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Up to 20% of patients are dissatisfied following total knee arthroplasty (TKA), most often due to pain and/or stiffness. The differential diagnosis includes immune reaction to the prosthesis. However, there is no consensus on diagnostic criteria for immune failure, an allergic reaction, to a TKA. Histologic evaluation could provide evidence as to whether an allergic reaction caused TKA failure. A recent study showed an increase in CD4+ lymphocytes compared to CD8+ lymphocytes in patients lymphocyte transformation testing (LTT) + for Ni. This finding is consistent with Ni sensitization, but can lymphocyte subsets be used to diagnose immune failure on a case-by-case basis?Periprosthetic tissues from 18 revision cases of well-fixed, aseptic, but painful and/or stiff primary TKAs were analyzed. Six patients LTT- for Ni were matched as a cohort for age, sex, and body mass index (BMI), to 12 patients LTT + for Ni. Periprosthetic tissue biopsies underwent immunohistochemical IHC staining for CD4+ and CD8+ lymphocyte subsets and were compared by LTT status. The immunohistochemicalIHC results were also compared with periprosthetic histology.There was no relationship between LTT status and mean CD4+ cells/hpf or CD4+:CD8+ lymphocyte ratio. No relationship was found between LTT stimulation index (continuous or categorical) and CD4+:CD8+ ratio or aseptic lymphocyte-dominant vasculitis-associated lesion ALVAL score.Lymphocytes in periprosthetic tissue are highly variable in number, subtype ratio, and location, and have no relationship to LTT result or ALVAL score on a case-by-case basis. Based on these results, lymphocyte subsets cannot diagnose immune failure. Further work is needed to determine criteria for the diagnosis of immune failure of a TKA.

Background An allergic reaction may rarely cause a painful or stiff total knee arthroplasty (TKA). However, no consensus diagnostic criteria for TKA immune failure exist. Lymphocyte transformation testing (LTT) measures immune sensitivity to various materials, but its role in diagnosing an allergic reaction to a TKA has not been established. This study compares TKA periprosthetic tissues in a) LTT-positive versus -negative patients and b) patients with conventional CoCrNi versus hypoallergenic implants. Methods Periprosthetic tissues from 26 revision cases of well-fixed, aseptic, but painful or stiff TKAs were analyzed. Twelve patients LTT positive for nickel (Ni) were matched as a cohort to 6 LTT-negative patients. In 4 patients LTT positive for Ni, tissue from first revision of CoCrNi implants was compared with tissue from subsequent revision of hypoallergenic implants. Histology was evaluated using the aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) score. Results No correlation was found between LTT and any ALVAL score component. The mean total ALVAL score was 3.8 ± 1.5 for LTT-negative patients and 3.3 ± 1.2 for LTT-positive patients (P = .44). The mean total ALVAL score at revision of CoCrNi implants was 3.0 ± 1.8 compared with 5.8 ± 0.5 at rerevision of hypoallergenic implants (P = .053). Conclusion Periprosthetic TKA tissue reactions were indistinguishable between LTT-positive and -negative patients. LTT does not predict the periprosthetic tissue response. ALVAL scores of hypoallergenic revision implant tissue trended higher than primary CoCrNi implant tissue. A positive LTT may not indicate that a periprosthetic immune reaction is the cause of pain and stiffness after TKA. Level of Evidence 3, retrospective cohort study.

Aims Loosening of the tibial component after total knee arthroplasty (TKA) is a common indication for revision. Increasing the strength of the initial tibial implant/cement interface is desirable. There is little information about the surgical techniques that lead to the highest strength. We investigated the effects of eight variables on the strength of the initial tibial baseplate/cement interface. Materials and Methods A total of 48 tibial trays were cemented into acrylic holders using cement from two manufacturers, at three different times (early, normal, and late) using two techniques: cementing the tibial plateau or the plateau and the keel; and involving two conditions of contamination with marrow fat (at the metal/cement and cement/cement interfaces). Push-out tests were performed with load continuously recorded. Results Compared with normal conditions, early cementing increased the mean strength of the interface when using the two cements, Simplex and Palacos, by 48% and 72%, respectively. Late cementing reduced the strength by 47% and 73%, respectively. Cementing the keel increased the mean strength by 153% and 147%, respectively, for the two cements. Contamination of the metal/cement interface with fat reduced the mean strength by 99% and 94% for the two cements but adding cement to the underside of the tibial tray prior to insertion resulted in the mean strength being lowered by only 65% and 43%, respectively. Conclusion In order to maximize the strength of the tibial tray/cement interface, cement should be applied to the component soon after mixing, contamination of the interface should be avoided, and the keel and the plateau should be cemented.

Activity monitoring has important applications in orthopaedic and medical research. There is a paucity of information on device accuracy. Thirty adults tested the accuracy of 10 devices in 5 activities: walk 400-M, run 400-M, walk 10-M, ascend and descend 10 steps. A second protocol tested slow walking speeds at 1.0, 1.5, 1.8, and 2.0MPH. The waist-based devices FitBit One and Omron HJ-321 were >90% accurate for all activities. The wristband devices and Smartphone Apps were 95% accurate at lower cadence activities, but undercounted running by ~25%. Waist-based, dedicated activity monitors are highly accurate in a variety of activities.

Background Cross-linked polyethylene (XLPE) has demonstrated significantly reduced wear and osteolysis into the second decade for total hip arthroplasty. There is a relative paucity of data with ≥36-mm bearings. Issues include potential effects of reduced liner thickness and component position on wear, osteolysis, and mechanical failure of the bearing. Methods Radiographs of 48 primary total hip arthroplasties with ≥36-mm modular XLPE bearings were analyzed at a minimum 5 years postoperative on serial radiographs using a validated, edge-detection-based algorithm. Subgroups were examined to assess the effect of bearing diameter, liner thickness, acetabular abduction angle, and acetabular anteversion on XLPE wear. Results There was no significant difference in volumetric wear when subgroups were stratified by component factors: liner thickness ( 3 /y vs 24.47 mm 3 /y, respectively ( P = .315); acetabular component abduction angle ( 3 /y vs 27.8 mm 3 /y, respectively ( P = .522); acetabular anteversion ( 3 /y vs 31.79 mm 3 /y, respectively ( P = .521). There were no dislocations, mechanical failures, or revisions. There were 7 hips with volumetric wear rates ≥80 mm 3 /y; 1 had possible osteolysis. Conclusion Larger-diameter XLPE wear was not measurably affected by liner thickness, acetabular abduction angle, or acetabular anteversion. However, there is a trend for increasing volumetric wear with increasing bearing size. Wear outliers do occur, and continued follow-up of larger-diameter XLPE bearings is warranted.

