In this prospective study we studied the effect of the inclination angle of the acetabular component on polyethylene wear and component migration in cemented acetabular sockets using radiostereometric analysis.

A total of 120 patients received either a cemented Reflection All-Poly ultra-high-molecular-weight polyethylene or a cemented Reflection All-Poly highly cross-linked polyethylene acetabular component, combined with either cobalt–chrome or Oxinium femoral heads. Femoral head penetration and migration of the acetabular component were assessed with repeated radiostereometric analysis for two years. The inclination angle was measured on a standard post-operative anteroposterior pelvic radiograph. Linear regression analysis was used to determine the relationship between the inclination angle and femoral head penetration and migration of the acetabular component.

We found no relationship between the inclination angle and penetration of the femoral head at two years’ follow-up (p = 0.9). Similarly, our data failed to reveal any statistically significant correlation between inclination angle and migration of these cemented acetabular components (p = 0.07 to p = 0.9).

Introduction. Restoration of normal hip biomechanics is vital for success of total hip arthroplasty (THA). This requires accurate placement of implants and restoration of limb length and offset. The purpose of this study was to assess the precision and accuracy of computer navigation system in predicting cup placement and restoring limb length and offset. Material and Methods. An analysis of 259 consecutive patients who had THA performed with imageless computer navigation system was carried out. All surgeries were done by single surgeon (KD) using similar technique. Acetabular cup abduction and anteversion, medialisation or lateralisation of offset and limb length change were compared between navigation measurements and follow-up radiographs. Precision, accuracy, sensitivity and specificity were calculated to assess navigation for cup orientation and student t-test used for evaluation of offset and limb length change. A p value of <0.05 was considered significant for evaluation. Results. Mean cup abduction and anteversion was 40.35° (SD, 5.81) and 18.46° (SD, 6.79) in postop radiographs compared to 41° (SD, 5.03) and 14.76° (SD, 6.11) for navigation measurements. Intraoperative navigation measurements had high precision and specificity for determining cup abduction and anteversion (precision >95%, specificity >90%). Accuracy for determining cup abduction was 96.13% compared to 72.2% for cup anteversion. Change in limb length and offset was mean 6.46mm (SD, 5.68) and −1.07mm (SD, 5.75) on radiograph evaluation and 5.41mm (SD, 5.11) and −2.24mm (SD, 5.87) from navigation measurements respectively, the difference being not significant in both (p value > 0.2). Radiograph and navigation had a mean difference of 1.01mm (SD, 2.83) for offset measurements and a mean difference of 1.05mm (SD, 4.37) for postop limb length assessment. Discussion. To the best of our knowledge this is the largest single surgeon study of navigated THA. We found that computer navigation assessment of acetabular cup abduction and anteversion and limb length and offset restoration has high probability of predicting correct placement of implants. To conclude, navigation can serve as an excellent tool for appropriate placement of implants and restoring limb length and offset in THA

Introduction:. Restoration of normal hip biomechanics is vital for success of total hip arthroplasty (THA). This requires accurate placement of implants and restoration of limb length and offset. The purpose of this study was to assess the accuracy of computer navigation system in predicting cup placement and restoring limb length and offset. Material and Methods:. An analysis of 259 consecutive patients who had THA performed with imageless computer navigation system was carried out. Acetabular cup abduction and anteversion, medialisation or lateralisation of offset and limb length change were compared between navigation measurements and follow-up radiographs. Sensitivity, specificity, accuracy and PPV were calculated to assess navigation for cup orientation and student t-test used for evaluation of offset and limb length change. Results:. Mean cup abduction and anteversion was 40.35° (SD, 5.81) and 18.46° (SD, 6.79) in postop radiographs compared to 41° (SD, 5.03) and 14.76°(SD, 6.11) for navigation measurements. Intraoperative navigation measurements had high PPV and specificity for determining cup abduction and anteversion (PPV >95%, specificity >90%). Accuracy for determining cup abduction was 96.13% compared to 72.2% for cup anteversion. Change in limb length and offset was mean 6.46 mm (SD, 5.68) and −1.07 mm (SD, 5.75) on radiograph evaluation and 5.41 mm (SD, 5.11) and −2.24 mm (SD, 5.87) from navigation measurements respectively, the difference being not significant in both (p value >0.2). Radiograph and navigation had a mean difference of 1.01 mm (SD, 2.83) for offset measurements and a mean difference of 1.05 mm (SD, 4.37) for postop limb length assessment. Discussion:. To conclude, navigation can serve as an excellent tool for appropriate placement of implants and restoring limb length and offset in THA

