Abstract
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. 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? 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. 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. The ACHE tool supports but does not replace the shared decision-making process required before an individual decides whether or not to undergo surgery. 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 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. The National Institute for Health Research Health Technology Assessment programme.
Highlights
Research questions specified in the National Institute for Health Research Health Technology Assessment research call l Can clinical tools for assessment of a patient’s suitability for knee or hip replacement be used to set thresholds for an operation?Hip and knee osteoarthritis is a common musculoskeletal condition causing significant pain and loss of function for patients
The study has shown that the Oxford Hip Score (OHS) and Oxford Knee Score (OKS) can be used for assessment of a patient’s suitability for knee or hip replacement using thresholds for candidacy based on the individual’s capacity for or probability of improving
Our work has shown that hip and knee replacement, when undertaken in any patients with preoperative scores below the absolute OKS and OHS thresholds, is extremely cost-effective
Summary
The national outcomes data have revealed that 10–15% of patients undergoing hip or knee joint replacement are not satisfied with their treatment, and these findings, for the knee patients, are supported by other recent studies.[8,9] It has been suggested that selecting patients too early in their disease process may play a role in producing dissatisfaction with surgery.[9] Overall, these findings suggest that there is no standardisation to the process by which patients are assessed and selected for hip and knee replacement surgery This is a particular concern given both the projected increased need for joint replacement over the decade to accommodate an ageing population and the pressure of potential reductions in NHS funding.[10].
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