Patients, and their femurs, come in all shapes, sizes, and types. Fortunately, so do cementless femoral stems. Each surgeon should have a "go to" cementless femoral component that can address over 90% of cases. A simple approach is to separately consider (A) the part inside the bone and (B) the part outside the bone. The inner-cortical geometry (Dorr type) and bone density influence stem size (the part inside the bone) and influence femoral canal preparation. Femoral deformity or old hardware can occasionally necessitate the use of a short stem or a modular stem. Restoration of limb length and offset is a function of the neck angle and length (the part outside the bone). Undersizing of cementless stems increases the risk of aseptic loosening while restoration of limb length and offset favorably affects patient satisfaction and function.

With improvements in implant modularity and polyethylene, it is important to assess the contemporary performance of cement vs. cementless fixation in total knee arthroplasty (TKA). Aseptic loosening is the most common indication for revision. Registry data indicates that the type of fixation (cemented, cementless, or hybrid) makes little difference in revision rates for younger patients (

The utilization of lymphocyte transformation testing (LTT) has increased for diagnosing metal sensitivity associated with total knee arthroplasty (TKA), but its validity for the diagnosis of TKA failure due to an immune reaction has not been established. In this study, we sought to characterize the relationship of a positive LTT result to histopathologic findings and clinical and functional outcomes.This was a retrospective study of 27 well-fixed, aseptic, primary TKA cases in which the patient had persistent pain and/or stiffness and underwent revision due to a suspected metal allergy to nickel, as determined on the basis of positive LTT. Revision procedures were performed by a single experienced arthroplasty surgeon. Periprosthetic tissue samples obtained at the time of revision surgery were scored using the aseptic lymphocyte-dominated vasculitis-associated lesion (ALVAL) scoring system.Eight patients were categorized as mildly reactive; 8 patients, moderately reactive; and 11 patients, highly reactive to nickel by LTT. The predominant findings on routine histopathologic analysis were fibrosis and varying degrees of lymphocytic infiltration in 17 (63%) of the 27 cases. The average ALVAL score of the cohort was 3.1 ± 1.9, of a maximum score of 10. Average Knee Society Score (KSS) values improved post-revision, as did range of motion (all p0.01). Neither LTT stimulation index as a continuous variable nor as a categorical variable (mildly reactive, moderately reactive, highly reactive) was correlated with ALVAL score, pre-revision function (as assessed by KSS-clinical, KSS-functional, and range of motion), or change in function at the most recent follow-up (0.015r0.30, 0.13p0.95). In addition, the ALVAL score did not correlate significantly with either pre-revision or post-revision KSS or range of motion (0.061r0.365, 0.09p0.88).On the basis of this analysis, including histopathologic assessment, LTT results alone were insufficient for the diagnosis of TKA failure due to an immune reaction. A positive LTT may not indicate that an immune reaction is the cause of pain and stiffness post-TKA. The role of LTT in assessing TKA failure from an immune reaction needs further investigation. Diagnostic criteria for such TKA failure need to be established.Diagnostic Level IV. See Instructions for Authors for a complete description of levels of evidence.

Cross-linked polyethylene (XLPE) has generally low rates of wear and osteolysis at 10 years, but component position may become important with longer follow-up. At 5-13 years, neither acetabular component lateral opening angle nor version were significantly correlated to wear. In the present study, we analyzed the effects of femoral anteversion and combined anteversion on XLPE wear.Forty-two well-functioning primary total hip arthroplasties in 36 patients, performed by a single surgeon via a posterior approach, were followed for a minimum of 5 years (mean, 7.1 years; range, 5.0-10.3). All hips had a modular, XLPE liner with a ≥36-mm bearing. Femoral anteversion was measured on the modified Budin view. Wear was measured on radiographs using a validated, computer-assisted, edge-detection-based algorithm. The mean lateral opening angle was 40.4° (range, 22.6°-50.3°). The mean acetabular version was 19.1° (range, 11.3°-27.5°). Neither of these variables was significantly correlated to wear. Effects of femoral anteversion and combined anteversion on XLPE wear were assessed using linear and polynomial regression analysis.Femoral anteversion (mean, 18.4°; range, 6.8°-30.7°) was significantly correlated to linear wear (mean, 0.06 mm/y; range, 0-0.16), showing an inverse parabolic relationship with the least wear occurring at 18.2° (P = .02). Combined anteversion (mean, 37.2°; range, 21.8°-54.3°) showed a similar significant relationship with the least wear at 38.1° (P.001). Based on regression, combined anteversion between 24.6° and 50.4° resulted in linear wear rates less than 0.1 mm/y.To the authors' knowledge, this is the first study to identify femoral anteversion as an independent factor influencing XLPE wear, with least wear occurring around 18°. At 5-10 years, average linear wear of XLPE is below 0.1 mm/y over a 25°-50° range of combined anteversion, with the least wear around 38°. Femoral-acetabular mating is a product of both components. Femoral component version and combined anteversion had a greater effect on wear than acetabular component lateral opening angle. Additional studies are warranted, but these results indicate that the sensitivity of wear studies is increased with version assessments.

Jumbo cups can be used to address many acetabular revision cases with bone loss. The technique of implantation is relatively straight forward, and there is the potential to maximize bone-to-cup surface area, approximate the natural hip center, and to obtain a construct that allows immediate weight bearing. Experience from multiple sources has demonstrated survivorship up to 83% at 20 years, limited mostly by the wear of conventional polyethylene. A contraindication to this method is irradiated bone and a limitation is restoration of peripheral acetabular bone stock, which could compromise further revision surgery.

There are practical and fiscal benefits of head–neck modularity. Taper corrosion occurs with all head sizes and rarely necessitates revision. The role of design and manufacturing variables continues to be investigated and debated. The utilization of ceramic heads has increased but the cost–utility ratio needs scrutiny. Changes in surgical practice, including smaller incisions and the increased use of cementless, tapered titanium stems are challenges to consistent and adequate taper assembly. Surgical taper assembly is variable and important regardless of the head material. Standardization of surgical taper assembly is desirable for all head materials: taper assembly has been implicated in ceramic head fracture as well as in fretting and corrosion.

