Late-stage medial compartment knee osteoarthritis can be treated using total knee replacement or partial (unicompartmental) knee replacement. There is high variation in treatment choice and insufficient evidence to guide selection.
To assess the clinical effectiveness and cost-effectiveness of partial knee replacement compared with total knee replacement in patients with medial compartment knee osteoarthritis. The findings are intended to guide surgical decision-making for patients, surgeons and health-care providers.
This was a randomised, multicentre, pragmatic comparative effectiveness trial that included an expertise component. The target sample size was 500 patients. A web-based randomisation system was used to allocate treatments.
Twenty-seven NHS hospitals (68 surgeons).
Patients with medial compartment knee osteoarthritis.
The trial compared the overall management strategy of partial knee replacement treatment with total knee replacement treatment. No specified brand or subtype of implant was investigated.
The Oxford Knee Score at 5 years was the primary end point. Secondary outcomes included activity scores, global health measures, transition items, patient satisfaction (Lund Score) and complications (including reoperation, revision and composite 'failure' - defined by minimal Oxford Knee Score improvement and/or reoperation). Cost-effectiveness was also assessed.
A total of 528 patients were randomised (partial knee replacement, 
It was not possible to blind patients in this study and there was some non-compliance with the allocated treatment interventions. Surgeons providing partial knee replacement were relatively experienced with the procedure.
Further (10-year) follow-up is in progress to assess the longer-term stability of these findings.
Current Controlled Trials ISRCTN03013488 and ClinicalTrials.gov NCT01352247.
This project was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme and will be published in full in 
Two types of knee replacement are available for patients with arthritis of the inner part of their knee: a partial knee replacement or a total knee replacement. It is not known which replacement offers most benefit for the patient or for the health-care system.
We performed a large study involving 528 patients at 27 hospitals with 68 experienced surgeons, in which half of the patients underwent partial knee replacement and the other half underwent total knee replacement. We took yearly scores and measures, including pain, function, whether or not the operation was successful, and the costs of each patient for 5 years. Comparison between treatments was assessed at 5 years post operation.
Good outcomes and relatively few complications were observed after both operations. The measurements taken to assess the clinical benefit were largely very similar between the two groups. Where differences did occur at 5 years, there were only small differences between the two knee replacements and partial knee replacement was generally favoured. Some measurements, however, did show a larger difference between the two groups, including whether or not the operation addressed the patients’ problems and whether or not the patient would have the operation again. These measurements were also in favour of partial knee replacement, but caution is required not to overstate importance, as patients in the study knew which device they had had implanted. The number of patients requiring further operations or revision surgery was similar in the two groups. This last finding contrasts with information from previously obtained, mainly non-randomised, studies and is of high relevance. The cost of each operation in relation to the benefit obtained was clearly in favour of partial knee replacement.
Both operations are effective for use in the NHS. There appear to be some modest clinical advantages for patients to undergo partial knee replacement over total knee replacement but, importantly, the study casts doubt over previous concerns on high reoperation rates for partial knee replacement. The study has shown that reoperation rates recorded from different sources (cohort or trials) can be conflicting.
Both total knee replacement and partial knee replacement are effective, offer similar clinical outcomes and have similar reoperation and complication rates. Some patient-reported measures of treatment approval were significantly higher for partial knee replacement than for total knee replacement. Partial knee replacement was more cost-effective (more effective and cost saving) than total knee replacement at 5 years.