip scores, WOMAC and SF-12 scores. All patients were assessed with serial radiographs immediately post-operatively, 3 months, 1 year, 2 years, every 2 years thereafter. Component migration and revisions (excluding infection and peri-prosthetic fractures) are reported as failures. Post-operative radiographs were evaluated for component migration. Kaplan-Meier survivorship curves were drawn to show survivorship for cup type and bearing type. Results. A total of 894 Pinnacle acetabular components implanted into 796 patients were available for inclusion in the final analysis. There were 358 males with an average age of 63.70 years and 438 females with an average age of 64.55 years. The average period for follow-up was 44.95 months with 133 patients having more than five years of follow-up. Only one cup showed signs of aseptic loosening and component migration on plain radiographs, this patient had previously sustained an acetabular fracture requiring open reduction and internal fixation ans subsequently developed osteoarthritis. The cup failed to adequately in-grow and migrated medially to an intra-pelvic position, this was revised to a Trabelcular Metal cup with bone grafting to the acetabulum. There were two cases revised for instability. Three revisions were performed for aseptic loosening of the femoral components which were revised with retention of the acetabular cups. Conclusion. Published data on the performance of various porous coated cups have demonstrated varying degrees of osteolysis, however the Pinnacle cup has shown excellent midterm results postulated to be associated with the taper lock liner mechanism of the Pinnacle cups resulting in less micromotion and, therefore, reduced hydraulic pressure pumping polyethylene wear debris behind the cup. Our study confirms excellent overall survivorship of the Pinnacle acetabular porous coated cup system at a minimum of two years followup in over 790 patients

Metal on metal press-fit acetabular cups are the worst performing acetabular cup type with severe failure consequences compared to cups made from more inert materials such as polyethylene or ceramic. The cause of failure of these cup types is widely acknowledged to be multi-factorial, therefore creating a complex scenario for analysis through clinical studies. A factorial analysis has been carried out using an experimentally validated finite element analysis to investigate the relative influence of four input factors associated with acetabular cup implantation on output parameters indicating potential failure of the implantation. These input factors were: cup material stiffness; cup inclination; cup version; cup seating; and level of press-fit. The output parameter failure indicators were: wear; tensile strains in the underlying bone; bone remodelling; and cup-bone micromotions. The factorial analysis concluded that the most significant influence was that of cup inclination on wear, and the second most significant was the influence of the level of press-fit on bone remodelling at the acetabular rim. Significant influence was also observed between version angle and wear, and cup-seating and micro-motion. The results demonstrated the clear multi-factorial nature of implant failure and highlighted the importance of correct implant positioning and fit

Total hip replacement (THR) is one of the most successful orthopedic operations, yet it continues to be plagued with problems despite the many advances in the procedure. Inconsistent placement of the acetabular cup persists even in the hands of most experienced surgeons, leading to early and late failure including instability, impingement, polyethylene wear, osteolysis, and component loosening. Cup mal-position is the single greatest cause of early instability and late polyethylene wear. Despite advent of recent technology including navigation and use of fluoroscopy cup mal-alignment persists. Several studies show 50% of experienced surgeons missing the target ranges using Lewinnnk desired safe zones. The act of impaction of the cup with a mallet is a crude and unreliable process. The surgeon's mallet imparts large and uncontrolled forces on the impaction rod creating variable torques, leading to inconsistent cup placement. Navigation and Fluoroscopy add precision to the operation however that level of precision is not maintained throughout the course of the operation. There is a market need for a tool that helps maintain “precision tolerance” through out the course of the operation. A new device is theoretically proposed and prototyped for this process (Patent Pending). The new paradigm involves elimination of impaction forces created by unpredictable blows of the mallet. A low energy and high frequency device is utilized to insert and position the acetabular cup without the use of the mallet. The cup is inserted (not impacted) with significantly less force than the typical 2000N forces created with a mallet. The cup is also simultaneously positioned to the desired alignment while the device is active with the surgeon effectively feeling minimal haptic resistance to the movement of the cup. The system therefore proposes to eliminate cup mal-alignment for all surgeons, removing the primary cause of hip dislocations as well as factors contributing to late failure. In addition the idea allows the academic surgeon to better study the relationship of the position of the cup and clinical outcomes eliminating the need to use “safe zone ranges”. As well, this process completely eliminates acetabular fractures as a complication of this operation. Two devices were prototyped with use of electrical and pneumatic energy. Both devices proved the concept. Both devices allowed modulation of the applied force and “effective” disarming of the frictional forces involved in cup impaction, allowing insertion and positioning of the acetbular cup to occur with smooth haptic control and without the use of violent force. The device can be used individually, with navigation and fluoroscopy, with robots and/or with any other intra-operative measurement device and can be a significant adjunct for THR. Cup Mal-Alignment is an unsolved problem in THR surgery causing poor outcomes for patients, anxiety and a sense of failure for the surgeons, and a great cost to society in general. A new device is described to solve this problem. The science involved is proposed and described in detail and primarily involves understanding and utilizing the mechanical properties of bone/pelvis and understanding and manipulating the complex frictional forces at play

Following hip arthroplasty carried out using the Slooff-Ling impaction grafting technique micro-motion of the acetabular cup is frequently seen within the bone graft bed. In some cases this can lead to gross migration and rotation of the acetabular cup, resulting in failure of the arthroplasty. The movement of the cup is thought to be due to the irrecoverable deformation of bone graft under shear and compressive forces. Previous experimental studies have addressed ways in which the behaviour of the bone graft material may be improved, for example through washing and the use of improved particle size distribution. However there has been a limited amount of research carried out into assessing the behaviour of the acetabular construct in-vivo. This study presents a 3D finite element model of the acetabular construct and hemi-pelvis following impaction grafting of a cavitory defect. A sophisticated elasto-plastic material model was developed based on research carried out by the group to describe the bone graft bed. The material model includes the non-linear stiffness response, as well as the shear and consolidation yield response of the graft. Loading associated with walking, sitting down, and standing up is applied to the model. Distinct patterns of migration and rotation are observed for the different activities. When compared in a pseudo-quantitative manner with clinical observations results were found to be similar. Walking is found to account for superior migration, and rotation in abduction of the acetabular cup, while sitting down and standing up are found to account for posterior migration, and lateral rotation. The developed 3D model can be used in the assessment of cup designs and fixation devices to reduce the rate of aseptic failure in the acetabular region

Introduction. Proper cup positioning is a critical component in the success of total hip arthroplasty surgery. A multicenter study has been initiated to study a new type of highly cross-linked polyethylene. This study provides a unique opportunity to a review the acetabular cup placement of over 500 patients implanted in the past 2 years from 13 medical centers from the U.S., Mexico, and Europe. Methods. 482 patients have received primary total hip arthroplasty using components from a single manufacturer in 5 centers in the US and Mexico and 7 centers in Europe. The acetabular anteversion and inclination were measured in post-operative radiographs. An acceptable window of cup position is defined at 5–25° of anteversion and 30–45° of inclination. Results. The measured cup anteversion and inclination averaged 15.89° ± 8.91° (0.00–42.25°) and 43.27° ± 7.17° (23.46–67.79°), respectively. Of the patient radiographs read, 71% were within the acceptable range of anteversion, 55% were in the acceptable range of inclination, and 41% satisfied both criteria. The best performing center had 86% of patients within the acceptable range of anteversion, 63% in the acceptable range of inclination, and 57% satisfied both criteria. The worst performing center had 54% within the acceptable range of anteversion, 29% in the acceptable range of inclination, and 17% satisfied both criteria. Conclusion. A significant variation in acetabular cup anteversion and inclination exists in this study both within and between the participating high volume centers. Correlation to mid- and long-term clinical outcome will show the clinical relevance of the finding, but liner designs with unsupported polyethylene should be used with caution

Initial stability of cementless components in bone is essential for longevity of Total Hip Replacements. Fixation is provided by press-fit: seating an implant in an under-reamed bone cavity with mallet strikes (impaction). Excessive impaction energy has been shown to increase the risk of periprosthetic fracture of bone. However, if implants are not adequately seated they may lack the stability required for bone ingrowth. Ideal fixation would maximise implant stability but would minimise peak strain in bone, reducing the risk of fracture. This in-vitro study examines the influence of impaction energy and number of seating strikes upon implant push-out force (indicating stability) and peak dynamic strain in bone substitute (indicating likelihood of fracture). The ratio of these factors is given as an indicator of successful impaction strategy. A custom drop tower with simulated hip compliance was used to seat acetabular cups in 30 Sawbone blocks with CNC milled acetabular cavities. 3 impaction energies were selected; low (0.7j), medium (4.5j) and high (14.4j), representing the wide range of values measured during surgery. Each Sawbone was instrumented with strain gauges, secured on the block surface close to the acetabular cavity (Figure 1). Strain gauge data was acquired at 50 khz with peak tensile strain recorded for each strike. An optical tracker was used to determine the polar gap between the cup and Sawbone cavity during seating. Initially 10 strikes were used to seat each cup. Tracking data were then used to determine at which strike the cups progressed less than 10% of the final polar gap. This value was taken as number of strikes to complete seating. Tests were repeated with fresh Sawbone, striking each cup the number of times required to seat. Following each seating peak push-out forces of the cups were recorded using a compression testing machine. 10, 5 and 2 strikes were required to seat the acetabular cups for the low, medium and high energies respectively. It was found that strain in the Sawbone peaked around the number of strikes to complete seating and subsequently decreased. This trend was particularly pronounced in the high energy group. An increase in Sawbone strain during seating was observed with increasing energy (270 ± 29 µε [SD], 519 ± 91 µε and 585 ± 183 µε at low, medium and high energies respectively). The highest push-out force was achieved at medium strike energy (261 ± 46N). The ratio between push-out and strain was highest for medium strike energy (0.50 ± 0.095 N/µε). Push-out force was similar after 5 and 10 strikes for the medium energy strike. However push-out recorded at ten strikes for the high energy group was significantly lower than for 2 strikes (<40 ± 19 N, p<0.05). These results indicate that a medium strike energy with an appropriate number of seating strikes maximizes initial implant stability for a given peak bone strain. It is also shown that impaction with an excessive strike energy may greatly reduce fixation strength while inducing a very high peak dynamic strain in the bone. Surgeons should take care to avoid an excessive number of impaction strikes at high energy. For any figures or tables, please contact the authors directly

Introduction: Correct placement of the acetabular cup is a crucial step in total hip replacement to achieve a satisfactory result and remains a challenge with free hand techniques. Imageless navigation may provide a viable alternative to freehand technique and improve placement significantly. The purpose of this study therefore was to assess and validate intra-operative placement values as displayed by the navigation unit to postoperative measurement of cup position using high resolution CT scans. Methods: 32 patients underwent primary hip joint replacement using imageless navigation. The average age was 66.5 years (range 32–87). 23 non-cemented and 9 cemented acetabular cups were implanted. During surgery we aimed for 45 degrees of inversion and 15 degrees of anteversion. A pelvic CT scan using a multi-slice CT was used to assess the position of the cup radiographically. Results: 2 patients were excluded because of dislodgement of the tracking pin. Pearson correlation revealed a strong significant correlation (r=0.68; p< 0.006), for cup inclination and a moderate non-significant correlation (r=0.53; p=0.45) between intra-operative readings and cup placement. Discussion: These findings can be explained with possible introduction of systematic error. Even though the acquisition of anatomic landmarks are simple they must be acquired with great precision. An error of 1 cm can result in a mean anteversion error of 6 degrees and inclination error of 2.5 degrees. Whilst navigation results in highly accurate cup placements in relation to inclination, ante-version of the cup can not be determined accurately

Introduction:. The lateral radiographs are useful in evaluation of the acetabular cup anteversion. However, this method was affected by variations in pelvic position and radiographic technique. In this study, we employed the ischial axis (IA) as an anatomical landmark on the lateral radiographs, and we investigated a relationship between IA and the anterior pelvic plane (APP) using three-dimensional computed tomography (3D-CT). Using these findings, we report a new method for accurate measurement of the acetabular cup anteversion on plain lateral radiographs using IA as an anatomical reference. Materials and Methods:. At first, preoperative3D-CT images were obtained in 109 patients who underwent total hip arthroplasty. The diagnosis was osteoarthritis in all patients. The angle between the IA (defined by a line connecting the anterior edge of the greater sciatic notch and the lesser sciatic notch) and APP (defined by the bilateral anterosuperior iliac spine and the symphysis) was measured on 3D-CT (Fig. 1). Secondly, postoperative lateral radiographs were obtained at 2 weeks, 4 weeks, 12 weeks, 24 weeks, and 52 weeks after surgery in 15 patients. The angle between a line tangential to the opening of the cup and a line perpendicular to APP was measured (Fig. 2). Three methods of acetebular cup position assessment were compared: 1) the present method, 2) Woo and Morrey method, and 3) software (2D template, Kyocera) method. Results:. The mean angle between IA and APP was 18.0 ± 3.5°. The mean acetabular cup anteversion measured using present method was 21.3°, Woo and Morrey method was 26.6°, and software method was 21.2°. The mean SDs of present method was 0.64°, Woo and Morrey method was 1.17°, and software method was 0.46°. Conclusions:. APP, considered as vertical in weight bearing, has a relatively consistent relationship between IA. The findings of this study provide a more consistent measurement of acetabular cup by reducing variation due to pelvic position

Originally introduced in 1997, porous tantalum is an attractive alternative metal for orthopaedic implants because of its unique mechanical properties. Porous tantalum has been used in numerous types of orthopaedic implants, including acetabular cups in total hip arthroplasty. The early clinical results from porous tantalum acetabular cups have been promising. The purpose of this study was to evaluate the presence of bone ingrowth and the incidence of osteolytic lesions in the acetabular cup -at 10 year follow up – in patients who had a total hip arthroplasty with a monoblock porous tantalum acetabular cup. 50 consecutive patients underwent a total hip arthroplasty with a monoblock porous tantalum acetabular component. All patients had computed tomography at an average of 10 years of follow-up. The computed tomography scan used a standard, validated protocol to evaluate bony ingrowth in the cup and for the presence of osteolysis. The computed tomographic scans showed evidence of extensive bony ingrowth, and no evidence of osteolysis. This study reports the 10-year results of a monoblock porous tantalum acetabular cup. This is the first study to evaluate a porous tantalum acetabular cup with the use of computed tomography. These results show that a porous tantalum monoblock cup has excellent bony ingrowth and no evidence osteolysis at 10 year follow-up. These results suggest that porous tantalum is an attractive material for implantation in young, active patients

Introduction. Durable bone fixation of uncemented porous-coated acetabular cups can be observed at a long-term, however, polyethylene (PE) wear and osteolysis may affect survivorship. Accurate wear measurements correlated with clinical data may offer unique research information of clinical interest about this highly debated issue. Objetive. We assessed the clinical and radiological outcome of a single uncemented total hip replacement (THR) after twenty years analysing polyethylene wear and the appearance of osteolysis. Materials and Methods. 82 hips implanted between 1992 and 1995 were prospectively evaluated with a mean follow-up of 20.6 years (range, 18 to 23). A hemispherical porous-coated acetabular cup matched to a proximally hydroxyapatite-coated anatomic stem and a 28 mm standard PE liner, sterilised by gamma irradiation in air, was used in all hips. Radiological position and the possible appearance of loosening and osteolysis were recorded over time. Penetration of the prosthetic head into the liner was measured by the Roentgen Monographic Analysis (ROMAN) Tool at 6 weeks, 6 months, one year and yearly thereafter. Results. Six cups were revised due to wear and four due to late dislocation. All cups were radiographically well-fixed and all stems showed radiographic ingrowth. Six un-revised hips showed osteolysis on the acetabular side and two on the proximal femoral side. Creep at one year was 0.30 (±0.23) mm. Mean total femoral head penetration was 1.23 mm at 10 years, 1.52 mm at 15 years and 1.92 mm at 23 years. Overall mean wear was 0.12 (± 0.1) mm/year and 0.09 (±0.06) mm/year after the creep period. Mean wear was 0.08 (± 0.06) mm/year in hips without osteolysis and 0.14 (±0.03) mm/year in revised hips or with osteolysis (p<0.001). Conclusions. Although continued durable fixation can be observed with a porous-coated cups and a proximally hydroxyapatite-coated anatomic stem, true wear continues to increase at a constant level over time. PE wear remains as the main reason for revision surgery and osteolysis in uncemented THR after twenty years

