Cross-linked Polyethylene Bearings Research Articles

Choice of Bearings Influences the Implant Survival of Total Hip Arthroplasty in Patients Who Have Osteoarthritis Aged 55 Years or More: Results of 158,044 Patients From the Nordic Arthroplasty Register Association From 2005 to 2017

BackgroundThe aim of our study was to compare implant survival rates of different total hip arthroplasty (THA) bearings in the Nordic Arthroplasty Register Association. MethodsAll conventional primary THAs performed between 2005 and 2017 in patients aged more than 55 years who had primary osteoarthritis were studied. Metal-on-highly cross-linked polyethylene (MoXLP), ceramic-on-highly cross-linked polyethylene (CoXLP), ceramic-on-ceramic (CoC), and metal-on-metal (MoM) bearings were included. The outcome was a revision. Kaplan-Meier (KM) estimates were calculated at 5 and 10 years. The risk for revision was analyzed using a flexible parametric survival model adjusted for nation, age, sex, femoral head size, and femoral fixation. ResultsA total of 158,044 THAs were included. The 5-year KM estimates were 95.9% (95% confidence interval [CI] 95.8 to 96.1) in MoXLP, 95.8% (95% CI 95.6 to 96.1) in CoXLP, 96.7% (95% CI 96.4 to 97.0) in CoC, and 93.9% (95% CI 93.5 to 94.4) in MoM. The 10-years KM estimates were 94.2% (94.0 to 94.5) in MoXLP, 94.3% (93.9 to 94.8) in CoXLP, 95.4% (95.0 to 95.9) in CoC, and 85.5% (84.9 to 86.2) in MoM. Compared with MoXLP, the adjusted risk for revision was lower in CoC (hazard ratio [HR] 0.6, CI 0.5 to 0.6), similar in CoXLP (HR 1.0, CI 0.9 to 1.0), and higher in MoM (HR 1.3, CI 1.2 to 1.4). ConclusionsWe found that MoXLP, CoXLP, and CoC bearings evinced comparably high implant survival rates up to 10 years, and they can all be regarded as safe options in this patient group. The MoM bearings were associated with clearly lower survivorship. The CoC bearings had the highest implant survival and a lower adjusted risk for revision compared with highly cross-linked polyethylene bearings.

Dynamic computational wear model of PEEK-on-XLPE bearing couple in total hip replacements.

Understanding wear mechanisms is a key factor to prevent primary failures causing revision surgery in total hip replacement (THR) applications. This study introduces a wear prediction model of (Polyetheretherketone) PEEK-on-XLPE (cross-linked polyethylene) bearing couple utilized to investigate the wear mechanism under 3D-gait cycle loading over 5 million cycles (Mc). A 32-mm PEEK femoral head and 4-mm thick XLPE bearing liner with a 3-mm PEEK shell are modeled in a 3D explicit finite element modeling (FEM) program. The volumetric and linear wear rates of XLPE liner per every million cycles were predicted as 1.965 mm3/Mc, and 0.0032 mm/Mc respectively. These results are consistent with the literature. PEEK-on-XLPE bearing couple exhibits a promising wear performance used in THR application. The wear pattern evolution of the model is similar to that of conventional polyethylene liners. Therefore, PEEK could be proposed as an alternative material to the CoCr head, especially used in XLPE-bearing couples. The wear prediction model could be utilized to improve the design parameters with the aim of prolonging the life span of hip implants.

How is hip anatomy reconstruction and inlay wear associated up to 10 years after primary THA using ceramic on highly crosslinked polyethylene bearings?