Introduction. One of the most common complications of ceramic on ceramic hip replacement is squeaking. The association of Accolade stem and Trident acetabular system has been reported to have squeaking incidence of up to 35,6%. There is doubt if this phenomenon occurs due to: the stem titanium alloy, the V40 femoral neck, the recessed liner of the trident cup or even the mal-seating of the trident insert on the cup. Objectives. Primary: The purpose of the present study was to determine the incidence of squeaking in association with the use of Exeter stem and Trident ceramic acetabular system. Secondary: Analysis of the correlation of the cup abduction angle and squeaking. Methods. During the period from March 2004 to December 2008, two surgeons performed 87 total hip arthroplasties in 77 patients with use of a ceramic-on-ceramic bearing (Exeter stem, alumina head, Trident ceramic acetabular system). Seventy six patients (86 THA) were available for review after at least 18 months follow-up. The incidence of squeaking and other noises was analyzed. Cup abduction angle was measured. The Pearson correlation coefficient was used to determine if a correlation existed between the cup abduction angle and squeaking. Results. The incidence of squeaking was 2,63% (2 patients). Both patients reported a “click” noise in hyperextension of the hip. The mean abduction angle was 44 degress (35–60), and 48 degrees (46 and 50) on the squeaking group. There was no statistically significant difference in the in the mean cup inclination between squeaky and quiet hips. Conclusion. The incidence of squeaking in association with the use of Exeter stem and Trident ceramic acetabular system was 2,63%. There was no correlation of the cup abduction angle and squeaking

Introduction:. Acetabular cup position is an important factor in successful total hip arthroplasty (THA). Optimal cup placement requires surgeons to possess an accurate perception of pelvic orientation during cup impaction, however, varying pelvic anatomy and limited visual cues in the surgical field may interfere with this process. The purpose of this study was to evaluate the utility of an inertial measurement unit (IMU) in monitoring pelvic position during THA. Materials & Methods:. Ten patients scheduled to undergo THA were IRB-approved and consented by four surgeons. A small IMU was placed over the patient's sacrum pre-operatively and zeroed in standing position. Pelvic orientation data was streamed and captured wirelessly throughout the procedure. Surgeons were blinded to all data throughout the study period. Prior to cup impaction, the surgeon indicated his intended cup abduction angle and the degree to which the cup impactor was manipulated to compensate for perceived AP pelvic tilt. The degree of pelvic tilt as determined by the IMU (angle β) was then recorded (Figure 1). AP-pelvis radiographs were measured in Martell Hip Analysis Suite post-operatively to calculate the cup abduction angle, which was then compared to the surgeon's intended abduction angle to determine surgeon accuracy. To predict the final cup abduction angle, the degree of pelvic tilt recorded by the IMU (angle β) was subtracted from the abduction angle of the cup impactor (angle α) that was positioned using the OR table as a reference (Figure 1). This value was then compared to the measured post-operative cup abduction angle in order to assess the accuracy of the IMU in measuring pelvic tilt. Surgeon accuracy and IMU accuracy were compared to determine if the IMU was more or less effective than surgeon perception at determining pelvic tilt. Results:. The mean intended abduction angle indicated by the surgeons intraoperatively was 43.7° (range 40°–45°), while the mean measured post-operative abduction angle was 40.1° (range 25.9°–49.4°). In five of the cases, the surgeon's post-operative abduction angle fell within 2° of his intended abduction angle. One cup was placed at a higher than intended abduction angle (4.4°), and four cups were placed in lower than intended abduction angles by an average of 10.8° (range 3.9°–19.1°). Film analysis revealed that surgeons placed the acetabular cup on average 5.4 ± 6.0° from their intended abduction angle (range 0.3°–19.1°). Following analysis of the IMU offset data, it was observed that the IMU deviated on average 3.1 ± 2.6° (range 0.7°–7.2°) from its expected orientation value. The IMU deviated more than 2° from expected pelvic tilt in five cases. Discussion:. The IMU was able to ascertain AP pelvic tilt to a higher degree of accuracy than four surgeons using standard surgical techniques. A system in which the pelvis could be monitored and adjusted intraoperatively based on accurate IMU data would allow the surgeon to place the pelvis in optimal position prior to cup impaction, which could potentially increase overall cup positioning accuracy. More data is needed to confirm these results