We measured the proximal migration of 265 acetabular cups over seven years and correlated the findings with clinical outcome and acetabular revision for aseptic loosening. Cups which eventually became aseptically loose were shown to migrate more rapidly than successful cups. The average proximal migration at two years postoperatively for four groups of cups showed a monotonic relationship to the acetabular revision rate for aseptic loosening at 6.5 years. We conclude that acetabular cups which develop aseptic loosening as evidenced by pain, revision or screw fracture show increased proximal migration by one year, and that the 'migration rate' at two years can be used to predict the acetabular revision rate from aseptic loosening at 6.5 years

In laboratory tests, the ultra-high molecular weight polyethylene used for the acetabular cups of Charnley hip prostheses has a very low wear rate against steel. In the body radiographic measurements indicate that the polyethylene wears more rapidly. In order to investigate this higher wear rate, the sockets of acetabular cups removed at post-mortem have been examined using optical and electron microscopy. It has been shown that a socket wears predominantly on its superior part and that this is a direct consequence of the orientation of the cup in the body and the direction of loading of the hip. In the worn region the femoral head in effect bores out a new socket for itself, a process which is visible with the naked eye after approximately eight years. Electron microscopy shows that the predominant wear mechanism is adhesion, but after about eight years the appearance of surface cracks suggests that surface fatigue is taking place in addition to this. Laboratory wear tests have shown that pure surface fatigue is not sufficient to account for the high clinical wear rate. Other deformation processes are suggested and discussed with regard to the higher clinical wear rate

Aims: Given that all previous reports on the increased-crystalinity, increased modulus of elasticity, yield strength and density Hylamer polyethylene have been based on observations on uncemented metal-backed acetabular cups, the aim of the present study is to investigate the rate of wear of a cemented Hylamer UHMWPE acetabular cup. Methods: 36 consecutive cases of THA (mean age: 54.7 years) using a cemented Hylamer UHMWPE acetabular cup and a cemented femoral stem were prospectively followed-up with yearly radiographs for an average period of 54.4 months. Two-dimensional femoral head penetration was determined from AP pelvic radiographs, using computeraided uniradiographic methodology. Multiple regression analysis was used to identify all predictor variables that may account for increased average linear and calculated volumetric wear (Kabo’s formula), as well as for increased total area of peri-prosthetic osteolysis on the femoral and acetabular sides. Results: The average linear wear rate was 0.35 mm/year (SD 0.12) with a significantly high average linear wear rate during the initial (‘wear-in’) period (approximately 12–18 months). The average total volumetric wear was calculated to 764.4 mm3 and the average volumetric wear rate to 169.8 mm3/year. Significant osteolysis was seen in an average of 1.5 (range: 0 to 7) out of the 7 Gruen zones on the femoral side and an average of 1 (range: 0 to 3) out of the 3 Charnley-Delee zones on the acetabular side. Conclusions: Increased rate of linear wear and a high rate of peri-prosthetic osteolysis have been observed in the early results of our series of cemented Hylamer UHMWPE acetabular cups

We examined radiographic polyethylene wear in 233 cemented total hip arthroplasties (201 patients) with either a metal-backed or a non-metal-backed acetabular cup. All patients had identical cemented one-piece titanium femoral stems with a femoral head diameter of 28 mm. The mean linear wear rate was 0.11 mm/yr in metal-backed sockets and 0.08 mm/yr in non-metal-backed sockets (p = 0.0002). The mean volumetric wear rate was 66.2 mm3/yr in the metal-backed sockets and 48.2 mm3/yr in the polyethylene sockets (p = 0.0002). The addition of metal backing to a cemented acetabular cup therefore resulted in a 37% increase in mean polyethylene wear rates which may partially explain the higher failure rate of cemented metal-backed cups. Linear regression analysis also implicated increased follow-up time (log), gross acetabular migration, metal backing and male gender in increasing polyethylene wear. We advocate the use of an all-polyethylene cup in cemented total hip arthroplasty. The increased polyethylene wear must also cause concern about the wear rate of uncemented metal-backed acetabular sockets

Background. Trust in the validity of a measurement tool is critical to its function in both clinical and educational settings. Acetabular cup malposition within total hip arthroplasty (THA) can lead to increased dislocation rates, impingement and increased wear as a result of edge loading. We have developed a THA simulator incorporating a foam/Sawbone pelvis model with a modified Microsoft HoloLens® augmented reality (AR) headset. We aimed to measure the trueness, precision, reliability and reproducibility of this platform for translating spatial measurements of acetabular cup orientation to angular values before developing it as a training tool. Methods. A MicronTracker® stereoscopic camera was integrated onto a HoloLens® AR system. Trueness and precision values were obtained through comparison of the AR system measurements to a gold-standard motion capture system”s (OptiTrack®) measurements for acetabular cup orientation on a benchtop trainer, in six clinically relevant pairs of anteversion and inclination angles. Four surgeons performed these six orientations, and repeated each orientation twice. Pearson”s coefficients and Bland-Altman plots were computed to assess correlation and agreement between the AR and Motion Capture systems. Intraclass correlation coefficients (ICC) were calculated to evaluate the degree of repeatability and reproducibility of the AR system by comparing repeated tasks and between surgeons, respectively. Results. The trueness of the AR system was 0.24° (95% CI limit 0.92°) for inclination and 0.90° (95% CI limit 1.8°) for anteversion. Precision was 0.46° for inclination and 0.91° for anteversion. There was significant correlation between the two methods for both inclination (r = 0.996, p<0.001) and anteversion (r = 0.974, p<0.001). Repeatability for the AR system was 0.995 for inclination and 0.989 for anteversion. Reproducibility for the AR system was 0.999 for inclination and 0.995 for anteversion. Conclusion. Measurements obtained from the enhanced HoloLens® AR system were accurate and precise in regards to determining angular measurements of acetabular cup orientation. They exceeded those of currently used methods of cup angle determination such as CT and computer-assisted navigation. Measurements obtained were also highly repeatable and reproducible, therefore this platform is accurately validated for use in a THA training simulator

Introduction. Appropriate acetabular cup orientation is an important factor in reducing instability and maximising the performance of the bearing after Total Hip Arthroplasty (THA). However, postoperative analyses of two large cohorts in the US have shown that more than half of cups are malorientated. In addition, there is no consensus as to what inclination and anteversion angles should be targeted, with contemporary literature suggesting that the orientation should be customised for each individual patient. The aim of this study was to measure the accuracy of a novel patient specific instrumentation system in a consecutive series of 22 acetabular cups, each with a customised orientation. Methodology. Twenty-two consecutive total hip replacement patients were sent for Trinity Optimized Positioning System (OPS) acetabular planning (Optimized Ortho, Sydney). The Trinity OPS planning is a preoperative, dynamic analysis of each patient performing a deep flexion and full extension activity. The software calculates the dynamic force at the hip to be replaced and plots the bearing contact patch as it traces across the articulating surface. The software modelled multiple cup orientations and the alignment which best centralised the load was chosen by the surgeon from the preoperative reports. Once the target orientations had been determined, a unique patient specific guide was 3D printed and used intra-operatively with a laser guided system to achieve the planned alignment, Fig 1. All patients received a post-operative CT scan at 3 months and the radiographic cup inclination and anteversion was measured. The study was ethically approved by The Avenue Hospital Human Research Ethics Committee, Trial Number 176. Results. The mean planned radiographic inclination, reference to the Anterior Pelvic Plane (APP), was 42.8° (range 36.2° – 50.1°). The mean planned radiographic anteversion, reference to the APP, was 28.3° (range 19.4° – 37.0°). Only 23% of the planned orientations fell within Lewinnek's “safe zone”, taking into consideration that that this safe zone is not comparable to the coronal plane of radiographs. However, all 22 cups were planned within a range of 40° ± 10° of inclination and 25° ± 10° of anteversion, when referenced to the coronal plane when supine. The mean inclination difference between the planned and achieved orientations was −1.3° (range −7.6° – 9.2°). The mean anteversion difference was 1.2° (range −5.3° – 7.0°). The mean absolute difference was 4.2° for inclination (range 0.4° – 9.2°) and 3.6° for anteversion (range 0.6° – 7.0°). All 22 cups were within ±10° of their intended target orientation, Fig 2. All 22 cups were within the range of 40° ± 10° of inclination and 25° ± 10° of anteversion, when reference to the coronal plane when supine, Fig 3. Conclusions. These are the early results of a new technology for planning and delivering a customised acetabular cup orientation. We expect further improvements in accuracy with current developments. However, the results suggest that Trinity OPS is a simple way to achieve a patient-specific cup orientation, with accuracy comparable to imageless navigation

Introduction. Durable bone fixation of uncemented porous-coated acetabular cups can be observed at a long-term, however, polyethylene (PE) wear and osteolysis may affect survivorship. Accurate wear measurements correlated with clinical data may offer unique research information of clinical interest about this highly debated issue. Objetive. We assessed the clinical and radiological outcome of a single uncemented total hip replacement (THR) system after twenty years analysing polyethylene wear and the appearance of osteolysis. Materials and Methods. 82 hips implanted between 1992 and 1995 were prospectively evaluated. The mean follow-up was 20.6 years (range, 18 to 23). A hemispherical porous-coated acetabular cup matched to a proximally hydroxyapatite-coated anatomic stem and a 28 mm standard PE liner, sterilised by gamma irradiation in air, was used in all hips. Radiological position and the possible appearance of loosening and osteolysis were recorded over time. Penetration of the prosthetic head into the liner was measured by the Roentgen Monographic Analysis (ROMAN) Tool at 6 weeks, 6 months, one year and yearly thereafter. Results. Six cups were revised due to wear and four due to late dislocation. All cups were radiographically well-fixed and all stems showed radiographic ingrowth. Six un-revised hips showed osteolysis on the acetabular side and two on the proximal femoral side. Creep at one year was 0.30 (±0.23) mm. Mean total femoral head penetration was 1.23 mm at 10 years, 1.52 mm at 15 years and 1.92 mm at 23 years. Overall mean wear was 0.12 (± 0.1) mm/year and 0.09 (±0.06) mm/year after the creep period. Mean wear was 0.08 (± 0.06) mm/year in hips without osteolysis and 0.14 (±0.03) mm/year in revised hips or with osteolysis (p<0.001). Conclusions. Although continued durable fixation can be observed with a porous-coated cups and a proximally hydroxyapatite-coated anatomic stem, true wear continues to increase at a constant rate over time. PE wear remains as the main reason for revision surgery and osteolysis in uncemented THR and does not stop after twenty years

Introduction: Hip resurfacing is a successful pain-relieving procedure which restores function in young patients. However, some patients have persisting pain. We suggest that load characteristics in relation to position of the cup may influence these symptoms. We aimed to determine the effect of acetabular cup inclination angle on pain following hip resurfacing. Methods: 92 consecutive hips in 81 patients were resurfaced with the ASR prosthesis. The average age was 56.5 years (35–72). 33 were female hips. Harris Hip Scores (HHS) and UCLA activity scores were recorded pre-operatively and at last follow-up. Patient satisfaction was recorded. Acetabular cup inclination angle was measured. An acceptable angle for hip replacement is 45 degrees +/− 5 degrees. We therefore grouped cups into those above 50 degrees and those below. Average follow-up was 17.9 months (8–31). There were 39 hips with an angle less than 50 degrees (A), and 53 greater than 50 (B). Patients in each group were comparable for age, sex, follow-up and BMI. Results: In group A HHS improved from 53.4 to 98.7 and UCLA activity score improved from 4.2 to 7.5. All patients were extremely or very pleased. In group B HHS improved from 49.0 to 94.0 and UCLA activity score improved from 3.9 to 7.1. 48 of 53 patients were extremely or very pleased. At follow up 37 of 39 (95%) of patients in group A had no pain. In group B 35 of 53 had no pain (66%). This is a statistically significant difference when analysed with Fisher’s exact test (p< 0.05). Discussion: This study shows that an excessively open acetabular cup may contribute to persisting pain and patient dissatisfaction. This may be a result of excessive eccentric wear and metal ion deposition, and may lead to early failure of the prosthesis

Iliopsoas tendonitis after total hip arthroplasty (THA) can be a considerable cause of pain and patient dissatisfaction. The optimal cup position to avoid iliopsoas tendonitis has not been clearly established. Implant designs have also been developed with an anterior recess to avoid iliopsoas impingement. The purpose of this cadaveric study was to determine the effect of cup position and implant design on iliopsoas impingement. Bilateral THA was performed on three fresh frozen cadavers using oversized (jumbo) offset head center revision acetabular cups with an anterior recess (60, 62 and 66 mm diameter) and tapered wedge primary stems through a posterior approach. A 2mm diameter flexible stainless steel cable was inserted into the psoas tendon sheath between the muscle and the surrounding membrane to identify the location of the psoas muscle radiographically. CT scans of each cadaver were imported in an imaging software. The acetabular shells, cables as well as pelvis were segmented to create separate solid models of each. The offset head center shell was virtually replaced with an equivalent diameter hemispherical shell by overlaying the outer shell surfaces of both designs and keeping the faces of shells parallel. The shortest distance between each shell and cable was measured. To determine the influence of cup inclination and anteversion on psoas impingement, we virtually varied the inclination (30°/40°/50°) and anteversion (10°/20°/30°) angles for both shell designs. The CT analysis revealed that the original orientation (inclination/anteversion) of the shells implanted in 3 cadavers were as follows: Left1: 44.7°/23.3°, Right1: 41.7°/33.8°, Left2: 40/17, Right2: 31.7/23.5, Left3: 33/2908, Right3: 46.7/6.3. For the offset center shells, the shell to cable distance in all the above cases were positive indicating that there was clearance between the shells and psoas. For the hemispherical shells, in 3 out of 6 cases, the distance was negative indicating impingement of psoas. With the virtual implantation of both shell designs at orientations 40°/10°, 40°/20°, 40°/30° we found that greater anteversion helped decrease psoas impingement in both shell designs. When we analyzed the influence of inclination angle on psoas impingement by comparing wire distances for three orientations (30°/20°, 40°/20°, 50°/20°), we found that the effect was less pronounced. Further analysis comparing the offset head center shell to the conventional hemispherical shell revealed that the offset design was favored (greater clearance between the shell and the wire) in 17 out of 18 cases when the effect of anteversion was considered and in 15 out of 18 cases when the effect of inclinations was considered. Our results indicate that psoas impingement is related to both cup position and implant geometry. For an oversized jumbo cup, psoas impingement is reduced by greater anteversion while cup inclination has little effect. An offset head center cup with an anterior recess was effective in reducing psoas impingement in comparison to a conventional hemispherical geometry. In conclusion, adequate anteversion is important to avoid psoas impingement with jumbo acetabular shells and an implant with an anterior recess may further mitigate the risk of psoas impingement

