Outcomes of metal-on-metal hip arthroplasties surveillance in a tertiary center

BACKGROUND: Appropriate monitoring of metal-on-metal (MoM) hip arthroplasties has been suggested by some international orthopedic societies due to the early failures and higher-than-expected revision rates. In this study we aimed to describe: 1) the clinical and radiographic evaluations; 2) the metal ion level assessment; and 3) the revision rates of a consecutive MoM cohort enrolled in a surveillance program in a tertiary center. METHODS: All the patients treated with a MoM hip implant at The Rizzoli Orthopedics Institute since 2000 were enrolled in a surveillance program. Clinical evaluations (Harris Hip Score), radiographic evaluation (degree of osteolysis around acetabular and femoral components) and serum samples to identify cobalt and chromium ion levels were performed. Revisions were recorded. RESULTS: One thousand fifty-seven patients were identified and contacted. Among these, 646 patients performed a clinical and radiographic evaluation plus ion dosage while 143 patients answered a questionnaire. Harris Hip Score greater than 90 was obtained by 60% of monolateral and bilateral hip resurfacing implants and by 40% of monolateral and bilateral stemmed hip arthroplasties at first follow-up. Patients with a cobalt ion level higher than 60 g/L were 3% at the first serum ion dosage. Revisions were performed in 5% of the cases. CONCLUSIONS: Metal-on-metal (MoM) hip arthroplasties surveillance in a tertiary center achieved a modest patients' adherence and identified less than 10% of problematic implants, mainly among stemmed hip arthroplasties.