Condition category
Musculoskeletal Diseases
Date applied
Date assigned
Last edited
Retrospectively registered
Overall trial status
Recruitment status
No longer recruiting

Plain English Summary

Background and study aims
In knee replacement surgery (knee arthroplasty), all or part of a damaged knee joint is 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 is safer. The aim of this study is therefore 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?

Who can participate?
Patients undergoing knee replacement surgery

What does the study involve?
Participants can take part in one or two of the four study comparisons depending on the extent and type of disease in their knee. In each comparison participants are randomly allocated to one of two knee operations (i.e., knee cap resurfacing or no resurfacing; fixed bearing or mobile bearing; all plastic or plastic-and-metal tibial component; partial or total knee replacement). All participants are asked to complete postal questionnaires after three months and annually thereafter up to 20 years after the surgery. The postal questionnaires ask about knee function, general quality of life and healthcare costs. Information is also collected about any complications and further hospital admissions and operations.

What are the possible benefits and risks of participating?
Participants may not benefit personally from taking part in the study but they will be helping doctors to assess which operations are best and safest. We do not think there are any additional risks or disadvantages to participants. Whichever group they are allocated, their operation will be performed by an experienced orthopaedic surgeon. Steps are always taken to make sure that any possible risks are minimised. As part of routine care, participants will be well informed of potential risks.

Where is the study run from?
University of Oxford (UK)

When is the study starting and how long is it expected to run for?
December 1998 to June 2023

Who is funding the study?
Health Technology Assessment Programme (UK)

Who is the main contact?
Prof. David Murray

Trial website

Contact information



Primary contact

Prof David Murray


Contact details

Nuffield Orthopaedic Centre
University of Oxford
Windmill Road
United Kingdom
+44 (0)1865 227457



Additional contact

Dr Suzanne Breeman


Contact details

University of Aberdeen
Health Services Research Unit
Health Sciences Building
AB25 2ZD
United Kingdom

Additional identifiers

EudraCT number number

Protocol/serial number

HTA 95/10/01

Study information

Scientific title

A randomised controlled trial of different knee prostheses


KAT (Knee Arthroplasty Trial)

Study hypothesis

A UK wide network of clinical centres will be established to conduct randomised partial factorial trials on current practice of knee replacement. Independent management by health services research units is a feature of the application. Individual surgeons will be invited to consider areas of uncertainty concerning current knee prosthetic and participate in randomisation between certain design aspects of knee replacement systems which are otherwise similar in all other respects.
The project will require two phases, each of six years. At end of first phase, the trial will demonstrate short to medium-term variations in costs and outcome relating to the four management options. The second phase is necessary in order to demonstrate prosthesis design-related adverse events. This trial will produce authoritative data to inform purchasers, providers, consumers and clinicians about this very commonly performed procedure in the NHS.

More details can be found at:

Protocol can be found at:

Ethics approval

Multi-centre Research Ethics Committee for Scotland, 30/11/1998, ref: MREC/98/0/100

Study design

Randomised controlled trial

Primary study design


Secondary study design

Randomised controlled trial

Trial setting


Trial type


Patient information sheet

Not available in web format, please use the contact details below to request a patient information sheet


Primary knee replacement surgery


Current interventions as of 23/01/2009:
The trial is evaluating four aspects of knee replacements:
1. Metal backing of the tibial component compared with a single high density polyethylene component (350 participants)
2. Patellar resurfacing compared with no resurfacing (1400 participants)
3. A polyethylene mobile bearing component between the tibia and femur compared with a fixed bearing arthroplasty (350 participants)
4. Uni-compartmental arthroplasty compared with total knee replacement (350 participants)

Individual patients can participate in a maximum of two comparisons and then only if the surgeon responsible for care is substantially uncertain about these particular aspects.

Previous interventions:
The four management options are:
1. Metal versus non-metal backing of the tibial component
2. Whether to resurface the patella
3. Unicompartmental versus total knee arthroplasty
4. Mobile versus fixed bearing

Intervention type



Not Applicable

Drug names

Primary outcome measure

Current primary outcome measures as of 23/01/2009:
Oxford Knee Score (postal questionnaire) at 3 months and then annually thereafter.

Previous primary outcome measures:
Outcomes will be in terms of complications and patient-assessed pain and function, principally conducted by post.
Costings include those relating to
1. Early complications expected immediately post operatively from medical effects
2. Medium-term complications such as dislocation and infection
3. Late complications of wear, loosening and infection.

Secondary outcome measures

Added as of 23/01/2009:
Complications and patient-assessed pain and function, assessed principally by postal questionnaires including:
1. SF-12
2. EQ-5D
3. Questions about any further hospital admissions and surgery
4. Costings:
4.1. Early complications expected immediately post-operatively from medical effects
4.2. Medium-term complications such as dislocation and infection
4.3. Late complications of wear, loosening and infection

Questionnaires are completed at 3 months and then annually thereafter.

Overall trial start date


Overall trial end date


Reason abandoned (if study stopped)


Participant inclusion criteria

Added as of 23/01/2009:
1. A decision has been made to have primary knee replacement surgery
2. The surgeon has no clear preference for a specific option in at least one of the comparisons
3. Both males ane females, no age limits

Participant type


Age group




Target number of participants


Participant exclusion criteria

Does not meet inclusion criteria

Recruitment start date


Recruitment end date



Countries of recruitment

United Kingdom

Trial participating centre

University of Oxford
United Kingdom

Trial participating centre

University of Aberdeen
Health Services Research Unit
AB25 2ZD
United Kingdom

Sponsor information


Department of Health (UK)

Sponsor details

Quarry House
Quarry Hill
United Kingdom

Sponsor type




Funder type


Funder name

Health Technology Assessment Programme

Alternative name(s)

NIHR Health Technology Assessment Programme, HTA

Funding Body Type

government organisation

Funding Body Subtype

National government


United Kingdom

Results and Publications

Publication and dissemination plan

To be confirmed at a later date

Intention to publish date

Participant level data

Available on request

Basic results (scientific)

Publication list

2009 results in
2012 cost-effectiveness analysis results in
2014 results in

Publication citations

  1. Results

    Murray DW, MacLennan GS, Breeman S, Dakin HA, Johnston L, Campbell MK, Gray AM, Fiddian N, Fitzpatrick R, Morris RW, Grant AM, , A randomised controlled trial of the clinical effectiveness and cost-effectiveness of different knee prostheses: the Knee Arthroplasty Trial (KAT)., Health Technol Assess, 2014, 18, 19, 1-235, vii-viii, doi: 10.3310/hta18190.

  2. , Johnston L, MacLennan G, McCormack K, Ramsay C, Walker A, 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, 2009, 91, 1, 134-141, doi: 10.2106/JBJS.G.01074.

  3. Dakin H, Gray A, Fitzpatrick R, Maclennan G, Murray D, , Rationing of total knee replacement: a cost-effectiveness analysis on a large trial data set., BMJ Open, 2012, 2, 1, e000332, doi: 10.1136/bmjopen-2011-000332.

Additional files

Editorial Notes

31/05/2016: the overall trial end date was changed from 31/12/2010 to 30/06/2023. 27/02/2009: Please note that an incorrect target number of participants was entered in this trial record at time of registration. Therefore, the number (413 participants) has been amended to the correct number (approximately 2,450).