SRS109 - Reducing the surveillance burden in metal-on-metal hips: a risk-adapted three-tier model based on a large patient cohort

Abstract Background Over 60 000 metal-on-metal (MoM) hip implants have been implanted in the UK. Since 2017, MHRA guidelines have mandated broad surveillance, classifying any risk factor as high risk. This approach places major demands on services and risks over-surveillance. We aimed to develop a risk-adapted, three-tier pathway to safely reduce unnecessary follow-up. Methods We analysed 845 patients with MoM hip resurfacing and large-head total hip arthroplasty. The primary outcome was abnormal MRI or revision. Logistic regression identified independent predictors, translated into a clinical risk score, and ranked by each predictor relative contribution. Kaplan–Meier survival and interval-specific revision rates guided long-term risk estimates and follow-up intervals. Results Tier-1 predictors (adjusted OR) were female sex (2.0), bilateral (1.7) GFR < 60 (1.6), age < 50y (1.4), head size < 48 mm (1.2), and high-risk implant (1.2). Tier-2 predictors were abnormal X-ray (9.6), pain (2.8), abnormal metal-ion level (2.6), and other symptoms (1.4). The hierarchical model achieved sensitivity 0.69, specificity 0.73, and AUROC 0.71 at the Youden threshold. The MHRA approach had sensitivity 0.85, specificity 0.33, and AUROC 0.68. At 20 years, survival was 91.2% overall, 86.8% in high-risk, and 92.7% in low-risk groups. Beyond 10 years, cumulative revision risk was higher in high-risk patients (9.4 versus 4.1%); notably, 73.9% of late revisions in the low-risk group were symptomatic. Conclusions We propose a three-tier pathway: (1) baseline stratification; (2) surveillance of high-risk patients every 3 years with symptoms, radiographs, and optional metal ions; (3) MRI for Tier-2 abnormalities. Low-risk patients have limited benefits from follow-up beyond 10 years unless symptomatic.