Outcomes following primary total hip arthroplasty with ceramic-on-metal and metal-on-metal bearings

Introduction

There is concern in the scientific community that patients implanted years ago with metal-on-metal (M-M) bearings for total hip arthroplasty (THA) may still have persistent and potentially toxic levels of chromium (Cr) and cobalt (Co). Studies suggest that blood metal levels may be elevated in both ceramic-on-metal (C-M) and M-M bearings. The objective of this study was to establish whether patients with THA and C-M bearing surfaces require the same follow-up as those with M-M THA and to evaluate the long-term survival of THAs with M-M and C-M bearing surfaces, blood Cr and Co levels and complications (especially metallosis).

Materials and Methods

A retrospective, observational, analytical, descriptive cohort study was conducted on the patients who underwent THA at a single centre with the use of M-M (64) and C-M (76) bearings and a control group (44 THA: 23 ceramic-on-ceramic, 8 metal-on-polyethylene, 13 ceramic-on-polyethylene) between 2005 and 2009 (an additional 12 THAs performed with the same implants between 2010 and 2012 were also included). The median follow-up period was 14.41 (interquartile range 11.6–15.7) years. The primary outcomes were blood levels of Cr and Co, complications, implant survival and patient survival (Kaplan Meier analysis). Multivariate binary logistic regression was performed to examine the risk of metallosis, prosthesis replacement and death between groups, adjusting for potential confounders.

Results

THA with M-M bearings produce more metallosis (47%, p < 0.001) than C-M bearings (16%). Thirty-one THA revisions were performed (17%), with significantly more revisions in the M-M group (33%) compared to both the C-M group (11%, p = 0.002) and the control group (4%, p = 0.003). There were no significant differences in 15-year patient survival between the groups.

Conclusions

Routine monitoring of C-M bearings should be recommended, similar to the protocols for M-M. In the long term, both metallosis and revision rates are unacceptably high for both types of bearings, with M-M bearings performing worse. Therefore, neither implant type is recommended for THA.