Abstract Background Second-generation metal-on-metal (MoM) bearings were reintroduced in total hip arthroplasty (THA) for their low wear rates, but despite initially promising results, concerns have emerged about adverse reactions to metal debris and poor long-term implant survival, with limited and conflicting evidence regarding the outcomes of small-diameter MoM implants. This study aimed to evaluate implant survival and metal wear complications in young patients with second-generation small-head MoM THA after more than 20 years. Methods A retrospective cohort study was conducted at a university center, analyzing 179 consecutive THAs in 160 patients aged under 55 years, using a small-head MoM bearing. After a minimum 20-year follow-up, clinical-radiological outcomes and systemic metal ion concentrations were assessed, with Kaplan–Meier analysis determining implant survival rates. Results Mean patient age at surgery was 46 years. After a mean follow-up of 23 years, 38 (21%) patients had deceased, and 9 (5%) patients were lost to follow-up. A total of 30 (16%) THAs had undergone revision surgery. The reasons for revision were metal wear-related complications in 11 hips (6%), aseptic loosening in 9 hips (5%), periprosthetic fractures in 6 hips (3%), periprosthetic joint infection in 3 hips (2%), and recurrent dislocation in 1 hip (1%). Of the non-revised THAs, the mean WOMAC score was 85.3. Osteolytic lesions were identified in 43% of hips with available radiographs (29/67), and elevated blood chromium or cobalt ion levels (> 2 µg/L) were detected in 22% of hips with available blood samples (11/51). Magnetic resonance imaging with metal artifact reduction sequence (MARS-MRI) was performed in 18 unrevised THAs, revealing a pseudotumor in 3 (17%). Kaplan–Meier survival rates at 25 years were 93% (95% CI: 87%–96%) for metal wear-related revisions and 77% (95% CI: 67%–85%) for any revision. Conclusions Second-Generation small-head MoM THA leads to acceptable implant survival rates and joint function more than 20 years after index surgery. Still, metal wear-related complications were the most frequent cause for revision (37%), and periprosthetic osteolysis was present in 43% of hips. This highlights the need for long-term monitoring into the third decade. Considering the superior performance of modern bearings, their use is recommended to avoid wear-related complications and revisions.
Falkenhayn et al. (Wed,) studied this question.