Cup Placement Research Articles

A Multiplanar Radiography Method for Assessing Cup Orientation in Total Hip Arthroplasty

Correct orientation of the acetabular cup considering patient-specific functional pelvic angles is an important factor for improving outcomes and avoiding complications after total hip arthroplasty. This study introduces a new, noninvasive radiographic tool for accurately determining a patient's specific pelvic tilt angle preoperatively, as well as accurately assessing acetabular cup orientation with respect to bony landmarks intraoperatively and postoperatively. The method was validated by imaging a bone replica model of the pelvis with implanted hip components, in comparison to digitized references, and verified with a cadaveric specimen. Pelvic tilt was measured with an accuracy of 0.1 deg and SD of 0.4 deg. Operative cup inclination and anteversion showed accuracies of 0.6 deg and 2.5 deg, with SD of 0.4 deg and 0.6 deg, respectively; these could be improved further by subtracting systematic bias. The method shows accuracy advantages over existing radiographic and fluoroscopic methods and exposes the subjects to a lower radiation dose compared to the similar computed tomography methods. These results suggest that the proposed method is feasible for assessing cup placement with reference to the functional and anatomical references. Furthermore, the ability to reference the same bony landmarks preoperatively, intraoperatively, and postoperatively has important research and clinical advantages.

Body mass index and acetabular component position in total hip arthroplasty

Correct acetabular component positioning during total hip arthroplasty affects the restoration of normal biomechanics, component wear and failure rates. This study examined whether a patient's body mass index (BMI) affects the accuracy of acetabular component placement in terms of the post-operative abduction angle. This was a retrospective review of 102 total hip arthroplasties performed from May 2009 in a single institution. The acetabular abduction angle was measured on the post-operative radiographs of the included patients. Statistical analysis of variance and t-tests were performed using Microsoft Excel to compare the mean abduction angles of patients grouped according to their BMI. Comparison of the mean abduction angle between those with BMI < 25 and BMI > 25 showed a statistically significant difference (P = 0.003). Analysis of variance between all BMI groups was statistically significant (P = 0.01). Patients in the lowest centile of abduction angle had an average BMI of 28. Patients in the highest centile of abduction angle had an average BMI of 33. This study shows that patients with a normal BMI tend to have smaller abduction angles. Overweight or obese patients, on average, have a normal abduction angle but are more likely to have an 'open cup'. A number of factors unique to obese and overweight patient may contribute to an 'open cup' and less accurate cup placement.

Acetabular Component Positioning Using Anatomic Landmarks of the Acetabulum

The acetabular cup should be properly oriented to prevent dislocation and to reduce wear. However, achieving proper cup placement is challenging with potentially large variations of cup position. We propose a new technique to position the acetabular cup. We used this technique, then determined actual cup position and subsequent dislocation rate. We measured acetabular abduction (α°) and anteversion (β°) on preoperative CT scans in 46 patients (50 hips) scheduled for THA. During the operation, we identified the transverse acetabular notch (TAN) and anterior acetabular notch (AAN), a notch at the anterior acetabular margin. We then marked two reference points for 40° abduction at the acetabular rim: the superior point, which is opposite the TAN, and the inferior point at |α - 40| mm inside (when α was > 40°) or outside the TAN (when α was < 40°). We also marked two reference points for 15° anteversion: the posterior point opposite the AAN and the anterior point at |β - 15| mm inside (when β was < 15°) or outside the AAN (when β was > 15°). During cup insertion, we aligned cup abduction to the line between the superior and inferior points and cup anteversion to the line between the anterior and posterior points. We measured cup abduction and anteversion and evaluated the dislocation rate. One patient was lost to followup before 60 months; the minimum followup for the other 45 patients was 60 months (mean, 62.8 months; range, 60-65 months). The mean cup abduction was 40° (range, 32°-47°) and the mean cup anteversion was 17° (range, 8°-25°). No dislocation occurred postoperatively in 49 hips (45 patients) for a minimum of 5 years followup. We obtained adequate cup position with our method and none of 45 patients (49 hips) had dislocation. Level IV, therapeutic study. See Guidelines for Authors for a complete description of level of evidence.