Introduction. This study reports outcomes of primary and revision total hip arthroplasties of a recalled metal-on-metal (MOM) monoblock prosthesis performed by a single surgeon. Methods. We performed a retrospective review of all patients who underwent both primary and revision total hip arthroplasties at our institution between 2006 and 2014. Only those patients who underwent primary recalled MOM monoblock prosthesis placement and/or revision of the recalled prosthesis were included. We evaluated revision group versus non-revision group for age, BMI, gender, existence of medical comorbidities, primary cup abduction and anteversion, primary combined angle, post-operative complications, cobalt and chromium ion levels, and Harris Hip Scores. Student t-test was used to compare groups. Results. During the study period, 105 patients underwent 115 primary total hip arthroplasties with the recalled system. Thirty-six patients underwent 40 revisions surgeries for pain, high metal ions, infection, aseptic loosening, failure of ingrowth, and/or pseudotumor. The revision rate was 34.8%. Except for a higher percentage of women undergoing revision (17.4% vs 50%, p=0.0002), there were no significant differences in patient demographics, medical comorbidities, or pre-operative Harris Hip Scores (Table 1). Revision group showed higher cup abduction angles (47.8 vs 42.4, p = 0.005), smaller average cup size (53.3 vs. 55.2, p = 0.003), smaller average femoral component size (4.7 vs 5.6, p = 0.02, respectively), and lower post-operative Harris Hip Scores (87.9 vs 93.8, p = 0.0007). The revision group had higher cobalt levels (34.5 vs 5.8, p = 0.00003) and higher chromium levels (14.0 vs 1.3, p = 0.00003). There were five post-operative complications in the revision group (2 infections, 2 dislocations, and one DVT) versus one DVT in the non-revision group (p=0.01). Harris Hip Scores for revision surgeries increased from a mean of 44.2 pre-operatively to 74.9 post-operatively (p=1.45×10. −5. ). Conclusion. This study presents 115 primary total hip arthroplasties and 40 revisions performed by a single surgeon at our institution. To our knowledge, this is the largest single-surgeon study reported in the literature. Hips requiring revision had significantly higher cup abduction angles, smaller cup and femoral component sizes, lower post-operative Harris Hip scores, and higher metal ion levels. Age, BMI and comorbidities did not contribute to revision in our study; however, there was a higher chance of undergoing revision if you are a woman (p=0.0002). There was a 30.7 mean improvement in Harris Hip Score after revision

Purpose. Ceramic-on-ceramic bearings in total hip arthroplasty (CoC THA) have theoretical advantages of wear resistance and favorable biocompatibility of ceramic particles to the surrounding bony and soft tissue. Long-time durability of CoC THA has been expected, however, clinical results over 10 years after operation were scarcely reported. In the present study, clinical results at follow of 10 years were examined for CoC THAs with a changeable femoral neck which allowed correction of anteversion of the femoral component in cases with abnormal femoral anteversion in dysplastic hips. Methods. During 1997 and 2000, 203 cementless CoC THAs in 158 patients were conducted in our hospital. Six patients died because of unrelated causes and 5 patients were lost to followup, and the remaining 188 hips in 147 patients were analyzed at the mean followup period of 10.8 years (3.7 to 13.5). There were 24 men and 123 women, and the average age at operation was 54 years (26 to 73). The hip diseases for operation were osteoarthritis in 165 hips, osteonecrosis of the femoral head in 21 hips and failure of hemiarthroplasty in 2 hips. The operation was performed in the lateral position through the posterior approach without trochanteric osteotomy. The articulation was composed of Biolox forte alumina liner fitted into beads-coated hiemispherical titanium shell, and a 28-mm Biolox forte alumina femoral head (Cremascoli). The femoral component was either AnCA stem or custom-designed stem, coupled with a modular neck allowing selection of 5 variable offsets and anteversions (Cremascoli). Clinical and radiological findings, and complications during the followup period were analyzed. Results. During the follow-up, 8 hips were revised, due to repeated dislocation (2 hips), periprosthetic fracture (1 hips), cup loosening (1 hip), fracture of ceramic liner rim (2 hips), and cup loosening along with ceramic liner rim fracture (2 hips). Cup abduction angle of the 4 cases with ceramic liner rim fracture were high at 49 degrees or more, as compared with the mean cup abduction angle of 41 degrees in the other hips without ceramic fracture. The survival rate at 10 years was 96.0 % when failure was revision. In the hips other than the revised cases, 6 hips showed cup loosening and no hip showed stem loosening on radiographs. Osteolysis was seen in 3 hips around the cup and 4 hips around the stem. Nineteen patients (10%) complained of abnormal noises around the hip, but most of the noises were click sound. Discussion. The 10-year results of cementless CoC THAs with a modular neck were favorable with few cases of osteolysis. However, relatively high frequency of cup loosening may be a concern, since increased cup abduction angle associated with cup loosening may cause ceramic liner fracture

