Long-term comparative study of large-diameter metal-on-metal bearings: Resurfacing versus total arthroplasty with large-diameter Durom™ bearing.

INTRODUCTION: Short-term results in total hip arthroplasty (THA) with large-diameter metal-on-metal (MoM) bearings were encouraging, but high failure rates have been reported in the long term, notably implicating corrosion due to modularity. Several studies compared resurfacing (to which modularity does not apply) versus large-diameter MoM THA; but, to our knowledge, none compared the same bearing in the two situations with more than 10 years' follow-up. We therefore conducted a retrospective case-control study, using a single cup model (Durom™, Zimmer, Warsaw, USA) for both resurfacing (R) and large-diameter THA, to determine the role of modularity in failure of large-diameter MoM bearings. The study compared (1) metallic ion levels, and (2) survival, functional scores and complications rates between R and THA. HYPOTHESIS: Large-diameter MoM bearing failure implicates not bearing wear but head-neck junction modularity in larger-diameter MoM THA. MATERIAL AND METHOD: Eighty-three THAs and 90 Rs were included between February 2004 and March 2006. All patients had clinical and radiologic follow-up with chromium (Cr) and cobalt (Co) ion blood assay. RESULTS: In the THA group, 24 of the 83 patients (28.9%) underwent revision for adverse reaction to metal debris (ARMD), versus none in the R group. Ten-year all-cause survival was significantly better in R (97.7%; 95% CI, 96.2-99.2) than THA (67.1%; 95% CI, 60.9-73.3). Median blood ion level was higher in THA (with a difference between Co and Cr: 5.75µg/L (range, 3.82-19.2) versus 1.75µg/L (range, 1.34-2.94) respectively) than in R (no difference: 0.89µg/L (range, 0.67-2.89) and 1.07µg/L (range, 0.67-1.65) respectively). In the THA group, there were positive correlations between Co and Cr elevation and implant revision (both p<0.0001). Co/Cr ratio was significantly higher in THA (2.57) than R (0.88) (p<0.0001), and higher again in the 24 cases of THA revision (4.67). There was no significant difference in mean PMA score (THA: 17.08±1.82 (range, 7-18); R: 17.50±0.74 (range, 15-18)), whereas mean Oxford score was better in R (14.32±2.5 (range, 12-24)) than THA (18.17±8.05 (range, 12-42)) (p=0.02). DISCUSSION: The present study confirmed the incontrovertible implication of modularity in failure of large-diameter MoM THA, by analyzing the same bearing in THA and in resurfacing. Trunnionosis was observed in the 24 cases of revision, with the THA adaptation ring inducing serious metallic ion release (with dissociated Co/Cr ratio), accounting for the high rate of revision. LEVEL OF EVIDENCE: III, case-control study.

The supinator muscle: anatomical bases for deep branch of the radial nerve entrapment.

PURPOSE: Our goals were to carry out an anatomical description of the internal architecture of the supinator muscle in order to describe potentially compressive structures for the deep branch of the radial nerve (DBRN) and to establish reference landmarks for the surgical treatment of radial tunnel syndrome. METHODS: Thirty upper limbs were dissected. The pennation angle of proximal and distal arcades of the supinator to the radial shaft axis was measured. Possible compressive structures of both superficial and deep heads of supinator were recorded. Proximal and distal arcades of the superficial layer of the supinator were classified according to their fiber content as tendinous, musculo-tendinous, muscular or membranous. The distances of superficial layer of the supinator muscle to the humeroradial joint line and lateral epicondyle were measured. RESULTS: Pennation angle was 33.6° (±4.2°) for the superficial layer and 50.2° (±6.6°) for the deep layer. The difference was statistically significant (p < 0.0001). The proximal arcade was purely tendinous in 20 cases (66.7 %). The distal arcade was mainly tendinous or musculo-tendinous (70 %). The average distance between the lateral epicondyle and the proximal arcade was 41.6 mm. We did not find any other potentially compressive structure within DBRN course between both layers. CONCLUSION: Our anatomical results about pennation angle could be used as a basis for a thorough functional study about the supinator. Both proximal and distal arcades appeared as the two zones ables to compress the DBRN. Their localization should help the surgeon for the DBRN neurolysis.

Metal-on-Metal Bearing: Is This the End of the Line? We Do Not Think So.

BACKGROUND: Recent studies have recommended the discontinuation of metal-on-metal (MoM) components in total hip arthroplasty (THA) because of adverse effects reported with large-diameter MoM THA. This is despite favorable long-term results observed with 28 and 32 mm MoM bearings. QUESTIONS/PURPOSES: The aim of this study was to assess the value of calls for an end to MoM bearings as THA components. Specifically, we wish to address the risks associated with MoM bearings including adverse soft tissue reactions, metal ion release, and carcinogenic risk. METHODS: The study evaluates the arguments in the literature reporting on MoM (adverse soft tissue reactions, metal ion release, and carcinogenic risk) and the experience of the current authors who re-introduced these bearings in 1995. They are balanced by a benefit-risk review of the literature and the authors' experience with MoM use. RESULTS: Adverse reactions to metallic debris as well as metal ion release are predictable and can be prevented by adequate design (arc of coverage, clearance), metallurgy (forged instead of cast alloy, high-carbide content), and appropriate component orientation. There is no scientific evidence that carcinogenicity is increased in subjects with MoM hip prostheses. MoM articulations appear to be attractive allowing safe hip resurfacing, decreasing the risk of THA revision in active patients, and providing secure THA fixation with cement in cages in severely deformed hips. MoM bearings in women of child-bearing age are controversial, but long-term data on metallic devices in adolescents undergoing spinal surgery seem reassuring. DISCUSSION: Adequate selection of MoM articulations ensures their safe use. These articulations are sensitive to orientation. Fifteen years of safe experience with 28- and 32-mm bearings of forged alloy and high-carbide content is the main reason for retaining them in primary and revision THA.