INTRODUCTION. Total hip arthroplasty (THA) is regarded as one of the most successful surgeries in medicine. However, recent studies have revealed that ideal acetabular cup implantation is achieved less frequently than previously thought, as little as 50% of the time. It is well known that malalignment of the acetabular component in THA may result in dislocation, reduced range of motion, or accelerated wear. This study reports accuracy of a tactile robotic arm system to ream the acetabulum and impact an acetabulur cup compared to manual instrumentation. METHODS. 12 fresh frozen cadaveric acetabulae were pre-operatively CT scanned and 3D templating was used to plan the center of rotation, and anteversion and inclination of the cup. Each specimen received THA, six prepared manually and six prepared with robotic arm guidance. Tactile, visual, and auditory feedback was provided through robotic guidance as well as navigated guided reaming and cup impaction. The robotic guidance constrained orientation of instruments thus constraining anteversion, inclination, and center of rotation for reaming, trialing, and final cup impaction. Post-operative CT scans were taken of each specimen to determine final cup placement for comparison to the pre-operative plans. RESULTS. In all cases, robotic arm guidance resulted in ±4° of anteversion and ±5° of inclination each relative to the pre-operative plan. Absolute RMS errors were 2.16 ± 1.35° for anteversion and 1.91 ± 1.55° for inclination. Cup placement with robotic guidance was significantly more accurate and precise than placement with manual instruments. With manual instrumentation the errors were, on average, 4.0 times higher in anteversion and 5.9 times higher in inclination compared to robotic instrumentation. CONCLUSION. This tactile robotic system substantially improved the accuracy of acetabular reaming and placement of the final cup compared to traditional manual techniques. With greater knowledge of ideal acetabular cup position, highly accurate techniques may allow surgeons to decrease the risk of dislocation, promote durability and improve the ability to restore appropriate leg length and offset. Tactile robotics has proven to be safe and effective in both knee and hip surgery and provides the potential to redefine the “instrument set” used for orthopedic procedures

Revision hip arthroplasty for severe acetabular deficiency is a technically challenging operation. Many different methods have been described for the management of acetabular deficiency. These include augmentation with bone cement, structural allografts, impaction grafting, support rings with graft and reconstruction with a high centre of rotation. The long term results of many of these methods were variable. We reviewed the outcome of a stemmed acetabular cup (McMinn cup, Link UK) used with morsellised bone graft for revision hip arthroplasty with severe acetabular deficiency. The implant was used only in the most severe cases of acetabular deficiency where it was impossible to achieve stable fixation using simpler methods. This device was used in only 13 out of 265 revision arthroplasties performed by the senior author. Between 1995 and 2002 13 acetabulae were reconstructed using a stemmed acetabular cup and non-structural morsellised bone graft. All were revision procedures with the number of previous operations on the same hip ranging between 1 and 4. 2 patients died from causes not related to surgery. 1 hip was revised for persistent discharge although no organisms were identified on repeated cultures. The mean follow-up of the remaining 10 hips was 72 months (range 46 – 108 months). All patients were satisfied with the results and their function improved significantly post-operatively. 8 of the 10 people report no pain from the hip and 2 reported slight or occasional pain which did not interfere with their activities at last follow-up. The mean Harris Hip Score was 84.6 (range 70 to 99.8). Radiological assessment showed regeneration of acetabular bone stock. Some X-Rays showed proximal migration of the cup but with no evidence of loosening at last follow-up. Acetabular reconstruction using the McMinn stemmed acetabular cup is a useful technique in revision hip arthroplasty with severe acetabular deficiency

Since the autumn of 2003, a computer-assisted system (VectorVision® Hip, version 2.1, Brain LAB, Germany) has been used to perform total hip arthroplasty (THA) operations in our hospital. In the present study, the postoperative acetabular cup position was evaluated using the records of the system and the data measured from postoperative radiographs. To date, 18 patients have been treated using this-system. We studied the cup inclination and anteversion records in this system recorded in the THA procedures. We also measured the cup inclination and anteversion using postoperative radiographs, according to the method described by Pradhan. The inclination and ante-version were the ‘operative’angles for this system and were the ‘radio graphical’ ones for measuring from the radiographs according to the definition described by Murray. The initial planning of the acetabular cup position was 45° ‘operative’ inclination and 20° ‘operative’ ante-version. From the system records, the average ‘operative’ inclination was 46.5°± 3.9° and the average ‘operative’ anteversion was 25.5°± 6.0°. The average ‘radio graphical’ inclination measured from the postoperative radiographs was 49.0°± 6.0°, and the average ‘radio graphical’ anteversion was 10.6°± 5.8°. Between the ‘operative’ angles from this system and the ‘radio graphical’ angles from the postoperative radiographs, the inclination was approximately the same, while the anteversion was different. When the ‘radio graphical’ anteversion was corrected for X-ray beam spreading and then converted to the ‘operative’ anteversion, the resulting ‘operative’ anteversion was 21.1°± 7.8°. And when the ‘operative’ anteversion recorded by this system was corrected for the pelvic tilt, the corrected ‘operative’ anteversion was 22.1°± 6.5°. The average difference between these corrected ‘operative’ anteversion in each case was 5.8°± 3.8°. Especially in 10 of the 18 cases, each difference was within 5°. The accuracy of the cup position using this computer-assisted system was shown by this study

Introduction: Tantalum Monoblock Acetabular cup was designed to reduce backside wear and stimulate osseo-integration of cup with bone. The cup has peripheral fit to improve the initial stability and further stability and longevity depends on the osseointegration of cup with acetabulum. The revision cup was intended to give added stability with screws in case of defective rim or large acetabulum. The aim of this study is to assess the radiological outcome following tantalum monoblock revision cup in total hip replacement. Methods: Between 1999 and 2000, 32 Tantalum mono-block revision acetabular cups was used in 31 patients. Standard hip radiographs were performed during post op, at three months, six months and then annually. X rays were assessed for loosening in De Lee and Charnley zones and for migration of cup. Results: At a minimum follow-up of 2 years (range 2 to 5 years), 31 hips in 30 patients were assessed. The average age of the patient was 62.4 years (39–78 years). Three Brookers type 1 and one type 2 heterotrophic ossification was seen. There was a gap of 2–5mm in Zone 1(6 patients), 1–5mm in Zone 2 (8 Patients) and 5mm in Zone 3 of one patient. At final follow up, all the gaps were filled, except for one, where 5mm gap was persistent. There was no migration of cup or problems with screws. All the patients were satisfied with the operation. Conclusion: Short term radiological result following uncemented revision tantalum monoblock acetabular cup in total hip replacement is highly encouraging. However, similar results from other centres and long term follow up studies are necessary to confirm the efficacy of the revision cups

Introduction. The National Joint Registry of England, Wales, Northern Ireland, and the Isle of Man (NJR) monitors the performance of primary total hip arthroplasty (THA) implants and summarizes usage and outcomes for specific hip systems. The objectives of this study were to 1) determine if survivorship for the PROCOTYL® L acetabular cup, a hemispherical press-fit cup coated with hydroxyapatite and a metal on XLPE articulation, is significantly different from all other cementless cups in the NJR and 2) to analyze patient reported outcomes measures (PROMs) at a minimum five year follow-up for the subject cup. Methods. The database of the NJR was searched for demographic information and survivorship data for all THAs performed with the PROCOTYL® L cup (metal on XLPE) and all other cementless cups. Survivorship data for both groups was adjusted to exclude metal on metal bearings and compared for all revisions and acetabular revisions only. The Cox Proportional Hazards model for the revision risk ratio of the subject cup to all cementless cups was also calculated. Patients with the subject cup implanted for at least five years were mailed a PROMs program questionnaire consisting of the Oxford Hip, EQ-5D, and EQ VAS scores. No pre-operative PROMs scores were collected. Results. Patient demographic information for the subject system and all cementless cups is provided in Figure 1. As seen in Figure 2, the six-year survivorship for the 1,172 THAs using the subject system (97.8%) was slightly higher than the survivorship for all cementless cups (97.5%), but the difference was not statistically significant (Figure 3). The 1, 2, and 5 year survivorship for the subject cup also exceeded the survivorship of all cementless cups, but without statistically significant differences. When just the cup was revised, the subject system survivorship was similar to survivorship for all cementless cups for years 1 through 6 (Figure 2). Patients with the subject system implanted for an average of 5.73 – 5.75 years reported average Oxford Hip, EQ-5D, and EQ VAS Scores of 39.13 ± 9.93, 0.775 ± 0.273, and 75.87 ± 17.71, respectively. Conclusions. The subject acetabular cup was associated with survivorship similar to that of other cementless acetabular cups. Patients implanted with the subject system for at least five years reported what are considered satisfactory Oxford Hip, EQ5D, and EQVAS score outcomes. These results represent the first report of midterm outcomes with the subject system. For figures/tables, please contact authors directly.

Introduction: Malpositioning of the acetabular cup component in total hip arthroplasty can result in increased wear, early nonseptic loosening and is the most common cause of dislocation. Previous research has defined a safe zone with an inclination of 40±10 degrees and anteversion of 15±10 degrees. The purpose of this study was to compare cup placement using imageless navigation to a historical control group using CT based measurements. Methods: 34 patients receiving a primary hip replacement between June 2005 and December 2006 were enrolled in the study. Alignment of the implant is based on the acquisition of landmarks (ASIS and pubic tubercle) and placement of tracking pins into the ASIS. The target position for all patients was 45 degrees of inclination and 15 degrees of anteversion. The position was determined by postoperative Ct scans of the pelvis. This group was compared to a matched control group. Results: Descriptive statistics revealed that the demographics of both groups were comparable. Mean cup placement in the navigation group was 46.6±5.9 deg of inclination and 18.8±5.6 deg of anteversion. Mean cup placement in the control group was 48.4±8.85 deg of inclination and 22.33±10.9 deg of anteversion. With navigation 73.7% resp 89.5% of cups were placed within the safe zone for inclination resp. anteversion whereas only 56.2% resp. 50% of cups were placed with freehand technique. Taking both inclination and anteversion into consideration 68.4% of cups were placed in the safe zone with navigation. Only 12.5% were placed for both inclination and anteversion were placed into the safe zone. Discussion: Computer navigation for total joint arthroplasty, if helpful to the surgeon, has to increase reliability of component placement and show a significant reduction in variation compared to freehand techniques. Our results demonstrate that imageless navigation is a reliable tool which significantly increases precision of acetabular cup placement. Further studies are needed to evaluate and further increase the accuracy of the system

We wanted to solve the problem of acetabular dysplasia with a cementless total hip endoprothesis by using a smaller acetabular cup in order to fit the size of the dysplastic acetabulum without using any additional bone transplantation for superstructure of the acetabulum. By using this type of acetabular reconstruction we can preliminarily conclude that the bone superstructure of the acetabulum can be avoided and that problems may occur if remodelation of the bone transplant has failed. Irregular biomechanical bending in the supraacetabular region can also be avoided. Uncured developmental dysplasia of the hip joint (DDH) is a huge problem to solve in elderly patients. DDH can be expressed in several forms according to stage, i.e., in young and elderly patients we can find different consequences, from slight to moderate supraacetabular dysplasia combined with anterior dysplasia, valgus and anteversion of the proximal femur, to high hip luxation. In efforts to find a better way to solve slight and moderate supraacetabular dysplasia (in some cases combined with high luxation), we have tried to use a smaller acetabular cup that will fit the dysplastic acetabulum, combined with a higher hip centre, dysplastic polyethylene, and a longer femoral neck to avoid leg length discrepancy and weakness of the gluteal musculature. From January 1999 to January 2000 we performed the above-mentioned type of operation in 33 patients (25 females, 8 males) with dysplastic coxarthrosis of the hip. Age range was from 32 to 63 years. In all cases we performed the application of a Zimmer or Biomet smaller acetabular cementless cup after reaming the acetabulum near the internal lamina of the iliac bone. Good primary fixation of the acetabulum was achieved in all of the cases. Supraacetabular reconstruction was not used. In some cases where the dysplasia was very expressive, we left the acetabular cup uncovered for about 0.5 cm. In the postoperative period we advised the patient to load the operated leg over two crutches without full weight bearing for approximately six weeks. After that time period and according to clinical and radiographic findings, we prescribed walking with one crutch, and walking without crutches four months later. The follow-up period is short but preliminary results of our study are satisfactory. There were no early postoperative complications. Incorporation of bone was good in the acetabular cups measured with radiographs and in some cases with Tc99m. In some cases where we left part of the cup uncovered, there was supraacetabular formation of new bone after six months

Objectives. Total hip replacement is increasingly being conducted in younger and more active patients, so surgeons often use bearing surfaces with improved wear characteristics, such as ceramic on ceramic. The primary objective of this study was to determine if survivorship for a BIOLOX® delta ceramic on delta ceramic couple used with the PROCOTYL® L acetabular cup is significantly different from all other cementless cups in a large arthroplasty registry. The secondary objective of this study was to analyze patient reported outcomes measures (PROMs) of the subject cup with a minimum five year follow-up. Methods. Patient demographics and survivorship data was collected from the National Joint Registry of England, Wales, Northern Ireland, and the Isle of Man (NJR) database for all total hip replacements performed with the PROCOTYL® L cup used in combination with a delta-on-delta articulation, as well as for all other cementless cups. Survivorship data was compared for all revisions and cup revisions only and data was adjusted to exclude metal on metal articulations. The hazard ratio of the subject system to all cementless cups was also calculated with the Cox Proportional Hazards model. Patients with the subject components implanted for a minimum of five years completed Oxford Hip, EQ-5D, and EQ VAS score questionnaires. Results. The patient demographic data collected for the subject components and all cementless cups is provided in Figure 1. Six-year survivorship for the subject cup (98.6%) was similar to survivorship for all cementless cup revisions in the NJR database (98.5%), as seen in Figure 2. When the cup alone was revised, six-year survivorship of the subject cup (98.6%) and all NJR cementless cups (98.5%) was also similar. However, the subject cup survivorship remained at 98.6% from 4 to 6 years post-implantation, while survivorship for all cementless cups decreased slightly from years 4 to 6. The similarities between the revision risk of the subject system and all cementless cups in the NJR can be seen in the Cox Proportional Hazards model for revision risk ratios provided in Figure 3. Patients with the subject cup implanted for an average of 5.88 years reported Oxford Hip, EQ-5D, and EQ VAS scores of 39.60 ± 10.78, 0.801 ± 0.259, and 75.49 ± 19.25, respectively. Conclusions. The subject acetabular cup with a ceramic on ceramic articulation exhibited similar survivorship to all other cementless acetabular cups, excluding those with metal on metal bearings, in the NJR. Patients implanted with the subject system for an average of 5.88 years reported what are considered satisfactory Oxford Hip, EQ-5D, and EQ VAS scores. This survivorship and PROMs data is the first report of mid-term outcomes with the subject components

One of important issues of concern in total hip arthroplasty (THA) is osteolysis due to wear debris of ultra-high molecular weight polyethylene (PE), and it often leads to aseptic loosening. Reduction of PE wear debris is essential to prevent osteolysis, and different bearing interfaces as well as improvement of the bearing material itself have been attempted. Alumina ceramics as the bearing material for THA was introduced in Europe and Japan in the 1970s in aim to reduce the PE wear debris. The clinical results have proved the superiority of ceramic on PE couples to metal on PE couples in wear resistance. PE materials cross-liked by irradiation have also demonstrated a significant low wear by in vitro studies. Several types of highly cross-linked polyethylene (CLPE), with the irradiation dose of 50 to 105 kGy, have been developed and extensively used since 1998. In this study, the in vivo wear and oxidation of CLPE acetabular cup combined with ceramic femoral head were evaluated using retrieved cups. Eight retrieved CLPE acetabular cups (Aeonian; Kyocera Corp., Kyoto, Japan, currently Japan Medical Materials Corp., Osaka, Japan) with clinical use for 3–80 months (mean 34 months) were examined. All cups were used against alumina or zirconia ceramic femoral heads. The linear wear of the retrieved CLPE cups was measured using a three-dimensional coordinate measurement machine. The worn surfaces of retrieved CLPE cups were observed by a scanning electron microscope (SEM). Oxidative degradation of the retrieved CLPE cups was expressed in terms of an oxidation index which was calculated from microscopic Fourier transformed infrared spectroscopy analysis, according to ASTM F2102. The linear wear rate of retrieved CLPE cups was in 0.006–0.08 mm/year range, which was similar to the results reported by the previous radiographic study. In the worn surface of the CLPE cup retrieved after clinical use shorter than 39 months, machine marks were observed. In contrast, those retrieved after clinical use of 70 and 80 months were smooth. Oxidation indices of retrieved CLPE cups were: 0.12–0.37 in worn surface and 0.13–0.34 in unworn surface, respectively. There was no difference in the oxidation indices between the worn surface and unworn surface. The retrieved CLPE acetabular cups in this study showed low and stable wear rates. The results showed a notable reduction in wear of the CLPE cups compared to that of conventional PE cups in the previous studies. And also, the oxidation indices of the retrieved CLPE cups were the same level as conventional PE cups. These findings from this retrieval study showed that there is neither progressive wear in the clinical use for 3–80 months, material failures due to wear, delamination nor cracks. The lower wear rate and smooth surface of the CLPE acetabular cup suggest the possibility of reduced wear debris from those cups articulated against the ceramic femoral head. We expect that the CLPE acetabular cup has favorable wear properties in long-term clinical use