In the Registry Era, in the Information Age, and with a competitive and expanding marketplace, the focus has been on the prosthetic joint devices. However, a distinction should be made between mechanical failure of a device, failure of an arthroplasty, and the limitations of technology. The patient and the surgeon play central roles in the majority of revisions (failure of an arthroplasty). Analysis of a large United States database indicates that the most common causes of revision are instability/dislocation (22.5%), mechanical loosening (19.7%), and infection (14.8%). Acetabular component position has been linked to higher wear and instability. Increased odds of component mal-position were found with lower-volume surgeons and patients with a higher body mass index. Medical co-morbidities significantly increase the risk for revision within 12 months of surgery. Patient demographics and pre-operative status have been shown to be more important than implant factors in predicting the presence of thigh pain, dissatisfaction, and a low hip score. The most predictive factors were ethnicity, educational level, poverty level, income, and a low pre-operative WOMAC score or pre-operative SF-12 mental component score.

Patient activity influences polyethylene wear. However, it is unclear how individual activity changes with patient aging after THA.We quantified changes in individual gait cycles and gait speed, assessed age-related differences in these parameters, and determined their relationship to polyethylene wear.A microprocessor was worn on the ankle to quantify the activity of 14 healthy patients with a well-functioning THA at two time periods: early (within 3.5 years of implantation) and late (10-13 postoperative years). Wear was measured on serial radiographs using edge detection-based software.Mean activity decreased by 16% from the early to the late period: 2.04 million gait cycles/year to 1.71 million gait cycles/year. Mean gait speed decreased by 9%: 15.4 cycles/minute to 14.0 cycles/minute. The activity of the 10 patients who were younger than 65 years at surgery decreased by 14% (2.34 million gait cycles/year to 2.02 million gait cycles/year), while the four patients 65 years or older at surgery decreased by 28% (1.29 million gait cycles/year to 0.94 million gait cycles/year). Gait speed was 26% slower for patients 65 years or older than for patients younger than 65 years. The mean linear penetration rate decreased by 42% from the first 5 years (early wear rate) to the next 8 years (late wear rate, 5-13 years): 0.043 mm/year to 0.025 mm/year.The greatest patient activity and wear occurred during the first 5 years. Walking speed and gait cycles both decreased with aging, resulting in deceasing wear over time.

Polyethylene wear rates in vivo are highly variable. A major factor contributing to the variability in clinical wear rates is patient activity. Pedometer studies have documented a 45-fold range in patient activity. A microprocessor worn on the ankle is more accurate than a pedometer and records the motion of the leg in real time, allowing the assessment of walking speed and pattern. Average patient activity approaches 2 million gait cycles/year. With adjustments for patient weight and activity, in vivo wear studies are highly correlated to pre-clinical hip wear simulator studies. Walking speed and pattern also influence polyethylene wear. The greatest patient activity and wear occur during the first 5 years post-implantation. Walking number of gait cycles and walking speed both decrease with aging, resulting in decreasing wear over time. The low wear rates of cross-linked polyethylene combined with decreasing patient activity with aging indicate a reduced risk of wear-related complications over the long term.

Since 1996 more than one million metal-on-metal articulations have been implanted worldwide. Adverse reactions to metal debris are escalating. Here we present an algorithmic approach to patient management. The general approach to all arthroplasty patients returning for follow-up begins with a detailed history, querying for pain, discomfort or compromise of function. Symptomatic patients should be evaluated for intra-articular and extra-articular causes of pain. In large head MoM arthroplasty, aseptic loosening may be the source of pain and is frequently difficult to diagnose. Sepsis should be ruled out as a source of pain. Plain radiographs are evaluated to rule out loosening and osteolysis, and assess component position. Laboratory evaluation commences with erythrocyte sedimentation rate and C-reactive protein, which may be elevated. Serum metal ions should be assessed by an approved facility. Aspiration, with manual cell count and culture/sensitivity should be performed, with cloudy to creamy fluid with predominance of monocytes often indicative of failure. Imaging should include ultrasound or metal artifact reduction sequence MRI, specifically evaluating for fluid collections and/or masses about the hip. If adverse reaction to metal debris is suspected then revision to metal or ceramic-on-polyethylene is indicated and can be successful. Delay may be associated with extensive soft-tissue damage and hence poor clinical outcome.

Acetabular component position is associated with joint function and bearing wear. Current techniques for determining acetabular component version on standard radiographs lack reliability. Other, more consistent techniques are time-consuming and require additional equipment or software.We compared three methods of acetabular component position assessment: (1) Einzel-Bild-Roentgen-Analyse (EBRA), (2) Woo and Morrey, and (3) the new ischiolateral method.We assessed axial component position for 52 hips, with at least three radiographic series, using EBRA, and on true lateral radiographs using the Woo and Morrey method and a new method that uses the ischium as a skeletal landmark, the ischiolateral method.The mean SDs of the ischiolateral (2.15°) and EBRA (2.06°) methods were lower than that of the Woo and Morrey method (3.65°) but were not different from one another. We observed a SD of greater than 4° in 19 (36.5%) hip series using the Woo and Morrey method, compared to six series (11.5%) for both the ischiolateral and EBRA methods. Twenty-four (12.6%) Woo and Morrey measurements were greater than 4° from the mean for the hip series, compared to seven (3.8%) for ischiolateral and nine (4.7%) for EBRA. The intraclass correlation coefficients for intra- and interobserver reliability for the ischiolateral method and EBRA were the same (0.9).Referencing the ischium standardizes pelvic position on each lateral radiograph and provides a simple and reliable means to assess axial component position, which is a surrogate for the planar anteversion measured by EBRA.

Total hip arthroplasty has shown excellent results in decreasing pain and improving function in patients with degenerative disease of the hip. Improvements in prosthetic materials, designs and implant fixation have now resulted in wear of the bearing surface being the limitation of this technology, and a number of hard-on-hard couples have been introduced to address this concern. The purpose of this article is to review the origins, development, survival rates and potential advantages and disadvantages of the following hard-on-hard bearings for total hip arthroplasty: metal-on-metal standard total hip arthroplasty; metal-on-metal hip resurfacing arthroplasty, ceramic-on-ceramic total hip arthroplasty; and ceramic-on-metal bearings. Improvements in the manufacturing of metal-on-metal bearings over the past 50 years have resulted in implants that provide low wear rates and allow for the use of large femoral heads. However, concerns remain regarding elevated serum metal ion levels, potential teratogenic effects and potentially devastating adverse local tissue reactions, whose incidence and pathogenesis remains unclear. Modern total hip resurfacing has shown excellent outcomes over 10 years in the hands of experienced surgeons. Current ceramic-on-ceramic bearings have demonstrated excellent survival with exceptionally low wear rates and virtually no local adverse effects. Concerns remain for insertional chipping, in vivo fracture and the variable incidence of squeaking. Contemporary ceramic-on-metal interfaces are in the early stages of clinical use, with little data reported to date. Hard-on-hard bearings for total hip arthroplasty have improved dramatically over the past 50 years. As bearing designs continue to improve with new and modified materials and improved manufacturing techniques, it is likely that the use of hard-on-hard bearings will continue to increase, especially in young and active patients.

