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Dates: Ongoing collaboration since 1999
Funding: NIHR Health Technology Assessment programme (HTA)
Collaborators: NDORMSUniversity of Aberdeen, University of Dundee 
Information: Helen Dakin

More than 20,000 knee replacements are performed annually in the UK. The hospital cost of these replacements is approximately £70 million per year. However, before the KAT trial, remarkably little was known about the actual cost of the procedure, hospital stay or complications in the short, medium or long term, or which type of prosthesis is best value for money.

KAT comprises a pragmatic, randomised controlled trial evaluating four knee replacement technologies:
• Metal backing of the tibial component compared with a single high-density polyethylene component
• Patellar resurfacing compared with no resurfacing
• Polyethylene mobile bearing compared with fixed bearing arthroplasty
• Uni-compartmental compared with total knee replacement

Recruitment was completed in 2003, with more than 2,300 participants being randomised at 34 UK centres. The fourth comparison was discontinued due to recruitment difficulties and has been evaluated in the TOPKAT trial.

The main clinical outcome measures used in the trial comprised the Oxford Knee Score (OKS), Short Form 12-Item Health Survey (SF-12), EuroQol (EQ-5D) and intra-operative and post-operative complications, including the need for further surgery. The economic analysis included a costing analysis at five years and a full cost-utility analysis at median 10 years to compare the costs, benefits and cost-effectiveness of each of the technologies evaluated in the trial. Patients have now been followed up for 20 years and a final analysis is currently underway.

Ten-year clinical and economic results for the first three comparisons demonstrated that:
• Participants had poor functional status and quality of life before undergoing knee replacement, although all study groups showed marked improvement within three months of surgery.
• Around 15% of patients were readmitted to hospital regarding their knee or underwent additional knee surgery within 10 years of their primary operation.
• There were no statistically significant differences between randomised groups in terms of functional status, quality of life or complications over the first 10 years after total knee replacement.
• Patella resurfacing dominated no resurfacing, non-significantly improving quality of life and decreasing cost.
• Metal backing improved quality of life at a small cost, costing £35 per QALY gained compared with all polyethylene.
• Mobile bearings were also associated with increased cost and small improvements in quality of life and cost £1,666 per QALY gained, although there was substantial uncertainty around this conclusion.


Murray, DW, Maclennan, GS, Breeman, S, Dakin, HA, Johnston, L, Campbell, MK, Gray, AM, Fiddian, N, Fitzpatrick, R, Morris, RW, and Grant, AM (2014). A randomised controlled trial of the clinical effectiveness and cost-effectiveness of different knee prostheses: the Knee Arthroplasty Trial (KAT). Health Technol Assess, 18(19):1-236.

Breeman S, Campbell M K, Dakin H, Fiddian N, Fitzpatrick R, Grant A, Gray A, Johnston L, Maclennan G S, Morris R W, and Murray D W (2013). Five-year results of a randomised controlled trial comparing mobile and fixed bearings in total knee replacement. Bone Joint J, 95-B(4):486-92.

Breeman, S, Campbell, M, Dakin, H, Fiddian, N, Fitzpatrick, R, Grant, A, Gray, A, Johnston, L, Maclennan, G, Morris, R, and Murray, D (2011). Patellar resurfacing in total knee replacement: five-year clinical and economic results of a large randomized controlled trial. J Bone Joint Surg Am, 93(16):1473-81.

Campbell, M, Fiddian, N, Fitzpatrick, R, Grant, A, Gray, A, Morris, R, Murray, D, Rowley, D, Johnston, L, MacLennan, G, McCormack, K, Ramsay, C, and Walker, A (2009). The Knee Arthroplasty Trial (KAT) design features, baseline characteristics, and two-year functional outcomes after alternative approaches to knee replacement. J Bone Joint Surg Am, 91(1):134-41

For further information on the trial, see:

KAT data are also being used for the ACHE study

Rationing Criteria for Knee Replacement

HERC researchers have evaluated the rationing criteria recently introduced by many UK Primary Care Trusts (PCTs) by assessing how the cost-effectiveness of knee replacement varies with Oxford Knee Score (OKS). In research published in the BMJ Open journal in January 2012, Helen Dakin, Alastair Gray and collaborators have analysed data from the knee arthroplasty trial (KAT) using regression techniques. They find that the cost-effectiveness of total knee replacement varies with OKS, but that knee replacement remains cost-effective for healthy patients with OKS <40. Furthermore, they found that the rationing criteria restricting knee replacement for patients with high-moderate OKS that have recently been introduced by many UK PCTs would deny a cost-effective treatment to more than 10,000 patients per year.


Dakin, H, Gray, A, Fitzpatrick, R, Maclennan, G, Murray, D, and Trial Group, (2012). Rationing of total knee replacement: a cost-effectiveness analysis on a large trial data set. BMJ Open, 2(1):e000332.

Mapping from Oxford Knee Score (OKS) to EQ-5D

KAT data were used to develop an algorithm mapping from the Oxford Knee Score (OKS) to the three-level EQ-5D using direct and response mapping techniques. The resulting response mapping algorithm was published in Quality of Life Research. A Stata command facilitating application of the mapping algorithm in other datasets was published in the Stata Journal and is available by typing “net describe st0305” into Stata. An Excel version (which includes a simplified mapping algorithm for situations where only secondary data are available) is available at


Dakin, H, Gray, A, and Murray, D (2013). Mapping analyses to estimate EQ-5D utilities and responses based on Oxford Knee Score. Qual Life Res, 22(3):683-94.

Ramos-Goñi, J, Rivero-Arias, O, and Dakin, H (2013). Response mapping to translate health outcomes into the generic health-related quality of life instrument EQ-5D: Introducing the mrs2eq and oks2eq commands. Stata Journal, 13(3):474-491.