Introduction
Differences between specific complications of metal-on-metal total hip resurfacing (RHA) versus total hip arthroplasty (THA) are unclear and clinical series with a long follow-up are limited. The goals of this study were to (1) compare the survivorship of large-diameter head MoM THA with the survivorship of MoM hip resurfacings; (2) identify the most common reasons for revision in both groups.
Methods
All the patients who underwent a metal-on-metal (MoM) hip replacement at our institution between January 1998 and October 2011 were retrospectively included in this study. 675 MoMHR were performed in 587 patients. Implant survival curves (Kaplan-Meier) were obtained and survival was stratified according to failure category (MoM-specific vs nonspecific) and cause of failure. Implant survival rate was obtained. Revision for any reason was considered the primary failure endpoint. Mean follow-up was 11 years (range 8 – 18.5), with a minimum of 96 months (8 years) and a maximum of 222 months (18 years and 6 months).
Results
At the latest follow-up, survival rate for the large diameter head MoM THA group was 83.4% (95% confidence interval [CI], 80.6-86.8%), i.e. was lower than the 88.8% survival rate (95% CI, 84.6%-95.2%) observed in MoM RHA (p<0.0001), with RHA cumulative survival curve being above the cumulative survival curve for THA at any time interval. THA was inferior to RHA both in terms of MoM specific and unspecific failure modes with p<0.0001. (figure 3 and 4). However, no statistically significant difference in time of ARMD onset was found (p=0.2755, figure 5), even if median time of ARMD onset was higher in the RHA group (124 months for THA vs 135 months for RHA).
Conclusion & perspectives
Causes for revision appear to be different for RHA and THA: the higher ARMD incidence in THA with respect to RHA is significant. Corrosion and fretting at the head-neck junction may contribute to higher ARMD incidence in THA, RHA is associated with a higher revision rate than non metal-on-metal bearing couples, and its implantation should be reserved to patients selected on an individual basis.
Level of evidence:
Level III, therapeutic study