In clinical and retrieval analyses, over-penetration of cement, incomplete seating of the prosthesis with a resultant polar cement mass, or both, have been associated with early femoral failures of resurfacing arthroplasties. We used human bone specimens to experimentally compare the initial stability of different cementing techniques.Twenty-six pairs of fresh frozen femora were prepared for resurfacing using original instruments (DePuy ASR). ASR femoral resurfacing prostheses were implanted using two different cementing techniques: (1) component filling and (2) cement applicator. Real-time measurements of pressure and temperature during implantation, analyses of cement penetration and micro motions under torque application were performed.Applicator use reduced significantly the cement penetration depth (9.2 mm vs 5.3 mm with the applicator, p = 0.001), polar mantle (8.1 mm vs 2.6 mm, p = 0.008), cement defects (3.7 mm vs 0.1 mm, p = 0.008) and interface temperatures (40.3°C vs 33.1°C, p0.001 ). Initial rotational stability showed statistically significant less extreme values with the cement applicator technique (range 3.4-51.7 m°/Nm, 11.0-29.7 m°/Nm, p = 0.024).The cement applicator technique significantly reduces cement defects, incomplete seating, over-penetration and interface temperatures with a more consistent initial stability of the ASR femoral resurfacing prostheses.

Cementing irregularities have been associated with femoral failures of resurfacing arthroplasties in retrieval studies. We used an in vitro model to measure pressure, temperatures, and cement penetration as a function of 6 different cementing techniques. Filling the component with cement can lead to overpenetration or increase the resistance to component seating with resultant polar cement mass. Both conditions result in high and long-lasting cement pressures, cement defects, as well as peak temperatures higher than 50°C. Manual application of cement provides complete penetration of the available fixation area with the lowest cement pressures, the smallest total cement mass, and a peak temperature of 36.0°C ± 4.1°C. Application of the principles elucidated by this study may reduce the risk of cement overpenetration and incomplete seating.

In clinical outcome studies, small component sizes, female gender, femoral shape, focal bone defects, bad bone quality, and biomechanics have been associated with failures of resurfacing arthroplasties. We used a well-established experimental setup and human bone specimens to analyze the effects of bone density on cement fixation of femoral hip resurfacing components. Thirty-one fresh frozen femora were prepared for resurfacing using the original instruments. ASR™ resurfacing prostheses were implanted after dual-energy X-ray densitometer scans. Real-time measurements of pressure and temperature during implantation, analyses of cement penetration, and measurements of micro motions under torque application were performed. The associations of bone density and measurement data were examined calculating regression lines and multiple correlation coefficients; acceptability was tested with ANOVA. We found significant relations between bone density and micro motion, cement penetration, cement mantle thickness, cement pressure, and interface temperature. Mean bone density of the femora was 0.82 ± 0.13 g/cm2, t-score was −0.7 ± 1.0, and mean micro motion between bone and femoral resurfacing component was 17.5 ± 9.1 µm/Nm. The regression line between bone density and micro motion was equal to −56.7 × bone density + 63.8, R = 0.815 (p

Seventy-seven patients implanted with unilateral resurfacing prosthesis were recruited from four centres. Serial whole blood samples were collected and ion levels were analysed. In most cases, the ion levels stabilized by 3 months. The 24 month median ion levels were 1.49ug/l for chromium and cobalt. In approximately 50% of patients the increase in chromium and cobalt level was less than 1ug/l. There were 6 patients with abnormally high metal ion levels. Of these 4 were significant outliers, had high ion levels that became apparent between 12 and 24 months after implantation, and had a high cup abduction angle. Not all patients with high cup abduction angles demonstrated high levels. There were differences in ion levels between the four centres that correlated with variation in acetabular component placement. Variability in ion levels was seen with the same prosthesis, underscoring the importance of surgical technique, longitudinal analysis, and multi-centre trials.

There are limited data to guide surgeon recommendations regarding activities after total joint arthroplasty. The present study aims to better clarify the current community standards. A questionnaire was distributed to the members of the American Association for Hip and Knee Surgeons attending the 2007 annual meeting inquiring about recommendations for 15 activities for patients with total hip arthroplasty or total knee arthroplasty. One hundred thirty-nine surveys were returned. Spearman rank correlation was used to analyze the data. More than 95% of the responses placed no limitations on low-impact activities including level surface walking, stair climbing, level surface bicycling, swimming, and golf. Higher-impact activities were more commonly discouraged, although there was considerable variability. Recommendations after total hip arthroplasty were more liberal compared to those after total knee arthroplasty. Higher-volume surgeons tended to be more liberal in their recommendations. No responder indicated that there was strong scientific evidence for their recommendations. Investigations are needed to elucidate the long-term effects of higher load and/or higher cycle activities on total joint arthroplasty.

The importance of proper cup placement cannot be overemphasized, regardless of the bearing material or diameter. Unsatisfactory acetabular component position has been associated with instability, increased wear, and pain. Pelvic, acetabular, and femoral anatomy are all variable, so it is illogical to have the same fixed target position for all patients. The hip arthroplasty surgeon actually faces 2 challenges: (1) determining the desired acetabular component position for each patient (the target), and (2) how to reasonably obtain that position in surgery (hitting the target). An abduction angle of 40° ± 10° is generally satisfactory. Anteversion is more complex. The desired amount of anteversion is influenced by (a) the amount of femoral anteversion and (b) the cup abduction angle. A combined anteversion of 25° ± 10° is generally satisfactory. A combination of internal and external landmarks can be used to assess the relative component position. Routine evaluation of intraoperative range of motion is an additional check. When in doubt, we try to obtain a quality intraoperative image.

