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This is a plain English summary of an original research article. The views expressed are those of the author(s) and reviewer(s) at the time of publication.

Partial knee replacements, when performed by experienced surgeons, can save costs and improve quality of life compared with total knee replacements. Partial replacements for selected patients improve quality of life and save between £600 and £2,000 over the patient’s lifetime, depending on age and gender.

Knee replacements are commonly performed for people with ongoing pain and poor function. If the damage is limited to one side of the knee, it may be suitable to replace just the affected side (unicompartmental replacement) rather than replacing the entire knee joint. This study compared costs and quality of life associated with both procedures using the National Joint Registry for England and Wales, with patients matched for baseline characteristics.

Partial knee replacements had the greatest certainty of being cost effective when performed for people aged over 60, and by surgeons familiar with the procedure. For the most benefit across the NHS orthopaedic surgeons may need further training in this procedure.

Why was this study needed?

Total knee replacement involves replacing the whole knee with an artificial joint. Partial knee replacement is less invasive, with faster recovery times, less pain and fewer complications. Currently about 11% of people need revision to a total knee replacement within ten years.

Up to half of the people referred for surgery could be eligible for a partial replacement but far fewer receive this and there is wide variation in availability across the UK. In 2017, there were about 100,000 knee replacements performed annually in England and Wales, and about 9% of these were partial replacements.

National guidelines do not recommend a particular approach. This study aimed to provide evidence about the cost-effectiveness of both procedures, which took account of factors such as surgeon experience and the revision rate.

What did this study do?

This cost utility analysis used data from the National Joint Registry in England and Wales collected between 2003 and 2012. Propensity scoring was used to match patients who would have been eligible for either procedure, giving a total 75,996 total knee replacements and 25,334 partial replacements. Subanalyses were performed by patient gender, age (younger than 60, 60-75 or over 75 years) and surgeon familiarity with partial knee replacement.

Lifetime primary and secondary healthcare costs, including any revision surgery performed in the following five years, were analysed using 2014/15 cost data.

Assumptions were made in the model, such as an estimation of revision rates and that patient quality of life would remain unchanged after six months. Researchers had no X-ray confirmation that patients would be eligible for partial knee replacement.

What did it find?

  • Partial knee replacement was estimated to be a more cost effective use of NHS resources than total knee replacement for all age and gender subgroups. However, it had greater certainty of being cost effective for older adults, and when performed by experienced surgeons.
  • For patients over 60 years partial replacement was 100% certain to be below the threshold of £20,000 per additional year of quality life gained (QALY). Compared with total replacement, the procedure was associated with gains of 0.19 to 0.20 QALYs at cost savings of £1,355 to £2,005 for men aged 60-75 years and over 70 years, respectively. Women in these age groups saw even greater QALY gains of 0.28 to 0.44 with savings of £935 to £1,102.
  • By comparison, partial replacement was only 87% certain to be the more cost effective option for men under 60 years (QALY gain 0.12 and £1,223 saving) and 72% certain to be cost effective for women under 60 years (QALY gain 0.10 and £601 saving).
  • Partial knee replacement was certain to be cost effective when performed by surgeons who carried out partial replacements at a ratio of at least 10% of all knee replacements they performed (average 27%). For these surgeons, there were 0.26 QALY gains at £758 saving compared with total knee replacement. Partial replacement was only 37% likely to be cost effective when performed by those less familiar with the procedure (usage under 10%, average 6%).
  • More revisions were required following partial knee replacement, across all age groups. However, quality of life was estimated to be better both before and following the revision than with total replacement, and the hospital costs of both the primary and revision procedure were lower. As such partial replacement remained the most cost effective option in all scenarios.

What does current guidance say on this issue?

NICE guidelines on the management of osteoarthritis (2014) cover patient criteria for referral for joint surgery, but do not include recommendations on a whether there is a preferred surgical procedure for knee replacement.

A NICE guideline on knee replacements is due to be published in March 2020 that looks at the clinical and cost-effectiveness of total compared with partial knee replacement.

What are the implications?

As with all economic models, there are inherent limitations from the assumptions made, and patient characteristics may still differ between those having partial or total replacement. Yet partial knee replacement in the right hands and for selected patients seems likely to be the better use of NHS resources, particularly for older patients.

Surgeon expertise and experience of the procedure seems important. If this procedure is to become more widely adopted across the NHS further training in its use may be required. Availability of newer unicompartmental techniques, such as the use of uncemented components, may also influence surgical choice, duration of surgery and patient outcomes.

Citation and Funding

Burn E, Liddle AD, Hamilton TW, et al. Cost-effectiveness of unicompartmental compared with total knee replacement: a population-based study using data from the National Joint Registry for England and Wales. BMJ Open. 2018;8(4):e020977.

This study was funded by Zimmer Biomet and the National Institute for Health Research Oxford Biomedical Research Centre.



Burn E, Liddle AD, Hamilton TW, et al. Choosing between unicompartmental and total knee replacement: what can economic evaluations tell us? A systematic review. Pharmacoecon Open. 2017;1:241–53.

Liddle AD, Judge A, Pandit H, Murray DW. Adverse outcomes after total and unicompartmental knee replacement in 101 330 matched patients: a study of data from the National Joint Registry for England and Wales. Lancet. 2014;384:1437-45.

NICE. Osteoarthritis: care and management. CG177. London : National Institute for Health and Care Excellence; 2014.

Produced by the University of Southampton and Bazian on behalf of NIHR through the NIHR Dissemination Centre


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