Cumulative revision rate is higher in metal-on-metal THA than metal-on-polyethylene THA: analysis of survival in a community registry.

BACKGROUND: Metal-on-metal (MOM) THA bearing technology has focused on improving the arc of motion and stability and minimizing wear compared with traditional metal-on-polyethylene (MOP) bearing couples. It is unclear whether this more costly technology adds value in terms of improved implant survival. QUESTIONS/PURPOSES: This study evaluated Kaplan-Meier survival, revisions for dislocation, and cost of MOM THA compared with metal-on-cross-linked polyethylene (MOXP) THA in a community joint registry, with subset analysis of the recalled Depuy ASR™ implant.
METHODS: All MOM THAs (resurfacings excluded) performed between January 2002 and December 2009 were included (n = 1118) and compared with a control group of MOXP THAs (n = 1286) done during the same time. Analysis was performed to compare age, gender, cost of implant, length of stay, year of index procedure, diagnosis, head size (< 32 mm versus ≥ 32 mm), revision and revision reason for both groups. Analysis at a mean of 3.6 years was done using Wilcoxon rank sum tests, Pearson's chi-square tests, Kaplan Meier methods, and Cox regression.
RESULTS: The cumulative revision rate (CRR) was higher in MOM implants than in MOXP implants (MOM CRR = 13%; MOXP CRR = 3%). MOM implants were three times as likely to be revised as MOXP implants after adjustment for age, head size, and year of procedure. The recalled DePuy ASR™ implant was six times as likely to be revised as other MOM THAs. After removing the ASR™ implants from analysis, survivorship of MOM implants was not better than that of the MOXP hips.
CONCLUSIONS: During the study time, MOM THAs showed inferior survival to MOXP THAs after adjusting for age, head size, and year of procedure. Longer followup is necessary to see whether MOM THAs add value in younger patient groups.