Total hip replacement (THR) is a very successful procedure, reporting very high success rates. The bearing surface is a key feature of replacement hip joints. It is generally accepted that excessive amounts of wear debris precludes their long-term survivorship. Hip simulator testing has resulted in a new generation of bearing surfaces. In general, these laboratory ( in vitro) improvements in wear performance have resulted in a similar improvement in performance in the body ( in vivo). However, there have been reports of components that have not performed as well as expected and this has been linked to the mal-positioning of components in the body. This article reviews bearing surface options and considers the effects of component mal-position on each of those bearings. There are three bearing surfaces in common use in THR. The effect of component mal-position in all cases is increased levels of wear. In metal/metal bearings this can result in cup rim wear and elevated blood metal ion levels. In metal (or ceramic)/polyethylene bearings wear can be measured radiographically and can result in increased osteolysis. In ceramic/ceramic bearings mal-positioning can result in stripe wear and squeaking.

There is evidence that high levels of physical activity following arthroplasty of the hip or knee can lead to early revision. However, the term ‘highly active’ is not well defined. A validated ankle accelerometer was used to quantify activity in 13 patients, who had undergone a total of 20 arthroplasties of the lower limbs and who had active lifestyles. The assessments were taken at a mean of 8.7 years post-operatively (1.8 to 15.8). The mean gait cycles per day was 8273 (5964 to 12 557), which extrapolates to 3.0 million cycles per year (cpy) (2.2 to 4.6). The mean percentage of time spent in high activity mode was 4.3%, or about one hour per day. The mean percentage of cycles in high activity was 40%. Based on these data, we propose the following definitions of high activity: > 3 million cpy; one hour per day in high activity mode; 40% of cycles in high activity mode. Extrapolating the sample of activity over the time since operation, the mean cycles per arthroplasty was 25.2 million, with a maximum of 44.1 million. No joint has been revised, or shows evidence of impending failure. Cite this article: Bone Joint J 2016;98-B(1 Suppl A):95–7.

Metal-on-metal bearings have been associated with the generation of metal particles and ions1,2 and, in comparison with that seen in other bearing surfaces, a measurable increase in the concentration of cobalt and chromium ions in blood and urine3-7. The risks of higher ion levels include delayed-type hypersensitivity, organ toxicity, and carcinogenesis8-10. Studies of cobalt and chromium ion levels have demonstrated variability from patient to patient4,7. Levels tend to be highest in the short-term and, with a well-functioning prosthesis, decrease with time4. Patient activity is a factor that theoretically could contribute to the variability in serum ion levels. The relationship between patient activity and the wear of polyethylene acetabular bearings has been demonstrated11. Cobalt and chromium ion levels in patients with metal-on-metal bearings might therefore be positively correlated with patient activity. Yet, Heisel et al. demonstrated that patient activity was not associated with serum ion levels in patients with a well-functioning metal-on-metal total hip prosthesis and normal renal function during a two-week test period12. To test the possibility that increases of serum ions associated with increased activity are compensated for by increased urinary excretion of the ions, we utilized the same two-week test protocol as Heisel et al.12 but also collected all urine from a single patient to measure total ion excretion and assess the relationships between serum ion levels, urine ion excretion, and patient activity. This study received the approval of the institutional review board at our institution. Our patient was informed that data concerning the case would be submitted for publication, and she consented. A sixty-four-year-old woman underwent an uncomplicated, cementless total hip arthroplasty for the treatment of osteoarthritis of the left hip. During this procedure, she …

Improvements in materials and fixation have addressed many of the limitations of resurfacing total hip arthroplasty (THA). The functional demands and the longevity of arthroplasty patients are increasing. Many patients have embraced the functional capacity, bone conservation, and revision options of hip resurfacing. Young men have historically been at increased risk for failure of total THA. In this patient subgroup, the survivorship of hybrid metal-metal resurfacing THA has been demonstrated to exceed that of THA, but patient selection is critical. The procedure is now also conservative on the acetabular side, and revision of the cementless acetabular component is rare. The operative parameters of femoral resurfacing revisions (conversion to a THA) are similar to that of a primary THA. Bearing technology will continue to evolve.

The following are 5 case presentations of interesting and challenging patients with hip pathology.

The resurgence of metal–metal bearings has renewed interest in hip resurfacing, but a paucity of information exists regarding femoral cementing technique. We developed a laboratory model in which 72 open-cell foam specimens were used to simulate bone. Analyses of two cement viscosities, two foam porosities, and six cementing techniques were performed: manual cement application only, manual application and filling of one quarter of the component with cement, filling of half of the component, manual application and half component filling, full component filling, and manual application and full component filling. For manual application, cement was pressurized into the foam by rolling the finger tips. For component filling, a defined quantity of cement was poured into the component before pressing it onto the foam. Specimens were cut into quarters, and cement penetration was quantified in seven areas: top, chamfer, wall, interior area, and proximal, medial, and distal stem. The manual technique showed a 3-mm thick, even cement penetration of the outer fixation surface (top = 26 ± 0 mm2, chamfer = 14.9 ± 0.2 mm2, wall = 55.6 ± 5.2 mm2). None of the other techniques showed a significantly higher penetration in these areas. Large differences were found between all techniques at the medial stem (27.7 ± 17.5 mm2, p

Hip resurfacing arthroplasty is a type of hip replacement that involves capping the femoral head and preserving bone of the proximal femur. Metal-on-metal surface replacements have been manufactured since the early 1990s. Recent studies indicate excellent clinical results with low failure rates at 1- to 5-year follow-up. Although these early results are encouraging, resurfacing devices must be used with caution because less is known about their long-term safety and efficacy. The best candidates for resurfacing are patients younger than age 60 years with good bone stock. The surgical approach is similar to that for standard total hip replacements, but with slightly more dissection because the femoral head must be preserved and displaced to visualize the acetabulum. To reduce complications, resurfacing arthroplasty should be performed by surgeons who have received training specifically in this technique.

Nerve palsy associated with total hip arthroplasty is an uncommon, but distressing complication, with an overall prevalence around 1%. An apparent peroneal palsy after a total hip replacement is almost always due to an injury to the peroneal division of the sciatic nerve near the hip. Females, revisions and dysplastic hips are at increased risk. Forty-one percent of sciatic nerve injuries have a complete or essentially complete recovery, 44% have a mild persistent deficit, and 15% have a poor outcome.

Quantitative assessment of patient activity is important in evaluating the outcomes of joint prostheses, and such methods are gaining popularity. The single greatest impediment to quantitative activity assessment is patient compliance. How many days of sampling are necessary to provide reliable and accurate estimates of walking activity? The current study analyzes how well sampling for 4 consecutive days of activity compares to assessing activity for 7 or more days with the same pedometer in 131 patients with either a total hip or total knee prosthesis. The mean steps per day obtained throughout the full-length sampling (7-123 days) was strongly correlated to the one obtained from the random consecutive 4-day sample (r2 = 0.94, P < .001) with only 5 outliers. The 4-day activity assessment gave an underestimation of 4.7% (P = .5). The number of outliers increased with fewer days of sampling. Monitoring activity for 4 consecutive days yields a quantitative assessment that is within 5% of a sampling of 7 or more days.