15-year Comparison of Cementless Total Hip Arthroplasty With Anatomical or High Cup Placement for Crowe I to III Hip Dysplasia

This study compared radiological and clinical results of Mallory-Head (Biomet, Warsaw, Indiana) cementless total hip arthroplasty (THA) by anatomical (AP group) or high cup placement (HP group) for Crowe I to III developmental dysplasia of the hip. Of the 68 hips studied, 43 hips were available for 15.3-year follow-up. Ten cups were placed at anatomical center with bulk bone grafting, and 33 cups were at high hip center without bulk bone grafting. No acetabular or femoral components showed loosening in either group. One standard polyethylene liner in a highly placed cup was revised due to excessive wear after 11 years. The average rate of polyethylene wear was 0.128 mm/year in the AP group and 0.148 mm/year in the HP group (except for the revision case). The extent of grafted bone coverage was 34.6% in the AP group. Hip center height was 24.5 mm from the inter-teardrop line in the HP group. The center of the hip horizontal location in the AP group (24.5 mm) and HP group (26.4 mm) was significantly shorter than in normal hips (35.6 mm). Postoperative center-edge angle was 11° (except grafted bone) in the AP group and 25° in the HP group. Mean Harris Hip Score in the AP group improved from 38 points preoperatively to 82 points postoperatively and in the HP group improved from 40 points preoperatively to 88 points postoperatively. Survivorship was 100% in the AP group and 97% in the HP group. Our results indicate that moderate high cup placement without bulk bone grafting at a horizontal locus more medial than that of a normal hip is an alternative durable solution.

Improving Acetabular Cup Orientation in Total Hip Arthroplasty by Using Smartphone Technology

Acetabular cup placement in total hip arthroplasty is often difficult to assess, especially in the lateral position and using the posterior approach. Conventional techniques and computer-assisted surgery are the 2 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 system that uses the accelerometer and camera function of the iPhone. A level indicator application and protractor application were downloaded to the iPhone and used to improve acetabular cup placement. This system has proven to be accurate and quick. Our series of 50 prospective cases showed good results with all our acetabular cups being placed within a narrow range in the safe zone and with less than 5% difference between the preoperative, intraoperative, and postoperative acetabular inclinations.

Secondary Hip Osteoarthritis due to Neurofibroma Treated with Total Hip Replacement

Background. Local plexiform neurofibroma can lead to deformity of the pelvis, valgus deformity of femoral neck, and joint capsule laxity. We report a case of secondary hip osteoarthritis with subluxation and coxa vara deformity resulting from an extra-articular neurofibroma treated with total hip replacement. Case Description. A 39-year-old man had a large benign plexiform neurofibroma at buttock which induced secondary osteoarthritis of the hip. Conservative treatment of tumor was selected because the patient had low chance of malignant transformation due to absence of other neurofibromatosis features. However, due to secondary osteoarthritis he underwent total hip arthroplasty. Anterior capsulotomy was selected to avoid large posterior hip tumor mass. In order to avoid the difficulties associated with setting tension of the abductor muscle, modified trochanteric slide osteotomy with trochanteric advancement, lateralized cup placement, and extended neck offset were used. One year after the surgery, the patient had excellent clinical function, hip stability, leg length equality and was satisfied with the outcome. Clinical Relevance. We concluded that the modified trochanteric slide osteotomy with trochanteric advancement represents a valuable approach for THR in patients with extremely elongation of the hip abductor and secondary hip osteoarthritis resulting from extra-articular neurofibroma.

Grundlagen und neue Konzepte in der computernavigierten Hüftendoprothetik

Combined component placement of cup and stem is closely correlated to stability, functionality and wear in total hip replacement (THA). Computer-navigated orthopedic surgery offers a reliable control method for a complex three-dimensional situation. Imageless navigation systems without the need of preoperative or intraoperative image acquisition and exposure to radiation have been proven to increase the accuracy of positioning the acetabular component and measure intraoperative leg length and offset changes precisely. A new development in this field is the noninvasive external femoral reference marker array system in conjunction with an imageless measurement technique. The future generation of imageless navigation systems will switch from simple measurement tasks to an integral part of the surgical process in navigated THA. The aim will be to find an optimized complementary component orientation with improved postoperative functionality and optimized range of motion without impingement.