Optimal alignment of the acetabular cup component is crucial for good outcome of total hip arthroplasty [THA]. Increased accuracy of implant positioning may improve clinical outcome. To achieve this, patient specific instrumentation was developed. A patient-specific guide manufactured by 3D printing was designed to aid in positioning of the cup component with a pre-operatively defined anteversion and inclination angle. The guide fits perfectly on the acetabular rim. An alignment K-wire in a pre-operatively planned orientation is used as visual reference during cup implantation. Accuracy of the device was tested on 6 cadaveric specimens. During the experiment, cadavers were positioned for a THA procedure using a posterolateral approach. A normal-sized incision was made and approach used as in the conventional surgical procedure. The PSI was subsequently fitted onto the acetabular rim and secured into its unique position due to its patient specific design. The metallic pin was placed in a drill hole of the PSI. Post-operative CT image data of each acetabulum with the placed pin were transferred to Mimics and the 3D model was registered to the pre-operative one. The anteversion and inclination of the placed pin was calculated and compared to the pre-operatively planned orientation. The absolute difference in degrees was evaluated. A secondary test was carried out to assess the error during impaction while observing the alignment K-wire as a visual reference. In a laboratory setting, error during impaction with a visual reference of the K-wire was measured. Deviation from planning showed to be on average 1.04° for anteversion and 2.19° for inclination. By visually aligning the impactor with this alignment K-wire, the surgeon may achieve cup placement as pre-operatively planned. The effect of the visual alignment itself was also evaluated in a separate test-rig showing minimal deviations in the same range. The alignment validation test resulted in an average deviation of 1.2° for inclination and 1.4° for anteversion between the metallic alignment K-wire used as visual reference and the metallic K-wire impacted by the test subjects. The inter-user variability was 0.9° and 0.8° for anteversion and inclination respectively. The intra-user variability was 1.6° and 1.0° for anteversion and inclination respectively. Tests per test subject were conducted in a consecutive manner. We investigated the accuracy of two factors affecting accuracy in the cup insertion with PSI, i.e. accuracies of the errors of bony fitting and cup impaction. Since the accuracy of the major contributing factors to the overall accuracy of PSI for cup insertion with linear visual reference of a metallic K-wire was within the acceptable range of 2 to 3 degrees, we state that the PSI we have designed assists to achieve the preoperatively planned orientation of the cup and as such leads to the reduction of outliers in cup orientation. This acetabular cup orientation guide can transfer the pre-operative plan to the operating room

INTRODUCTION. Dislocation is one of the most important complications in THA. Dual mobility cup (DMC) inserts reduce the risk for dislocation after total hip arthroplasty by increasing the oscillation angle. A lower rate of dislocation with use of a DMC insert has been reported in different studies. But there is no available research that clearly delineates the stability advantages of DMC inserts in primary THA. The aim of our study was to evaluate the area of the safe zone for a DMC insert, compared to a fixed insert for different anteversion angles of the femoral component. Material and Methods. A model of the pelvis and femur were developed from computed tomography images. We defined the coordinate system of the pelvis relative to the anterior pelvic plane and the coordinate system of the femur relative to the posterior condylar plane. In our model, we simulated a positive anteversion position of the acetabular cup. The lower border for cup inclination is 50°. The safe zone was evaluated for the following range of motion of the implant: 120° of flexion, 90° of flexion 30° of internal rotation, 30° of extension, 40° of abduction, 40° of adduction, and 30° of external rotation. (Fig.1) The safe zone was calculated for both a fixed insert and a DMC insert over a pre-determined range of three-dimensional motion, and the effect of increasing the anteversion position of the femoral component from 5° to 35° quantified. The ratio of the safe zone for a DMC insert to a fixed insert was calculated. Results. A wider safe zone was obtained for a DMC insert over all range of motion conditions. A DMC insert increased the stability of the implant between 10° and 15° along both anterior-posterior and vertical axes of the acetabular cup. (Fig.2) When stem anteversion were varied 5°, 10°, 15°, 20°, 25°, 30°, 35°, ratio of safe zone (a DMC insert / a fixed insert) were changed 8, 10.1, 6.3, 4.9, 5.2, 6.6, 10.6. (Fig.3). Discussion. The safe zone of a DMC insert is always larger than a fixed type insert. In every stem anteversion patterns, safe zones were expanded to all direction with 10° to 15°. Under 15° of stem anteversion, area of both inserts are almost stable. Area ratio is lowest with 20° of stem anteversion. Over 25° of stem anteversion, both area decreased and area ratio increased gradually. Over 30° of stem anteverison, safe zone of a fixed type are very small area. It is difficult for us to set acetabular shell in that small area. But we will get a larger area by using DMC. We performed a simulation analysis to evaluate the increase in area of the safe zone when using DMC inserts, compared to fixed inserts. To use of a DMC insert would bring in a 5–11-fold expanded area of the safe zone. In especially, DMC is a useful when stem anteversion is over 30°. For figures/tables, please contact authors directly.

Cup implantation is a critical stage during THR Surgery. It is mainly because of the rudimentary mallet-based impaction technique, whereby mal-positioning and unknown forces are present. There are some technological attempts to solve this problem partially: dealing with mal-positioning while patient remains subjected to non-standardized impaction forces. Our comprehensive approach to the problem allows the surgeon to monitor cup positioning and perform controlled insertion with a completely known force profile. Positioning is monitored by means of IMU (Inertial Measurement Unit) technology, while placement is controlled by force feedback and vibratory insertion device. Both technological building blocks (IMU and vibratory insertor) are embedded on a single device containing signal processing and automatic control strategies. This mechatronic device is called BMD3. This work covers the entire device development life cycle illustrated in figure 1: the roadmap starts at the conceptual inspiration through scientific investigation and concept proof/demonstration up to the BMD3 prototype. Smooth insertion was the main purpose initially; this led to concept demonstration by means of electrical and pneumatic actuated devices. They employ low-amplitude/high-frequency vibratory input forces into the Acetabular Cup to explore constant sliding in the microscale. Although successful, it was noted that there is optimization potential as vibration is used to decrease friction resistance and either impose or prevent specific shape modes on the pelvic structure. A scientific investigation on frictional and structural behavior allowed us to define suitable instrumentation for an automatic insertion strategy (figure 2a). Our technical solution to the smooth insertion problem involves positioning monitoring by means of IMU, simultaneously available to the surgeon while using this tool. An operating procedure was proposed to reliably map and feedback surgeon's movement in the OR (Operating Room) space. Concept demonstration was also performed for this additional feature before complete device integration, see figure 2b. Three main subsystems compose the BMD3: PPU (Power and Processing Unit); Mechatronic Handle; and Replaceable Head. The Replaceable Head allows 1kHz and 20kHz operating ranges; each implemented on a specific mechanism detachable from the Mechatronic Handle. A user (surgeon) may choose one of these versions according to the insertion strategy adopted. The Mechatronic Handle houses sensors, initial signal conditioning stages, and surgeon interaction interfaces like: Thin Film Transistor screen for visual positioning feedback; and a pushbutton for OR space mapping setup. The Mechatronic Handle itself is an interface between Replaceable Head and the PPU. Every insertion and positioning strategy may be updated directly at the PPU; firmware updates deal with real-time processing of pressure, IMU, and vibration measurements. Conclusions of the work summarize intangibles such as inspiration and insights on THR improvement spots; scientific analysis; and technology to the effective problem approach

Purpose:. Correct placement of the acetabular cup is a crucial step in hip replacement to achieve a satisfactory result and remains a challenge with free hand techniques. Imageless navigation may provide a viable alternative to freehand technique and improve placement significantly. The purpose of this project was to assess and validate intra-operative placement values as displayed by an imageless navigation system to postoperative measurement of cup position using high resolution CT scans. Methods:. Thirty-two subjects who underwent primary hip joint arthroplasty using imageless navigation were included. The average age was 66.5 years (range 32–87). 23 non-cemented and 9 cemented acetabular cups were implanted. The desired position for the cup was 45 degrees of inversion and 15 degrees of anteversion. A pelvic CT scan using a multi-slice CT was used to assess the position of the cup radiographically. Results:. Two subjects were excluded because of dislodgement of the tracking pin. Pearson correlation revealed a strong and significant correlation (r=0.68; p<0.006) for cup inclination and a moderate non-significant correlation (r=0.53; p=0.45) between intra-operative readings and cup placement for anteversion. Conclusion:. These findings can be explained with the possible introduction of systematic error. Even though the acquisition of anatomic landmarks is simple, they must be acquired with great precision. An error of 1 cm can result in a mean anteversion error of 6 degrees and inclination error of 2.5 degrees. Whilst computer assisted surgery results in highly accurate cup placements for inclination, anteversion of the cup cannot be

Introduction. Total hip arthroplasty is considered to be one of the most successful orthopaedic interventions. Acetabular component positioning has been shown to affect dislocation rates, component impingement, bearing surface wear rates, and need for revision surgery. The safe zones of acetabular component positioning have previously been described by Lewinnek et al. as 5 to 25 degrees of cup version and 30 to 50 degrees of inclination. Callanan et al. later modified the inclination to 30 to 45 degrees. Our aim was to assess whether THA via robotic assisted posterior approach (PA) improves acetabular component positioning compared to fluoroscopic guided anterior approach THA (AA). Methods. Subjects. This study is a matched-pair case-control study using prospectively collected data from THAs done between January 2012 and December 2013. Patients who underwent primary THA using the PA or AA by the senior surgeons (MH and JAR) were included in the study. Ninety-six patients (of 176; 55%) underwent AA and 80 (of 176; 45%) underwent PA THAs. The matching process was performed by an observer blinded to the radiographic outcomes (EK). Patients were matched for sex and BMI +− 8 units. Seventy-nine patients who had AAs were manually matched to 79 patients who had PAs. Surgical Techniques. For the AA THAs, the patient is supine and the approach is performed through a modified smith Peterson approach. Acetabular cup positioning is assessed intraoperatively with fluoroscopy. For the PA THAs, the patient in the lateral position using the posterior approach. Acetabular cup positioning was guided by the MAKO robotic hip system using preoperative CT scans of the involved hip. Radiographic Measurements. The radiographic measurements were done manually using a standardized technique by two observers blinded to the type of arthroplasty performed. Spearman's rank correlation coefficient was used to test user dependent variability. Means were used for final calculations. Statistical Analysis. The average cup inclination and anteversion angles were calculated. Calculation of the number of hips that were in the safe zones of Lewinnek (inclination, 30°–50°; anteversion, 5°–25°) and Callanan (inclination, 30°–45°; anteversion, 5°–25°) regarding inclination, anteversion, and a combination of both were done for both groups. Independent t-tests were performed to compare both groups for sex, BMI, and inclination and anteversion angles. Fisher's exact test was used to compare both groups regarding the number of hips in the safe zones of Lewinnek and Callanan. Relative risk and absolute risk reduction were calculated. Results. There was no significant difference in BMI between the two groups. Intraobserver agreement was found to be .92 and 0.82 for inclination and anteversion, respectively. Compared to fluoroscopic guided THAs, THAs performed with robot assistance were found to be more often in the safe zone of Lewinnek (90% vs. 75%, p=0.02, RR 0.40 [0.19–0.85] p=0.01). This pattern was observed in the zone of Callanan and approached statistical significance (80% vs. 68%, p=0.11, RR 0.64 [0.37–1.10] p=0.11). Conclusion. Compared to fluoroscopic assisted THA, robot assisted THAs are more likely to be within the safe zone of Callanan and Lewinnek

Between March 1990 and May 1991 we performed 85 primary total hip replacements in 74 patients using the Landos Atoll hydroxyapatite (HA)-coated cup and the Corail HA-coated stem. The patients were followed up for a mean of ten years. Of the 85 cups, 26 (31%) have already been revised and a further six are radiologically unstable and awaiting revision. Two femoral stems have been revised for infection without loosening. The retrieved acetabular cups were studied by SEM and image-processing techniques to quantify the amount of residual HA on the cup. This was correlated with the clinical variables and modes of failure. The residual HA (as a percentage of the surface) on the loose cups correlated negatively with the duration of implantation (r = −0.732, p < 0.001). Six cups were stable at revision and had more residual HA coating than those which were loose (p < 0.01). The rate of failure of the Landos Atoll HA-coated, smooth hemispherical cup with screw fixation is unacceptably high. Resorption of the HA coating is markedly increased in loose cups compared with stable cups. HA coating cannot substitute for stable mechanical fixation

Fracture of the polyethylene acetabular cup is a rare late complication of total hip replacement. Five cases are reported. In each one this followed a fall, and involved a Muller arthroplasty which had previously been symptomless. It is postulated that ridges or other irregularities of bone, produced by keying holes, could lead to areas of thin cement and potential weakness of support for the cup

Purpose. The aim of the study was to assess the efficacy of a cementless acetabular cup without bone grafting in a cohort of patients with protrusio acetabuli who were treated with total hip arthroplasty. Methods. We retrospectively reviewed the records of a cohort of 45 patients with protrusio acetabuli who received elective total hip replacements between 2009 and 2011 at Tygerberg Academic Hospital. We reviewed pre- and post-operative radiographs and the most recent follow-up radiographs (minimum of three months) to assess cup osteointegration. We classified protrusio acetabuli according to Sotelo-Garza and Charnley into mild, moderate and severe, by evaluating pre-operative radiographs. Results. Our cohort of had a median age of 63 years and had a female of male ratio of 4 to 1. The mean follow up was 11 months. We had 9 mild, 29 moderate and 7 severe protrusio cases. At follow-up all cups showed signs of osteointegration with no signs of loosening. Conclusion. The use of a cementless, plasma coated, dual radius acetabular cup without bone grafting in primary THR in protrusio acetabuli provides good primary stability with satisfactory short term radiological outcome. NO DISCLOSURES

Introduction: The Opera Acetabular cup (Smith and nephew) was designed in North Manchester General and has been in use since 1997. The initial results were with multiple surgeons, different approaches and 2 different stems. We report the early results of the opera cup in primary hip replacements using the C-Stem. Methods: This is a prospective radiological follow up of patients operated on between June 2000 and November 2004. 202 consecutive primary hip replacements were carried out using the Opera cup and a standard C-stem. All operations were performed by a single surgeon using the posterior approach. Initial and annual x-rays were studied and the following measurements taken: cup angle; radiolucent lines in the bone-cement interface of the acetabulum; heterotopic ossification; radiolucent lines or osteolysis in the femoral component and stem orientation. Results: Full data is available in 166 hips performed on 149 patients. Average follow up is 37 months (12–65). 84 patients were female and 65 male. There were 56 left hip replacements, 76 right hip replacements and 17 were bilateral. 162 hips had an elite head whereas 4 had a ceramic head. Average cup angle was 44.6 degrees. 20 Cups had 0.5mm lucency in zone 1 of the acetabulum and 1 cup had 1mm lucency in zone 1. None were progressive. 14 patients had grade 1 heterotopic ossification 3 patients had grade 2. 1 stem was in valgus and 13 stems were in varus. Complications were 1 calcar fracture and 1 greater trochanter fracture (both of which required circlage wires). There was also 1 temporary femoral nerve palsy which resolved in 3 months. There were no fatal PE’s, deep infections or dislocations. No hips have required revision. Discussion: We conclude that in the short term the Opera cup is performing to the standard required by NICE