Background: Total hip replacements with metal-on-metal bearings are frequently implanted in young, active patients. The relationship between patient activity and cobalt and chromium ion levels has not been investigated, to our knowledge. Methods: Seven patients with well-functioning metal-on-metal bearing hip prostheses and one control subject (no implants), all with normal renal function, were monitored during a two-week-long activity protocol. Lower-extremity activity was continuously assessed with use of a computerized, two-dimensional accelerometer. During the first week, the subjects were requested to limit physical activity. The subjects then completed an hour-long treadmill test followed by a week in which they were encouraged to be as physically active as practically possible. Serum levels of cobalt and chromium ions and urine levels of chromium were assessed at ten time-points during these two weeks. Results: Regardless of activity, the serum ion levels for a given patient were essentially constant and no correlation was found between patient activity and serum levels of cobalt or chromium, or urine levels of chromium. A mean increase in activity of 28% during the week of high-intensity activity was associated with a mean decrease of 2.7% in the serum cobalt level and a mean increase of 2.0% in the serum chromium level. During the treadmill test, a mean increase in activity of 1621% was associated with a mean increase of 3.0% in the serum cobalt level and a mean increase of 0.8% in the serum chromium level. These results fall within the variability for the measurement accuracy of these tests. Conclusions: For these patients, serum cobalt and chromium ion levels were not acutely affected by patient activity. Periodic measurements of serum ion levels could be used to monitor the tribologic (lubrication, friction, and wear) performance of a metal-on-metal bearing without adjusting for patient activity. Additional research is needed into the kinetics of ion production, transport, and excretion. Level of Evidence: Therapeutic Level II. See Instructions to Authors for a complete description of levels of evidence.

Metal-on-metal bearings have wear rates that are 20 to 100 times lower than metal-on-conventional polyethylene. The amount of wear generally is the same order of magnitude for the head and the cup. There is an initial run-in period of higher wear followed by lower, steady-state wear. Wear rate is a function of the interplay of material(s), macrogeometry, microgeometry, and the resultant type and amount of lubrication. The wear resistance and clinical performance of a metal-on-metal bearing are more sensitive to macrogeometry and lubrication than a metal-on-polyethylene bearing. Metal wear particles are nanometers in linear dimension. They are much smaller and more numerous than the submicron polyethylene wear particles, but the volume of periprosthetic inflammatory tissue is less. Osteolysis seems to be relatively rare. Little is known about the systemic distribution of metal particles and ions. The significance of systemic distribution also is not known. The levels of serum and urine Co and Cr ions are elevated in patients with metal-on-metal bearings, but the long-term, steady-state levels are not much higher than those from corrosion of modular femoral components. Because of the elevated levels of Co and Cr ions, there is a greater risk of delayed type hypersensitivity. There also is concern about the potential for malignant degeneration secondary to prolonged exposure to these elements. The available data are insufficient to address this concern. Rigorous long-term studies are needed. It will take decades of close clinical observation to determine if the benefits of metal-on-metal bearings outweigh the associated risks.

There is insufficient clinical data to demonstrate the overall superiority of any one bearing couple for all total hip cases. It is therefore reasonable to individualize the choice of bearing surface. The fundamental exercise in choosing a bearing surface is maximizing the benefit to risk ratio. There are at least 3 perspectives to consider: the patient's, the surgeon's, and that of the health care delivery system. The following question should be addressed on a patient-by-patient basis: what available bearing is most likely to meet the needs of this patient, with an acceptable risk of revision surgery during his or her lifetime, is accepted in my community, and is there a means to pay for it?

With the resurgence of metal-on-metal bearings, there is renewed interest in total hip resurfacing. A cementless acetabular component used for resurfacing with a wall thickness of fewer than 5 mm is comparable in size to acetabular components used for total hip replacement. The fixation of a porous-ingrowth acetabular component used for resurfacing has been shown to be reliable and durable. There are few clinical reports of total hip resurfacing that stratify results by diagnosis. However, available evidence indicates that the pain relief, function, and activity after total hip resurfacing for osteonecrosis are superior to the results reported for hemiresurfacing and similar to the results of total hip replacement. Femoral-side failure is the main issue occurring with total resurfacing for osteonecrosis, and the femoral side failure rate is higher than that of hemiresurfacing. There are no simple guidelines for the extent of femoral head necrosis that are compatible with successful resurfacing. Refined patient selection and surgical technique can improve the outcomes and durability of total hip resurfacing for osteonecrosis.

Background: Cross-linked polyethylene was developed to reduce volumetric wear in prosthetic joints. Hip simulator studies have shown promising results with regard to wear reduction. This study evaluated the short-term in vivo wear of a moderately cross-linked polyethylene. Methods: Linear head penetration, as an assessment of in vivo polyethylene wear, was measured in two groups of patients after total hip replacement. Twenty-four hips received a conventional polyethylene insert and thirty-four, a cross-linked polyethylene liner; both inserts were manufactured by the same company. Linear and volumetric wear rates were measured on radiographs with use of a validated computer-assisted technique and were adjusted for patient-related factors. Patient activity was assessed by a computerized two-dimensional accelerometer worn on the ankle. Results: Patients with a conventional polyethylene insert showed a mean linear wear rate of 0.13 mm per year and a mean volumetric wear rate of 87.6 mm 3 per year. The group with a cross-linked polyethylene liner showed a mean linear wear rate of 0.02 mm per year and a mean volumetric wear rate of 17.0 mm 3 per year. Wear in the group with cross-linked polyethylene was 81% lower than that in the group with conventional polyethylene (p < 0.00001). Accounting for differences in patient activity, the adjusted wear rates per million cycles for a patient weight of 70 kg were 53 mm 3 per million cycles for conventional polyethylene and 15 mm 3 per million cycles for cross-linked polyethylene, a 72% reduction (p = 0.0002). No factor, other than the type of polyethylene, was found to influence the difference in wear rates between the two groups. Conclusions: The results of this study are promising. The in vivo wear reduction with this cross-linked polyethylene is consistent with the predictions of hip simulator studies. Level of Evidence: Therapeutic study, Level II-1 (prospective cohort study). See Instructions to Authors for a complete description of levels of evidence.

