OrthoBuzz occasionally receives posts from guest bloggers. This guest post comes from Richard S. Yoon, MD.
We’re entering the “midterm” follow-up period for the metal-on-metal (MoM) hip devices implanted in the early 2000s, and recent reports from around the world are confirming early concerns. Several studies published during the first few months of 2016 report unacceptably high failure rates.
In the Open Orthopaedics Journal, Mogensen et al. reported an 18.4% revision rate in more than 100 CONSERVE MoM hips, at a mean follow-up of 4.5 years. These results led the Danish authors to terminate the use of MoM at their centers.
In the BMJ Open, Langton et al. reported a 16% failure rate among more than 350 Pinnacle MoM hips after about nine years of follow-up. Greiner et al. published a follow-up of prior research in a recent edition of the Journal of Arthroplasty. Among more than 150 MoM modular acetabular components with 5- to 12-year follow-ups, the results related to adverse local tissue reactions and revisions were inferior when compared with those of metal-on-polyethylene articulations. Dhotare et al., in Hip International, reported an alarming failure-rate increase from 7% at six years to 29% at ten years for the Birmingham MoM cup and large metal head.
While we cannot turn back the clock on the past use of MoM devices, we have some information about surveillance and treatment that may help us prevent catastrophic failure.
Data regarding the effects of increasing serum metal ions are mixed. Some studies have found a direct correlation between high metal ion levels and the incidence of adverse tissue reactions (and the need for subsequent revision), while other studies have not. A recent JBJS study identified cobalt-ion thresholds that could help stratify patients with Birmingham and Corail-Pinnacle hips who are at low risk of metal-debris adverse reactions.
The systemic effects of increased serum metal ions are also being debated. Some case reports have cited neurotoxicity presenting as tinnitus, gait imbalance, and other issues, while a more recent, larger longitudinal study published in the Journal of Arthroplasty did not confirm this correlation. Those authors surmised that increased serum ion levels may cause neurotoxicity-associated symptoms primarily in MoM patients with metal hypersensitivity.
Metal artifact reduction sequence (MARS) MRI has been helpful in early identification of adverse soft tissue reactions. However, there is no general consensus or guideline as to when and how often this technology should be utilized in order to provide consistent surveillance and/or indications for revision.
While we are still trying to understand the finer points of the many variables related to MoM, there is an obvious need to forge consensus. Recently, in the Bone and Joint Journal, Berber et al., representing the International Specialist Centre Collaboration on MoM Hips (ISCCoMH), conducted a survey among six international tertiary referral centers to assess the overall consensus in surveillance and treatment practices. Only a moderate agreement value (kappa = 0.6) was found. This inconsistent agreement led the group to call for international coordination to help set forth guidelines that would standardize and improve surveillance of and treatment for those with MoM hips.
Richard S Yoon, MD is executive chief resident at the NYU Hospital for Joint Diseases.
