Late detachment modular femoral component after primary total hip replacement

Three years after total hip replacement surgery, a patient's modular femoral head separated from the stem portion of a primary total hip replacement while the patient was rising from a chair. The modular femoral head was in a polyethylene acetabular socket. Modular femoral and acetabular components now widely are used in hip replacement. The use of modular components greatly increases the flexibility during primary or revision total hip arthroplasty, but introduces the risks of component dissociation and intraoperative errors in matching. We report an unusually late dislocation of a primary modular total hip replacement.     

A polyethylene liner scratch after revision hip arthroplasty performed to repair ceramic fracture

A 61-year-old man who had undergone revision total hip arthroplasty in 2000 was evaluated at our clinic in 2008, 1 day after feeling an abnormal clicking sensation in his left hip. Radiographs showed a fracture of the alumina ceramic liner of his acetabular component. A second revision total hip arthroplasty was performed with a 28-mm highly crosslinked polyethylene acetabular liner and an alumina femoral head. Sixteen months after the second revision, the patient experience sudden-onset hip pain. Radiographs revealed a fatigue fracture of the neck of a displaced stem. Analysis by scanning electron microscopy of the surface of the retrieved alumina ceramic femoral head revealed no scratches or wear, but analysis of the highly crosslinked polyethylene socket revealed third-body wear, scratches, irregularly shaped dips, and white ceramic particles. Elemental analysis of the white particles by an x-ray microanalyzer revealed the presence of aluminum and oxygen.     

Ten-year results after cementless THA with a sandwich-type alumina ceramic bearing

We analyzed the long-term results of a single-surgeon series of 102 cementless total hip arthroplasties (THAs) performed using a sandwich-type alumina ceramic bearing. The prostheses involved a porous-coated acetabular socket, a polyethylene-alumina composite liner, a 28-mm alumina head, and a grit-blasted titanium-alloy stem. Mean patient age at the time of THA was 39 years (range, 18-66 years), and 76% of the patients were younger than 50 years. All procedures were performed with use of the same surgical technique and the same implant at a single center. Mean follow-up was 115 months (range, 84-133 months). When failure was defined as revision of either the acetabular or the femoral component for any reason, Kaplan-Meier survival probability at 10 years was 95.3% (95% confidence interval, 89.5%-100%). Mean Harris Hip Score improved from 47 points (range, 16-70 points) preoperatively to 95 points (range, 85-100 points) at final follow-up. No radiographically detectable osteolysis around the acetabular or femoral component was observed in any hip. No patient reported squeaking in the operated hip. During the follow-up period, 3 hips (3%) required revision surgery; 2 underwent acetabular revision because of a ceramic liner fracture and 1 underwent revision for early loosening of the acetabular cup. Ten-year results of cementless THA with a sandwich-type alumina ceramic bearing were encouraging, and no great increase in ceramic failure rate was observed, which contrasts with the findings of previously reported short-term follow-up studies.     

Unexpected Finding of a Fractured Metal Prosthetic Femoral Head in a Nonmodular Implant During Revision Total Hip Arthroplasty

Though there are many reports of fractured femoral components after total hip arthroplasty; there are no reports of a fractured metal femoral head. This is a report of a fractured metal femoral head in a nonmodular total hip replacement discovered unexpectedly during revision total hip arthroplasty for acetabular failure. This surprise finding, which was not appreciated on preoperative x-rays, required unplanned extraction of a well-ingrown, fully porous coated cylindrical femoral stem. Though rare, fracture of the metal femoral head in a DePuy (Warsaw, Ind.) monoblock Anatomic Medullary Locking (AML) component is possible, and one cannot expect the fracture to be apparent on preoperative radiographs as the 2 pieces may not necessarily dissociate. As usual, the surgeon performing revision arthroplasty should be prepared to revise all components.     

Revision of an acetabular liner has a high risk of dislocation

Polyethylene liners of modular acetabular components wear sometimes need to be replaced, despite the metal shell being well fixed. Replacing the liner is a relatively simple procedure, but very little is known of the outcome of revision. We prospectively followed up 1126 Harris-Galante I metal-backed, uncemented components for between nine and 19 years. We found 38 (3.4%) liners of 1126 acetabular components wore and required revision. These revisions were then followed up for a mean of 4.8 years. The rate of dislocation was 28.9%. Nine of the dislocations occurred once and two were recurrent. The overall secondary revision rate was three of 38 total hip replacements (7.9%) at a mean follow-up of 4.8 years. This gives a 92.1% survivorship (35 of 38) at under five years. In isolated revision of a liner, we had a complication rate of 23% (three of 13). In revision of a liner combined with revision of the femoral stem, there was a complication rate of 48% (12 of 25). We discuss possible reasons for the high dislocation rates. Leaving the well-fixed acetabular shell in situ leads to an increased risk of instability. However, this needs to be balanced against the otherwise low complication rate for revision of the liner. Patients should be consented accordingly.     