Background: With the advent of more wear-resistant bearings, there is renewed interest in resurfacing total hip arthroplasty. However, there is a paucity of information on the biomechanical results of this type of arthroplasty compared with those of contemporary total hip arthroplasty. Methods: Using standardized radiographs, we measured and compared the biomechanical parameters that affect the hip joint reactive forces in fifty hips that had a metal-metal surface replacement with those parameters in forty hips that had a contemporary cementless total hip replacement performed during the same time-period by the same surgeon. Results: On the average, the arthritic hips that were treated with metal-metal surface replacement had had a more valgus preoperative neck-shaft angle and less horizontal femoral offset than the normal, contralateral hips (p = 0.0003). After both the metal-metal surface replacements and the cementless total hip replacements, the hip center of rotation was medialized by approximately 6 mm. Both procedures were associated with an average increase in limb length of approximately 3 or 4 mm. After the metal-metal surface replacements, the horizontal femoral offset was essentially equal to the preoperative value, but both values averaged about 8 mm less than those on the normal, contralateral side (p < 0.00001). In the hips with a conventional total hip replacement, the horizontal femoral offset increased an average of 9.5 mm compared with the preoperative value and was an average of 5 mm more than that for the normal, contralateral hip (p = 0.001). Conclusions: The biomechanical results of total hip resurfacing depend on the preoperative anatomy of the proximal part of the femur. Limb lengthening of 1 cm can be achieved, but horizontal femoral offset is essentially unchanged by hip resurfacing. Horizontal femoral offset can be increased reliably with a contemporary total hip replacement. Arthritic hips of limbs that are more than 1 cm shorter than the contralateral limb or that have a comparatively low horizontal femoral offset may be better served by a contemporary total hip replacement. These biomechanical limitations should be considered in the selection of hips for resurfacing. Level of Evidence: Therapeutic study, Level III-1 (case-control study). See Instructions to Authors for a complete description of levels of evidence.

A two-dimensional accelerometer worn on the ankle (step activity monitor [SAM]; Prosthetic Research Study, Seattle, WA) has been proved to be highly accurate for assessing walking activity. The walking activity of 33 patients with well-functioning total hip arthroplasties was measured continuously during daily life, simultaneously with a pedometer and a SAM. The SAM recorded an average of 1.9 million cycles/y. The pedometer under-recorded an average of 34% cycles per day compared with the SAM (P=.0007), but the 2 measures were highly correlated (r=0.66; P=.001). No difference was seen in the number of gait cycles per day between men and women. The previously reported difference in average walking activity between men and women is due to greater under-recording of the pedometer in women, especially those with a body mass index > or =27. The pedometer is more reliable in quantifying the walking activity of men, less obese women, and patients with >1 million gait cycles/y.

The effect of total knee arthroplasty design on extensor mechanism function was evaluated prospectively in a consecutive, single-surgeon series. Group 1 knees (n = 83) were implanted with a prosthesis that has a multiradius femoral component, and group 2 knees (n = 101) were implanted with a femoral prosthesis that has a single flexion-extension axis. Group 2 knees gained flexion more rapidly: At 6 weeks, the average flexion for was 94.5 degrees for group 1 and 107.1 degrees for group 2 (P

The resurgence of metal-on-metal articulating surfaces for hip arthroplasty has also heightened concerns about the degree and magnitude of metal particle generation and the accompanying increase in circulating metal ion concentrations. In this study, we measured the concentration of chromium in serum and urine and the concentration of cobalt in serum in twenty-five patients with modern metal-on-metal surface arthroplasty of the hip in a prospective manner. The results showed that the mean post-operative chromium in serum levels were 22-fold, 23-fold and 21-fold higher at 3, 6 and 12 months post-operative, respectively, than pre-operative levels. The mean post-operative cobalt in serum levels were 8-fold, 7-fold and 6-fold higher at 3, 6 and 12 months post-operative, respectively, than pre-operative levels. The mean post-operative chromium in urine levels were 9-fold, 10-fold and 14-fold higher at 3, 6 and 12 months post-operative, respectively, than pre-operative levels. The values seen in this study with the current generation of surface arthroplasties are: (a) lower than those seen in an earlier generation of surface arthroplasties; (b) in the same range as those observed in association with metal-on-metal conventional total hip replacements, which typically have smaller head sizes; (c) higher than values observed in patients with conventional metal-on-polyethylene articulating couples.

A 65-year-old man with osteoarthritis of the hip underwent a cementless total hip replacement with a modern generation, metal-on-metal bearing. Two years later the patient presented with localized osteolysis at the tip of the femoral stem. At the time of revision, the stem was found to be well-fixed. Extensive analyses of the bearing surfaces and periprosthetic tissues were done. There was minimal bearing surface wear and only small numbers of inflammatory cells, such as macrophages, in the tissues, and it was concluded that this was not a typical case of particle-induced osteolysis. All cultures and laboratory studies were negative for infection. This case report supports the multifactorial nature of osteolysis, which includes the osteolytic potential of joint fluid access to and fluid pressures within, the effective joint space.

The first well‐documented case of cancer associated with total joint replacement was in a patient in whom a malignant fibrous histiocytoma developed three and one‐half years after a McKee-Farrar total hip replacement that was performed in December 19691. At least twenty-four additional cases of malignant disease occurring in association with a total hip or knee prosthesis have been reported in the English-language literature2‐20. On the basis of this small number of case reports, there is no apparent relationship between any specific implanted material and cancer. The carcinogenic properties of the metals used in joint prostheses have been studied. Cobalt and chromium wear particles have been shown to induce carcinoma in animal models21, giving rise to the concern that such alloys could have the same effect in human tissue if present in sufficient amounts for a sufficient length of time. Elevated levels of chromium and cobalt have been found in human tissues surrounding orthopaedic implants and in tissues at remote sites22. There also has been concern that metal‐on‐metal bearings used in total hip arthroplasty may pose a higher risk of malignant degeneration because of an increased exposure to metal particles and ions. Although metal particles and ions have been the prominent concern, there also have been reports of cancer induction in association with polymethylmethacrylate (bone cement)23 and polyethylene24 in animal models. The speculation that total hip and total knee replacements could cause malignancy has inspired epidemiological studies aimed at evaluating this concern. Of the twenty‐five reported cases of cancer following a total hip or knee replacement, twenty‐one1‐9,11‐16,18‐20 involved sarcomas. Because the prevalence of such cancers is low in the general population, combining the available data enhances the ability …

