Muscle atrophy and metal-on-metal hip implants

Background and purpose — Muscle atrophy is seen in patients with metal-on-metal (MOM) hip implants, probably because of inflammatory destruction of the musculo-tendon junction. However, like pseudotumors, it is unclear when atrophy occurs and whether it progresses with time. Our objective was to determine whether muscle atrophy associated with MOM hip implants progresses with time.

Patients and methods — We retrospectively reviewed 74 hips in 56 patients (32 of them women) using serial MRI. Median age was 59 (23–83) years. The median time post-implantation was 83 (35–142) months, and the median interval between scans was 11 months. Hip muscles were scored using the Pfirrmann system. The mean scores for muscle atrophy were compared between the first and second MRI scans. Blood cobalt and chromium concentrations were determined.

Results — The median blood cobalt was 6.84 (0.24–90) ppb and median chromium level was 4.42 (0.20–45) ppb. The median Oxford hip score was 34 (5–48). The change in the gluteus minimus mean atrophy score between first and second MRI was 0.12 (p = 0.002). Mean change in the gluteus medius posterior portion (unaffected by surgical approach) was 0.08 (p = 0.01) and mean change in the inferior portion was 0.10 (p = 0.05). Mean pseudotumor grade increased by 0.18 (p = 0.02).

Interpretation — Worsening muscle atrophy and worsening pseudotumor grade occur over a 1-year period in a substantial proportion of patients with MOM hip implants. Serial MRI helps to identify those patients who are at risk of developing worsening soft-tissue pathology. These patients should be considered for revision surgery before irreversible muscle destruction occurs.     

Analysis of 118 second-generation metal-on-metal retrieved hip implants

Osteolysis is due to particulate wear debris and is responsible for the long-term failure of total hip replacements. It has stimulated the development of alternative joint surfaces such as metal-on-metal or ceramic-on-ceramic implants. Since 1988 the second-generation metal-on-metal implant Metasul has been used in over 60 000 hips. Analysis of 118 retrieved specimens of the head or cup showed rates of wear of approximately 25 microm for the whole articulation per year in the first year, decreasing to about 5 microm per year after the third. Metal surfaces have a 'self-polishing' capacity. Scratches are worn out by further joint movement. Volumetric wear was decreased some 60-fold compared with that of metal-on-polyethylene implants, suggesting that second-generation metal-on-metal prostheses may considerably reduce osteolysis.     

The Otto Aufranc Award. Wear and lubrication of metal-on-metal hip implants

The implication of polyethylene wear particles as the dominant cause of periprosthetic osteolysis has created a resurgence of interest in metal-on-metal implants for total hip arthroplasty because of their potential for improved wear performance. Twenty-two cobalt chromium molybdenum metal-on-metal implants were custom-manufactured and tested in a hip simulator. Accelerated wear occurred within the first million cycles followed by a marked decrease in wear rate to low steady-state values. The volumetric wear at 3 million cycles was very small, ranging from 0.15 to 2.56 mm3 for all implants tested. Larger head-cup clearance and increased surface roughness were associated with increased wear. Independent effects on wear of material processing (wrought, cast) and carbon content were not identified. Implant wear decreased with increasing lambda ratio, a parameter used to relate lubricant film thickness to surface roughness, suggesting some degree of fluid film lubrication during testing. This study provided important insight into the design and engineering parameters that affect the wear behavior of metal-on-metal hip implants and indicated that high quality manufacturing can reproducibly lead to very low wear.     

Failure modes of 433 metal-on-metal hip implants: how, why, and wear

Metal-on-metal total hip replacements (THRs) and hip resurfacings are coming under increasing scrutiny in light of concerns that they fail because of high wear and elevated metal ions. The aim of this study was to investigate the modes of failure in a collection of 433 metal-on-metal THRs and hip resurfacings and to examine the correlations between the reasons for revision and a range of patient and implant variables considered relevant to implant wear.     