Disappointing Short-Term Results With the DePuy ASR XL Metal-on-Metal Total Hip Arthroplasty

Outcomes of ultralarge-diameter femoral heads used in metal-on-metal (MOM) total hip arthroplasty (THA) are relatively unknown. This study reports on early failures of the ASR XL (Depuy, Warsaw, Ind) and assesses whether a correlation with cup positioning exists. A retrospective review of 70 consecutive MOM THAs with ultralarge-diameter femoral head and monoblock acetabular component was conducted. Minimum follow-up was 24 months. Of 70 THAs, 12 (17.1%) required revision within 3 years for pain (7), loosening (3), and squeaking (2). Three additional THAs noted squeaking, 2 noted grinding, and 3 additional hips had persistent pain. In total, 20 (28.6%) of 70 demonstrated implant dysfunction. Acetabular components for all symptomatic hips were in acceptable range of cup abduction and anteversion. The failures noted with this design do not correlate to cup placement. The high rate of implant dysfunction at early follow-up suggests serious concerns with the concept of MOM THA with an ultralarge-diameter femoral head paired with a monoblock acetabular cup.

Morphometric Study of the Acetabular in Malay Population Normal Hips and its Clinical Applications

The morphology study of acetabular is vital in clinical applications particularly through planning before acetabulum surgery and for determining the dysplastic hip. Several studies show that the acetabular morphology varies between populations; which lead to the difficulty to align the implant by following western standard. This prospective, cross sectional study focused on Malay population by providing essential information regarding normal value of acetabular which will enhance knowledge of the anatomical aspects and eventually aiding the acetabular cup placement during Total hip arthroplasty (THA). The acetabular images were obtained using computed tomography scanner and the measurement has been taken from 120 hips. We excluded from the study: pregnant woman, experienced hips injury, wearing implant or prosthesis. Our data were compared using Kolmogorov-Smirnov method and t-test. The findings for the acetabular as follows: center edge angle (CE) 31.69±5.48°; acetabular index angle (AA) 4.27±4.03°; acetabular angle of Sharp 42.35±3.24°; acetabular version (AcetAV) 14.99±5.05°; acetabular depth (AD) 15.49±1.70 mm; joint space width (JSW) 5.84±0.80 mm; anterior acetabular sector angle (AASA) 61.19±6.72°; posterior acetabular sector angle (PASA) 92.80±6.27°. This study documents for the first time the acetabular morphometric value on Malay population which will improve data, aiding the orthopedic surgeons during acetabular placements in THA and designing better implant.

Validation of navigation assisted cup placement in total hip arthroplasty

Computer navigation has the potential to provide precise intraoperative knowledge to the surgeon. Previous studies with navigation have confirmed its function for improved component position but few studies have reported the accuracy and precision of navigation system in clinical use. With this study we propose to evaluate the efficacy of navigation in guiding cup placement. Fifty-six patients undergoing primary total hip arthroplasty were prospectively included in this study. Stryker imageless navigation system which is accurate to 0.5° was used in all cases. Intraoperative data was collected for the acetabular component position using navigation for the freehand cup placement and the final cup placement done using navigation. Postoperative evaluation of component position was done with computed tomography (CT) and the deviation from intraoperative freehand and navigation values were calculated. The mean inclination of the freehand reading was 39.5° (range, 20°-58°), mean version of freehand reading was 10.7° (-6°- 27°), and the mean navigation reading was 43.2° (37°-49°) for inclination and 13.0° (-8° - 24°) for version. On postoperative CT scan analysis the mean inclination was 45.3° (34°-56°) and mean version was 15.1° (4°-25°). The deviation of the freehand inclination from the post operative CT scan reading was 11.4° (1°-30°) and the version deviated by a mean of 10.8° (2°-26°). The deviation of the navigation reading from the CT scan reading had a mean of 5.3° (1°-13°) for inclination and 5.6° (1°-17°) for version. The accuracy of the navigation system over conventional freehand cup placement is validated by this study.

