Reducing the Surveillance Burden in Metal-on-Metal Hip Arthroplasties: A Risk-Adapted Three-Tier Model Based on a Large Patient Cohort.

BACKGROUND: Since 2017, the Medicines and Healthcare products Regulatory Agency (MHRA) in the United Kingdom (UK) has mandated comprehensive surveillance for patients with metal-on-metal (MoM) hips. We aimed to develop a risk-adapted follow-up pathway, with the goal of safely reducing unnecessary visits and investigations.

METHODS: We analyzed 845 MoM hip resurfacings and large-head MoM Total Hip Arthroplasty (THA). The primary outcome was abnormal magnetic resonance imaging (MRI) or revision. Logistic regressions identified the predictors, which were translated into a clinical risk score for Tier-1 and Tier-2.

RESULTS: In Tier-1, the strongest predictors (by adjusted odds ratio, aOR) were women (2.0), bilateral (1.7), glomerular filtration rate less than 60 (1.6), age less than 50 years (1.4), head size less than 48 mm (1.2), and high-risk implant (1.2). In Tier-2, the predictors were abnormal X-ray (10.6), pain (3.7), abnormal metal-ion level (2.5), and other symptoms (1.6). The hierarchical model, using thresholds of Tier-1 ≥ 3 and Tier-2 ≥ 2, achieved a sensitivity (0.84), a specificity (0.51), and an area under the receiver operating characteristic curve (AUROC) of 0.67. By comparison, the MHRA approach demonstrated a sensitivity (0.88), specificity (0.34), and an AUROC of 0.61. The hierarchical model reduced annual follow-up from 69 to 53%. High-risk reviews were extended to three-yearly, and low-risk surveillance was discontinued. This resulted in savings of £46,000 to £59,000 [$61,400 to $78,800] per 1,000 patients annually, a 75% reduction in workload compared with the MHRA approach.

CONCLUSIONS: We propose a risk-adapted, three-tier pathway: (1) baseline stratification into high- and low-risk groups using the clinical risk score; (2) surveillance of high-risk patients every three years, including symptom review, radiographs, and optional metal-ion testing; and (3) MRI reserved for patients who have Tier-2 abnormalities above the risk score. Low-risk patients have limited benefits from follow-up beyond 10 years unless symptomatic.