病灶清除植骨保留髋臼假体的翻修术治疗假体周围局灶性骨溶解

目的 探讨病灶清除植骨保留髋臼假体的翻修术治疗全髋关节置换(total hip arthroplasty,THA)术后稳定固定的髋臼假体周围局灶性骨溶解的疗效.方法 2006年3月至2009年3月,THA术后髋臼假体稳定固定的假体周围局灶性骨溶解患者23例(23髋),男13例,女10例;年龄39～54岁,平均46.6岁.23例均为非骨水泥髋臼.初次THA至诊断髋臼假体周围骨溶解的时间为4.6～7.4年,平均5.5年.术前HarTis髋关节评分74分.手术经腹股沟入路,行髂骨内板开窗,清除髋臼骨溶解病灶、同种异体颗粒骨植骨;经后外侧人路更换聚乙烯内衬、股骨头假体,保留髋臼假体.翻修术后1、3、6、12个月及之后每年随访1次,以髋关节Harris评分评价临床疗效,摄X线片、CT扫描观察植骨区愈合、新发骨溶解病灶及假体移位情况.结果 16例获得随访,随访时间8～38个月,平均28个月.末次随访时Harris髋关节评分86～100分,平均93.8分.16例植骨区成骨均良好,12例植骨区完全被周围骨爬行替代,髋臼假体固定好,无髋臼假体松动及移位,无新发髋臼假体周围骨溶解,无异位骨化、脱位、深静脉血栓形成及感染等并发症.结论 清除病灶植骨、保留髋臼假体、更换聚乙烯内衬和股骨头假体的翻修术可有效减少聚乙烯磨损颗粒产生,避免骨溶解病灶进展导致的假体松动,近期随访结果良好.     

Hybrid alumina total hip arthroplasty using a press-fit metal-backed socket in patients younger than 55 years. A six- to 11-year evaluation

Between 1990 and 1992, we implanted 71 hybrid alumina-on-alumina hip arthroplasties in 62 consecutive patients under the age of 55 years, with a mean age of 46 years at surgery. There were 56 primary and 15 secondary procedures. The prostheses involved a cemented titanium alloy stem, a 32 mm alumina head, and a press-fit metal-backed socket with an alumina insert. Three patients (four hips) died from unrelated causes. Four hips had revision surgery for either deep infection, unexplained persistent pain, fracture of the alumina head, or aseptic loosening of the socket. The nine-year survival rate was 93.7% with revision for any cause as the end-point and 98.4% with revision for aseptic loosening as the end-point. The outcome in the surviving patients (50 patients, 57 hips) with a minimum five-year follow-up (mean eight years) was excellent in 47 hips (82.5%), very good in eight (14%), good in one and fair in one. A thin, partial, lucent line, mainly in zone III was present in 38% of the sockets and one socket had a complete lucency less than 1 mm thick. One stem had isolated femoral osteolysis. There was no detectable component migration nor acetabular osteolysis. This hybrid arthroplasty gave satisfactory medium-term results in active patients. The press-fit metal-backed socket appeared to have reliable fixation in alumina-on-alumina hip arthroplasty. The excellent results using cemented fixation of the stem may be related to the low production of wear debris.     

Alumina-on-alumina total hip arthroplasty: a minimum 18.5-year follow-up study.