IntroductionConventional polyethylene (PE) wear has been reported to be associated with femoral offset reconstruction and cup orientation after THA. Thus, the present study aimed (1) to determine the polyethylene wear rate of 32 mm ceramic heads with highly cross-linked polyethylene (HXLPE) inlays up to 10 years postoperatively and (2) to identify patient and surgery-related factors affecting the wear rate.MethodsA prospective cohort study was performed, investigating 101 patients with 101 cementless THAs and ceramic (32 mm) on HXLPE bearings after 6–24 months, 2–5 years and 5–10 years postoperatively. The linear wear rate was determined using a validated software (PolyWare®, Rev 8, Draftware Inc, North Webster, IN, USA) by two reviewers, blinded to each other. A linear regression model was used to identify patient and surgery-related factors on HXLPE -wear.ResultsAfter an initial bedding-in phase of 1 year after surgery, the mean linear wear rate was 0.059 ± 0.031 mm/y at ten years (mean 7.7 years; SD 0.6 years, range 6–10), being below the osteolysis relevant threshold of 0.1 mm/year. The regression analysis demonstrated that age at surgery, BMI, cup inclination or anteversion and the UCLA score were not associated with the linear HXLPE-wear rate. Only increased femoral offset showed a significant correlation with an increased HXLPE-wear rate (correlation coefficient of 0.303; p = 0.003) with a moderate clinical effect size (Cohen’s f²=0.11).ConclusionIn contrast to conventional PE inlays, hip arthroplasty surgeons may be less concerned about osteolysis-related wear of the HXLPE if the femoral offset is slightly increased. This allows focusing on joint anatomy reconstruction, hip stability and leg length.

Large Femoral Heads and Select Dual-Mobility Bearings Are Associated With Reduced Instability in Contemporary Posterior Approach Total Hip Arthroplasty

BackgroundPostoperative dislocation is considered the main drawback of posterior approach total hip arthroplasty (THA). Thinner highly cross-linked polyethylene and dual-mobility bearings allow maximizing femoral head diameter per a given cup size. This study evaluated dislocation rates as large femoral head bearings were introduced into a practice over an 11-year period. MethodsA total of 1,511 consecutive primary THAs were retrospectively reviewed. Demographics, implant sizes, femoral head-acetabular cup ratio, and dislocation status were collected from the electronic medical record. Data were evaluated using time series analysis techniques as larger femoral heads, thinner polyethylene liners, and dual-mobility bearings were introduced. The cohort was 57% women with mean age and body mass index of 62 years (range, 13 to 93) and 31 kg/m2 (range, 13 to 54), respectively. ResultsThe overall dislocation rate was 0.98%. Use of femoral head sizes ≥ 40 millimeters increased from 4% in the years 2010 to 2016 to 51% in the years 2017 to 2021, correlating with a 50% reduction in dislocation rate from 1.4% to 0.7% (P = .279). Also, no dislocations occurred in patients who had dual-mobility bearings or ≥ 40-millimeter femoral heads (P = .007). Twelve of 14 dislocations occurred in cases with head-cup ratio < 0.7 (P = .013). Thirteen of 14 dislocations were in women (P = .005). ConclusionMaximizing the femoral head diameter per given cup size correlated with a decrease in dislocation rate in modern posterior approach THA. Furthermore, these results suggest that dual-mobility articulations should be reserved for high-risk patients or patients in whom a 40-millimeter femoral head is not possible. Level of EvidenceIV–consecutive case series; no control group.

The Open Triradiate Cartilage: How Young Is Too Young for Total Hip Arthroplasty?

There is, to our knowledge, no published literature regarding primary total hip arthroplasty (THA) in pediatric patients with an open triradiate cartilage. The purpose of this study was to report the outcomes following primary THA in pediatric patients with open triradiate cartilage at a single intuition. Using a single institution's Total Joint Registry, 12 patients (13 hips) were identified as having undergone primary THA with open triradiate cartilage between the years of 2000 and 2019. The mean age and body mass index of this group were 13.1 years and 25.5 kg/m2, respectively. The cohort was composed of 10 males, and the mean follow up was 5.5 years. Indications for surgery, functional outcomes, and radiographic signs of stable fixation were analyzed. The most common indication for surgery was avascular necrosis secondary to corticosteroid use (31%), followed by avascular necrosis after operative management of slipped capital femoral epiphysis (23%). The proportion of patients able to achieve independent, gait-aid free, ambulation improved from 23% to 100%. Mean postoperative Harris Hip Score was 92.3. All constructs were cementless, and bearing surfaces included ceramic-on-ceramic in 62% and ceramic on highly crosslinked polyethylene bearings in the remainder. Radiographic review at final follow up demonstrated osseointegration in 12 of 13 (92%) acetabular components. Although 1 patient experienced both acetabular component loosening and instability, on separate occasions, there were no incidences of infection, wound dehiscence, thromboembolic events, or failure secondary to wear. In this study, THA in patients with an open triradiate cartilage yielded significant clinical improvement, low complication rates and good initial implant survivorship at early follow up. Awaiting closure of the triradiate cartilage for concerns of decreased fixation and implant survivorship may be unnecessary. Level IV-case series.

