Pseudotumors in small-head metal-on-metal total hip arthroplasties at a minimum follow-up of 20 years.

Abstract Background Metal-on-metal (MOM) surfaces in total hip arthroplasty (THA) have been used widely. Serum cobalt and chromium levels have been the standard investigation for follow-up examinations, but magnetic resonance imaging (MRI) with metal-artifact reducing sequences has shown good results in detecting pseudotumors. The aim of the study was to check for a significant correlation between MRI findings, serum metal levels and clinical scores in patients with small-head metal-on-metal implants and if serum cobalt and chromium levels are sufficient in detecting patients with pseudotumors in the long-term follow-up. Methods At a minimum follow-up of 20 years, 26 patients (29 THAs) of the originally 98 patients (105 THAs), included in this study between November 1992 and May 1994 were available for follow-up examination. Clinical scores, serum metal-ion levels and MRI were obtained. Results We found mean serum cobalt levels of 1.87 μg/L (±3.44) and chromium levels of 2.23 μg/L (±2.96) and very good clinical and functional results (mean HHS 88.6) in the long-term follow-up. Pseudotumors were detected in MRIs of 21 hips. There were no significant differences between patients with or without pseudotumors regarding serum metal levels and the correlation for clinical outcome scores, demographic data and cup inclination. The cumulative rate of survival was still at 91.4% at 22.8 years. Conclusion This study presents the first published data on small-head metal-on-metal hips, comparing metal ion levels, pseudotumors, clinical and radiological results in a follow-up period of more than 20 years and reveals that serum metal levels are not significantly higher in patients with pseudotumors.