BACKGROUND: The purpose of this retrospective study was to report the results, after a minimum of 18.5 years of follow-up, in a consecutive series of total hip arthroplasties performed with an alumina-on-alumina combination. METHODS: One hundred and eighteen consecutive total hip arthroplasties were performed in 106 patients between 1979 and 1980. The prostheses combined a 32-mm alumina head and an all-alumina socket. Both components were cemented in eighty-five hips, both components were implanted without cement in twenty-nine, and only the stem was cemented in four. The mean age of the patients at the time of the index arthroplasty was 62.2 years (range, thirty-two to eighty-nine years). RESULTS: At the 18.5 to 20.5-year follow-up evaluation, forty-five patients (fifty-one hips) were alive and had not had a revision, twenty-five patients (twenty-five hips) had undergone revision of one or both components, twenty-seven patients (thirty hips) had died, and nine patients (twelve hips) had been lost to follow-up. The mean Merle d'Aubigné hip score (and standard deviation) was 16.2 +/- 1.8 points at the latest follow-up evaluation. The rate of survival at twenty years, with revision for any reason as the end-point, was 85.6% for the cementless cups compared with 61.2% for the cemented cups and 84.9% for the cementless stems compared with 87.3% for the cemented stems. Wear of the prosthetic components was undetectable on plain radiographs. Periprosthetic cystic or scalloped lesions requiring the use of allograft bone during revision were present in three of the twenty-five revised hips. In addition, seven hips had moderate acetabular osteolysis treated with a 4-mm-larger cup. No fracture of the alumina socket or head was recorded. The mean acetabular wear rate in this series was <0.025 mm/yr. CONCLUSION: With the alumina-on-alumina total hip arthroplasty, minimal wear rates and limited osteolysis can be expected up to twenty years after the operation, provided that sound acetabular component fixation is obtained.     

Femoral revision in hip resurfacing compared with large-bearing metal-on-metal hip arthroplasty

It has been suggested that revision of the femoral component of hip resurfacing after femoral failure would be straightforward and have an outcome comparable to primary total hip arthroplasty (THA). We have compared the outcome of femoral side-only revision resurfacings to the results of primary modular large-bearing metal-on-metal THA. Fourteen consecutive patients underwent revision surgery of the failed femoral component, to a cemented tapered stem (CPT, Zimmer, Warsaw, Indiana) with a large modular metal head (Smith and Nephew Orthopaedics Ltd, Memphis, Tennessee, or Adept, Finsbury Orthopaedics, Surrey, England). The acetabular component was found to be well fixed, well orientated, and was left in situ. The 14 matched patients in the primary THA group received the same components. At a mean follow-up of 49 months (range, 30-60 months), clinical outcome measured using the Oxford and Harris Hip Scores showed no significant difference (P = .11, P = .45, respectively). Operative time and blood loss were comparable for both groups. We conclude that revision of the failed femoral resurfacing component gives excellent results.     

Dislocation After Debridement,Antibiotics, and Implant Retention for Periprosthetic Joint Infections of the Hip

BackgroundDebridement, antibiotics, and implant retention (DAIR) is a common treatment option for hip periprosthetic joint infection (PJI). However, noninfectious outcomes of DAIR such as instability are not well reported. The purpose of this study was to evaluate risk factors for hip dislocation post-DAIR for PJI of both primary and revision total hip arthroplasty (THA).MethodsA retrospective chart review identified all patients who underwent DAIR of a primary or revision THA over a 20-year period with a minimum 1-year follow-up. A total of 151 patients met inclusion criteria, 19.9% of whom had a post-DAIR dislocation. Demographic and intraoperative variables were obtained. Patients who had modular components exchanged during DAIR to those with increased offset, increased “jump distance”, or a more stable acetabular liner were defined as patients who had “components exchanged to increase stability.” Predictors of hip dislocation post-DAIR were inserted into a multivariate linear regression.ResultsPost-DAIR dislocation rates were 16.3% in primary THAs and 25.4% in revision THAs. In patients who had “components exchanged to increase stability” during hip DAIR, there was at least an 11-fold reduction (1/odds ratio (OR), 0.09) in dislocation risk compared to patients who had no components altered during modular component exchange during hip DAIR (OR, 0.09; 95% confidence interval, 0.02-0.44; P < .001), while a 13-fold increased dislocation risk was seen in patients with a history of neuromuscular disease (OR, 13.45; 95% confidence interval, 1.73-104.09; P = .01).ConclusionsDuring DAIR of hip PJI, surgeons should consider prophylactically exchanging components to increase stability even if components appear stable intraoperatively.     