Introduction. Total hip replacement (THR) is one of the most widely used and most successful orthopedic procedures performed in developed countries. The burden of revision surgery, however, has become a major issue in terms of both volume and cost. Technical errors at the time of the index operation are known to be associated with an increased rate of revision. Statistical methods, such as the CUSUM test, which have been developed for the manufacturing industry to monitor the quality of products, have come to the attention of health-care workers as a result of centers with protracted periods of inadequate performance. In orthopedics, these methods have been used to monitor the quality of total hip replacement in a tertiary care department using conventional imaging techniques. Biplane low-dose X-ray imaging (EOS) may allow an easy, patient-friendly, way to retrieve data on the position of implants immediately postoperatively. Therefore real-time feedback is provided to surgeons and performance adjusted accordingly. Objectives. To assess the usefullness of EOS imaging in providing the position of implants immediately postoperatively. Methods. Thirty-six patients who underwent a primary hip replacement at a tertiary care department had a standing EOS acquisition before discharge (around day 5). The following parameters were collected: cup abduction, cup anteversion, leg length, stem anteversion, stem inclination. Cup inclination was considered inadequate if more than 55 degrees or less than 35 degrees; cup abduction was considered inadequate if more than 30 degrees or less than 0 degrees; leg length was considered inadequate if more than 1cm; stem anteversion was considered inadequate if more than 30 degrees of less than 0 degrees; stem inclination was considered inadequate if more than 4 degrees varus or valgus. A procedure was considered inadequate if any criterion was outside the appropriate range. A CUSUM test was used to detect inadequate performance for each criterion and for the whole procedure (more than 20% of the implants poorly positioned). Results. On this preliminary sample of 36 patients only cup inclination demonstrated to be inadequate. Other parameters were within the expected limits. The acquisition of images proved to be easy, without interrupting the flow of patient care and physician work. Conclusions. Biplane low-dose X-ray imaging (EOS) provides an easy way to continuously evaluate the quality of THR implant positioning at a tertiary care department

Introduction. Orientation of the acetabular component in total hip arthroplasty has been shown to influence component wear, stability, and impingement. Freehand placement of the component can lead to widely variable radiographic outcomes. Accurate abduction, in particular, can be difficult in the lateral decubitus position due to limited ability to appreciate and control positional obliquity of the pelvis. A CT-based mechanical navigation device has been shown to decrease cup placement error. This is an independent report of a single-surgeon's radiographic results using the device to control cup abduction. Patients and Methods. Sixty-four (64) consecutive elective THRs in 58 patients were performed via a supercapsular percutaneously-assisted (SuperPATH) surgical approach. Intraoperatively, the acetabular components were aligned with the aid of the CT-based mechanical navigation device (HipXpert; Surgical Planning Associates, Medford, MA). The cup orientation was then further adjusted to ensure that the anterior rim of the acetabular component was not prominent to avoid psoas impingement. Postoperatively, radiographic abduction was measured on standing postoperative radiographs. Results. Measured on standing postoperative radiographs, the cup radiographic abduction angle averaged 42.7° with a standard deviation of ± 3.9° and a range of 35° to 51°. Conclusions. Total hip arthroplasty using a CT-based navigation device as a guide for abduction led to cup implantation within a very narrow abduction range. This navigation device deserves more widespread interest and study, as acetabular component malposition remains a major concern in THR