Purpose:. Malpositioning of the acetabular cup component in total hip arthroplasty can result in increased wear, early nonseptic loosening and is the most common cause of dislocation. Previous research has defined a safe zone with an inclination of 40±10 degrees and anteversion of 15±10 degrees. The purpose of this study was to compare cup placement using imageless navigation to a matched control group using CT based measurements. Methods:. 30 patients receiving a primary hip replacement were included. Alignment of the implant is based on the acquisition of landmarks (ASIS and pubic tubercle) and placement of tracking pins into the ASIS. The target position for all patients was 45 degrees of inclination and 15 degrees of anteversion. A multi-slice CT scan was used to assess cup position. Results:. There was no significant difference between mean inclination (p=0.11) and anteversion (p=0.24) but a statistically significant difference for mean deviation from the desired position for inclination (p=0.003) and anteversion (p=0.007). There was a significant difference in the percentages of correctly placed cups with inclination (p=0.046) and with anteversion (p=0.006). Combining both anteversion and inclination there was a significant difference (p=0.01). Conclusion:. Computer navigation for total joint arthroplasty, if helpful to the surgeon, has to increase reliability of component placement and show a significant reduction in variation compared to freehand techniques. We demonstrated a significant increase in accuracy of placement of acetabular cups within the desired position and safe zone using imageless navigation

The existing image-free Total Hip Arthroplasty (THA) navigation systems conventionally utilise the patient-specific Anterior Pelvic Plane (APP) as the reference to calculate orientations of the implanted cup, e.g. anteversion and inclination angles. The definition of APP relies on the intra-operative digitisation of three anatomical landmarks, the bilateral Anterior Superior Iliac Spine (ASIS) and the pubicum. Due to the presence of the thick soft tissue around the patient's pubic region, however, the landmark on pubic area is hard to be digitised accurately. A novel reference plane called Intra-operative Reference Plane (IRP) was proposed by G. Zheng et al to address this issue. To determine the IRP, bilateral ASIS and the cup center of the operating side instead of the pubicum are digitised intra-operatively. It avoids the error-prone digitisation of pubicum, and the angle between the patient-specific APP and the suggested IRP can be computed pre-operatively by a single X-ray radiograph-based 2D/3D reconstruction approach developed by G. Zheng et al. Based on this angle, the orientation of the APP can be intra-operatively estimated from that of the IRP such that all measurements with respect to IRP can be transformed to measurements with respect to APP. In order to implement and validate this new reference plane for image-free navigation of acetabular cup placement, we developed an IRP-based image-free THA navigation system. All cup placement instruments were mounted with passive markers whose positions could be traced by a NDI Polaris® infrared camera (Northern Digital Inc, Ontario, Canada). The cup center was obtained by first pivoting a tracked impactor with appropriate size of the mounted trial cup and then calculating the pivoting center through a least-squares fitting. The bilateral ASIS landmarks were acquired through the percutaneous pointer-based digitisation. We tested this new IRP-based image-free THA navigation system in our laboratory by conducting twelve studies on two dry cadaver pelvises and two plastic pelvises. The ground truth for each study was established using the conventional APP-based method, i.e., in addition to those landmarks required by our IRP-based method, we also digitised the pubicum on respective pelvic bones and calculated cup orientations on the basis of the digitised APP. The mean and standard deviation of differences between the proposed IRP-based anteversion measurement and the ground truth are 1.0 degree and 0.7 degree, while the maximal and minimal differences are 2.1 degree and 0.3 degree respectively. The mean and standard deviation of differences between the proposed IRP-based inclination measurement and the ground truth are respective 0.2 degree and 0.2 degree. Moreover, the maximum of differences is 0.5 degree and the minimum is 0.0 degree. Our laboratory experimental results demonstrate that the new IRP-based image-free navigation system is accurate enough for acetabular cup placement. In comparison to existing image-free navigation systems that use APP as the reference plane, the newly developed system employs IRP as the reference plane, which has the advantage to eliminate the digitisation of landmarks around the pubic region. The successful validation with the laboratorial study has led us to the next step of clinical trials. We expect to report preliminary clinical cases in the near future

Background. Complications such as dislocations, impingement and early wear following total hip arthroplasty (THA) increase with acetabular cup implant malorientation. These errors are more common with low-volume centres or in novice hands. Currently, this skill is most commonly taught during real surgery with an expert trainer, but simulated training may offer a safer and more accessible solution. This study investigated if a novel MicronTracker® enhanced Microsoft HoloLens® augmented reality (EAR) headset was as effective as one-on-one expert surgeon (ES) training for teaching novice surgeons hip cup orientation skill. Methods. Twenty-four medical students were randomly assigned to EAR or ES training groups. Participants used a modified sawbone/foam pelvis model for hip cup orientation simulation. A validated EAR headset measured the orientation of acetabular cup implants and displayed this in the participant”s field of view. The system calculated the difference between planned and achieved orientation as a solid-angle error. Six different inclination and anteversion combinations, related to hypothetical patient-specific anatomy, were used as target orientations. Learning curves were measured over four sessions, each one week apart. Error in orientations of non-taught angles and during a concealed pelvic tilt were measured to assess translation of skills. A post-test questionnaire was used for qualitative analysis of procedure understanding and participant experience. Results. Novice surgeons of similar experience in both groups performed with a similar error prior to training (ES: 15.7°±6.9°, EAR: 14.2°±7.1°, p>0.05). During training, EAR participants were guided to significantly better orientation errors than ES (ES: 6.0°±3.4°, EAR: 1.1°±0.9°, p<0.001). After four training sessions, the orientation error in both groups significantly reduced (ES: 15.7°±6.9° to 8.2°±4.6°, p<0.001; EAR: 14.2°±7.0° to 9.6°±5.7°, p<0.001). Participants in both groups achieved the same levels of orientation accuracy in non-taught angles and when the pelvis was tilted (p>0.05). In post-training evaluation, participants expressed a preference towards ES rather than EAR for learning orientation skills and related visuospatial and procedure-specific skills. 79% of participants indicated EAR simulator training and ES in combination would be their preferred training method. Discussion. A novel head-mounted EAR platform delivered training to novice surgeons more accurately than an expert surgeon. Both EAR and ES enabled novices to acquire and retain skills on a learning curve to orientate the implant. These skills were translated to non-taught orientations and in the presence of a pelvic tilt. Conclusions. Augmented-reality simulators may be a feasible and valid method for teaching novice surgeon”s visuospatial skills for THA on a learning curve, to compliment traditional intraoperative training

1. Prosthetic acetabular cups of the Charnley and McKee-Farrar designs were cemented into cadaveric pelves using different procedures for preparing the acetabulum. 2. The torsional moments needed to loosen these cups were measured. 3. The torsional moments so measured were found to be from about four to more than twenty times higher than the frictional moments measured in independent tests on the two designs of prosthesis. 4. It is argued that late looseness of the acetabular component after total hip replacement, in the absence of infection, seems most likely to be due to thermal damage to the bone occurring at the time of polymerisation of the cement, and to subsequent bone resorption. 5. Surgical preparation of the acetabulum should include removal of all the articular cartilage and cleaning of the acetabular fossa, but the drilling of additional holes in the floor of the acetabulum seems unimportant. 6. The possibility of fatigue fracture in bone as a factor contributing to late loosening is an argument in favour of metal-on-polyethylene prostheses with their lower frictional moments, although the importance of this factor cannot be estimated

Aims:Malpositioning of implant components plays a signiþcant role in instability of THR. Our aim was the determination of the inßuence of anteversion of the acetabular cup. Methods: The biomechanical study was performed on a model which enables different deþned implant positions. Rotation of the femoral stem are carried out in different anteversion positions of the acetabular cup with the hip joint in neutral position and in 90¡ ßexion, as well as inclination of the cup. The range of motion (ROM) is determined until impingement or dislocation is evident, as well as the recording of the resisting moment. Results: While the resisting moment shows minor deviation in several anteversion (AV) positions with the joint in neutral position, being almost independent from the inclination, a major difference is determined with minimal resisting moment with minor retroversion (RV) and with the hip joint in 90¡ ßexion (0,51 Nm/15¡ RV vs. 3,69 Nm/30¡ AV). Dislocation occurs very early due to low ROM at retroversion. Variation of inclination of 30¡ can only increase ROM until dislocation by 2,8¡. With same inclinations angles ROM is increased by 38,1¡ in the 30¡ AV. Conclusions: Correct anteversion of the acetabular component is a signiþcant factor in prevention of dislocation. Minor differences in anteversion are more important than inclination variation to improve stability of THR

Introduction. Plain radiograph underestimates the lysis extent while bone defect determines acetabu-lar revision. We determine the multislice computed tomography (CT) efficacy with metal-artifact minimization to calculate the volume, extent and location of lytic lesions around a loose acetabular cup. Patients and Methods. 48 hips with a loose acetabular cup were evaluated before cup revision. Multislice CT scans with metal-artifact minimization (Toshiba-MEC CT) were done. Scans were taken at 135 kV and 250 mA to maximize the resolution and bone contrast. CT slice thickness was 3 mm and reconstruction index 1.5 mm. Evidence of osteolytic lesion on these scans was compared with plain radiographs and with intraoperative findings. Bone defects were classified according to Paprosky. Results. Acetabular lysis were found in the radiographs of 18 hips and in the CT scans of 36 hips. The most frequent locations of osteolysis were medial (32 hips) and posterior walls (23 hips). Radiographs underestimated the extent of the lysis: there were 28 hips with radiographic type 1 defects and 16 hips with CT defects; 6 and 11 with type 2; 8 and 10 with type 3A; and 6 and 11 with type 3B respectively (Wilcoxon test, p< 0.001). The mean volumetric bone loss was 35.4 cm3 . Intraoperative findings confirmed CT findings. Conclusions. Multislice CT scans with metal-artifact minimization is more sensitive for identifying and quantifying osteolysis around the cup than are plain radiographs. Since CT scans allow us to show the extent and location of the osteolysis, they are useful to plan cup revision

Introduction. Plain radiograph underestimates the lysis extent while bone defect determines acetabular revision. We determine the multislice computed tomography (CT) efficacy with metal-artifact minimization to calculate the volume, extent and location of lytic lesions around a loose acetabular cup. Patients and Methods. 48 hips with a loose acetabular cup were evaluated before cup revision. Multislice CT scans with metal-artifact minimization (Toshiba-MEC CT) were done. Scans were taken at 135 kV and 250 mA to maximize the resolution and bone contrast. CT slice thickness was 3 mm and reconstruction index 1.5 mm. Evidence of osteolytic lesion on these scans was compared with plain radiographs and with intraoperative findings. Bone defects were classified according to Paprosky. Results. Acetabular lysis were found in the radiographs of 18 hips and in the CT scans of 36 hips. The most frequent locations of osteolysis were medial (32 hips) and posterior walls (23 hips). Radiographs underestimated the extent of the lysis: there were 28 hips with radiographic type 1 defects and 16 hips with CT defects; 6 and 11 with type 2; 8 and 10 with type 3A; and 6 and 11 with type 3B respectively (Wilcoxon test, p< 0.001). The mean volumetric bone loss was 35.4 cm3 . Intraoperative findings confirmed CT findings. Conclusions. Multislice CT scans with metal-artifact minimization is more sensitive for identifying and quantifying osteolysis around the cup than are plain radiographs. Since CT scans allow us to show the extent and location of the osteolysis, they are useful to plan cup revision

Laboratory wear testing of ultra high molecular weight polyethylene from 12 Charnley acetabular cups, removed after periods of up to 17.5 years showed that the large patient-to-patient variations in clinical penetration rate cannot be explained by batch-to-batch variation in the wear resistance of the material. Nor was there any evidence of a time-dependent degradation in wear resistance of the material

Hydroxyapatite-coated acetabular cup were used in revision hip arthroplasty without using bone grafts or bone substitutes to achieve osseointegration in 30 consecutive hips (29 patients). The mean age was 72.5 years (range 54 to 88). Primary prosthesis was 14 Charnley’s, 12 Capital 3M, one Furlong, one Exeter and one MacKee Farrar. Indication for revision was aseptic loosening in 20, recurrent dislocation in four, periprosthetic fracture in two, prosthesis fracture in one, and three infected hips. Patients were assessed clinically using Harris Hip Score, satisfaction questionnaire and quality of life SF 36 questionnaire, and radiologically using DeLee and Charnley, Harris-Barrack, and Hodgkinson’s Engh’s classification, and Bassetlaw Digital Scoring System (BDSS) that we have devised. The acetabular defects were assessed preoperatively using the American Academy of Orthopaedic Surgeons (AAOS) classification. Mean follow up was 38.7 months (range 18.5–76.4). Ninety present of acetabular cups had preoperative radiolucency in all DeLee and Charnley’s zones. 26 hips (87%) had no superior or lateral cup migration. Two hips had 3 mm superior migration at one year then remained stable. Mean improvement of Harris hip score was 42.2. 83.3% of hips had no or slight pain at final follow up. Five patients had dislocations one of which was recurrent that required acetabular cup revision. Two patients had postoperative foot drop that recovered fully. Two patients had postoperative wound infection that healed with antibiotics apart from one who died due to multi-organ failure. Four patients died due to unrelated causes. Postoperative radiographs showed stable fixation of all acetabular cups. 83.3% of hips had no or slight pain at final follow up. Early results show that stable fixation in revision hip surgery can be obtained with HAC acetabular cups without bone grafts or bony substitute

Introduction. Iliopsoas tendonitis after total hip arthroplasty (THA) can be a considerable cause of pain and patient dissatisfaction. The optimal cup position to avoid iliopsoas tendonitis has not been clearly established. Implant designs have also been developed with an anterior recess to avoid iliopsoas impingement. The purpose of this cadaveric study was to determine the effect of cup position and implant design on iliopsoas impingement. Materials. Bilateral THA was performed on three fresh frozen cadavers using oversized (jumbo) offset head center revision acetabular cups with an anterior recess (60, 62 and 66 mm diameter) and tapered wedge primary stems through a posterior approach. The relatively large shell sizes were chosen to simulate THA revision cases. At least one fixation screw was used with each shell. A 2mm diameter flexible stainless steel cable was inserted into the psoas tendon sheath between the muscle and the surrounding membrane to identify the location of the psoas muscle radiographically. Following the procedure, CT scans were performed on each cadaver. The CT images were imported in an imaging software for further analysis. The acetabular shells, cables as well as pelvis were segmented to create separate solid models of each. To compare the offset head center shell to a conventional hemispherical shell in the same orientation, the offset head center shell was virtually replaced with an equivalent diameter hemispherical shell by overlaying the outer shell surfaces of both designs and keeping the faces of shells parallel. enabled us to assess the relationship between the conventional shells and the cable. The shortest distance between each shell and cable was measured. To determine the influence of cup inclination and anteversion on psoas impingement, we virtually varied the inclination (30°/40°/50°) and anteversion (10°/20°/30°) angles for both shell designs. Results. The CT analysis revealed that the original orientation (inclination/anteversion) of the shells implanted in 3 cadavers were as follows: Left1: 44.7°/23.3°; Right1: 41.7°/33.8°; Left2: 40.0/17; Right2: 31.7/23.5; Left3: 33.0/2908; Right3: 46.7/6.3. For the offset center shells, the shell to cable distance in all the above cases were positive indicating that there was clearance between the shells and psoas. For the hemispherical shells, in 3 out of 6 cases, the distance was negative indicating impingement of psoas. With the virtual implantation of both shell designs at orientations 40°/10°, 40°/20°, 40°/30° we found that greater anteversion helped decrease psoas impingement in both shell designs. When we analyzed the influence of inclination angle on psoas impingement by comparing wire distances for three orientations (30°/20°, 40°/20°, 50°/20°), we found that the effect was less pronounced. Further analysis comparing the offset head center shell to the conventional hemispherical shell revealed that the offset design was favored (greater clearance between the shell and the wire) in 17 out of 18 cases when the effect of anteversion was considered and in 15 out of 18 cases when the effect of inclinations was considered. Discussion. Our results indicate that psoas impingement is related to both cup position and implant geometry. For an oversized jumbo cup, psoas impingement is reduced by greater anteversion while cup inclination has little effect. An offset head center cup with an anterior recess was effective in reducing psoas impingement in comparison to a conventional hemispherical geometry. In conclusion, adequate anteversion is important to avoid psoas impingement with jumbo acetabular shells and an implant with an anterior recess may further mitigate the risk of psoas impingement

