The use of patient-reported outcome measures to guide referral for hip and knee replacement: Part 1 – the development of an evidence based model linking pre-operative score to the probability of gaining benefit from surgery

Objective: To calculate how the likelihood of obtaining measurable benefit from hip or knee replacement varies with pre-operative patient-reported scores to guide decision-making and referrals. Design: Existing UK data from 222,933 knee and 209,760 hip replacement patients were used to model an individual’s probability of gaining meaningful improvement after surgery based on their pre-operative Oxford Knee or Hip Score (OKS/OHS). A clinically-meaningful improvement after joint replacement was defined as an ≥8 point improvement in OHS, and ≥7 for OKS. Results: The upper pre-operative score threshold, above which patients are unlikely to achieve any meaningful improvement from surgery, is 41 for knees and 40 for hips. At lower scores, the probability of improvement increased towards a maximum of 87% (knee) and 94% for (hips). Conclusion: Patients with pre-operative scores above 41 (OKS) and 40 (OHS) should not be routinely referred to secondary care for possible joint replacement. Using lower thresholds would incrementally increase the probability of meaningful benefit for those referred but will exclude some patients with potential to benefit. The findings are useful to support the shared decision-making process for referral to secondary care and should not be used in isolation. The output can also help, but not replace, the complex shared decision-making process in secondary care delivered by experienced clinicians.