Imaging of metal-on-metal hip resurfacing

Conventional radiography is the primary imaging modality to evaluate the condition of hip resurfacing implants and the preferred method of assessing implant stability over time. Radiographs assess the angle of inclination of the femoral and acetabular components, implant stability, and femoral neck narrowing. Ultrasonography detects solid or soft tissue masses adjacent to the implant. Magnetic resonance imaging (MRI) detects osteolysis and complications in the periprosthetic soft tissues such as wear-induced synovitis, periprosthetic collections, neurovascular compression, and quality of the muscle and tendons of the rotator cuff of the hip. For pain after hip resurfacing, early use of optimized MRI is recommended.     

Painful metal-on-metal total hip arthroplasty

Two patients were evaluated for the possibility of hypersensitivity to a Metasul articulation (Centerpulse, Austin, Tex) coupled with total hip arthroplasty. Serum was tested with a lymphocyte proliferation assay, and the capsular tissues from the hip were examined for perivascular lymphocytes. The diagnosis of hypersensitivity to Metasul could not be confirmed in these patients, and ultimately, the painful hip arthroplasties were felt to be caused by a combination of musculoskeletal problems.     

Pseudotumours associated with metal-on-metal hip resurfacings

We report 17 patients (20 hips) in whom metal-on-metal resurfacing had been performed and who presented with various symptoms and a soft-tissue mass which we termed a pseudotumour. Each patient underwent plain radiography and in some, CT, MRI and ultrasonography were also performed. In addition, histological examination of available samples was undertaken. All the patients were women and their presentation was variable. The most common symptom was discomfort in the region of the hip. Other symptoms included spontaneous dislocation, nerve palsy, a noticeable mass or a rash. The common histological features were extensive necrosis and lymphocytic infiltration. To date, 13 of the 20 hips have required revision to a conventional hip replacement. Two are awaiting revision. We estimate that approximately 1% of patients who have a metal-on-metal resurfacing develop a pseudotumour within five years. The cause is unknown and is probably multifactorial. There may be a toxic reaction to an excess of particulate metal wear debris or a hypersensitivity reaction to a normal amount of metal debris. We are concerned that with time the incidence of these pseudotumours may increase. Further investigation is required to define their cause.     

Rationale for metal-on-metal total hip replacement

Traditional metal-on-polyethylene total hip replacements are prone to wear with secondary osteolysis and aseptic loosening, especially in younger, more active patients. Metal-on-metal represents an alternative bearing surface that offers much lower wear rates with the aim of improving longevity and the use of larger femoral heads that confer increased inherent stability, resulting in fewer patient restrictions and improved patient satisfaction. This article discusses the science and clinical evidence in support of choosing metal-on-metal as a bearing as well as its limitations.     

Current concepts of metal-on-metal hip resurfacing

The second-generation, metal-on-metal (MOM) bearing for total hip replacements was launched in the 1980s, and resurfacing followed in the mid-1990s. Remaining challenges include long-term bone remodeling of the femoral resurfacing and consideration of adverse MOM wear conditions. Precise understanding of manufacturing variables such as alloy types, bearing diameters, design tolerances, and surface finish is imperative in obtaining clinical consistency and safety in the patient. This review examines femoral fixation, bone remodeling, and wear studies of MOM implants and provides a brief overview of the latest outcome and retrieval data and how these data integrate with the in vitro wear studies.     

Chinese experience with metal-on-metal hip resurfacing

The aim of this study was to study the actual clinical and laboratory results of metal-on-metal resurfacing hip arthroplasties by comparing with other implants. A total of 127 cases were operated on at the Department of Orthopaedics of Wuhan Union Hospital from 2005 to 2011. An important cause of failure is the fracture of the femoral neck. The chromium and cobalt levels of resurfacing hip arthroplasty and large-diameter head total hip arthroplasty (THA) are higher than those of a conventional metal-on-polyethylene total hip arthroplasty. There was a high ion level associated with an abduction angle of more than 45° and repetitive extreme hip motion in the 3 revision cases. The findings of this study are novel and quite controversial with that of the previously published literature.     