A Comparison Between Imageless Navigated and Manual Freehand Technique Acetabular Cup Placement in Total Hip Arthroplasty

The purpose of this study was to compare acetabular component positioning using an imageless system to a matched control group using conventional techniques. Thirty procedures were performed using navigation. A multislice computed tomographic scan was used to assess cup position. There was no significant difference between mean inclination ( P = .11) and anteversion ( P = .24) but a statistical significant difference for mean deviation from the desired position for inclination ( P = .003) and anteversion ( P = .007). There was a significant difference in the percentages of correctly placed cups with inclination ( P = .046) and with anteversion ( P = .006). Combining both anteversion and inclination, there was a significant difference ( P = .01). We demonstrated a significant increase in accuracy of placement of acetabular cups within the desired position and safe zone using imageless navigation.

Accuracy of acetabular cup positioning using imageless navigation

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

Decreased accuracy of acetabular cup placement for imageless navigation in obese patients

BackgroundOptimal acetabular cup position is an important determinant of the success of total hip arthroplasty (THA), and navigation systems have been developed and applied to improve placement precision. However, the registration method touching bony landmarks through soft tissues may decrease the accuracy in obese cases and in patients with acetabular dysplasia. MethodsPlacement accuracy in 69 joints in which THA was performed with imageless navigation was calculated by comparing the placement angle in the anterior pelvic plane and the placement angle in the x-ray table plane with the patient in the supine position. We defined the difference between the placement angle in the anterior pelvic plane and the angle displayed on the navigation screen as the error and the difference between the placement angle in the plane of the x-ray table and the target angle of acetabular component position as the difference in target angle. Patients were divided into obese (BMI ≥ 25) and nonobese (BMI < 25) groups and into acetabular dysplasia and nondysplasia groups. ResultsThe mean ± SD navigation errors for all cases were 2.4° ± 2.0° for inclination and 3.7° ± 2.3° for anteversion. The mean difference in target angle for all cases was 2.8° ± 2.5° for inclination and 4.2° ± 3.0° for anteversion. The error in anteversion was significantly higher in the obese group (4.8° ± 2.5°) than in the nonobese group (3.2° ± 2.6°) (P = 0.01). No significant difference was observed between the acetabular dysplasia and nondysplasia groups. ConclusionsImageless navigation can be performed with an error of approximately 3° at the anterior pelvic plane. However, accuracy was found to decrease in obese cases.

Limitations of Imageless Computer-Assisted Navigation for Total Hip Arthroplasty

We prospectively evaluated acetabular cup placement in total hip arthroplasty with an imageless computer navigation system or using conventional manual technique. The achieved cup orientation in the manual group had substantially larger variances and greater placement error than the navigation cases. The use of navigation was abandoned in 3 cases because of excessive pelvic tilt and unreliable registration of the pelvis. Computer navigation system helped improve the accuracy of the acetabular cup placement for total hip arthroplasty in this study. The variation between the intraoperative navigation readings and the computed tomographic values suggests that relying on palpation of bony landmarks through drapes and tissue is a limitation of this method. Further, the variation in pelvic tilt has an effect on cup placement that requires further studies.

