The trial was approved by the relevant national and local research ethics committees and was registered in a public trials registry (International Standard Randomized Trial No. ISRCTN45837371). Any orthopaedic surgeon in the United Kingdom who performed knee replacements regularly was eligible to participate in the trial. One hundred and sixteen surgeons in thirty-four centers in the United Kingdom participated in the KAT study, and ninety-nine (85%) of these surgeons recruited patients to the patellar resurfacing comparison.
All patients under the care of a participating surgeon were potentially eligible for inclusion in the overall study if they were scheduled to undergo a primary total knee arthroplasty. A patient was not eligible for a particular comparison within the study if the surgeon considered only one of the two surgical procedures in that comparison to be indicated.
Suitable alternative prosthesis designs were available for each of the possible randomized choices within the study. Surgeons followed their standard practice, and the outcomes would thus not have been influenced by a so-called learning-curve effect. We did not influence surgeons regarding the choice between a cruciate-retaining and a cruciate-substituting implant. All other aspects of patient care were left to the discretion of the responsible surgeon.
The primary outcome measure was the functional status as measured with use of the Oxford Knee Score (OKS)21, which was developed specifically to measure outcomes of knee replacement and has been shown by independent studies to perform well compared with alternative outcome instruments22-24. A power calculation indicated that 1400 participants would provide 80% power to detect a 1.5-point difference in the OKS (two-tailed p < 0.05). Secondary outcome measures included the quality of life as measured with use of the Short Form-12 (SF-12)25 and the EuroQoL 5D (EQ-5D)26,27, intraoperative and postoperative complications including the need for subsequent surgery, cost, and cost-effectiveness. In addition, question 12 of the OKS was analyzed in isolation as a secondary outcome since it assesses the ability to walk downstairs, which is one aspect of knee function that patellar resurfacing may influence. The five possible responses for question 12 were “No, impossible” (scored as 0), “With extreme difficulty” (1), “With moderate difficulty (2), “With little difficulty” (3), and “Yes, easily” (4).
Patients were randomized to receive or not receive patellar resurfacing with use of computer-generated random numbers obtained via an automated, centralized telephone service. Randomization was stratified by surgeon, with minimization according to patient age (less than 60 years, 60 to 79 years, or 80 years or older), sex, and location of disease (one knee, both knees, or general arthritis). Patients were not blinded to treatment allocation.
Preoperative, operative, and postoperative data on the surgery, knee components used, length of hospital stay, operative time, and complications were collected prospectively on standard forms. This information was supplemented with routinely collected information from the Hospital Episode Statistics (HES) database in England or the Information Services Division (ISD) in Scotland if such data were available. Data describing functional status and quality of life were obtained directly from questionnaires completed by participants preoperatively, at three months after the operation, at one year, and annually thereafter. Patients who did not return the questionnaire were offered the option of completing the questionnaire over the telephone. The questionnaire included the OKS, SF-12, and EQ-5D, as well as questions regarding hospital admissions and ambulatory consultations with general practitioners, physical therapists, and hospital physicians related to the involved knee. The patient's case notes were reviewed if the questionnaire or the HES or ISD data indicated subsequent knee-related surgery or hospital readmissions, and such events were classified according to severity. The severity categories were (1) patella-related reoperation (late patellar resurfacing or surgical treatment of a patellar fracture), (2) major reoperation (revision arthroplasty or amputation), (3) minor or intermediate reoperation (an operation with a degree of severity between that of wound closure and that of manipulation under anesthesia, or an operation due to arthrofibrosis), and (4) readmission or other subsequent intervention (any readmission or any intervention such as an injection).
List prices for knee components were obtained from manufacturers; a 30% discount was applied to list prices to reflect the price likely to be paid by a typical hospital, although the actual discounts would vary. Other estimated unit costs are listed in the Appendix, along with the sources from which they were derived. Unit costs and resource use data were combined to calculate the total cost per patient associated with the knee arthroplasty during the first five years. The total cost included the costs associated with the hospital stay for the primary arthroplasty and for any related readmissions, the operating room used for the primary arthroplasty and for any subsequent related surgery, the knee arthroplasty components, blood transfusions, computed tomography or ultrasonographic scans, and consultations with general practitioners, physical therapists, and outpatient physicians related to the involved knee. Cost analyses were conducted from the perspective of the health system and thus excluded any costs incurred by patients or their employers. Costs incurred after the first postoperative year were discounted at 3.5% per year28. Full details of the cost analysis and the results of sensitivity analyses will be reported separately.