Purpose:. Imageless navigation has improved the accuracy of acetabular cup placement but relies on manual identification of pelvic anatomy. Thick soft tissues in obese patients could obscure these landmarks and result in large variances of cup placement. The purpose of this study was to investigate the relationship between BMI, soft tissue thickness, navigated cup and final post-operative cup position. Methods:. Thirty patients with an average age of 66.5 years underwent primary navigated THA. Final intra-operative cup position was recorded. Soft tissue thickness and final post-operative cup alignment were measured on a multi-slice pelvis CT scan. Results:. There were no significant relationships between the variables for inclination. Larger ranges were observed in the obese group. It reached significance for the difference between the desired and final post-operative cup position (p=0.007). There was a moderately significant relationship (r=0.41, p=0.0002) between soft tissue thickness and final cup anteversion and a strong and near significant correlation (r=0.6, p=0.07) for the difference between the desired and final post-operative cup position for anteversion. Similar to inclination larger ranges were observed in the obese group. However, significant differences were only observed for final post-operative cup position (p=0.002) and the difference between the desired and final post-operative cup position (p=0.0003). Conclusion:. Despite the potential introduction of error with acquisition of landmarks, our data suggests that in obese patients the overlying soft-tissue thickness has no significant effect on the accuracy on acetabular cup inclination. In contrast anteversion is influenced by the overlying soft tissue thickness and obesity

Malpositioning of the acetabular cup component in total hip arthroplasty can result in increased wear, early nonseptic loosening and is the most common cause of dislocation. Previous research has defined a safe zone with an inclination of 40±10 degrees and anteversion of 15±10 degrees. The purpose of this study was to using CT based measurements. 32 patients receiving a primary hip replacement between June 2005 and December 2006 were enrolled in the study. Alignment of the implant is based on the acquisition of landmarks (ASIS and pubic tubercle) and placement of tracking pins into the ASIS. The target position for all patients was 45 degrees of inclination and 15 degrees of anteversion. The position was determined by postoperative Ct scans of the pelvis. This group was compared to a historical control group. Descriptive statistics revealed that the demographics of both groups were comparable. Mean cup placement in the navigation group was 46.6±5.9 deg of inclination and 18.8±5.6 deg of anteversion. Mean cup placement in the control group was 45.8±9.5 deg of inclination and 27.3±15.0 deg of anteversion. With navigation 73.7% resp 89.5% of cups were placed within the safe zone for inclination resp. anteversion whereas only 60.9% resp. 39% of cups were placed with freehand technqie. Taking both inclination and anteversion into consideration 68.4% of cups were placed in the safe zone with navigation. Only 25.7% were placed for both inclination and anteversion were placed into the safe zone. Computer navigation for total joint arthroplasty, if helpful to the surgeon, has to increase reliability of component placement and show a significant reduction in variation compared to freehand techniques. Our results demonstrate that imageless navigation is a reliable tool which significantly increases precision of acetabular cup placement. Further studies are needed to evaluate and further increase the accuracy of the system

Introduction: Trabecular metal associated with monob-lock elliptical design represents a valid surgical solution for orthopaedic acetabular reconstructive procedures and second surgery. Materials and methods: From 1999 to 2004, 61 patients between 45 and 81 years with osteoathritis underwent total hip primary arthroplasties with porous tantalum elliptical cup. We performed clinical evaluation through Harris Hip Score test. Bone-implant interface was studied through radiography with reference to the three Charnley’s areas. Follow-up were performed preoperatively at six months and yearly thereafter. Results: Clinical results showed high improvement of Harris Hip Score (average preoperatively score was 46, postoperatively 90). Radiographic evaluation revealed a bone apposition to the porous tantalum without radiolucent lines around the acetabular interface. No local (osteolysis) or general (DVT) complication was seen. Conclusions: Tantalum monoblock elliptical acetabular cup with high volumetric porosity, flexibility and high biocompatibility associated with particular microstructure permits direct apposition of bone, more extensive osseointegration with the maximum bone contact. The trabecular metal cup increases the initial stability helping in the prevention of osteolysis and loosening in a five years follow up

We report the long-term radiological results of 58 total hip arthroplasties (THA) using the Charnley offset-bore acetabular socket. Wear was measured at four sites and radiolucent lines and possible migration were recorded. Four cups were retrieved at revision and were examined using light microscopy, SEM and X-ray microanalysis. At a mean follow-up of seven years the mean wear in the DeLee and Charnley zone I was 0.4 mm and in zone II 0.26 mm. The wear rate was 0.06 and 0.04 mm/year, respectively. Progression of radiolucent lines was seen in five cases (8.6%). Three sockets (5.2%) were revised because of aseptic migration at a mean follow-up of 9.8 years and one socket for infection at two years. The offset-bore acetabular cup had excellent wear behaviour and a low migration and revision rate. We recommend that it should be considered in THA since the use of small cups is increasing, particularly in revision cases

We describe a new method for the accurate measurement of the angle of anteversion of an acetabular cup from standard anteroposterior radiographs, and provide the conversion tables required. The effect of the centering of the radiograph is discussed and a method of distinguishing between anteversion and retroversion by using a caudally directed x-ray beam is described

Obtaining consistently an optimal cup orientation in THA is vital to obtain adequate head coverage and maximum impingement free range of motion and thus reduce the incidence of polyethylene wear, cup loosening, and dislocation rates associated with a limited range of motion. It is clear that THA instability, the most frequent cause of early failure, is a complex problem related to a wide range of causes. However cup orientation is one of the surgeon dependant potentially modifiable variables that continue to have an important influence due to the lack of reliable means of assuring an adequate orientation of the components, particularly the cup anteversion. Standard mechanical guides like Muller’s have been shown to be inaccurate and imprecise. Not surprisingly, dislocation is the most frequent short term complication after a THA. Acetabular cup orientation is a key factor determining joint stability and one of the most important ones under the surgeons’ control. An in vitro study was used to determine the precision, reproducibility and ease of use of a new mechanical guide in comparison to a standard mechanical guide Müllers. The new guide (Gravity Assisted Navigation System) consists of a simple to use navigation tool. It uses the constant direction of the force of gravity identified by two bulls’ eye levels providing real time intraoperative augmented reality thus controlling the orientation of the pelvis. Visualisation of the guide from a single perspective is enough to determine in real time, the orientation of the cup in abduction and anteversion. By using anatomic repairs within the pelvis its flexion/extension is taken into consideration. As part of an invitro study, 310 press-fit acetabular cups were impacted into a plastic model of a pelvis by 5 surgeons (Power 90%, Type I error 5%), The orientation obtained was measured with respect to a fixed reference of 15° of anteversion and 45° of abduction. Results: an average of 10.4° anteversion ,(Range 3°to 21°, Standard of Deviation 5.0°) for Müller s guide and of 0.4° anteversion (Range 1° to 3°, Standard of Deviation 0.7°) for the new guide and an average of −4.7° abduction (Range 7° to −11°, Standard of Deviation 2.3°) for Müllers guide and 0.3° abduction (Range 0° to 3°, Standard of Deviation 0.5°) for the new guide. The average time required for the orientation of the cups was similar with both guides. (6 seconds for Mullers guide and 5 seconds for the new guide) The precision and reproducibility of the cup orientation obtained with the new guide were significantly better than those obtained with Müllers guide (p< 0.00001). The results obtained with with the new mechanical guide are encouraging. The in vitro results are encouraging, the high precision and accuracy are comparable to results obtained by computer assisted navigation systems in similar studies

Introduction. Acetabular cup lucency predicts cup survival. The relationship of subchondral plate removal and cup survival is unclear. Using data from a prospective study conducted between January 1999 and January 2002 we investigated the role of subchondral plate removal in cemented acetabular cup survival at five years. Methods. A number of cemented cups were implanted using antero-lateral and posterior approaches.1400 cups were inserted. 935 cups (67%) were followed up at 5 years and acetabular radiolucency (AR) recorded. Results. F: M ratio was 1.88. The mean age was 66 (range 23–94). 325 cups had AR. AR was commonest in zone 1 (274). 126 cups has AR isolated to zone 1 only. AR ranged from 1–3 mm. Bone surface was clean and dry in 780 cases. High viscosity cement was used in 1391cases. Simplex was the commonest cement used (749) followed by CMW1 (347). Conventional UHMWPE acetabular liner was used in 755 and “Duration” in 644 patients. 719 Exeter cups and 363 flanged cups were inserted. Acetabular roof was decorticated in 844 and cement pressurised in 1269 cups. AR was more common if cement was not pressurised (52/78 not pressurised vs 268/850 pressurised, p=0.000), if subchondral plate was removed (219/561, p=0.002), and if Simplex or CMW1 was used instead of Palacos (p=0.000). AR after subchondral plate removal was equally common in the young and the older patients (>65 years). There was no difference in cup (p=0.55) or pressuriser type (p= 0.45) between those with or without AR. In a logistic regression model only cement pressurisation and type of cement used were predictive of AR (n=895, p=0.000). Subchondral bone removal became insignificant (p=0.443). Discussion. AR was only affected by cement pressurisation and type of cement used. Subchondral plate removal did not prove likely to affect 5 year cup survival

Failure of an acetabular cup is uncommon and has been attributed to wear or creep, trauma or bony irregularities in the acetabulum. We report ten cases in which fracture of the cup occurred at the site of drill holes used to anchor the marker wire. The role of such indentations as stress raisers has not been previously reported; we suggest that deep indentations or grooves should not be placed in the most highly stressed areas and that the cup thickness should allow for predicted wear rates

Introduction. Computer-assisted methods for acetabulum cup navigation have shown to be able to improve the accuracy of the procedure, but are time-consuming and difficult to use. The goal of this project was to develop an easy-to-use navigation technique, requiring minimal equipment for acetabular cup alignment. Material. A preoperative CT scan was obtained, a 3D model of the acetabulum was created, the pelvic plane determined and the cup orientation planned. A registration area, which included the accessible part of the acetabular fossa and the surrounding articular surface, was chosen for the individualised guide. A guidance cylinder, aligned along the planned cup orientation, was attached in the centre of the guide. To transfer the planned alignment information from the registered guide to the impacting of the cup, we developed an intraoperative guidance method based on inertia sensors. The sensors were aligned orthogonal to the central cylinder of the patient-specific guide and the orientation was recorded. At the time of impacting the cup, the sensors were attached to the impactor and the surgeon used the recorded information for the alignment of the impactor. Results. To measure the accuracy of the proposed registration method, we performed an in-vitro trial on three fresh-frozen hemipelves with seven participants. The deviation between the planned and registered inclination averaged 3.01° (StDev 5.7). In anteversion, we measured an average error of 4.33° (StDev 2.8). We tested the feasibility of the proposed method in a clinical trial. The postoperative radiographic measured angles in this trial were 45° anteversion (planned 45°) and 25° inclination (planned 20°). Discussion. We introduce a novel method for computer-assisted cup alignment, which is easy to integrate into the surgical workflow. Our preliminary results suggest that this method is accurate. However, further clinical studies are necessary to verify its clinical feasibility and accuracy

Purpose of the study: Dislocation of total hip arthroplasty remains a frequent complication, occurring for 0.5% to 10% of implants depending on the series. In about 30% of the cases, the orientation of the acetabular cup is involved. It is sometimes difficult to visualize the acetabular landmarks during surgical procedures performed for revision or with a minimally invasive technique. The surgeon uses the position of the pelvis on the operative table as a guide. It can be noted however that the patient’s weight bearing on the table is not constant during the entire operation, potentially changing the position of the pelvis during the procedure. We evaluated the use of a visual referential visible within the operative field for implanting the prosthetic cup. Material and methods: The method materialized the anterior plane of the pelvis then transferred geometrically this plane for display on the ipsilateral iliac crest. The pelvis was masked under a drape, in lateral decubitus. The cup was implanted 12 times using the plane of the floor as the reference, 8 times using the acetabular rim as the reference, and 10 times using the iliac reference. The goal was 20° anteversion in the sagittal plane and 45° inclination in the frontal plane. The position of the pelvis was randomized. The final positions of the cup, of the iliac reference, of the anterior plane of the pelvis and of the floor were recorded with an optical system. Spearman’s test was used to search for correlations. Results: Using the floor referential, mean anteversion was 21.8° (15–30.9°) and mean inclination 43.2° (37–47.6°). Using the acetabular referential, mean anteversion was 21.7° (18.1–26.6°) and mean inclination 45.8° (40.9–48.6°). With the iliac referential, mean anteversion was 20.3° (17.3–25.5°) and mean inclination 43.3° (41.1–44.8°). Mean error between the pelvic plane and the iliac referential was, for anteversion −0,32° (−1.07 to 0.8°) and for inclination, −0.1° (−0.95 to 1.43°). Implantation with the iliac referential was not correlated to the position of the pelvis. When the plane of the floor was used, the position of the implant was correlated with pelvic anteversion (p< 0.01) and inclination (p< 0.01). Discussion: Insertion of the cup was independent of the position of the pelvis within a 3D referential in the operative field. In addition to computer-assisted navigation, simple tools can be developed to improve the surgeon’s perception in difficult indications, especially when they can provide satisfactory accuracy. A clinical feasibility study is currently under way

Ten acetabular cups coated with hydroxyapatite (HA) had originally been inserted in five primary and five revision total hip replacements. The thickness of the HA was 155 ± 35 μm. The cups, which were well-fixed, were retrieved, with their adherent tissue, at reoperation after 0.3 to 5.8 years because of infection (five hips), wear of polyethylene (three hips), and instability (two hips). Undecalcified sections showed a direct contact between bone and osteoid-like tissue which had formed directly onto the HA coating. The area within the threads and their mirror images, as well as the implant-tissue interfaces consisted of similar amounts of bone and soft tissue. Degradation of HA was seen in all hips. The mean thickness of the remaining HA coating was 97 μm (95% CI 94 to 101). The metal interface comprised 66% HA. The HA-tissue interface contained more bone than soft tissue (p = 0.001), whereas the metal-tissue interface included more soft tissue than bone (p = 0.019). Soft tissue at the implant interface and poor replacement of HA by bone may interfere with long-term fixation

Introduction. In total hip arthroplasty, the positioning of the acetabular cup, in particular, has been shown to play an important role in the survivorship of the prosthetic joint. The commonly accepted “safe zone” extends from 5–30° of anteversion to 30–50° of inclination. However, several studies have utilized a more restrictive safe zone of 5–25° of anteversion and 30–45° of inclination, a modification of the Lewinnek zone. Many attempts have been made to develop a more reliable method of positioning the acetabular component. Robotic-assisted surgery is one such method. The purpose of this study was to compare the resulting position of the acetabular component after robotic-assisted surgery with the intraoperative robotic data to determine if improved accuracy can be achieved with the robotic-assisted method. Methods. One hundred and nineteen patients received THA, at four different medical centers in the United States, using a haptic robotic arm. Pre-operative CT scans were obtained for all patients and used during the planning of the procedure, at which point the proposed component size and positioning was determined. Preparation of the acetabular bone bed, as well as impaction of the acetabular component itself, was performed using the robotic device. Using an AP Pelvis and Cross-Table Lateral radiograph, each patient's resulting acetabular inclination and version was measured using the Hip Analysis Suite software. The component position retrieved from the robot was compared to the measured values from the radiographs. The positioning data was compared to two safe zones described above. Results. Of the 119 surgeries performed, 110 could be read with the hip analysis suite software. Radiographically, the average inclination was 40.4° ± 4.1° with a range of 27.4°–53.7° and the average anteversion was 21.5° ± 6.1° with a range of 5.2°–42.6°. As measured inter-operatively, 100% of the components fell within the Lewinnek safe zone and 96% fell within the more restrictive safe zone. Radiographically, 88% of the cases fell within the Lewinnek safe zone and 73% fell within the restrictive safe zone. The mean difference between the inclination and version of the component determined by the robot and by radiographic analysis was 0.31° and 2.1° respectively. Conclusions. The inclination and version of the acetabular components implanted with robotic assistance as determined inter-operatively were within the commonly accepted limits in all cases. Variations between the cup positions determined inter-operatively and from the post-operative radiographs are related to differences in the radiographic project of the hip and the robotic registration of the pelvis from CT images. In no procedure was the radiographic inclination greater than 54° or version less than 5°. In this study, the use of robotic-assisted positioning of the acetabular component has significantly reduced the variability of component orientation. This improved reliability of positioning should result in an increase of favourable functioning, and a decrease in early complications such as dislocation, impingement, and component wear