Purpose. Placement of the acetabular cup in accurate and optimal position is important in total hip arthroplasty (THA) to obtain satisfactory result. On the other hand, inaccurate manual cup placement with conventional cup placement guide was reported. We therefore have been applied the mechanical acetabular alignment guide for accurate cup placement. The purpose of this study was to validate the accuracy of the acetabular alignment guide for total hip arthroplasty. Materials and methods. Between 2003 and 2014, 52 primary THAs were performed in 48 patients with using the acetabular alignment guide by one surgeon (HT). There were 42 female and 6 male with a mean age at operation of 71.1 years old (47 to 91). The original diagnosis were osteoarthritis in 43 patients (46 hips), and avascular necrosis of femoral head in 5 patients (6 hips). Used acetabular implants were Stryker® Trident AD HA cup in 24 hips and Wright medical® Acetabular Cup System in 28 hips. After completion of anesthesia, half pins were inserted at the both anterior superior iliac spine vertically and the frame was attached to the pins horizontally in supine position. Then, the patients were placed in lateral decubitus position. Finally, the alignment rod, which indicated the optimal direction of the cup (abduction angle 40°, ante-version angle 20°), was connected to the frame. All operations were done by postero-lateral approach. Assessment of the cup abduction angle and ante-version angle was performed by Lewinnek's method using postoperative AP radiograph in supine position. Results. The average cup abduction angle was 41.9±6.1° and ante-version angle was 15.2±4.1° (corrected ante-version angle was 20.2±4.1°). In 49 hips (94%) out of 52 hips, cup was placed within safe zone which was described by Lewinnek (from 30° to 50° of abduction angle, from 5° to 25° of ante-version angle). We had only 3 outliers which abduction angles were 25, 27, and 52 degrees. In terms of the ante-version angle, there was no outlier. Discussion. Our study showed that acetabular alignment guide could help accurate cup placement in THA. To hold the patients in true lateral decubitus position during THA is quite difficult and pelvis can tilt intraoperatively, sometimes resulting in malposition of the cup. The acetabular alignment guide used in this study was stabilized firmly to both iliac crests with two half pins of external fixator. Once we attach a cup angle guide to the acetabular guide frame in supine position, we can know the exact direction for cup placement without being affected by change of the pelvic orientation. We conclude that the acetabular alignment guide is useful tool in case of lateral decubitus position for THA

Background. High cup abduction angles generate increased contact stresses, higher wear rates and increased revision rates. However, there is no reported study about the influence of cup abduction on stresses under head lateralisation conditions for ceramic-on-Ceramic THA. Material and method. A finite elements model of a ceramic-on-ceramic THA was developed in order to predict the contact area and the contact pressure, first under an ideal regime and then under lateralised conditions. A 32 mm head diameter with a 30 microns radial clearance was used. The cup was positioned with a 0°anteversion angle and the abduction angle was varied from 45° to 90°. The medial-lateral lateralisation was varied from 0 to 500 microns. A load of 2500 N was applied through the head center. Results. For 45° abduction angle, edge loading appeared above a medial-lateral separation of 30 μm. Complete edge loading was obtained above 60 μm medial-lateral separation. For 45 degrees inclination angle, as the lateralisation increased, the maximal contact pressure increased from 66 MPa and converged to an asymptotic value of 205 MPa. A higher inclination angle resulted in a higher maximum contact pressure. However, this increase in contact pressure induced by higher inclination angle, became negligible as the lateral separation increased. Discussion Both inclination angle and lateral displacement induced a large increase in the stresses in Ceramic-on-Ceramic THA. Edge loading appeared for a small lateralisation. The influence of acetabular inclination angle became negligible for a lateral displacement above 240 μm, as the stresses reached an asymptotic value

