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

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

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: 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. 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

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

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

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

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

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. 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

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

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

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)