Radiographic review of limb-length discrepancy after total hip arthroplasty

Background A clinical and radiographic review was undertaken to evaluate technical causes for limb-length discrepancy (LLD) after total hip arthroplasty and the resultant effect on function. We hypothesized that limb lengthening most commonly occurs as a result of low placement of the acetabular implant. Methods A sample of 116 primary total hip arthroplasties performed between 2005 and 2007 with complete 1-year postoperative clinical outcomes scores and appropriate radiographs available on the Picture Archiving and Communication System were identified from a prospective arthroplasty database. Significant limb lengthening was defined as lengthening of more than 8 mm as compared with the contralateral limb postoperatively. Preoperative and 1-year postoperative anteroposterior bilateral hip radiographs were reviewed by two orthopaedic surgeons and one orthopaedic resident. Preoperative and postoperative LLD as well as the respective acetabular and femoral contribution to any postoperative LLD (if present) were measured. Results Nineteen of 116 (16.4%) patients had limb lengthening of more than 8 mm, of which the majority were women (14 of 19, P=0.015). Of those over-lengthened, the mean difference from preoperative to postoperative LLD was 1.3 mm (SD 7.6 mm). A mean of 6.2 mm (SD 6.2 mm) of lengthening was contributed by the femoral stem, and 5.3 mm (SD 6.3 mm) by low placement of the acetabular implant (P=0.738). Lengthening and femoral placement of the stem (r=0.489, P=0.000), and lengthening and low cup placement (r=0.596, P=0.000) were significantly correlated. There was no correlation between LLD and Harris Hip or Oxford Score at 1-year postoperatively. Conclusions Limb lengthening results from a combination of low acetabular implant and high femoral stem placement but did not result in inferior outcomes in the current study.

Biomechanical Evaluation of Acetabular Cup Implantation in Cementless Total Hip Arthroplasty

To report biomechanical properties of the Biologic Fixation System (BFX) acetabular cup impacted into a normal canine pelvis and to compare the effect of implant positioned to and beyond the medial acetabular wall. In vitro cadaveric study. Hemipelves of mature, large-breed dogs (n=6). For each dog, 1 hemipelvis was reamed to the depth of the acetabular wall (group A) and 1 was reamed an additional 6 mm after penetration of the medial cortex of the acetabulum (group B). The hemipelves were implanted with acetabular cups and loaded in compression through a matching femoral prosthetic component until failure. Specimen stiffness, and failure displacement, load, and energy were determined from load and displacement data and results between groups compared with a paired t-test. Mean failure load was greater in group A (3812 ± 391 N) than group B (2924 ± 316 N; P<.014). No other differences (P>.05) were observed between groups. Bone fracture (n=5) and cup displacement (1) occurred in group A whereas in group B there were 3 fractures and 3 cup displacements. Although medial placement of the BFX cup affected compressive failure loads, failure loads for both groups exceeded normal physiologic loads. Medial positioning of the acetabular cup does not appear to compromise acetabular implant-pelvic stability under normal physiologic loads. Because arthroplasty candidates often have abnormal acetabular architecture, mechanical properties of the cup placed in acetabula without a dorsal rim should be investigated.

Accuracy of acetabular cup placement in computer-assisted, minimally-invasive THR in a lateral decubitus position

In a prospective and randomised clinical study, we implanted acetabular cups either by means of an image-free computer-navigation system (navigated group, n = 32) or by free-hand technique (freehand group n = 32, two drop-outs). Total hip replacement was conducted in the lateral position and through a minimally invasive anterior approach (MicroHip). The position of the component was determined postoperatively on CT scans of the pelvis using CT-planning software. We found an average inclination of 42.3° (range 32.7-50.6°; SD ± 3.8°) and an average anteversion of 24.5° (range 12.0-33.3°; SD ± 6.0°) in the computer-assisted study group and an average inclination of 37.9° (range 25.6-50.2°; SD ± 6.3°) and an average anteversion of 23.8° (range 5.6-46.9°; SD ± 10.1°) in the freehand group. The higher precision of computer navigation was indicated by the lower standard deviations. For both measurements we found a significant heterogeneity of variances (p < 0.05, Levene's test). The mean difference between the cup inclination/anteversion values displayed by computer navigation and the true cup position (CT control) was 0.37° (SD 3.26) and -5.61° (SD 6.48), respectively. We found a bias (underestimation) with regard to anteversion determined by the imageless computer navigation system. A bias for inclination was not found. Registration of the landmarks of the anterior pelvic plane in lateral position with undraped percutaneous methods leads to an error in cup anteversion, but not to an error in cup inclination. The bias we found is consistent with a correct registration of the anterosuperior iliac spine (ASIS) and with a registration of the symphysis 1 cm above the bone, corresponding to the less compressible overlying soft tissue in this region. There was no significant correlation between the bias and the thickness of soft tissue above the pubic tubercles. We suggest use of a percutaneous registration of ASIS and an invasive registration above the pubic tubercles when computer-assisted navigation is performed in minimally invasive THR in a lateral position.