Is patient satisfaction related to patient reported sounds from ceramic on ceramic total hip arthroplasty? A study of 265 hips.

The ideal method and implant to perform total hip arthroplasty (THA) is still a debated topic. Ceramic on ceramic (CoC) bearings have favourable wear properties, but squeaking has been reported as an unwanted side effect. We aimed to determine the rate of noise generation from CoC hips and investigate whether there is a relationship with patient satisfaction. A total of 246 consecutive CoC bearing uncemented THA were retrospectively identified in a single institution. Post-operatively patients were sent a postal questionnaire to evaluate their reported sounds and satisfaction with their THA. Uni- and multi-variate analyses were performed to identify potential predictor variables for reported post-operative sounds. Questionnaires were returned by 172 patients (70% return rate). 24% reported sounds from their hips with 11% reporting a squeak. Median satisfaction levels were minimally, but significantly less for "noisy" (9/10) than "quiet" hips (10/10) (median difference = - 1, 95% CI - 2 to 0, p < 0.001). Compared to those with "noisy" hips, patients with "quiet" hips were 1.7 times (95% CI 1.3-2.5, p = 0.0002) more likely to report a "forgotten" hip. Younger age (p < 0.043) and increased anteversion (p < 0.021) were predictors for reported sounds. We have identified a high rate of "noisy" hips in this series of CoC THA with a significant inverse relationship between "noisy" hips and patient satisfaction levels. In our unit, we are moving towards the use of ceramic on cross-linked polyethylene bearings as a result of these findings and the excellent survivorship of this bearing combination.

Survie de l’arthroplastie totale de hanche sans ciment metal-polyéthylène hautement réticulé versus céramique céramique : une étude cas-contrôle à 5–9 ans de recul

BackgroundCurrently, there is a lack of evidence on the medium-term follow-up of cementless total hip arthroplasty (THA) using metal-on highly cross-linked polyethylene bearing (MoXPE), ceramic on ceramic bearing (CoC) at more than 5 years follow-up. Therefore, we performed a case control study to: 1) compare the incidence rate of osteolysis, 2) compare the longevity for both types of THAs, and 3) to evaluate the wear rate of MoXPE THAs. HypothesisCoC THAs will have a lower rate of osteolysis and better longevity than MoXPE THAs. Patients and methodsWe performed a retrospective analysis of 77 MoXPE (68 women, 9 men) and 105 CoC (85 women, 20 men) THAs, with an average patient age at the time of surgery of 64.7 years (range, 27 to 76 years). The cohorts were matched according to sex, body mass index, or diagnosis of hip joint disease. Clinical and radiologic measurements were analyzed at a mean follow-up of 6.7 years (range, 5–9 years). ResultsThere were no between-group differences with regard to the Harris hip score (87.0 (64.0–98.0) and 89.9 (70.0–100.0) for the MoXPE and CoC group, respectively) and the incidence rate of osteolysis (2.6% and 1.9%, respectively). Revision was required for 1 case for each THA type. The Kaplan–Meier survival at 8 years, using implant loosening or revision as the end-point of analysis, was 96.1% (95% confidence interval (CI), 90.0–99.3) for the MoXPE group and 98.9% (95% CI, 92.2–99.8) for the CoC group (p=0.189). The mean annual liner wear rate was 0.0160mm/year (range, 0.0050 to 0.0390mm/year) for the MoXPE THAs. DiscussionThere was no difference between CoC and MoXPE THAs in the incidence of osteolysis or in survival rate at 8 years post-surgery. Excellent clinical and radiological outcomes were obtained for both types of bearings. Level of evidenceIII, Case control study, case control retrospective design.

Hydrated Phospholipid Polymer Gel-Like Layer for Increased Durability of Orthopedic Bearing Surfaces.

