Predictive factors of ion release in large head metal-on-metal THA: what really matters?

METHODS: Patients treated with metal-on-metal total hip arthroplasty (MoM-THAs) from 2007 to 2012 were preliminarily included. Clinical registered data included: age, gender, BMI, time between surgery and blood sample, physical activity, Harris Hip Score at follow-up, leg length discrepancy and femoral head size. At postoperative X-ray were collected: acetabular inclination and anteversion, femoral offset, stem subsidence and osteolysis. A multivariate linear regression model was used to determine factors that influence metal ion release. RESULTS: A total of 191 MOM-THAs were included. The average levels of metal ions were 2.03 and 1.95 μg/L respectively for cobalt (Co) and chromium (Cr). Thirty-four patients showed values of Cr or Co out of the range of normality. Ten patients (10/34) underwent revision surgery performed in 7 cases for a pseudotumor. The female gender, the UCLA Score and the cup inclination showed a direct correlation with Cr serum levels. The BMI<25 and an increase in femoral offset (FO) showed a direct correlation with Co serum levels. CONCLUSIONS: Our data suggest that female gender, physical activity, cup inclination, BMI<25 and an increase in FO are predictors of higher serum metal ion levels. These patients might be at increased risk for adverse reaction to metal debris thus a particular surveillance is suggested. KEY WORDS: Metal-on-metal joint prostheses; Arthroplasty, replacement, hip; Chromium; Cobalt; Pseudotumor cerebri