Complications after metal-on-metal hip resurfacing arthroplasty

This article determines the incidence and cause of the complications commonly associated with metal-on-metal hip resurfacing implants and the proposed methods to prevent these complications. The literature available in PubMed was reviewed. Complication rates after hip resurfacing are low, and the procedure has shown both safety and efficacy in the hands of surgeons trained in specialized centers. Proper surgical technique can further reduce the incidence of femoral neck fracture, component loosening, and abnormal wear of the prosthesis. A more systematic detection of adverse local tissue reactions is needed to provide accurate assessments of their prevalence.     

Influence of the clearance on in-vitro tribology of large diameter metal-on-metal articulations pertaining to resurfacing hip implants

Large-diameter metal-on-metal articulations may provide an opportunity for wear reduction in total hip implants because earlier studies have shown that the formation of a fluid film that completely separates the bearing surfaces is theoretically possible. In such a lubrication mode and under ideal conditions, there is theoretically no amount of wear. Studies have suggested that the two primary parameters controlling the lubrication mode are the diameter and the clearance of the articulation. The goal of the present study was to experimentally investigate the influence of these two parameters on the wear behavior of large-diameter metal-on-metal articulations pertaining to resurfacing hip implants. The results of this in vitro investigation showed that longer running-in periods and higher amounts of running-in wear were associated with larger clearances.     

Femoral neck narrowing after metal-on-metal hip resurfacing

We reviewed 40 Corin Cormet 2000 (Corin, Cirencester, UK) metal-on-metal resurfacing hips, in 36 patients, for the presence of femoral neck narrowing. A neck-to-prosthesis ratio was calculated by dividing the diameter of the femoral neck with that of the implant. This ratio was measured on plain anteroposterior pelvis radiographs taken immediately and 2 years postoperation. Subsequent radiographs were measured up to a maximum 7 years (mean, 5.3 years) postoperation. Femoral neck narrowing was observed in 90% of hips at 2 years, with the average neck narrowing ranging from a ratio of 0.865 to 0.811. Importantly, no further narrowing occurred beyond this point up to 7 years postoperation. We described a simple reproducible method of measuring neck narrowing on plain radiographs and discuss possible causal factors for neck narrowing after hip resurfacing.     

金属对金属髋关节表面置换术的短期随访研究

目的探讨金属对金属(MOM)混合固定型髋关节表面置换术(HRA)的近期疗效,分析手术技术要点。方法 2004年10月至2008年6月,对52例(58髋)股骨头缺血性坏死、骨关节炎、髋关节发育不良、强直性脊柱炎患者行MOM-HRA。其中男32例,女20例;年龄16～65岁,平均42.6岁。手术方法按照K.De.Smet标准方法进行,术后对Harris评分、关节活动度和X线片进行随访。结果失访7例(8髋),45例(50髋)获得随访,随访时间平均22个月(12～54个月)。术前平均Harris评分(37.0±1.2)分,术后22个月平均(93.0±1.0)分;术前屈髋度平均(25.3±1.6)°,术后22个月平均(105.0±1.8)°;术前外展度平均(18.8±0.8)°,术后22个月平均(40.6±1.0)°。评价:46髋优,3髋良,1髋差。无股骨颈骨折,无松动,无脱位,无感染,无翻修,1例异位骨化BrookerⅢ型。结论 HRA具有保留股骨头骨量、术后关节活动度恢复快、近期结果好等优点,对于获得优良的术后结果,严格的患者选择和精确的手术技术至关重要。     

Neo-capsule tissue reactions in metal-on-metal hip arthroplasty

Background Modern-generation metal-on-metal articulations have a high wear resistance and may therefore be able to improve the long-term performance of artificial joints. However, the biological effects are still under debate. This study was undertaken to review the histopathological changes in neo-capsule tissues of different metal-on-metal hip arthroplasties.