Data were analyzed on the basis of the procedure allocation, regardless of the method of knee replacement that was actually used (i.e., analysis was performed on the basis of the intention-to-treat principle). Functional status and quality-of-life outcomes were compared with use of an analysis of covariance that adjusted for baseline scores and the minimization factors. The proportion of patients with readmissions and/or subsequent surgery was analyzed with use of logistic regression analysis; rare events were analyzed with use of the exact logistic regression command in Stata Version 11.0 (StataCorp, College Station, Texas). Descriptive statistics are presented when appropriate, and effect sizes are presented with associated 95% confidence intervals (CIs) estimated with use of robust standard errors to account for potential surgeon effects.
Since 44% (732) of the 1671 patients analyzed had missing data for at least one resource use item and some missing data (for example, length of stay for a revision procedure) were not missing completely at random, a complete case analysis of cost data would have been inefficient and prone to bias29. We therefore used the ICE command30 in Stata to impute missing data regarding component prices and resources with use of multiple imputation29,31. Multiple imputation predicts missing values by iteratively estimating regression models based on observed and imputed data; this enabled missing data on specific resource items to be imputed on the basis of the patient's age, sex, and treatment allocation; the quantities of other resources that they required; and the correlations observed among these variables for other patients. Imputation was performed on the entire trial dataset (with the exception of patients excluded after randomization). Costs are presented as the mean and standard deviation for each group and are expressed in pounds Sterling at 2007-2008 prices (£1 = US$2 in 2007-2008). The mean difference (and 95% CI) between groups was calculated across the ten imputed datasets with use of the MICOMBINE command in Stata.
Source of Funding
The Knee Arthroplasty Trial was funded by the National Institute for Health Research (NIHR) Health Technology Assessment programme (project number 95/10/01). Additional funding for research support at the clinical centers was provided by Stryker Orthopaedics (formerly Howmedica Osteonics) (Newbury, Berkshire, United Kingdom); Zimmer (Swindon, Wiltshire, United Kingdom); DePuy, a Johnson & Johnson company (Leeds, United Kingdom); Corin Medical (Cirencester, Gloucestershire, United Kingdom); Smith & Nephew Healthcare (Cambridge, United Kingdom); Biomet Merck (Bridgend, South Wales, United Kingdom); and Wright Medical (formerly Wright Cremascoli) (Woking, Surrey, United Kingdom). Core funding for the Health Services Research Unit was provided by the Chief Scientist Office of the Scottish Government Health Directorates. The Musculoskeletal Biomedical Research Unit in Oxford was funded by the NIHR. The Health Economics Research Centre in Oxford received some core funding from NIHR.
The results of the current study indicate that patient functional status, patient quality of life, and total cost during the first five years after total knee arthroplasty are not significantly affected by the addition of patellar resurfacing to the initial surgical procedure. The 95% confidence interval for the difference in the OKS between the patellar resurfacing group and the nonresurfacing group was –0.6 to 1.8 at five years postoperatively. A clinically important difference on the OKS scale is believed to be approximately 3 points, and a 2-point difference is of possible clinical significance. This study was adequately powered to detect a clinically important difference, even taking into account the fact that some participants did not receive the allocated procedure. Similarly, there was no evidence of a clinically relevant difference in the EQ-5D or the SF-12.