Thirty-seven hips with Ficat Stage II, III, or early IV osteonecrosis were treated with hemiresurfacing. The purpose of this study is to analyze specifically the clinical and radiographic results of patients who had hemiresurfacing to refine the indications for the procedure and identify factors substantially affecting clinical outcome and survivorship. At an average followup of 6.5 years, the average University of California Los Angeles hip scores for pain, walking, function, and activity improved significantly from 4.3, 6.0, 5.3, and 4.2 to 8.0, 8.8, 7.9, and 5.8. The overall survivorship was 79%, 59%, and 45% at 5, 10, and 15 years. Eleven hips have been converted: 10 hips for acetabular cartilage wear and one hip for femoral loosening. The average time to conversion was 7.5 years. A longer duration of symptoms before surgery (16.6 months versus 12.1 months) was associated with a worse acetabular cartilage grading and suggested a relationship with a shorter time to conversion, although the difference was not statistically significant at the 5% level. Survivorship is better when preoperative symptoms are present for 1 year or less, possibly because the articular cartilage is healthier. When necessary, conversion to total hip replacement can be done without adverse results.

Background: Aseptic loosening and osteolysis are rarely associated with cemented posterior-cruciate-substituting total knee replacements. Consequently, there is a paucity of information on this topic. Methods: After a mean follow-up interval of fifty-six months (range, thirty-seven to eighty-nine months), sixteen (2.9%) of 557 posterior-cruciate-substituting primary total knee replacements were revised by a single surgeon because of loosening and osteolysis. Clinical, radiographic, and retrieval analyses were conducted to determine the mechanism of loosening and to identify associated risk factors. Results: All sixteen knees (fifteen patients) were rated as good or excellent at one year after the primary replacement, with mean clinical and functional Knee Society scores of 95 and 86 points, respectively. Nine of the fifteen patients who had a revision because of loosening and osteolysis had had a total knee arthroplasty on the contralateral side compared with only 18% of the patients who did not have a revision (p = 0.026). No evidence of transmission of substantial anteroposterior stresses from the posterior-cruciate-substituting mechanism was found. All twelve retrieved knee implants, however, had damage to the lateral and medial side walls of the polyethylene posterior-cruciate-substituting post. Damage to the inferior surface of the polyethylene inserts had a rotational pattern, with the axis of rotation in the medial compartment. Surface damage in a rotational pattern was also present on the superior and inferior surfaces of the titanium tibial base-plates. Conclusions: In the knees in our study, rotational forces were generated by impingement of the side walls of the intercondylar box on the polyethylene post. Such box-post impingement can occur throughout the range of motion. Rotational stresses are transmitted to the modular interfaces and to the metal-cement interfaces, resulting in loosening and osteolysis. A reduction in rotational constraint would be desirable. Patients with bilateral total knee replacement may be at increased risk for this type of loosening.

A literature review was performed to determine when direct exchange was most likely to be successful. Twelve reports provided outcome data on infected hip replacements treated with direct exchange. The average duration of followup was 4.8 years, but the range was broad (0.1-17.1 years). Of the 1,299 infected hip replacements treated with direct exchange, 1,077 (83%) were thought to be free of infection at the last followup. Antibiotic-impregnated bone cement was used in 1,282 of the cases (99%). There was wide variability in the duration of parenteral antibiotic therapy, ranging from just 24 hours to as many as 8 weeks. In some cases, no oral antibiotics ever were given, whereas in others, oral antibiotics were given for as many as 8 months after parenteral therapy. Factors associated with a successful direct exchange included: (1) absence of wound complications after the initial total hip replacement; (2) good general health of the patient; (3) methicillin-sensitive Staphylococcus epidermidis, Staphylococcus aureus, and Streptococcus species; and (4) an organism that was sensitive to the antibiotic mixed into the bone cement. Factors associated with failure included: (1) polymicrobial infection; (2) gram-negative organisms, especially Pseudomonas species; and (3) certain gram-positive organisms such as methicillin-resistant Staphylococcus epidermidis and Group D Streptococcus. Methicillin-resistant organisms have become more common. Many current revision surgical techniques use cementless implants. Fixation without any cement (no depot antibiotics) may be a contraindication to direct exchange. Additionally, there essentially are no data on the use of bone graft in association with direct exchange. For these reasons, the indications for direct exchange are limited.

Polyethylene wear (linear penetration) in 37 hip replacements was assessed from digital images using a validated two-dimensional, edge detection-based computer algorithm. Patient activity was assessed with a pedometer, a step activity monitor and a simple visual analog scale. Joint use was related to wear at the 90% confidence level. Without three recognized outliers, wear was highly correlated to use. The visual analog scale activity rating was significantly related to wear for the 24 hip replacements with standard polyethylene. Univariate regression analysis indicated that male gender, height, weight (which were both highly correlated to male gender) and hip center of rotation were significantly correlated to wear. Multivariate regression analysis indicated that male gender, femoral off-set, and Hylamer® were significantly correlated to wear. Based on the wear and activity data from the 24 hip replacements with standard polyethylene, the average volumetric wear rate per million cycles with a 70 kg patient weight was 30 mm 3 . This unique in vivo result can be considered a target wear rate for standard polyethylene in hip simulator studies.

There have been several reports of osteolysis associated with rapid wear of Hylamer. A detailed analysis of retrieved implants and tissues can identify factors contributing to rapid wear and osteolysis. The mean linear wear rate of 12 liners was 0.49 mm/y, and 11 of 12 hips had progressive retroacetabular osteolysis. The average patient age was 50 years, and the mean implantation time was 50 months. All liners were sterilized by gamma irradiation in air. There was an 11-month difference in the average shelf-life of the 3 liners that were white and those that were darker in color. The volumetric wear rate of the white liners was 30% less than that of the others, suggesting a difference in the wear resistance of the liners as a function of shelf life. The mean average surface roughness (R a ) and the mean maximum surface roughness (R max ) of the femoral heads were increased 3-fold and 50-fold compared with typical values for unused femoral heads. Evidence of 3-body wear, such as metal particles embedded in the liners, was commonly present. The pattern of backside liner deformation and burnishing was consistent with relative motion between the liner and the shell. In addition to generating Hylamer wear particles, repetitive axial motion between the liner and shell could generate fluid pressure, which transmitted through holes in the acetabular shell could cause or contribute to the development of retroacetabular osteolysis. Hylamer particles of variable shape and size, consistent with generation by several wear modes, were isolated from periprosthetic tissues.