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Standardised Thresholds for Hip and Knee Replacement Surgery – the Arthroplasty Candidacy Help Engine (ACHE) Tool: A Systematic Review, & Clinical & Economic Analysis

Research output: Contribution to journalArticle

Original languageEnglish
JournalHealth Technology Assessment
DateAccepted/In press - 11 May 2018


There is no good evidence to support the use of patient reported healthcare measures (PROMs)in setting pre-operative thresholds for referral for hip and knee replacement surgery. Despitethis, the practice is widespread in the NHS.Objectives/Research QuestionsCan clinical outcome tools be used to set thresholds for hip or knee replacement? What is therelationship between the choice of threshold and the cost-effectiveness of surgery?MethodsA systematic review identified patient-reported outcome measures used to assess patientsundergoing hip/knee replacement. Their measurement properties were compared andsupplemented by analysis of existing datasets. For each candidate score, we calculated theabsolute threshold (a pre-operative level above which there is no potential for improvement)and relative thresholds (pre-operative levels above which individuals are less likely to improvethan others). Due to their measurement properties and the availability of data from their currentwidespread use in the NHS, the Oxford Knee and Hip Scores (OKS/OHS) were selected as themost appropriate scores to use in developing the ACHE tool. The change in score and theprobability of an improvement were then calculated and modelled using pre and post-operativeOKS/OHS, PROM scores thereby creating the ACHE tool. Markov models were used to assessthe cost-effectiveness of total hip/knee arthroplasty (THA/TKA) in the NHS for different preoperativevalues of OKS/OHS over a 10-year period. The threshold values were used to modelhow ACHE may change the number of referrals in a single UK musculoskeletal hub. A usergroup was established including patients, the public and healthcare representatives, to providestake-holder feedback throughout the research process.ResultsFrom a short-list of four scores, the OHS and OKS were selected for ACHE, based on theirmeasurement properties, calculated pre-operative thresholds, and cost-effectiveness data. Theabsolute threshold for the OHS was 40 and 41 for the OKS using the preferred improvementcriterion. A range of relative thresholds were calculated based on the relationship between a13patient’s pre-operative score and their probability of improving after surgery. For example apre-operative OHS of 35 or an OKS of 30 translates to a 75% probability of achieving a goodoutcome from surgical intervention. The economic evaluation demonstrated that hip and kneearthroplasty cost <£20,000 per quality-adjusted life-year (QALY) in patients with any preoperativescore below the absolute thresholds (41 for OHS and 42 for OKS). Arthroplasty wasmost cost-effective at lower pre-operative scores.LimitationsThe ACHE tool supports but does not replace the shared decision making process requiredbefore an individual decided whether to undergo surgery or not.ConclusionThe Oxford hip and knee scores can be used in the ACHE tool to assess individual patients’suitability for hip/knee replacement surgery. The system enables evidence-based and informedthreshold setting according to local resources and policies. On a population level bothinterventions are highly cost-effective right up to the absolute threshold for intervention. Ourstake-holder user group felt the ACHE tool was a useful evidence-based clinical tool to aidreferrals which should be trialled in NHS clinical practice to establish its feasibility.Future work1. A real-world study of ACHE determining its acceptability with patients and GPs.2. A study of the role of ACHE in supporting referral decisions.Funding detailsThe research was funded through the NIHR HTA programme.KeywordsKnee, Hip, Osteoarthritis, Arthroplasty, Referral, Outcome, Systematic review, Outcome,Threshold, Cost-utility analysis

    Research areas

  • Knee, Hip, Osteoarthritis, Arthroplasty, Referral, Outcome, Systematic review, Threshold, Cost-utility analysis



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