应用锥形沟槽式股骨组配柄假体行全髋关节翻修术的中期疗效

目的 探讨应用锥形沟槽设计的股骨组配柄假体行全髋关节股骨侧假体翻修术的中期疗效.方法 2000年5月至2005年8月采用锥形沟槽式股骨组配柄假体行全髋关节翻修术19例,男6例,女13例;年龄47～86岁,平均67岁.单髋17例,双髋2例.术前诊断均为股骨柄和臼杯假体无菌性松动合并股骨侧骨缺损,按Paprosky标准诊断为Ⅱ型缺损4髋,Ⅲa型缺损14髋,Ⅲb型缺损3髋.股骨侧翻修均采用锥形沟槽式股骨组配柄假体(Lima-Lto,意大利),髋臼侧均采用SPH臼杯假体(LimaLto,意大利)行生物学固定.关节头臼界面采用陶瓷-陶瓷组合17髋,金属-聚乙烯组合4髋.结果 全部病例随访5～10年,平均7年.Harris髋关节评分由术前平均(46.2±15.2)分改善至翻修术后半年平均(90.3±5.3)分,末次随访平均(92.2±3.5)分.X线片显示翻修柄获广泛骨长入骨性固定者20髋(95%,20/21),纤维性稳定者1髋(5%,1/21).假体下沉0～10 mm,平均2.4 mm.随访期间无一例因假体松动或其他原因需行再次翻修.结论 采用锥形沟槽式股骨组配柄假体行伴有PaproskyⅡ型、Ⅲa和Ⅲb型骨缺损的股骨侧假体翻修术,可获得理想的初始稳定和永久生物学固定,中期随访疗效满意.

Abstract：

Objective To evaluate the midterm results of the revision total hip replacement with a fluted and tapered modular stem. Methods Nineteen patients (21 hips) underwent revision total hip arthroplasty from May 2000 to August 2005 were reviewed. There were 13 females and 6 males, with an average age of 67 years. Pre-revision diagnosis included aseptic loosening of the cups and stems associated with femoral defects (Paprosky classification) type Ⅱ 4 hips (19%), type Ⅲa 14 hips (67%), and type Ⅲb 3 hips (14%). The adopted acetabular component was SPH (Lima-Lto, Italy), and femoral component was a fluted and tapered modular stem (Lima-Lto, Italy). Clinical and radiographic evaluations were performed postoperatively. Results The mean follow-up was 7 years (range, 5-10). The Harris hip score improved from 46.2±15.2 preoperatively to 90.3±5.3 postoperatively, and maintain 92.2±3.5 at the latest follow-up. The X-ray films showed bone ingrowths fixation in 20 hips (95%) and fibrous stable fixation in 1 hip (5%). The average stem subsidence was 2.4 mm (range, 0-10 mm). There were no re-revisions of the femoral stem for any reason. Conclusion The midterm results of revision total hip replacement with a fluted and tapered modular stem in Paprosky type Ⅱ, Ⅲ a, Ⅲ b femoral defect associated aseptic loosening of the femoral stem was encouraging.     

Polyethylene liner dislocation in Harris Galante acetabular components

AIM: Dislocation and subsequent dissociation of the polyethylene liner as a result of failure of the acetabular locking mechanism is a potential source of failure in the Harris-Galante acetabular component. The purposes of this study are to present seven cases with a liner dislocation due to failure of the liner locking mechanism. METHOD: Between March 1997 and December 2001, seven patients who had had a total hip arthroplasty presented with clinical and radiologic signs of liner dislocation and signs of polyethylene wear of the liner from a Harris Galante acetabular shell. In all cases the intraoperative findings showed evidence of failure of the liner locking mechanism and subsequent dislocation. The medical records, radiographs, operative notes and explanted retrieved components were reviewed. RESULTS: The components had been in situ for an average of 5.3 years (range 1-9 years). Two components were first generation, five were second generation. The symptoms developed spontaneously in five patients, the other two patients described a minor trauma. Radiographs showed eccentric position of the head in all cases. All acetabular components showed an excellent stability intraoperatively, nevertheless we had to remove the well fixed acetabular shell due to complete destruction of the liner locking mechanism in two cases. Treatment consisted of revision of the shell in two patients and exchange of the liner in five patients. All retrieved liners showed severe deformation and/or fracture of the rim. CONCLUSION: Harris Galante modular acetabular components have been used widely for primary and revision arthroplasty. The survival of this implant has been well documented in the literature. Failure of the liner locking mechanism and following dislocation or fracture of the polyethylene liner is a potential cause of failure which may possibly occur more often than the literature to date has documented. We report seven cases of liner dislocation, in which two acetabular components had to be removed completely due to destruction of the liner locking mechanism. In the other five cases exchange of the liner was possible thanks to well timed revision. We believe that, as the liner wears and becomes loose due to an inefficient locking mechanism, the load increases on the polyethylene rim until it deforms or fractures. As a consequence of the prosthetic design at that stage nothing can prevent the liner from rotating out of the shell.     