Recently, traditional strategies for manipulating orthopedic bearing substrates have attempted to improve their wear resistance by adjusting polyethylene substrate through cross-linking and antioxidant blending. However, further research is required on the substrate, as well as the surface focused on the structure and role of articular cartilage. We therefore develop an orthopedic bearing surface comprising a nanometer-scale hydrated gel-like layer by grafting highly hydrophilic poly(2-methacryloyloxyethyl phosphorylcholine), with the aim of mimicking the lubrication mechanism of articular cartilage, and investigate its surface characteristics, bulk characteristics, and behavior under load bearing conditions upon accelerated aging. Neither the hydrophilicity nor lubricity of the gel-like surface was influenced by accelerated aging; instead, high stability was revealed, even under strong oxidation conditions. The characteristics of the hydrated gel-like surface potentiated the wear resistance of the cross-linked polyethylene liner, irrespective of accelerated aging. These results suggest that the hydrated gel-like surface enhances the longevity of cross-linked polyethylene bearings even under load-bearing conditions. Furthermore, the inflection point on the time series of wear can be a suitable indicator of the durability of the life-long protectant. In conclusion, the hydrated gel-like surface can positively increase orthopedic implant durability.

Ceramic bearings for total hip arthroplasty are associated with a reduced risk of revision for infection.

Periprosthetic joint infection (PJI) is a serious complication after total hip arthroplasty (THA) and bearing material's associations to PJI prevalence is largely unknown. The main purposes of this study were to determine if revision for infection varied depending on the type of bearing surface used in primary THA and to study whether patient or implant related factors had an effect on this variation. A total of 177,237 primary THA procedures from the Australian Registry (AOANJRR) were analysed. 3 bearing surfaces were compared. Metal-on-highly cross-linked polyethylene (MoXP) bearing had been used in 95,129 hips, ceramic-on-highly cross-linked polyethylene (CoXP) in 24,269 hips, and ceramic-on-ceramic (CoC) in 57,839 hips. Revision rates for infection were compared between the 3 groups. Both MoXP and CoXP had a higher revision rate for infection compared to CoC hips (hazard ratio [HR] 1.46 (1.25, 1.72), p < 0.001) and HR 1.42 (1.15, 1.75), p = 0.001 respectively). Patients aged 70 years or less had a lower revision rate for infection when a CoC bearing was used. This difference was independent of sex, and prostheses selection. No difference was evident if the femoral component was cemented or a head size of 28 mm was used. In this registry-based material, use of a CoC bearing was associated with a lower risk of revision for infection in patients younger than 70 years when cementless femoral components were used. Further studies are needed to verify this finding.

Contemporary Dual Mobility Head Penetration at Five Years: Concern for the Additional Convex Bearing Surface?

BackgroundDual mobility (DM) bearings are increasingly popular and second-generation designs contain highly cross-linked polyethylene. The purpose of this study is to report head penetration rates in modern DM bearings. MethodsA review of 63 consecutive DM bearings was performed. Radiographs were analyzed for head penetration using Martell methodology at regular postoperative intervals. ResultsThirty-four DM bearings were analyzed. Mean linear head penetration was 1.59 mm/y at 1 year, 1.07 mm/y at 2 years, and 0.27 mm/y at 5 years following an exponential regression model (R2 = 0.999). Mean volumetric wear was 783 mm3/y at 1 year, 555 mm3/y at 2 years, and 104 mm3/y at 5 years following an exponential regression model (R2 = 0.986). ConclusionInitial head penetration of DM bearings is larger than contemporary cross-linked polyethylene bearings; however, rates approach steady state after 2 years, analogous to traditional bearings. The larger “bedding-in” head penetration may be due to the additional convex bearing surface, creating 2 surfaces for deformation/wear.

Significantly Lower Wear of Ceramic-on-Ceramic Bearings Than Metal-on-Highly Cross-Linked Polyethylene Bearings: A 10- to 14-Year Follow-Up Study

