Rationing of total knee replacement: a cost-effectiveness analysis on a large trial data set

Abstract

Objectives

Many UK primary care trusts have recently introduced eligibility criteria restricting total knee replacement (TKR) to patients with low pre-operative Oxford Knee Scores (OKS) to cut expenditure. We evaluate these criteria by assessing the cost-effectiveness of TKR compared with no knee replacement for patients with different baseline characteristics from an NHS perspective.

Design

The cost-effectiveness of TKR in different patient subgroups was assessed using regression analyses of patient-level data from the Knee Arthroplasty Trial, a large, pragmatic randomised trial comparing knee prostheses.

Setting

34 UK hospitals.

Participants

2131 osteoarthritis patients undergoing TKR.

Interventions and outcome measures

Costs and quality-adjusted life years (QALYs) observed in the Knee Arthroplasty Trial within 5 years of TKR were compared with conservative assumptions about the costs and outcomes that would have been accrued had TKR not been performed.

Results

On average, primary TKR and 5 years of subsequent care cost £7458 per patient (SD: £4058), and patients gained an average of 1.33 (SD: 1.43) QALYs. As a result, TKR cost £5623/QALY gained. Although costs and health outcomes varied with age and sex, TKR cost <£20 000/QALY gained for patients with American Society of Anaesthesiologists grades 1–2 who had baseline OKS <40 and for American Society of Anaesthesiologists grade 3 patients with OKS <35, even with highly conservative assumptions about costs and outcomes without TKR. Body mass index had no significant effect on costs or outcomes. Restricting TKR to patients with pre-operative OKS <27 would inappropriately deny a highly cost-effective treatment to >10 000 patients annually.

Conclusions

TKR is highly cost-effective for most current patients if the NHS is willing to pay £20 000–£30 000/QALY gained. At least 97% of TKR patients in England have more severe symptoms than the thresholds we have identified, suggesting that further rationing by OKS is probably unjustified.

Trial registration number

ISRCTN 45837371.

Article summary

Article focus

• We assess the cost-effectiveness of total knee replacement (TKR) compared with no knee replacement for patients with different baseline characteristics from a NHS perspective.

• In particular, we assess the appropriateness of eligibility criteria recently introduced by many UK primary care trusts, which restrict TKR to patients with low (ie, poor) pre-operative Oxford Knee Scores (OKS) to cut expenditure.

Key messages

• We find TKR to be highly cost-effective, costing £5623 per quality-adjusted life year gained for the average patient.

• TKR costs <£20 000 per quality-adjusted life year gained for healthy patients with OKS of <40 or <35 for patients who have other conditions restricting their daily activities.

• We find no evidence to support the criteria for restricting access to TKR that have been proposed by some primary care trusts and calculate that restricting TKR to those patients with pre-operative OKS of 26 or less would deny a highly cost-effective treatment to >10 000 patients/year.

Strengths and limitations of this study

• This is the first study assessing how the cost-effectiveness of TKR varies with OKS and the first assessing the clinical/economic implications of the newly introduced rationing criteria.

• Analyses are based on patient-level data from a large pragmatic trial with detailed prospective collection of utilities, baseline characteristics and all major knee-related NHS resource use, including revisions and ambulatory care.

• Our study makes several highly conservative assumptions: in particular, assuming that patients would have accrued no knee-related costs and remained at baseline utility without TKR. Furthermore, the Knee Arthroplasty Trial sample included only 37 patients with pre-operative OKS >35. As result, TKR may be also cost-effective for some patients with OKS above 39.