Femur first beim Hüftgelenksersatz – Das Konzept der kombinierten Anteversion

The concept of combined anteversion for total hip arthroplasty (THA) proposes a relationship between the cup and stem components that theoretically maximises the postoperative range of motion and minimises the risk for impingement of the joint. Using computer-assisted navigation tools, an anteversion angle of the cup component can be made to be dependent on the antetorsion angle of the stem component (or vice versa). We studied how this functional concept would be different from the traditional cup placement according to the Lewinnek safe zone. We prospectively reviewed 42 patients (42 hips) who underwent imageless, computer-assisted THA with cementless implants due to osteoarthritis between May and October 2008. Using computer navigation, we determined the cup anteversion with optimised containment and measured femoral stem antetorsion. Our goal was to implant the original implants with a combined anteversion of 37 degrees. Mean cup anteversion was 22.5 degrees, mean combined anteversion was 35.2 degrees. Femoral antetorsion ranged from -13 to 38 degrees (mean: 18 degrees). Mean anteversion of the trial cup with optimised containment was 15.9 degrees and therefore close to the recommendation according to the Lewinnek safe zone. The total postoperative range of motion (flexion, extension, abduction, internal/external rotation) as measured with the navigation system intraoperatively was 209 degrees compared to 94 degrees measured clinically preoperatively. No THA dislocation occurred during the test. The combined anteversion concept results in a cup position with more anteversion when compared to the traditional cup placement according to the Lewinnek safe zone. In this context, modern navigation techniques open a new frontier for an optimised component position. Placing the cup and stem in relation to the anteversion for both components allows consideration of the patient-specific biomechanics.

Effect of Cementless Acetabular Component Orientation, Position, and Containment in Total Hip Arthroplasty for Congenital Hip Disease

We evaluated the effect of the inclination angle, position, and containment of 53 cementless cups inserted in patients with congenital hip disease (CHD), after a minimum of 10 years of follow-up. The polyethylene wear rate was significantly greater when the cup was placed in more than 45° inclination ( P = .045) or if the cup was placed lateral to the teardrop position by more than 25 mm ( P = .001). Aseptic loosening of the femoral component was significantly greater when the cup was placed more than 25 mm superiorly to the teardrop ( P = .049). Cup placement of more than 25 mm lateral to the teardrop affected significantly periacetabular osteolysis ( P = .032). In CHD cases, it is preferable to avoid excessive vertical inclination, lateral, and superior placement of cementless cups in an attempt to obtain better containment.

Reply to Letter to Editor: THA with the ABG I Prosthesis at 15 Years: Excellent Survival with Minimal Osteolysis

We agree with the comments made by Dr. Gallo. The literature relating to this prosthesis is contradictory, with significant variation in the rates of implant survival, periacetabular osteolysis, and polyethylene wear. Numerous reports mirror Dr. Gallo’s experience of poor outcomes with this implant. Unfortunately we cannot offer additional insight regarding reasons why our results are better than those previously published. There is increasing evidence in relation to hard bearing surfaces that surgical technique and correct cup placement are more important than previously thought [1, 3]. It seems likely that these factors plus cup diameter/polyethylene thickness and polyethylene quality also will influence outcomes in other prostheses using conventional bearings. Recently Gallo et al. [2] suggested the position of the cup relative to Kohler’s line, increasing abduction angle of the cup, traumatic and inflammatory arthritis as a primary diagnosis, and patient weight all influence the rate of wear of the ABG I cup. Unlike that study, we did not see any relationship between cup abduction angle and polyethylene wear and unfortunately were unable to record these other determinants for our patient population. We also were unable to determine either the polyethylene thicknesses or the self lives and manufacturing batches of the polyethylene used in our series that may have been a marker of polyethylene quality. There is wide variation in reported details for surgical technique, surgeon numbers, bearing materials, and cup position for the ABG I. Missing information and the heterogeneity for the reports make it difficult to draw any direct comparison between series. What remains clear, however, is that the patients in whom an ABG I prosthesis has been implanted should continue to be closely monitored.