Retrieval analysis of 240 metal-on-metal hip components, comparing modular total hip replacement with hip resurfacing

Abstract

This study compared component wear rates and pre-revision blood metal ions levels in two groups of failed metal-on-metal hip arthroplasties: hip resurfacing and modular total hip replacement (THR). There was no significant difference in the median rate of linear wear between the groups for both acetabular (p = 0.4633) and femoral (p = 0.0872) components. There was also no significant difference in the median linear wear rates when failed hip resurfacing and modular THR hips of the same type (ASR and Birmingham hip resurfacing (BHR)) were compared. Unlike other studies of well-functioning hips, there was no significant difference in pre-revision blood metal ion levels between hip resurfacing and modular THR. Edge loading was common in both groups, but more common in the resurfacing group (67%) than in the modular group (57%). However, this was not significant (p = 0.3479). We attribute this difference to retention of the neck in resurfacing of the hip, leading to impingement-type edge loading. This was supported by visual evidence of impingement on the femur. These findings show that failed metal-on-metal hip resurfacing and modular THRs have similar component wear rates and are both associated with raised pre-revision blood levels of metal ions.

Pseudotumors Are Common in Well-positioned Low-wearing Metal-on-Metal Hips

“…Third, although the distribution of resurfacings and THAs was similar between the study groups, we did not investigate the influence of wear and corrosion occurring at the modular junctions of MOM THA. This likely had some effect on the accumulation of metal wear debris, although we have shown, in a previous study, metal ion levels were similar before revision of these two types of hip prostheses [30]. Finally, patients in this retrieval study may not have represented the general population of patients with MOM hip prostheses.…”

“…Therefore, we compared our patient population with the largest published single-center series of patients with current-generation MOM hip prostheses [4,20,29,40,43] (Table 4). We also compared the outcome variables of this study with all of the published retrieval studies of current-generation MOM hip implants [10,14,22,25,30,32,41] (Table 5). We found 72 of 105 patients (69%) had evidence of a pseudotumor before revision of their hip arthroplasty for any cause.…”

“…Due to differences in methods and reporting of wear rates in the literature, we based our calculation on our own previous experience of wear measurement [14,30]. Using Altman's nomogram, we determined the minimum number of components required in each group to show a 5-lm/year difference in wear rate.…”

“…We mounted and rotated the components on a spindle (spindle accuracy, ± 0.02 lm), while a stylus (2-mm-diameter ruby), in contact with the surface of the component, measured deviations from a perfect circle (resolution of stylus gauge, 10 nm). Using a previously described method [30], we took three sets of measurements for each hip. For the cup components, we measured the out-of-roundness along lines of latitude and longitude.…”

“…Retrieval studies of current-generation MOM hips have suggested edge loading, resulting from adverse cup orientation, leads to a higher wear of the components and raised blood metal ion levels [7,27,30,32]. In vivo studies have suggested disparities in certain design features, such as the clearance [41] and arc of cover [27], are important factors affecting component wear rates and the risk of edge loading.…”