Methods Neo-capsule tissue samples from 46 hips with modern second-generation metal-on-metal articulations (39 hip resurfacings and 7 non-cemented total hip replacements) with a variety of failure mechanisms were examined histopathologically and immunohistochemically.

Results A distinct lymphocytic infiltration was found in all cases with in situ times of more than 7 months, consisting of CD20-positive B-lymphocytes and CD3positive T-lymphocytes and sometimes thinly distributed CD138-positive plasma cells without dominant T-cell or plasma cell infiltrates.

Interpretation This distinct lymphocytic infiltration has not been reported in tissue analyses of metal- or ceramic-on-polyethylene hip replacements, and may therefore be considered to be a characteristic histological pattern of tissue reactions on metal particles and/or ions around metal-on-metal bearings.     

Early osteolysis following second-generation metal-on-metal hip replacement

BACKGROUND: Total hip arthroplasty with use of metal-on-metal bearings has been reintroduced as an alternative to the use of metal-on-polyethylene bearings because of theoretical advantages such as reduced wear and a lower prevalence of osteolysis. However, we observed early osteolysis in a cohort of patients who had been managed with second-generation metal-on-metal hip replacements and investigated the possible etiologic role of metal hypersensitivity. METHODS: We retrospectively analyzed 165 patients (169 hips) who had undergone primary cementless total hip replacement with a contemporary metal-on-metal total hip design between 2000 and 2002. After a minimum duration of follow-up of twenty-four months, nine patients (ten hips) had an osteolytic lesion localized to the greater trochanter. Skin-patch tests for hypersensitivity to metals were performed on the nine patients and on nine randomly selected patients with total hip replacements who did not have osteolytic changes and who were matched to the study cohort for age and gender. Microbiological cultures, histopathologic examinations, and immunohistochemical analysis were performed on samples of periprosthetic tissue that were collected during revision arthroplasty on two hips with early osteolysis. RESULTS: The patients with early osteolysis had a significantly higher rate of hypersensitivity reaction to cobalt compared with controls (p = 0.031). The retrieved periprosthetic tissues showed no evidence of metallic staining, but histologic analysis revealed a perivascular accumulation of CD3-positive T-cells and CD68-positive macrophages and an absence of both particle-laden macrophages and polymorphonuclear cells. Immunohistochemical analysis demonstrated that bone-resorbing cytokines such as IL-1beta and TNF-alpha were produced mainly by infiltrating lymphocytes and activated macrophages. CONCLUSIONS: These findings raise the possibility that early osteolysis in patients with this second-generation metal-on-metal hip replacement is associated with abnormalities consistent with delayed-type hypersensitivity to metal. A prospective study in which a large group of patients is evaluated with multiple diagnostic methods is needed in order to establish whether there is a causal relationship between metal hypersensitivity and osteolysis.     

Present state of metal-on-metal hybrid hip resurfacing

Bone conservation and preservation, joint stability, and low wear of the large metal-on-metal resurfacing bearings have been convincingly demonstrated in the current literature. The clinical results of 600 MM Hybrid Conserve Plus Resurfacing in 519 patients with an average follow-up of 6.9 years (range, 4.0-10.4 years) have been excellent. The average age was 48.9 years, 74% of the patients were male, and the study included all etiologies of the young with arthritis. The complication rates other than dislocation and fracture of the femoral neck are comparable between resurfacing and conventional total hip replacement. The incidence of femoral neck fracture is low (1.2% worldwide) with less than 0.6% in this series and none occurring in the last 5 years due to proper patient selection and improved surgical technique. Component loosening after metal-on-metal resurfacing has been significantly reduced and acetabular component loosening is uncommon and has not happened in this series. Femoral bone preparation and optimal cementing techniques are paramount to prevention of femoral loosening. Clearance between the cylindrically reamed part of the head and the component varies in different designs, and the surgeon must note the need for different cementing strategies for different recommended clearances. The learning curve of a surgeon undertaking resurfacing can be greatly reduced by observation and hands-on training in specialized centers with surgeons experienced in resurfacing.