Background: There is no good evidence to support the use of patient-reported outcome measures (PROMs) in setting preoperative thresholds for referral for hip and knee replacement surgery. Despite this, the practice is widespread in the NHS.
Objectives/research questions: Can clinical outcome tools be used to set thresholds for hip or knee replacement? What is the relationship between the choice of threshold and the cost-effectiveness of surgery?
Methods: A systematic review identified PROMs used to assess patients undergoing hip/knee replacement. Their measurement properties were compared and supplemented by analysis of existing data sets. For each candidate score, we calculated the absolute threshold (a preoperative level above which there is no potential for improvement) and relative thresholds (preoperative levels above which individuals are less likely to improve than others). Owing to their measurement properties and the availability of data from their current widespread use in the NHS, the Oxford Knee Score (OKS) and Oxford Hip Score (OHS) were selected as the most appropriate scores to use in developing the Arthroplasty Candidacy Help Engine (ACHE) tool. The change in score and the probability of an improvement were then calculated and modelled using preoperative and postoperative OKS/OHSs and PROM scores, thereby creating the ACHE tool. Markov models were used to assess the cost-effectiveness of total hip/knee arthroplasty in the NHS for different preoperative values of OKS/OHSs over a 10-year period. The threshold values were used to model how the ACHE tool may change the number of referrals in a single UK musculoskeletal hub. A user group was established that included patients, members of the public and health-care representatives, to provide stakeholder feedback throughout the research process.
Results: From a shortlist of four scores, the OHS and OKS were selected for the ACHE tool based on their measurement properties, calculated preoperative thresholds and cost-effectiveness data. The absolute threshold was 40 for the OHS and 41 for the OKS using the preferred improvement criterion. A range of relative thresholds were calculated based on the relationship between a patient's preoperative score and their probability of improving after surgery. For example, a preoperative OHS of 35 or an OKS of 30 translates to a 75% probability of achieving a good outcome from surgical intervention. The economic evaluation demonstrated that hip and knee arthroplasty cost of < £20,000 per quality-adjusted life-year for patients with any preoperative score below the absolute thresholds (40 for the OHS and 41 for the OKS). Arthroplasty was most cost-effective for patients with lower preoperative scores.
Limitations: The ACHE tool supports but does not replace the shared decision-making process required before an individual decides whether or not to undergo surgery.
Conclusion: The OHS and OKS can be used in the ACHE tool to assess an individual patient's suitability for hip/knee replacement surgery. The system enables evidence-based and informed threshold setting in accordance with local resources and policies. At a population level, both hip and knee arthroplasty are highly cost-effective right up to the absolute threshold for intervention. Our stakeholder user group felt that the ACHE tool was a useful evidence-based clinical tool to aid referrals and that it should be trialled in NHS clinical practice to establish its feasibility.
Future work: Future work could include (1) a real-world study of the ACHE tool to determine its acceptability to patients and general practitioners and (2) a study of the role of the ACHE tool in supporting referral decisions.
Funding: The National Institute for Health Research Health Technology Assessment programme.
Keywords: ARTHROPLASTY; COST–UTILITY ANALYSIS; HIP; KNEE; OSTEOARTHRITIS; OUTCOME; REFERRAL; SYSTEMATIC REVIEW; THRESHOLD.
Patients with severe hip and knee arthritis may require joint replacement. General practitioners make the decision to refer patients to hospital based on an assessment of their symptoms. Pain and function can be measured using patient questionnaires and the questionnaire scores can indicate whether or not the severity of disease warrants referral (i.e. whether or not the patient is a candidate for joint replacement based on their ‘capacity to benefit’). However, we do not know whether or not basing treatment decisions on such scores is correct, nor do we know what exact pain score thresholds should be used for referral. After a thorough search, we found that the Oxford Hip and Knee Scores were the best instruments. A high score (i.e. a maximum score of 48) indicates less pain and better function. The threshold values for referral for surgery were scores of 40 for hips and 41 for knees. The process of evaluating scoring systems, the choice of scoring systems and the threshold values were discussed and agreed by a panel of patients and by doctors throughout the study. Most patients with severe joint pain benefit from joint replacement, and these operations are cost-effective. However, above a certain level (a score of 40 for hips and 41 for knees), patients are not thought to typically benefit from surgery. Below these values, lower presurgery scores indicate a steadily increasing likelihood of benefit in terms of reduced pain and better function. This information provides the basis for a tool to help doctors decide who to refer for joint replacement: the Arthroplasty Candidacy Help Engine (ACHE). Use of the ACHE tool prevents patients who are unlikely to benefit from joint replacement being referred unnecessarily and allows the NHS to concentrate resources on those who will benefit most from arthroplasty treatment.