Cementless hemispheric porous-coated sockets implanted with press-fit technique without screws: average ten-year follow-up

BACKGROUND: Press-fit implantation of a porous-coated hemispheric acetabular component without screws is an option for primary total hip replacement. The purpose of the present study was to evaluate the results of this technique after an average duration of follow-up of ten years to determine if there was any loss of fixation or increase in osteolysis over time. METHODS: From June 1988 to November 1990, 132 primary total hip replacements were performed with a porous-coated socket that was implanted with use of a press-fit technique. Twenty-two hips were excluded because the patient had died or had been lost to follow-up, leaving 110 hips (103 patients) available for inclusion in the study after an average duration of follow-up of 10.2 +/- 1.0 years. The average age of the patients at the time of operation was 60.7 years (range, 23.7 to 86.2 years). Radiographs were evaluated with regard to initial gaps, radiolucent lines, migration, polyethylene wear, and osteolysis. Kaplan-Meier survivorship analysis was performed to calculate the rate of survival of the acetabular component. RESULTS: One hip (0.9%) had revision of the socket because of aseptic loosening, and four hips (4%) had revision of a stable socket. With the numbers available, the presence of gaps on the initial postoperative radiographs was not associated with the occurrence of radiolucent lines (p = 0.039). Pelvic osteolysis was seen in four hips, with an average time to radiographic appearance of six years. Increased wear was directly related to an abduction angle of >40 degrees. The twelve-year survival rate was 99.1% with revision because of failure of fixation of the metal shell as the end point, 95.3% with revision for any reason as the end point, and 79.6% with exchange of the liner as the end point. CONCLUSIONS: The fixation of this press-fit socket did not deteriorate over time and was associated with a low rate of osteolysis. The most common reasons for reoperation were wear and dissociation of the polyethylene insert.     

Prevention of dislocation after hip arthroplasty: lessons from long-term followup.

Regarding dislocation after total hip arthroplasty, prevention is worth an ounce of cure. The current authors evaluated dislocation after total hip arthroplasty during the 26-year practice of one surgeon to identify potential variables that can contribute to the prevention of dislocation. Between 1970 and 1996, dislocation after total hip replacement occurred after 7.2% of primary hip arthroplasty procedures (298 of 4164 primary hip replacements) and 11.2% of revision hip arthroplasty procedures (90 of 803 revision hip replacements). Significant findings included an increase in dislocation when 22-mm modular femoral heads were used and a decrease in dislocation after revision for dislocation when constrained liners were used. An additional finding was that 26% of first time dislocations occurred more than 2 years after surgery. Concerning prevention of dislocation, small head modular femoral components should be used cautiously, and constrained liners should be considered in complex revision cases. Patients should be counseled concerning the potential for dislocation many years after their arthroplasty.     

The incidence of modular tibial polyethylene insert exchange in total knee arthroplasty when polyethylene failure occurs

One of the primary reasons for utilizing modular tibial polyethylene inserts (MTPI) at the time of total knee arthroplasty is to have the ability to simply exchange the polyethylene at the time of revision surgery when polyethylene failure has occurred. During a 2-year period from January 1993 to December 1994, 62 revision total knee arthroplasties were reviewed from five different institutions in North America, which were performed secondary to modular tibial insert failure. In 55 cases (88.7%), significant scoring and/or damage to the femoral and/or tibial components occurred necessitating revision of one or both components. This series does not support the premise that polyethylene exchange is common at the time of revision surgery for MTPI failure. Of the patients 88.7% had MTPI failure resulted in femoral and/or tibial component revision secondary to surface damage to the femoral component and/or tibial component baseplate. In order to avoid femoral and tibial component wear secondary to MTPI failure, early recognition is necessary to allow the much simpler operation consisting of polyethylene liner exchange only.     

Long-term survivorship of cemented all-polyethylene acetabular components in patients > 75 years of age

Between 1974 and 1982, 132 consecutive hips in 112 patients >75 years of age were treated with primary total hip arthroplasty for osteoarthritis using a cemented all-polyethylene T28 socket and cemented T28 or TR28 stem with a 28-mm head size. At the time of review, 94 patients (110 hips [83%]) had died and 18 patients (22 hips [17%]) were still living (mean age at follow-up, 93 years). Five hips (5 patients) were lost to follow-up. Clinical follow-up averaged 8.9 years for the entire group and 14.6 years for patients still living. Only 2 acetabular components have been revised (1 for recurrent dislocation, 1 for infection). No acetabular component has required revision for aseptic loosening. Survivorship free of acetabular revision for aseptic loosening at 10 years was 100%; free of symptomatic acetabular loosening, 97.4% (95% confidence interval, 91.8-100%); and free of acetabular loosening, 95.9% (95% confidence interval, 89.7-100%). The commonest complication was postoperative hip dislocation, which occurred in 11 hips (8.7%) and which required reoperation in 2 hips. Cemented acetabular components implanted in patients >75 years of age with a diagnosis of osteoarthritis showed a high rate of survivorship free of revision and free of symptomatic aseptic loosening.     

