Abstract
Medical and Health care products Regulatory Agency (MHRA) released an alert in 2010 regarding metal on metal (MoM) bearings in hip arthroplasty owing to soft tissue reactions to Metal debris. Following this, we adopted a targeted screening protocol to review patients with this bearing couple.
218 Patients (252 hips), mean age 53.2 (25–71) years were assessed clinically using Oxford hip score (OHS) and X-ray examination. The mean follow up was 44.5 (12–71) months. Patients were considered at higher risk (118 patients/133 hips) if they had deterioration of OHS (50 hips), Small sized heads <50mm (114 hips), acetabular inclination >500 (37 hips), neck thinning (17 hips). These patients (107/118), (120/133 hips) were further investigated through measuring metal ion levels and magnetic resonance imaging (MRI).
The mean blood levels of cobalt and chromium in this group were 6.7, 8.62 ug/L respectively. Metal ions increased significantly with high acetabular inclination angles (p=0.01, 0.004 respectively), but was not affected by the size of the head (p=0.13). MRI showed periprosthetic lesions around 28 hips (26 fluid collections, 2 pseudotumours).
The screening protocol detected all patients who subsequently required elective revision. We believe that this protocol was beneficial in detecting problematic MoM hip replacements.