BackgroundThis study aimed to retrospectively compare clinical and radiographic results between consecutive total hip arthroplasties (THAs) using ceramic on ceramic (CoC) and metal-on-highly cross-linked polyethylene (MoP), with >10 years of follow-up. MethodsSixty-seven patients (52 women and 15 men) underwent CoC THA, whereas 81 (67 women and 14 men) underwent MoP THA. The average patient age at the time of surgery was 54.0 years in the CoC group and 54.2 years in the MoP group. ResultsThe mean postoperative Harris Hip Scores were 88.9 and 86.4 in the CoC and MoP groups, respectively (P = .063), and the mean annual liner rates of wear were 0.0043 and 0.0163 mm/year, respectively (P < .001). Osteolysis was observed on the femoral side of 1 joint (1.5%) in the CoC group and in 1 (1.2%) acetabular and femoral (1.2%) joint each in the MoP group. Three joints (3.7%) in the MoP group showed aseptic cup loosening, one of which (1.2%) required revision THA because of progression of the loosening. Revision THA was also required in 1 joint (1.5%) in the CoC group because of ceramic fracture. The Kaplan–Meier survival rate at 10 years with implant loosening or revision THA as the end point was 98.5% for CoC and 96.3% for MoP (P = .416). ConclusionThe wear rate of CoC implants was significantly lower than that of MoP implants. Kaplan–Meier survival at 10 years with implant loosening and revision THA as end points did not differ significantly between these implants.

In Vivo Oxidative Stability Changes of Highly Cross-Linked Polyethylene Bearings: An Ex Vivo Investigation

The development of highly cross-linked UHMWPEs focused on stabilizing radiation-induced free radicals as the sole precursor to oxidative degradation. However, secondary in vivo oxidation mechanisms have been discovered. After a preliminary post-operative analysis, we subjected highly cross-linked retrievals with 1–4years in vivo durations and never-implanted controls to accelerated aging to predict the extent to which their oxidative stability was compromised in vivo. Lipid absorption, oxidation, and hydroperoxides were measured using infrared spectroscopy. Gravimetric swelling was used to measure cross-link density. After aging, all retrievals, except vitamin E-stabilized components, regardless of initial lipid levels or oxidation, showed significant oxidative degradation, demonstrated by subsurface oxidative peaks, increased hydroperoxides and decreased cross-link density, compared to their post-operative material properties and never-implanted counterparts, confirming oxidative stability changes.

Dual mobility bearings withstand loading from steeper cup-inclinations without substantial wear.

Steep cup abduction angles with adverse joint loading may increase traditional polyethylene bearing wear in total hip arthroplasties. However, there have been few reports evaluating the effect of cup inclination on the wear of dual-mobility devices. In a hip joint simulation, we compared the short-term wear of two-sizes of modular highly cross-linked dual-mobility bearings (28 mm femoral head diameter/42 mm polyethylene insert outer diameter/54 mm acetabular shell diameter; 22.2 mm femoral head diameter/36 mm polyethylene insert outer diameter/48 mm acetabular shell diameter) at 50 and 65° of cup inclination with modular 28 mm femoral head on 54 mm cup diameter metal-on-highly cross-linked polyethylene bearings. Increasing inclination from 50-65° had no changes in volumetric wear of 28/42/54 mm (mean, 1.7 vs. 1.2 mm3 /million cycles, respectively; p = 0.50) and 22.2/36/48 mm (mean, 1.7 vs. 1.2 mm3/million cycles, respectively; p = 0.48) dual mobility bearings. At 65°, 22.2/36/48 mm dual-mobility bearings had lower volumetric loss (mean, 2.2 vs. 6.3 mm(3) ; p = 0.03) and wear rates (mean, 1.2 vs. 2.7 mm3/million cycles; p = 0.02) compared to metal-on-highly cross-linked polyethylene bearings. Modern-generation dual-mobility designs with highly cross-linked polyethylenes may potentially withstand edge-loading from steeper cup-inclinations without substantial decreases in wear.

Is Ultrasound Screening Reliable for Adverse Local Tissue Reaction After Hip Arthroplasty?

There is increasing awareness of prevalence of adverse local tissue reaction (ALTR) surrounding metal-on-metal (MoM) and highly cross-linked polyethylene (HXLPE) bearings, and sensitive and simple screening modalities for ALTR are required. We examined reliability of ultrasound screening for ALTR in 131 hips of 105 patients who received both ultrasound and MRI examinations after hip arthroplasty with MoM or HXLPE bearings. Using the MRI results as reference, sensitivity, specificity and accuracy of ultrasound were 74%, 92% and 84% around MoM bearings, and 90%, 83%, and 85% around HXLPE bearings. Ultrasound detected ALTR in 11 hips that were not shown with MRI. Ultrasound examination is assumed to be a reliable screening tool for detecting clinically important ALTR lesions developing in the anterior region around MoM or HXLPE bearings.