Erosion with loosening of an aluminum oxide ceramic acetabulum. Case report

The arthrodised hip of a 52 year-old female patient that had been absolutely trouble free for 9 years was remobilised by implanting a Mittelmeier, Autophor prosthesis (Al2O3 socket, Al2O3 head). Two years later, the hip joint had to be revised because of loosening of the socket. Since the shaft of the prosthesis was still firmly anchored within the femur, only the socket und the head were replaced. About three years following this revision, signs of loosening of the acetabular component again developed. Finally 4 1/3 years after the first revision (6 1/3 years after primary implantation) the hip was again revised. A polyethylene socket was then cemented into an acetabulum supporting shell and the prosthesis shaft furnished with a ceramic head of 32 mm diameter. Possible disadvantages of ceramic-ceramic bearing surfaces in patients with an altered bone structure of the pelvis and with a high risk of subluxation, due to weakened pelvi-trochanter muscles, are discussed.     

Catastrophic failure of a modular revision total hip polyethylene insert

Early catastrophic failure of a modular polyethylene component is a potential problem after revision total hip arthroplasty. We describe an unusual case of polyethylene failure that occurred within 18 months of implantation in which no obvious technical error or mechanical failure was identified. The acetabular polyethylene insert was prepared with gas plasma sterilization, and the shelf life was 4 months. Radiographic evaluation used generalized Hough transforms to assess the cup articulation. We identified cup penetration of 2.8 mm before revision and catastrophic destruction of the polyethylene liner at the time of revision. Possible factors implicated for failure included a thin polyethylene liner, increased hip separation, femoral head mismatch, and the high activity level of a younger patient. We believe that this case report highlights the need for future investigations of these subtle factors.     

Modular femoral stem removal during total hip arthroplasty using a universal modular stem extractor.

Removal of a modular head femoral prosthesis may be extremely difficult during revision total hip arthroplasty (THA). A universal modular stem extractor was developed that achieves a secure attachment to the stem taper, and applies tensile forces with a five-pound slaphammer. Clinical use indicates that this new device facilitates uncomplicated modular femoral stem removal.     

Effect of acetabular modularity on polyethylene wear and osteolysis in total hip arthroplasty.

BACKGROUND: Debris from polyethylene wear causes osteolysis. In this study, we examined the effect of acetabular liner modularity on polyethylene wear and osteolysis. METHODS: We compared forty-one hips (thirty-nine patients) treated with a nonmodular, porous-coated acetabular component with a matched group of forty-one hips (forty patients) treated with a modular acetabular component. The groups were matched by patient gender and age, type of polyethylene material, method of polyethylene sterilization, femoral head size and manufacturer, and stem manufacturer. The mean follow-up period was 5.3 years (range, 3.8 to 6.8 years) for the nonmodular group and 5.5 years (range, 3.8 to 8.0 years) for the modular group. Using serial radiographs and a computer-assisted method, we measured two-dimensional head penetration into the polyethylene liner. Temporal head-penetration data and linear regression analysis were used to calculate the true wear rates. RESULTS: The nonmodular acetabular components demonstrated a lower, but not a significantly lower, mean true wear rate than did the modular components (0.11 compared with 0.16 mm/yr, p = 0.22), and they were associated with a significantly lower rate of osteolysis (2% compared with 22%, p = 0.01). In addition, the true wear rates of the nonmodular components were less variable than those of the modular components. The 95% confidence interval for the wear rates of the nonmodular components (0.08 to 0.13 mm/yr) was nearly half that of the modular group (0.11 to 0.20 mm/yr). CONCLUSIONS: The lower and more consistent true wear rates of the nonmodular components could be attributed to the fact that these cups were designed to have greater liner-shell conformity, greater liner thickness, and less liner-shell micromotion than modular components. These design factors could have favorably altered the stress distribution throughout the liner and could have thereby decreased wear. Although nonmodular components may present a partial solution to the problems of wear and osteolysis, they pose a disadvantage when a failed liner in a bone-ingrown acetabular component needs to be revised.