Although the proportion of patients who underwent a patella-related reoperation was higher in the nonresurfacing group than in the patellar resurfacing group (2% compared with 1%), the difference was not statistically significant. The 2% rate of late resurfacing in the nonresurfacing group compares favorably with those in other published series of total knee arthroplasty in which the patella was not resurfaced12. The rate of late resurfacing was 5% in the subgroup of patients who were allocated to receive resurfacing during the initial operation but did not receive resurfacing at that time. The explanation for this observation is not obvious, but these patients may have been more likely to request resurfacing if they were aware that they had not received the expected patellar resurfacing previously, or their surgeons may have been more likely to advise them to have patellar resurfacing to treat any residual anterior knee pain. The results of this study suggest that a patient who receives a late resurfacing typically undergoes a gradual reduction in the knee functional score during the years prior to the resurfacing followed by an improvement after the resurfacing, but that the postoperative score does not reach the typical score reached by a patient following a first procedure. Patients to whom late resurfacing is recommended should be advised that this procedure is unlikely to provide complete relief of knee pain.
Although the proportion of patients undergoing a reoperation was higher in the nonresurfacing group than in the resurfacing group (5.8% compared with 4.4% for minor to intermediate reoperation and 2.9% compared with 1.6% for major reoperation), the differences were not statistically significant. It is striking that the rate of further surgery for almost every reason, and particularly for the treatment of an infection, was higher in the nonresurfacing group than in the resurfacing group. Nevertheless, we believe that these findings are probably due to random variations and do not indicate clinically important differences.
Patellar resurfacing significantly increased component costs for the primary operation by £85 (US$170 in 2007-2008) and also increased the costs associated with operating room time and the length of the hospital stay, although the latter increases did not reach statistical significance. A more detailed cost breakdown that specifically accounted for the cost of the bone cement and sterilization of the instruments required for patellar resurfacing (rather than including the latter in the operating room overhead) might have resulted in a further slight increase in the incremental cost of resurfacing. However, the added cost incurred during the primary hospital stay was offset by a significant (p = 0.033) reduction in the cost associated with readmission for major surgery during the first five postoperative years. As a result, the economic analysis showed that the total health care cost during the first five years did not differ significantly between the groups. The price that National Health Service (NHS) hospitals in the U.K. pay for knee components is currently highly variable, and consequently the cost at a particular hospital may differ from the mean cost used in this analysis. However, varying the estimated discount between 0% and 50% of the manufacturer's list price did not alter our overall conclusions. A full economic evaluation is planned once all patients have been followed for eight years.
In conclusion, on the basis of five years of follow-up, there is no clear benefit to resurfacing the patella during total knee arthroplasty, as resurfacing had no significant effect on patient functional status, total treatment cost, or patient quality of life. Five years after the total knee arthroplasty, 2% of nonresurfaced patellae had required late resurfacing and 0.2% of resurfaced patellae had failed because of fracture. While the number of patellar failures may increase somewhat by ten years postoperatively, some surgeons may consider resurfacing the patella to be the preferred option because it is expected to offer a lower reoperation rate. Conversely, there should be no criticism of surgeons who elect not to resurface the patella during total knee arthroplasty, as the majority of patients will require no further patellar surgery.