No Differences Found in Bearing Related Hip Survivorship at 10–12 Years Follow-Up Between Patients With Ceramic on Highly Cross-Linked Polyethylene Bearings Compared to Patients With Ceramic on Ceramic Bearings

At a minimum follow-up of ten years we compared clinical and radiographic findings and survivorship in a cohort of 412 patients (447 hips) who received alumina on alumina CoC bearings to findings from a cohort of 216 patients (228 hips) with alumina on highly cross-linked polyethylene (HXLPE) bearings. All patients were operated for osteoarthritis. With bearing-related complications as endpoint, analysis showed no significant difference in survivorship between cohorts (99.8% for the CoC vs. 99.4% for HXLPE). In addition, there were no significant differences in clinical and radiographic findings between cohorts. We concluded that alumina on HXLPE bearings are a reasonable lower cost alternative to ceramic on ceramic bearing couples.

Osteonecrosis of the femoral head

Symptomatic hip osteonecrosis is a disabling condition with a poorly understood aetiology and pathogenesis. Numerous treatment options for hip osteonecrosis are described, which include non-operative management and joint preserving procedures, as well as total hip replacement (THR). Non-operative or joint preserving treatment may improve outcomes when an early diagnosis is made before the lesion has become too large or there is radiographic evidence of femoral head collapse. The presence of a crescent sign, femoral head flattening, and acetabular involvement indicate a more advanced-stage disease in which joint preserving options are less effective than THR. Since many patients present after disease progression, primary THR is often the only reliable treatment option available. Prior to the 1990 s, outcomes of THR for osteonecrosis were poor. However, according to recent reports and systemic reviews, it is encouraging that with the introduction of newer ceramic and/or highly cross-linked polyethylene bearings as well as highly-porous fixation interfaces, THR appears to be a reliable option in the management of end-stage arthritis following hip osteonecrosis in this historically difficult to treat patient population.

A randomised prospective evaluation of ceramic-on-ceramic and ceramic-on-highly cross-linked polyethylene bearings in the same patients with primary cementless total hip arthroplasty

Very few studies have compared alumina-on-alumina ceramic and alumina-on-highly cross-linked polyethylene bearings in the same patient. The purpose of this prospective randomised study was to compare the clinical and radiographic results and the prevalence of osteolysis in cementless total hip arthroplasty using an alumina-on-alumina and alumina-on-highly cross-linked polyethylene bearings in young active patients. We prospectively compared the results of 100 patients (200 hips) who had undergone a cementless total hip arthroplasty with an alumina-on-alumina ceramic bearing in one hip and an alumina-on-highly cross-linked polyethylene in the other. There were 66 men and 34 women with a mean age of 45.3 years (range, 21-49 years) at the time of surgery. The mean follow-up was 12.4 years (range, 11-13 years). The patients were assessed clinically and radiographically at three months, one year, and annually thereafter. Harris hip, Western Ontario and McMaster Universities Osteoarthritis Index, and University of California, Los Angeles activity scores did not show statistically significant differences between the two groups of bearings preoperatively or at the time of final follow-up. Radiographic findings of the component were not significantly different between the two groups. The mean polyethylene linear penetration was 0.031 ± 0.004 mm per year. No hips in either group displayed osteolysis. The Kaplan-Meier survivorship with revision as the end point at 12.4 years was 100% (95% confidence interval [CI], 94-100%) for the femoral component in both groups and 99% (95%CI, 93-100%) for the acetabular component. The clinical and radiographic results of using an alumina-on-alumina ceramic and alumina-on-highly cross-linked polyethylene bearings were similar.