Reconstruction following internal hemipelvectomy for bone tumors remains a major surgical challenge. Most of the cases are considered not suitable for reconstruction because of high complication occurrence. Allografts coupled with standard prosthesis is a reliable method of reconstruction. 26 patients received a McMinn stemmed cup (Link, Germany) after periacetabular tumor resection from February 1999 to 2006. In 18 patients the reconstruction followed resection of the acetabular area while in other 8 an extrarticular resection of the proximal femur was performed. In 21 cases a stemmed acetabular cup were associated with massive bone allograft. There were 13 female and 13 male with a mean age of 41 years (13 to 70). Average follow-up was 45 months (7 to 105). Six patients were affected by local recurrence of the tumour and five underwent hindquarter amputation. In 4 of them the index surgery followed a previous recurrence of the tumour. Finally 6 patients died for related causes within 2 years. All the other 20 have been followed clinically and radiographically for a minimum of 24 months. Deep infection occurred in one case, there were no cases of dislocation. Radiolucency at the prosthesis-bone interface was observed in 3 cases, 2 patients had proximal migration < of 20 mm. Only one patient was treated for aseptic loosening because of incorrect initial position of the implant. The iliac osteotomy was consolidated in all cases, while a delayed union was frequently observed in the pubic osteotomy, however without compromise the stability of implant. Functional result were evaluated according to the MSTS system and this showed 65% of excellent or good clinical results. The procedure requires appropriate patient selection, accurate preoperative planning, meticulous selection and preparation of allograft. Usually artificial ligaments are applied to reduce hip instability, however, this type of reconstruction do not require complex fixation, thus reducing surgical time and early complications

Malorientation of the acetabular cup in Total Hip replacement (THR) may contribute to premature failure of the joint through instability (impingement, subluxation or dislocation), runaway wear in metal-metal bearings when the edge of the contact patch encroaches on the edge of the bearing surface, squeaking of ceramic-ceramic bearings and excess wear of polyethylene bearing surfaces leading to osteolysis. However as component malorientation often only occurs in functional positions it has been difficult to demonstrate and often is unremarkable on standard (usually supine) pelvic radiographs. The effects of spinal pathology as well as hip pathology can cause large rotations of the pelvis in the sagittal plane, again usually not recognized on standard pelvic views. While Posterior pelvic rotation with sitting increases the functional arc of the hip and is protective of a THR in regards to both edge loading and risk of dislocation, conversely Anterior rotation with sitting is potentially hazardous. We developed a protocol using three functional positions – standing, supine and flexed seated (posture at “seat-off” from a standard chair). Lateral radiographs were used to define the pelvic tilt in the standing and flexed seated positions. Pelvic tilt was defined as the angle between a vertical reference line and the anterior pelvic plane. Supine pelvic tilt was measured from computed tomography. Proprietary software (Optimized Ortho, Sydney) based on Rigid Body Dynamics then modelled the patients’ dynamics through their functional range producing a patient-specific simulation which also calculates the magnitude and direction of the dynamic force at the hip and traces the contact area between prosthetic head/liner onto a polar plot of the articulating surface. Given prosthesis specific information edge-loading can then be predicted based on the measured distance of the edge of the contact patch to the edge of the acetabular bearing. Results and conclusions. The position of the pelvis in the sagittal plane changes significantly between functional activities. The extent of change is specific to each patient. Spinal pathology can be an insidious “driver” of pelvic rotation, in some cases causing sagittal plane spinal imbalance or changes in orientation of previously well oriented acetabular components. Squeaking of ceramic on ceramic bearings appears to be multi factorial, usually involving some damage to the bearing but also usually occurring in the presence of anterior or posterior edge loading. Often these components will appear well oriented on standard views [Fig 1]. Runaway wear in hip resurfacing or large head metal-metal THR may be caused by poor component design or manufacture or component malorientation. Again we have seen multiple cases where no such malorientation can be seen on standard pelvic radiographs but functional studies demonstrate edge loading which is likely to be the cause of failure [Fig 2]. Clinical examples of all of these will be shown

A novel CT-free image-guided navigation system for acetabular cup placement has been designed, implemented and evaluated in laboratory and clinical environments. The most common postoperative complications for total hip arthroplasty (THA), subluxation and dislocation, is directly related to acetabular component orientation. Recent developments in the area of CT-based cup navigation have proven to be a valuable aid. However, a CT scan often unwarranted and has a significant impact on the total cost of treatment. The method proposed in this paper utilizes reference coordinates from the anterior pelvic plane (APP) to compute the angular orientation of the cup. The APP is aligned to a vertical plane of a standing patient defined by the two anterior superior iliac spines and the pubic tubercles. A hybrid strategy for the acquisition of these landmarks has been introduced involving percutaneous pointer-based digitization with the possibility of non-invasive bi-planar landmark reconstruction using multiple registered fluoroscopy images. An intuitive graphical user interface, combined with a sterile virtual keyboard control, effectively support the navigation of acetabular preparation and cup placement. A detailed validation of the system was performed in a laboratory setting. Seven full body human specimens were used to confirm the APP reference concept using custom made software to simulate worst case scenarios. System usability was evaluated throughout an early clinical trial involving 25 patients. A postoperative study of all patients found that the accuracy was better than 4° inclination and 5° anteversion under standard clinical conditions. This implies that there is no significant difference in performance from the established CT-based navigation methods

Introduction: Many designs exist for the femoral component of cemented total hip arthoplasty, but cemented acetabular cups are largely similar. All are essentially hemispheres, made of polyethylene. An important factor determining survival time of cemented implants is cement penetration into the surrounding bone. To ensure sufficient penetration, many surgeons remove the smooth subchondral bone in the acetabulum and drill anchoring holes. This may however weaken the bone. Larger cement pressure during setting will improve penetration. For an acetabular cup, fixation at the rim is most important to prevent loosening, and therefore cement pressure should be high at the rim. A spherical geometry is not ideal to ensure high rim cement pressures. Based on a computer model of cement pressure generation during cup insertion, we designed an improved geometry to ensure higher rim pressures. The aim of this study is to compare the fixation strength of this new design to a conventional design. The effect of the design change will be compared with that of drilling anchoring holes and removing subchondral bone. Methods: From a larger stock of young bovine acetabula, 14 similarly sized specimens were chosen. Twelve were prepared for a factorial experiment with three factors, based on three cup designs (Ogee either with or without flange, DePuy, Leeds, and the alternative design), preservation or removal of subchondral bone, and presence or absence of anchoring holes. Depth, diameter and position of the anchoring holes were chosen to optimise fixation strength. Two were prepared for replicates of two experiments with the new design, both with sub-chondral bone removed. The order of the experiments was randomised. CMW-3 cement (CMW-DePuy, UK) was hand-mixed for one minute. After four minutes, it was packed in the acetabulum and pressurised for one minute. Then a cup was inserted and manual force applied until setting of the cement. Next, acetabulum and cup were mounted in a materials testing machine and torque applied to the cup until gross failure. Applied force and displacement were sampled into a computer, and used to determine maximum torque. Results and Discussion: Analysis was done in two steps. First, two-way ANOVA of main effects plus first order interactions was performed. Anchoring holes significantly increased strength (41±8 vs. 114±9 Nm; p=0.004, mean±SEM). No significant effect of reaming or cup design was found. For all experiments, the conventional cups with or without flange behaved almost identical. In step two, these two variations were combined into one “conventional” group, and three-way ANOVA with interactions was performed. Significant interaction between all three factors was found (p=0.02). This indicates that one unique combination (new cup design in acetabula with subchondral bone removed and without anchoring holes) achieved a high average strength. Under these circumstances, the fixation strength of the new design (114±9 Nm) was equal to the overall average achieved with anchoring holes. On average, the new design also had significantly larger fixation strength than a conventional spherical design (95±5 vs. 69±4 Nm; p=0.009). These results justify further studies

In total hip arthroplasty (THA), cementless cup without screw holes has the putative benefits of maximizing host bone contact and reducing osteolysis by eliminating channels to backside wear particles. However, supplemental trans-acetabular screws cannot be used.

74 hips in 60 patients receiving same model of cementless cup without screw holes (Depuy Duraloc 100 HA cup) from 6/1999 to 3/2003 were prospectively followed up. All patients were allowed to have immediate full weight bearing. Age at THA was 53 ± 13 (range 24–74) years. Osteonecrosis was the leading hip disease (45% of hips). Survivorship was assessed using revision of the cup as the end point. Radiological parameters, including lateral opening angle, vertical and horizontal migration distances of the cups were measured. Paired t-test was used to compare between the measurements in early postoperative period and at final follow up.

51 hips were assessed at minimum 20 years follow-up. The mean follow-up was 22.6 (range 21 – 25) years. All the cups were well fixed. There were two cup revisions. Conventional polyethylene (PE) was used in both hips; osteolysis occurred 17 and 18 years later. Both cups were well fixed but were revised, one due to cup mal-positioning, one due to need in upsizing the articulation. 14 other hips were revised but these cups were well fixed and not revised; 9 loosened stems (most were cemented Elite plus stems), 5 PE wear and osteolysis (all were conventional PE). At 20 years, the survivorship of cups was 96.1%. Changes in lateral opening angle, vertical and horizontal migration distances were 0.44±1.59°, 0.01±1.52mm and -0.32±1.47mm respectively, without statistical significance.

This study provided evidence of excellent long-term survivorship of cementless cup without screw holes. Immediate postoperative weight-bearing also did not lead to cup migration in the long-term.

Background: The purpose of this prospective study was to asses the reliability of image-free navigated cup positioning and its correlation with biometrical parameters (age, sex, body mass index, soft tissue thickness overlying anterior superior iliac spine and symphysis pubis, and lumbar lordosis) and three different orientations of pelvis (tilt, obliquity, and rotation) in patients of Asian ethnicity. Methods: Intraoperative data was obtained from 50 consecutive total hip arthroplasties in which acetabular cup implantation was done with a cementless cup (Plasma Cup SC. ®. , Aesculap AG, Tuttlingen, Germany) using Orthopilot. ®. image-free navigation system. The data was then compared with mathematically calculated synchronized anteversion and inclination obtained postoperatively through computed tomography and 3-dimensional processing. Results: Mean navigated and synchronized inclination obtained were 40.1°±5.34° and 41.79°± 7.96° respectively (mean difference 1.69°±6.95°, range −20.72° ~ 18.47°), while the mean navigated and synchronized anteversion were 19.98°± 6.44° and 20.00°± 6.33° (mean difference 0.01°±6.35°, range −15.15° ~ 11.10°). A discrepancy of > 10° was observed in 5 hips in inclination and 5 hips in anteversion. No correlation was found between all of biometrical parameters and discrepancy of cup orientation. A statistically significant correlation was found between discrepancy of anteversion and pelvic tilt (1.78 + 0.55 x pelvic tilt°, r=0.493, p=0.0016). Conclusion: In spite of variations in pelvic geometry, image-free navigation assisted acetabular cup positioning showed the significant reliability. The next generation of navigation systems must be combined with data on precision of pelvic orientation intraoperatively for complete validation. *Index; Synchronized Inclination = arctan [tan (Operative AV) ÷ tan (Anatomic AV)] Synchronized AV = arctan[tan (Anatomic AV) x sin (synchronized Inclination)] or arctan[tan (Operative AV) x cos (Synchronized Inclination

Introduction. The goal of total hip arthroplasty (THA) should be to reconstruct the acetabulum by positioning the hip center as close as possible to the anatomical hip center. However, the true position of the anatomic hip center can be difficult to determine during surgery on an individual basis. In 2005, we designed, produced an acetabular reaming guide, and clinically used to enable cup placement in the ideal anatomical position. This study was examined the accuracy the reaming guide for THA in prospective study. Methods. This guide was applied consecutive 230 patients in primary THA. During planning, the distance from the acetabular edge to the reaming center and from the center to the perpendicular of the inter-teardrop line was measured on an anteroposterior (AP) X-ray. The reaming guide was adjusted depend on the reaming center by based planning. Acetabular reaming was performed with the process reamer. Results. At planning, the position of the hip center was 18.1 mm in the vertical offset (VO) and 29.6 mm in the horizontal offset (HO). After surgery, the position of the hip center had a VO of 18.1 mm and an HO of 29.9 mm. The absolute error between planning and post-operation was a VO of 2.7 mm and an HO of 2.9 mm. Overall, 199 cases (86.5%) had an HO error of less than 5 mm and 204 cases (89.6%) had a VO error of less than 5 mm. The vertical height from the teardrop line to the inferior edge of the acetabular cup was 0.5 ± 3.5 mm. Conclusion. The new reaming guide was closely reproduced the preoperative planning position in this prospective study. Our original acetabular reaming guide is a very useful tool for performing reaming during THA and for ensuring accurate cup placement at the anatomical hip center

Achieving the correct inclination angle for the acetabular component in total hip arthroplasty (THR) can be technically challenging. The aim of this study is to validate the use of a simple, laser-guided system to address the acetabular cup inclination angle intraoperatively and quantify its accuracy and repeatability across users. A simple inclinometer system was manufactured, consisting of a laser that snaps into both the inclinometer and the handle of a standard trial cup impacter. The system functions as follows:. desired inclination angle is set on the inclinometer,. inclinometer is positioned on the acetabulum,. laser beam is projected onto and marked on a screen outside of the surgical exposure,. the impacter is reoriented in the acetabulum until the laser beam aligns with the recorded mark on the screen. A validation study was performed on this system using intact cadavers (N=4). A THR-specific. Trial acetabular components were installed unilaterally in each donor using both the laser inclinometer system with an in-line mounted intraoperative navigation system (NaviVision, Vector Vision Hip 3.1, BrainLab) serving as the measurement standard. Three orthopaedic surgeons participated in the study, two experienced with the device (“experts”) and one “novice”, and each surgeon performed two sequential validation experiments:. 10 trials at a set device inclination angle, and. 5 trials of matching the trial cup placement to this set angle. Using the laser-guided system, the inclination angle of the trial cup deviated from the desired orientation by 1.1±0.9° (mean st. dev; range: 0–3°) for all specimens across all operators. The corresponding error in anteversion angle was 1.4±1.3° (range: 0–5°). There was no difference in inclination angle between expert and novice surgeons (1.0±0.8° versus 1.1±1.2°, respectively; p> 0.10 for unpaired t-test). To set the desired inclination angle on the trial cup, original and final laser target positions were within 4.1±2.5 cm at 1 m screen placement. Results suggest that the laser-guided system has sufficient accuracy and repeatability for use intra-operatively. Inclination angles differed from prescribed angles by 1° on average, and malalignment in anteversion was subclinical, ≤5° for all cases. Furthermore, the tolerance for laser re-alignment sufficiently large (5–10 cm) to make the device functional intraoperatively. Future work will focus on expanding the sample size and correcting simple design limitations in the device