Introduction. Uncemented components necessitate accurate intraoperative assessment of size to avoid complications such as calcar fracture and subsidence whilst maintaining bone stock on the acetabular side. Potential problems can be anticipated pre-operatively with the use of a templating system. We proposed that pre-operative digital templating could accurately assess femoral and acetabular component size. Methods. Pre-operative templating data from 100 consecutive patients who received uncemented implants (Trident cup, Accolade stem) and who were operated on by the senior author were included in the study. Calibrated pelvis anterior-posterior X-rays were templated with Orthoview™ software. Demographic data, templating data (stem and cup size, femoral neck cut), operative records (actual stem and cup size, head size) and post-operative data (femoral stem alignment, radiographic leg length, acetabular cup abduction angle) were collected. Results. There were 51 males and 49 females with a mean age of 60 yrs (SD = 7.3 yrs). Seventy five percent of stems were templated to within 0.5 size and 98% to within 1 size. A total of 80% of cups were templated to within 2mm and 98% to within 4mm. 62% of head length was accurately template. Seven patients were converted from a templated 132° to a 127° femoral prosthesis neck angle. The acetabulum cup abduction angle was 45° (SD = 4.81) and stem alignment was 1.5° (SD = 1.13). The mean lower limb length discrepancy was +0.05mm (SD = 5.1 mm) post-operatively. Conclusion. Digital templating is a accurate method of assessing femoral and acetabular component sizes. This allows surgeons to foresee potential problems and also recognize an intra-operative error when a large discrepancy exists between a trial component and the templated size

In image-free navigation system, three bony landmarks (typically both anterior superior iliac spines (ASIS) and pubic symphysis) are registered intraoperatively by manual palpation. If the registration of bony landmarks is inaccurate, the final orientation of the cup determined by the navigation system will also be inaccurate. We therefore examined intra-and intersurgeon variability in registration and the distance between registration points in each bony landmark with two surgical positions. Thirty-seven THAs were performed in the lateral position and 15 THAs were performed in the supine position. The cup was fixed using the image-free Ortho-Pilot hip navigation system (B. Braun Aesculap, Tuttlingen, Germany). The registration was repeated two more times by operator and assistant, and the intra-and intersurgeon variability of cup abduction angle and anteversion was analyzed by ICC (intraclass correlation coefficients). In 25 hips, the distance between intrasurgeon registration points and that between intersurgeon registration points in each landmark were calculated. The ICC in the lateral position ranged between 0.59 and 0.81, and between 0.85 and 0.95 in the supine position. The ICCs of cup abduction angle for the intra-and intersurgeon variability were 0.92 and 0.95 for the supine position and 0.65 and 0.59 for the lateral position. Those of anteversion were 0.93, 0.85, and 0.81, 0.72, respectively. The variability of registration of collateral and contralateral ASIS in the lateral position was greater than that in the supine position. In image-free navigation system, the variability of registration points depended on bony landmarks and patient position. The registrations of pubic symphysis in the supine position and all bony landmarks in the lateral decubitus position are standing further improvement

Purpose: There is no report concerning about long-term comparison result of high placed cementless cup stability with or without screws for developmental dysplasia of the hip. The aim of this study was to ascertain whether or not there are any differences in high placed cementless cup stability with or without screws at the mean 10-year (6–14) follow-up period. Method: We divided 109 hip-cases who underwent identical cementless total hip arthoplasty system (Mallory – Head : Biomet Inc.) to two groups: 57 cups with screw (screw group) and 52 cups without screw (no screw group). No case in both group underwent bulk bone graft for acetabular roof. Radiographic signs of cup instability were defined as the development of radiolucent line (> 2mm) or migration (> 4mm). Degree of subluxation by Crowe classification, cup size and cup abduction angle were also measured. Results: In both groups, there was no significant difference in terms of degree of subluxation (each grade’s %) (screw vs no screw = I (68, 73), II (21, 25), III (11,0), IV (0, 2)), age (yrs) (58, 60), cup size (mm) (46, 47) and cup abduction angle (49, 47). In screw group, one case was revised by replacing only polyethylene insert due to excessive ware. No case in both group showed any sign of component instability. Conclusion: High placed Mallory-Head type cementless cup without screws showed stable radiographic fixation as well as cup with screws at mean 10 years follow-up period

