Title: A randomised controlled trial of different knee prostheses - extended follow-up
Funder: Department of Health and Social Care

Abstract: The Knee Arthroplasty Trial (KAT) is the largest randomised trial of total knee replacement (TKR) conducted to date. It addresses three key aspects of TKR design: patella resurfacing, mobile bearings, and metal backed tibial components. A total of 116 surgeons in 34 UK centres participated and 2352 participants were randomised between June 1999 and December 2002. Participants were randomised, using a partial factorial design, to receive patella resurfacing or not (1715 participants), a mobile or fixed bearing (539 participants), and a metal backed or all polyethylene tibial component (409 participants). Demographic and surgical information was collected at baseline and at the time of the operation. Patient reported outcome data (Oxford Knee Score (OKS), SF-12 and EQ-5D) were collected through annual questionnaires. Information about complications, readmissions, reoperations and costs were also collected through a combination of postal questionnaire and data linkage. The results at a median of 10 years of follow-up identified a number of small but important differences in knee function, quality of life and complications of the different approaches. 1. No significant difference in clinical outcome, in terms of pain and function, complications, readmission or reoperations was found between participants with or without patella resurfacing. However, there was a non-significant trend towards improved quality of life and decreased costs associated with resurfacing. As a result patella resurfacing was found to be cost-effective compared with no resurfacing. 2. No definite advantage or disadvantage of mobile bearings in OKS, quality of life, reoperation and revision rates or cost-effectiveness was found. 3. An improved functional result for metal-backed tibias was found, although complication, reoperation and revision rates were similar. The metal-backed tibia was found to be cost-effective, particularly in the elderly. However, with TKR, problems tend to occur after ten years and clinical differences between designs are likely to occur at this stage. Further follow-up was therefore required to assess the stability of these findings over time. This extended follow-up study will therefore continue to collect the same outcome measures (OKS, SF-12, EQ-5D, postoperative complications including the need for additional surgery, costs, and cost-effectiveness) to 20 years post-randomisation through a combination of patient–reported annual questionnaires and data linkage.

Lay abstract: In knee replacement surgery (knee arthroplasty), all or part of a damaged knee joint are replaced with metal and/or plastic components. Various approaches to knee replacement surgery are used and different designs are available. It was not clear which works better or are safer. The KAT trial therefore set out to answer three questions: • Should the back surface of the knee cap routinely be resurfaced with an additional plastic part? • Should the metal and plastic parts of the knee replacement be firmly fixed together (fixed bearing), or should the plastic part be mobile to allow more normal knee movement (mobile bearing)? • Should the part of the knee replacement that attaches to the shin bone (the tibial component), be all-plastic or plastic with a metal backing? Between July 1999 and December 2002, 2,352 people who were having knee replacement surgery in 34 hospitals across the UK agreed to take part. Surgical complications, knee function, quality of life, and healthcare costs up to an average of 10 years after surgery was initially assessed and a number of small but important differences in knee function, quality of life and complications of the different approaches were identified. 1. Knee cap resurfacing was associated with slightly improved quality of life and slightly lower costs than not resurfacing. This meant that there was high level of certainty (at least 95%) that knee cap resurfacing gives good value for money compared to not resurfacing. 2. No appreciable differences were found between knee replacement with mobile and fixed bearings. 3. People who had metal-backed tibial components had improved quality of life compared to people who had all-plastic tibial components. However the metal-backed tibial components had slightly higher costs. There was a high level of certainty (91%) that metal-backed components offered better value for money compared with all-plastic components. Because people are now living longer with knee replacements and problems tend to occur in the long term, we will continue to follow-up participants for 20 years after surgery to assess how the knee replacements function in the long term.

Research activity codes: 6.4 SURGERY
Health categories: MUSCULOSKELETAL