Background: The aim of this study was to validate
the Knee Society Clinical Rating System (knee and function scores)
and to compare its responsiveness with that of the Western Ontario
and McMaster University Osteoarthritis Index (WOMAC) and the Medical
Outcomes Study Short Form-36 (SF-36).
Methods: Patients were recruited as part of a prospective
observational study of the outcomes of primary total knee arthroplasty
for the treatment of osteoarthritis in four centers in the United
States, six centers in the United Kingdom, and two centers in Australia.
Independent research assistants at each site collected the Knee
Society clinical data. The WOMAC, SF-36, patient satisfaction, and
demographic data were obtained with self-administered questionnaires.
Results: A total of 862 eligible patients were recruited,
and complete preoperative and twelve-month data were available for
697 (80.9%) of them. The mean age was seventy years (range,
thirty-eight to ninety years), and the majority of the patients
(58.9%) were women. Low correlations were found among the
items of both the knee and the function score at both assessment
times. The Knee Society pain and function scores had moderate-to-strong
correlations with the corresponding pain and function domains of
the WOMAC and SF-36 (r = 0.31 to 0.72). Measurement of
the standardized response mean showed the Knee Society knee score
to be more responsive (standardized response mean, 2.2) than the WOMAC
(standardized response means, 2.0 for pain and 1.4 for function)
and the SF-36 (standardized response means, 1.0 for bodily pain
and 1.1 for physical functioning). The Knee Society function score
was the least responsive measure (standardized response mean, 0.8).
Correlation of changes in scores at twelve months with patient reports
of satisfaction and improvement in health status showed the WOMAC
and SF-36 to be more responsive than the Knee Society scores.
Conclusions: There is a poor correlation among the
items of the Knee Society Clinical Rating System, but the rating
system has adequate convergent construct validity. The WOMAC and
SF-36 are more responsive measures of outcome of total knee arthroplasty.
As they are less labor-intensive for researchers to use and as use
of these instruments removes observer bias from the study design,
they are preferable for knee arthroplasty outcome studies.