Polyethylene Wear and Osteolysis After Cementless Total Hip Arthroplasty with Alumina-on-Highly Cross-Linked Polyethylene Bearings in Patients Younger Than Thirty Years of Age

We asked whether cementless total hip arthroplasties that made use of alumina-on-highly cross-linked polyethylene bearings would improve hip score and functional activity and reduce the prevalence of polyethylene wear, osteolysis, and aseptic loosening. Consecutive primary total hip arthroplasties were performed in fifty patients (a total of sixty hips among thirty-four men and sixteen women) who were younger than thirty years of age. The average age at the time of the index arthroplasty was 28.3 years (range, twenty-one to twenty-nine years). The average follow-up was 10.8 years (range, ten to twelve years). Osteolysis and polyethylene wear rates were evaluated with use of radiography and computed tomography. The mean Harris hip score, which was 38 points (range, 6 to 45 points) preoperatively, had improved to 95 points (range, 85 to 100 points) at a mean follow-up time of 10.8 years. The mean penetration (and standard error of the mean) of the polyethylene liner was 0.031 ± 0.004 mm per year. No hip had osteolysis or aseptic loosening. At a minimum of ten years and an average of 10.8 years postoperatively, the current generation of cementless acetabular and femoral components with alumina-on-highly cross-linked polyethylene bearings was functioning well and was not associated with the development of osteolysis in our group of patients younger than thirty years of age. While the long-term prevalence of polyethylene wear and osteolysis remains unknown, the midterm data are promising.

Outcomes of Open Reduction for Developmental Dysplasia of the Hip: Does Bilateral Dysplasia Have a Poorer Outcome?

The purpose of this study was to compare the outcomes of surgical treatment in children of walking age with unilateral and bilateral developmental dysplasia of the hip (DDH). We examined the records of fifty-six children of walking age with bilateral dysplasia and 156 children of walking age with unilateral dysplasia treated with open reduction and pelvic osteotomy with or without femoral osteotomy from 1990 to 2000. The minimum duration of follow-up was five years. The mean age at surgery was thirty-four months in the bilateral group and twenty-five months in the unilateral group. Preoperative radiographs were evaluated to determine the Tönnis grade of the dislocation and the acetabular index, and the latest radiographs were evaluated to determine the Severin classification. The Kalamchi and MacEwen classification was used to assess osteonecrosis, and the McKay classification was used to assess the clinical outcome at the time of the latest follow-up. For the statistical analyses, we selected the worse side in patients in the bilateral group as the index hip if the outcome was asymmetrical and the left hip if the outcome was symmetrical. The Fisher exact and Student t tests were used for comparisons of outcomes between the groups. Multiple logistic regression models were used to analyze factors associated with osteonecrosis and with the McKay classification. Age at surgery and preoperative Tönnis grade differed significantly between the groups. Forty-five (80.3%) of the patients in the bilateral group and 135 (86.5%) of the patients in the unilateral group had a satisfactory Severin classification (Ia, Ib, or II); the difference between the groups was not significant. According to the McKay classification, twenty-six (46%) of the patients in the bilateral group had an satisfactory outcome compared with 111 (71%) of the patients in the unilateral group (p = 0.006). Osteonecrosis was significantly greater in the bilateral group as well (p = 0.01). Patient age at surgery and Tönnis grade were risk factors for osteonecrosis. Older age and bilaterality were associated with a poorer McKay classification. The logistic regression analysis was repeated after removing the nineteen patients (34%) in the bilateral group who had an asymmetrical outcome, and this analysis confirmed that asymmetrical outcome was a risk factor for a poorer McKay classification. Our data confirmed that the clinical outcome of bilateral developmental dysplasia of the hip was worse primarily because of asymmetrical outcomes. Age and Tönnis grade played an important role in the risk of occurrence of osteonecrosis. The radiographic outcome according to the Severin classification did not differ significantly between the groups.

Inflammatory Pseudotumor Complicating Metal-On-Highly Cross-Linked Polyethylene Total Hip Arthroplasty

Inflammatory masses or cysts occurring in the pelvis, thigh, and gluteal regions, often mimicking infection, occasionally arise after total hip arthroplasty procedures. Inflammatory pseudotumors comprise a subgroup of these lesions. Pseudotumors have been associated with pain, rashes, instability, neuropathy, and premature loosening of prosthetic components, often leading to early and difficult revision surgery. The association between such pseudotumors and metal-on-metal bearings has led to questions regarding the performance of these bearings in hip arthroplasty. We present a case of pseudotumor requiring revision surgery, which occurred uniquely around a metal-on-highly cross-linked polyethylene bearing.