Aim: Evaluate a novel horseshoe shaped cup designed by the senior authors to minimise the resection of healthy bone in total hip arthroplasty. Method: Fifty female patients with a displaced, subcapital, femoral neck fractures were chosen for the study. In half of the group of patients, the composite support shell was coated with HA, with the other half remaining uncoated. Clinical and radiological assessments were undertaken regularly for 5 years. Results: To date 20 patients have died and 13 have withdrawn from the study due to poor medical health unrelated to the study. Charnley modified Merle d’Aubigne score at 5 years was as good as the preoperative score with 80% of patients having full range of movement, no pain and walking unaided. Radiographic results showed no evidence of loosening of HA coated cups, in contrast to non HA coated cups which migrated significantly in 80% of cases. Four patients with loose non HA coated cups underwent revision surgery. Conclusion: It replaces the cartilage and underlying sub-chondral bone of the acetabulum socket with a cup that is designed to flex in harmony with the surrounding bony structure. This trial has demonstrated success at 5 years with the HA coated Cambridge Acetabular Cup. Cups from which HA coating has been removed have migrated significantly in 80% of cases. There is an advantage of the HA fixation which will be taken into account before wider clinical usage is advocated

The novel horseshoe shaped cup was designed by the senior authors to minimise the resection of healthy bone in total hip arthroplasty. It replaces the cartilage and underlying sub-chondral bone of the acetabulum socket with a cup that is designed to flex in harmony with the surrounding bony structure. Fifty female patients with a displaced, subcapital, femoral neck fractures were chosen for the study. In half of the group of patients, the composite support shell was coated with HA, with the other half remaining uncoated. Clinical and radiological assessments were undertaken regularly for five years. To date 20 patients have died and 13 have withdrawn from the study due to poor medical health unrelated to the study. Charnley modified Merle d’Aubigne score at five years was as good as the preoperative score with 80% of patients having full range of movement, no pain and walking unaided. Radiographic results showed no evidence of loosening of HA coated cups, in contrast to non HA coated cups which migrated significantly in 80% of cases. Four patients with loose non HA coated cups underwent revision surgery. This trial has demonstrated success at 5 years with the HA coated Cambridge Acetabular Cup. Cups from which HA coating has been removed have migrated significantly in 80% of cases. There is an advantage of the HA fixation which will be taken into account before wider clinical usage is advocated

Achieving optimal acetabular cup orientation in Total Hip Replacement (THR) remains one of the most difficult challenges in THR surgery (AAOR 2013) but very little has been added to useful understanding since Lewinnek published recommendations in 1978. This is largely due to difficulties of analysis in functional positions. The pelvis is not a static reference but rotates especially in the sagittal plane depending upon the activity being performed. These dynamic changes in pelvic rotation have a substantial effect on the functional orientation of the acetabulum, not appreciated on standard radiographs [Fig1]. Studies of groups of individuals have found the mean pelvic rotation in the sagittal plane is small but large individual variations commonly occur. Posterior rotation, with sitting, increases the functional arc of the hip and is protective of a THR in regards to both edge loading and risk of dislocation. Conversely Anterior rotation, with sitting, is potentially hazardous. We developed a protocol using three functional positions – standing, supine and flexed seated (posture at “seat-off” from a standard chair). Lateral radiographs were used to define the pelvic tilt in the standing and flexed seated positions. Pelvic tilt was defined as the angle between a vertical reference line and the anterior pelvic plane (defined by the line joining both anterior superior iliac spines and the pubic symphysis). In the supine position pelvic tilt was defined as the angle between a horizontal reference line and the anterior pelvic plane. Supine pelvic tilt was measured from computed tomography. Proprietary software (Optimized Ortho, Sydney) based on Rigid Body Dynamics then modelled the patients’ dynamics through their functional range producing a patient-specific simulation which also calculates the magnitude and direction of the dynamic force at the hip and traces the contact area between prosthetic head/liner onto a polar plot of the articulating surface, Fig 2. Given prosthesis specific information edge-loading can then be predicted based on the measured distance of the contact patch to the edge of the acetabular liner. Delivery of desired orientation at surgery is facilitated by use of a solid 3D printed model of the acetabulum along with a patient specific guide which fits the model and the intra-operative acetabulum (with cartilage but not osteophytes removed) - an incorporated laser pointer then marks a reference point for the reamer and cup inserter to replicate the chosen orientation. Results and conclusions. The position of the pelvis in the sagittal plane changes significantly between functional activities. The extent of change is specific to each patient. Spinal pathology is a potent “driver” of pelvic sagittal rotation, usually unrecognised on standard radiographs. Pre-operative patient assessment can identify potential orientation problems and even suitability for hard on hard bearings. Optimal cup orientation is likely patient-specific and requires an evaluation of functional pelvic dynamics to pre-operatively determine the target angles. Post-operatively this technique can identify patient and implant factors likely to be causing edge loading leading to early failure in metal on metal bearings or squeaking in ceramic on ceramic bearings

After experimental and preclinical evaluation (HAP Paul Award 2001) of a CT-free image guided surgical navigation system for acetabular cup placement, the system was introduced into clinical routine. The computation of the angular orientation of the cup is based on reference coordinates from the anterior pelvic plane concept. A hybrid strategy for pelvic landmark acquisition has been introduced involving percutaneous pointer-based digitisation with the non-invasive bi-planar landmark reconstruction using multiple registered fluoroscopy images. From January 2001 to May 2002 a total of 118 consecutive patients (mean age 68 years, 82 male, 36 female, 62 left and 56 right hip joints) were operated on with the hybrid CT-free navigation system. During each operation the angular orientation of the inserted implant was recorded. To determine the placement accuracy of the acetabular components the first 50 consecutive patients underwent a CT scan seven to ten days postoperatively to analyse the cup position related to the anterior pelvic plane. This was done blinded with commercial planning software. There was no significant learning curve observed for the use of the system. Mean values for postoperative inclination read 43° (SD 3.0, range 37 to 49) and anteversion 19° (SD 3.9, range 10 to 28). The resulting system accuracy, i.e., the difference between intraoperatively calculated cup orientation and postoperatively measured implant position shows a maximum error of 5° for the inclination (mean 1.5°, SD 1.1) and 6° for the anteversion (mean 2.4°, SD 1.3). An accuracy of better than 5° inclination and 6° ante-version was achieved under clinical conditions, which implies that there is no significant difference in performance from the established CT-based navigation methods. Image guided CT-free cup navigation provides a reliable solution for future THA

Aim: To determine the incidence of periacetabular osteolysis in an uncemented, press-fit, one-piece, titanium plasma spray backed acetabular cup used in conjunction with a cemented or uncemented femoral component followed for 10 years. Method: Patients undergoing primary total hip arthroplasty in 1989 were reviewed and new radiographs obtained. These were compared with the initial post-operative radiographs and the presence of osteolysis in the three zones of Delee and Charnley were recorded. Results: Of 57 patients, 14 were deceased at the time of follow-up and nine were lost to follow-up. Ten patients had undergone revision for problems related to the femoral stem. There was only one possible case of periacetabular osteolysis seen in this series. In this case the lytic lesion was seen on the early post-operative radiograph and did not change in 10 years, and thus may not have been osteolysis. Conclusions: The reported incidence of periacetabular osteolysis with two-piece cups varies between 30 and 50%. Thus, this cup has an extremely low possible osteolysis incidence. This study raises the wisdom of the continued use of two piece cups of any design

The purpose of this study was to examine the utility of the acetabular component introducer as a tool to intra-operatively predict implant inclination in total hip arthroplasty. This study investigated (1) the correlation between intra-operative photographic assessment of cup inclination using the acetabular introducer and that measured on post-operative radiograph; and (2) the accuracy of intra-operative prediction of abduction angle. For this study, we prospectively recruited 56 patients scheduled to receive primary hip arthroplasty from one of two senior surgeons. During the procedure, the lead surgeon provided a prediction of the abduction angle based on the alignment of the impactor attached to the cup in its final seated position. A standardized anteroposterior (AP) photograph was then taken of the acetabular impactor in situ. Abduction angles were measured by two observers on the photographs and post-operative AP pelvis radiographs. Linear regression was used to determine the correlation between the angle of the guide measured on the photographs and the actual position of the implant measured on the radiograph. Descriptive statistics were further used to analyze the accuracy of the intra-operative prediction as compared with the abduction angle measured on the photographs. Measurements of cup position made from post-operative radiographs were significantly correlated with the measurements as assessed by intra-operative photographs (r = 0.34, p = 0.00). Our findings demonstrate that radiological abduction angles tend to be greater than that assessed by intra-operative photographs by a mean of 5.6 degrees (SD = 6.6 degrees; 95% CI = 7.3 to 3.9 degrees). Conversely, surgeon prediction of cup inclination based on the acetabular introducer differed from the radiographic measurements by a mean of 6.8 degrees (SD = 8.7 degrees). There was good agreement between the two observers in both photographic and radiographic measurement (k = 0.95, k = 0.96, respectively). In conclusion, we found that the intra-operative photographic assessment of acetabular cup inclination by acetabular impactor alignment tends to underestimate the abduction angle by a mean of approximately 5 degrees. In addition, intra-operative surgeon estimation of acetabular inclination did not appear accurate in this study demonstrating that cup position should rely on additional visual cues beyond that captured in the anteroposterior view of the cup introducer

Prosthetic reconstruction of high-riding hips is technically demanding. Insufficient bony coverage and osteopenic bone stock frequently necessitate transacetabular screw fixation to augment primary stability of the metal shell. We sought to determine the validity of the previously reported quadrant system, and if needed, to define a specialized safe zone for augmentation of screw fixation to avoid vascular injuries in acetabular cup reconstruction for high-riding hips. Volumetric data from computed tomography enhancement scanning and CT angiography of eighteen hips (twelve patients) were obtained and input into a three-dimensional image-processing software. Bony and vascular structures were reconstructed three-dimensionally; we virtually reconstructed a cup in the original acetabulum and dynamically simulated transacetabular screw fixation. We mapped the hemispheric cup into several areas and, for each, measured the distance between the virtual screw and the blood vessel. We found that the rotating centers of the cups shifted more anterior-inferiorly in high-riding hips than those in ordinary cases, and thus the safe zone shifted as well. Screw fixation guided by the quadrant system frequently injured the obturator blood vessels in high-riding hips. We then defined a specialized safe zone for transacetabular screw fixation for high-riding hips. We conclude that the quadrant system can be misleading and of less value in guiding screw insertion to augment metal shells for high-riding hips. A new safe zone specific to high-riding hips should be used to guide transacetabular screw fixation in these cases

Different types of highly cross-linked polyethylene (HXLPE) have been introduced widely in acetabular cups in hip prostheses to reduce the incidence of wear debris-induced osteolysis. Also, we reported that HXLPE cups with 28-mm alumina ceramic femoral head exhibited lower wear than conventional PE cups. Recently, the combination of HXLPE cup and larger diameter femoral head is used widely to prevent dislocation. In this study, we examined the wear of HXLPE with 32-mm alumina ceramic femoral head and compared it with the wear of HXLPE with 28-mm alumina ceramic femoral head. The in vivo wear of 60 HXLPE cups (Aeonian; Kyocera Corp., Kyoto, Japan, currently Japan Medical Materials Corp., Osaka, Japan) with 28-mm alumina ceramic femoral head with clinical use for 3.1–9.1 years (mean 7.4 years) and eight HXLPE cups with 32-mm alumina ceramic femoral head used for 2.3–3.2 years (mean 2.8 years) were examined by radiographic analysis. The early wear rate for the first year of HXLPE cups with 28-mm and 32-mm alumina ceramic femoral head were 0.24±0.10 mm/year and 0.29±0.12 mm/year respectively. There was no significant difference in both femoral head groups (p>0.05). The steady wear rate after 1 year were 0.001±0.03 mm/year and −0.03±0.10 mm/year respectively. There was no significant difference either in both femoral head groups (p>0.05). These findings from this radiographic analysis suggest that the early wear rate in the first 1 year probably represents the creep deformation in bedding-in stage; and the steady wear rate after 1 year probably represents mainly the wear than of the creep deformation. By the radiographic analysis, HXLPE cups in both femoral head groups exhibited low steady wear rate. In conclusion, we expect that the combination of HXLPE cup and 32-mm diameter alumina ceramic femoral head has favorable wear properties with possibility of prevention of dislocation in long-term clinical use

Background. The accuracy of cup placement in navigated THA depends on the bony landmark registration intraoperatively. The usual patient position for registration is supine, but supine position has some drawbacks such as it's more difficult for femoral canal visualisation. The alternate patient position is lateral decubitus, but registration in this position may be unreliable because of the contralateral ASIS can't be palpated accurately. The other technique is registration in supine position first and then placing the patient in lateral decubitus for operation. The drawbacks of this technique are time consumption and increased risk of contamination. We created a semilateral decubitus position which combined the advantage of supine position for registration and lateral decubitus position for better femoral canal visualisation. We modified the registration technique by compressing the soft tissue above Pubic Symphysis(PS) to the abdomen and registered at the Antero-Superior-Pubic-Symphysis(ASPS). Objective. Evaluate the accuracy of cup placement within the “safe zone” and the accuracy of imageless navigation measurement by comparing the intraoperative values of acetabular cup abduction and anteversion to postoperative computed tomography (CT) values. Method. The prospective study consisted of 30 patients who received short stem navigated THA in semilateral decubitus position from May to October 2012. The abduction and anteversion angle measured on postoperative CT were compared to the intraoperative measurement with a paired t-test and a correlation test at a 0.05 level of significance. Results. The mean CT abduction was 41.37° (range, 37° to 45°, SD 2.01) and the mean navigated abduction was 40.29° (range, 37.6° to 45.5°, SD 1.99). The mean paired difference was 1.26° (range, −0.8° to 4.6°, SD 1.05), this difference was significant (p = 0.02) but considered to be clinically irrelevant. There was a significant correlation between the CT abduction and navigated abduction (p < 0.001). All cases showed a difference of less than 5° between the two measurements and all cases were within the safe zone of CT measurement. The mean CT anteversion was 13.57° (range, 7° to 18°, SD 3.28) and the mean navigated anteversion was 11.18° (range, 5.9° to 15.5°, SD 2.52). The mean paired difference was 3.02° (range, −2.6° to 8.6°, SD 2.33), this difference was significant (p = 0.001) but considered to be clinically irrelevant. There was a significant correlation between the CT anteversion and navigated anteversion (p = 0.005). Twenty-two cases (22/30, 73%) showed a difference of less than 5° between the two measurements and all cases were within the safe zone of CT measurement. Soft tissue thickness overlying the PS and ASIS were measured in axial CT images and averaged 28.53 mm. (range, 11.7 to 54.6, SD 9.97) and 8.03 mm. (range, 3.2 to 26, SD 4.86) respectively. We found no significant correlation between the difference and the thickness of the soft tissue above the PS (p = 0.09) nor above ASIS (p = 0.09). Conclusion. The navigated THA with modified registration technique in semilateral decubitus position offered a more precise cup position. All cases were within the safe zone in both abduction and anteversion angles

In a prospective and randomised clinical study, acetabular cups were implanted free-hand (control group n=25) or with computer assistance using an image-free navigation system (study group n=25). Total hip replacement was performed in lateral position and through minimally invasive anterior approach (MicroHip). The cup position was measured postoperatively on pelvic CT using the CT-planning software. An average inclination of 42.3° (range: 35°–56°; SD±8.0°) and an average anteversion of 24.0° (range: −5° to 54°; SD±16.0°) were found in the control group, and an average inclination of 45.0° (range: 40°–50°; SD±2.8°) and an average anteversion of 14.4° (range: 5°–25°; SS±5.0°) in the computer-assisted study group. The deviations from the desired cup position (45° inclination, 15° anteversion) were significantly lower in the computer-assisted study group (p< 0.001 each). While only 10/25 of the cups in the control group were within the Lewinnek safe zone, 18/25 of the cups in the study group were placed in this target region (p=0.003). We saw no disadvantage compared to previous studies in supine position with standard approach