Introduction. To control implant alignments (anteversion and abduction angle of the acetabular cup and antetorsion of the femoral stem) within an appropriate angle range is essentially important in total hip arthroplasty to avoid implant impingement. A navigation system is necessary for accurate intraoperative evaluation of implant alignments but is too expensive and time-consuming to be commonly used. Therefore, a cheaper and easier tool for intraoperative evaluation of the alignments is desired in the clinical field. I presented an idea of marking ruler-like scales on a trial femoral head in the last ISTA Congress. The purpose of this study is to introduce an idea further improved in evaluating the combined implant alignment intraoperatively. Materials and Methods. We can evaluate the combined anteversion (sum of cup anteversion and stem antetorsion) and cup abduction angle by reading the scales at the most proximal point of inner edge of the liner when horizontal and vertical scales are marked on the femoral head appropriately and the hip joint is kept at the neutral position after implant settings and trial reduction. Whether the impingement occurred within the target ROM (Flx 130, IR40@Flx90, Ext 40, ER 40) was judged under specific conditions of the oscillation angle (139), neck-shaft angle of the stem (130), stem adduction angle (7), stem antetorsion (20 or 30), and cup anteversion and abduction angles. Cup anteversion and abduction angles were changed from 0 to 40 and 30 to 50 degrees in 1-degree increments, respectively. Impingement judgment was performed mathematically for each combination of implant alignment based on matrix transformations and trigonometric formulas. Results. Impingement-free combinations of implant alignments were identified using spreadsheet software. Points which indicated impingement-free when they matched with the most proximal point of the inner edge of the liner when the hip joint was kept neutral were plotted on the surface of the head on a 3-dimensional computer graphic software. Thus, the safe zone could be indicated visually on the trial head by a collection of these points. Discussion. We can easily judge whether the implant impingement occurs or not by using this trial head intraoperatively. However, there are several factors which make the judgment inaccurate. First, the safe zone varies according to the stem antetorsion. Second, the position at which the hip is kept intraoperatively is not necessarily neutral. Third, stem adduction angle varies according to the length of the femur. Conclusion. Safe zone mapping on the trial femoral head is low cost and easy method to be introduced in the clinical practice for the purpose of a rough judgment of implant impingement

Purpose: The short-term results of metal-on-metal hip resurfacing (HR) have been excellent. However, extensile approaches such as the posterior and trochanteric slide have been used to ensure proper component placement. The minimally invasive (MI) anterior Hueter approach is both muscle and vascular sparing to the femoral head. The purpose of this study is to evaluate the learning curve of this approach in performing hip resurfacing. Method: The first 50 MI HR done by a single high volume arthroplasty surgeon were compared with his previous fifty procedures performed through a trochanteric slide osteotomy, with respect to (BMI, sex, etiology and age) were comparable (p=.372,.122,.143 and .353, respectively). Results: Overall, the traditional transtrochanteric lateral approach took significantly longer to perform compared to MI RAH (97 versus 109 minutes, p=0.014). If we exclude the first 25 MI RAH cases (mean, 106 minutes), the difference is greater (89 versus 109 minutes, p=0.002). The mean femoral component stem to femoral shaft angle (SSA) was not significantly different between the two groups (MI RAH=142.7, lateral approach=140.0, p=0.053). The cup abduction angle (CA) was slightly different between the two groups (MI RAH 42.5°, lateral approach=39.2°, p=0.03). More patients had cup abduction angles in the 45°–55° range (p=0.009) in the MI HR group but none had a cup angle over 55° of abduction in either group. On the femur side, component positioning was comparable. Conclusion: Based on our early results, the anterior-Hueter approach is a reasonable alternative to more extensile surgical approaches. Like any MI approach to hip surgery, great care has to be taken not to put the cups too vertical. Further long-term studies as well as comparisons to other approaches such as the posterior approach will determine if the anterior approach can be recommended for hip resurfacing

Aims: To determine the precision of conventional versus computer assisted techniques for positioning the acetab-ular component in total hip arthroplasty (THA). Methods: Using a lateral approach, 150 cups were placed by 10 different surgeons in 10 identical plastic pelvis models. Only the immediate operating þeld was visible. Preoperative planning was performed with a computerized tomographic scan. Fifty cups were placed free hand, 50 others with the standard cup ancillary, and the remaining 50 cups using computer-assisted orthopaedic surgery. The accuracy of cup abduction and ante-version was assessed with an electromagnetic system. Results: Using conventional techniques, free hand placement revealed a mean precision of cup anteversion and abduction of 10¡ [range: 5.5–14] and 3.5¡ [2.5–5] respectively. With the cup positioner, these angles measured 8¡ [5–10.5] and 4¡ [3–5.5] respectively, and using the computer assisted method, the mean cup anteversion precision was 1.5¡ [1–2] and mean cup abduction measured 2.5¡ [2–3.5]. Conclusions: Computer assisted cup placement is a very accurate and reproducible technique during THA. It is clearly more precise than either of the two traditional methods of cup positioning, even for well-trained surgeons