Note: Central Trial Office (Aberdeen): Suzanne Breeman, Marion Campbell, Susan Campbell, Adrian Grant, Mark Kelaher, Anne Langston, Graeme MacLennan, Kirsty McCormack, Craig Ramsay, Sue Ross, Luke Vale, Allan Walker. Regional Coordinators (Dundee and Oxford): Kim Clipsham (Oxford), Jo Copp (Oxford), Linda Johnston (Dundee), Doug McGurty (Dundee), Lesley Morgan (Oxford), Sarah Poulter (Oxford). Other Collaborators: Alan Price, Julie Rowsell (Alexandra Hospital, Redditch); Rose Finley, Sue Gardner, Richard W Parkinson (Arrowe Park Hospital, Wirral); Liz Jackson, Iain Lennox, Timothy Peckham, John Targett, Rob Wakeman (Basildon & Thurrock University Hospital, Basildon); Stephen Hughes, Karen Humby, Carol Quick (Birmingham Heartlands Hospital); Jennifer Burbidge, Tony Chapman, Nicola Sheehan (Calderdale Royal Hospital, Halifax); Polly Emmitt, Marek Karpinski, Margaret Newman, Andre T. Plotka, Javed Salim, Kevin P. Sherman (Castle Hill Hospital, Hull); Ian Braithwaite, David Campbell, Janet Durrans, Karen Edwards, Sandra D. Flynn, Andrew Phillipson (Countess of Chester Hospital); Debbie Carpenter, Charles Grant, Linda Smith (Diana, Princess of Wales Hospital, Grimsby); Anthony Brewood, Carmel Cliffe, Ronan McGiveney, Diane Ross (Fairfield General Hospital, Bury); Lesley Plummer, Lavinia Psarras, Timothy Tasker, Norma White, Andrew Williams (Gloucestershire Royal Hospital); Julie Cunningham, Jane Hopkins (Goole & District Hospital); Kathleen Duncan, Robert Allan Dunsmuir, Alberto Gregori (Hairmyres Hospital, East Kilbride); Samir N. Amarah, Carol Donald, Peter Sewell, Timothy Vaughan-Lane, Alison Rosen (Hinchingbrooke Hospital, Huntingdon); Ian Archer, Stuart Calder, Mark Emerton, Gillian Johnston, David MacDonald, Martin Stone (Leeds General Infirmary & St James University Hospital); Susan Finch, Graham Keys, Susan Smith (Macclesfield District General Hospital); Paul Gregg, Anthony Chi Wing Hui, Ian Wallace, Lisa Wood (Middlesbrough General Hospital); Anna David, Malcolm Downes, Ceri Hodinott, Mark Holt, Tim James, Kath Law, Robert Leyshon, Sharon Maggs, David Newington, Neil Price (Morriston Hospital, Swansea); Graham Foubister, Amir Jain, Linda Johnston, Doug McGurty, Manhal Nassif, David Rowley (Ninewells Hospital, Dundee); Nagi Darwish, William Farrington, Nigel Giles, Sunil Jain, Debbie Ludwell, Christopher Mills, Michael Podmore, Nicholas Treble, Peet Van Der Walt (North Devon District Hospital, Barnstaple); Lesley Boulton, David Miller (North Tees General Hospital, Stockton-on-Tees); Gavin Bowden, Kim Clipsham, Chris Dodd, Max Gibbons, Damion Griffin, Roger Gundle, Peter McLardy Smith, Lesley Morgan, David Murray, Sarah Poulter, Rob Sterling (Nuffield Orthopaedic Centre, Oxford); Arthur Espley, Jamie McLean, Lorna O'Donnell, Audrey Reilly (Perth Royal Infirmary), Katrina Boeree, Peter Cox, Keith Eyres, Graham A. Gie, Nigel Giles, Matthew Hubble, Peter Schranz, John Timperley (Princess Elizabeth Orthopaedic Centre, Exeter); Anthony Fogg, Michael Foy, John Ivory, Ian M.R. Lowden, Eve Middleton, David M. Williamson, David Woods (Princess Margaret Hospital, Swindon), Tim Cane, Hugh Clark (Queen Alexandra Hospital, Portsmouth); Ganapathyraman Mani, Anthony Percy, Sudhir Rao, Mark Rowntree, Colin Smart, Helen Stanger (Queen Mary's Hospital, Sidcup); Nick Fiddian, Gwen Newton (Royal Bournemouth Hospital); John Davidson, Simon Journeaux, Jill Pope (Royal Liverpool University Hospital); Janet Jessop, Una Jude, Louise Mitchell, Peter Molitor, Karen Watts (Scunthorpe General Hospital); Benjamin Bolton Maggs, Grahame Robertson (St. Helens & Knowsley Hospitals NHS Trust); Richard Buckley, Sarah Jane Keogh, Pete Rickhuss, Val Sutherland, Neil Valentine (Stracathro Hospital, Brechin); Colin M. Mainds (Victoria Infirmary, Glasgow); Clark Dreghorn, Eric G. Gardner, Peter D. Scott, Rhona Shields (Victoria Infirmary, Glasgow); G. Paddy Ashcroft, Ann Galt, Peter H. Gibson, Jimmy D Hutchison, Alan Johnstone, David Knight, William Ledingham, Anne Potter (Woodend Hospital, Aberdeen); Noor Ahmed, Tracey Dennehy, Alison Lawrence, E. Rouholamin (Worcester Royal Infirmary Trust); Laura Hobbs, Geoffrey Taylor, Kenneth Wise (Wycombe General Hospital)