Long-term outcome following total knee arthroplasty: a controlled longitudinal study

Janet Cushnaghan ¹, James Bennett ¹, Isabel Reading ¹, Peter Croft ², Patricia Byng ¹, Ken Cox ¹, Paul Dieppe ³, David Coggon ¹ and Cyrus Cooper ^1*

¹ University of Southampton, United Kingdom
² School of Postgraduate Medicine, United Kingdom
³ University of Bristol, United Kingdom

^* To whom correspondence should be addressed. E-mail: cc{at}mrc.soton.ac.uk.

Accepted 22 April 2008

Abstract

Objectives: To assess long-term outcome and predictors of prognosis following total knee arthroplasty (TKA) for osteoarthritis.

Methods: We followed-up 325 patients from three English health districts approximately six years after TKA, along with 363 controls selected from the general population. Baseline data, collected by interview and examination, included age, sex, comorbidity, body mass index (BMI), functional status, and pre-operative radiographic severity of osteoarthritis. Functional status at follow-up was assessed by postal questionnaire. Predictors of change in physical function were analysed by linear regression.

Results: Between baseline and follow-up, patients reported an improvement of 6 points in median SF-36 physical function score whereas in controls there was a deterioration of 14 points (p<0.0001). Median SF-36 vitality score declined by 10 points in patients and 5 points in controls (p=0.005), while their median SF-36 mental health scores improved by 12 and 13 points respectively (p=0.2). The improvement in physical function was smaller in obese than in non-obese patients, but compared favourably with a substantial decline in the physical function of obese controls. Better baseline physical function and older age predicted worse changes in physical function in both patients and controls. Improvement in physical function tended to be greater in patients with more severe radiological disease of the knee, and was less in those who reported pain at other joint sites at baseline.

Conclusions: Improvements in physical function following TKA for osteoarthritis are sustained beyond five years. The benefits are apparent in obese as well as non-obese patients, and there seems no justification for withholding TKA from obese patients solely on the grounds of their body mass index.