The aim of the study was to determine the precision of conventional versus computer-assisted techniques for positioning the acetabular component in total hip arthroplasty (THA). Malposition of the acetabular component during THA increases the occurrence of impingement, reduces range of motion, and increases the risk of dislocation and long-term wear. To prevent malpositioned hip implants, an increasing number of computer assisted surgery systems have been described, but their accuracy is not well established. Using a lateral approach, 150 cups were placed by 10 different surgeons in 10 identical plastic pelvis models. Only the immediate operating field was visible. Pre-operative planning was performed with a computerised tomography scan. Fifty cups were placed free hand, 50 others with the standard cup positioner, and the remaining 50 cups using computer-assisted orthopaedic surgery (Medivision). The accuracy of cup abduction and anteversion was assessed with an electromagnetic system (Fastrak™). Using conventional techniques, free hand placement revealed a mean precision of cup anteversion and abduction of 10° [range 5.5 to 14] and 3.5° [2.5 to 5] respectively. With the cup positioner, these angles measured 8° [5 to 10.5] and 4° [3 to 5.5] respectively, and using the computer assisted method, the mean cup anteversion precision was 1.5° [1 to 2] and mean cup abduction measured 2.5° [2 to 3.5]. Computer assisted cup placement is a very accurate and reproducible technique during THA. It is clearly more precise than either of the two traditional methods of cup positioning, even for well-trained surgeons

To determine the precision of conventional versus computer assisted techniques for positioning the acetabular component in total hip arthroplasty (THA). Malposition of the acetabular component during THA increases the occurrence of impingement, reduces range of motion, and increases the risk of dislocation and long-term wear. To prevent malpositioned hip implants, an increasing number of computer assisted surgery systems have been described, but their accuracy is not well established. Using a lateral approach, 150 cups were placed by 10 different surgeons in 10 identical plastic pelvis models. Only the immediate operating field was visible. Pre-operative planning was performed with a computerised tomography scan. Fifty cups were placed free hand, 50 others with the standard cup positioner, and the remaining 50 cups using computer-assisted orthopaedic surgery (Medivision). The accuracy of cup abduction and anteversion was assessed with an electromagnetic system (Fastrak™). Using conventional techniques, free hand placement revealed a mean precision of cup anteversion and abduction of 10° (range 5.5 to 14) and 3.5° (2.5 to 5) respectively. With the cup positioner, these angles measured 8° (5 to 10.5) and 4° (3 to 5.5) respectively, and using the computer assisted method, the mean cup anteversion precision was 1.5° (1 to 2) and mean cup abduction measured 2.5° (2 to 3.5). Computer assisted cup placement is a very accurate and reproducible technique during THA. It is clearly more precise than either of the two traditional methods of cup positioning, even for well-trained surgeons

Purpose: The purpose of this study was to monitor serum cobalt (Co) and chromium (Cr) levels in patients after metal-on-metal resurfacing hip arthroplasty with the Cormet 2000® prosthesis, and to evaluate the effect of patient characteristics, prosthesis characteristics, clinical and radiographic measures on metal levels. Methods: Serum Co and Cr levels were determined in 32 patients with Cormet resurfacing prostheses at 0.5, 1 and 2 years postoperatively using ICP-MS and are reported as & #61549;g/L. Control levels were measured in 20 patients without implants. Results: Medium Co and Cr were 0.21 and 0.16 in controls without implants. Medium Co at 6 months (2.65), 1 year (3.62) and 2 years (2.80), and Cr at 6 months (3.74), 1 year (4.73) and 2 years (4.68) were signifi-cantly increased in the Cormet group when compared to control levels (p < .0001). Metal levels did not correlate with cup inclination, component position, head size, age, weight, sex or Harris Hip scores. Markedly elevated Co (35, 63) and Cr (13, 70) levels were found in two patients with excessive cup abduction. In addition, one patient with a loose implant that required revision had markedly elevated Co (19) and Cr (44) levels. Conclusions: Significantly increased levels of cobalt and chromium were released from Cormet 2000 articulations at all time points. Excessive cup abduction was associated with markedly elevated ion levels indicating that accurate cup placement is an important consideration in resurfacing arthroplasty. The significantly increased trace metal levels following resurfacing with the Cormet prosthesis is a concern and warrants further monitoring