Traditional assessment of health outcome following total knee arthroplasty was confounded by response shift phenomenon.

OBJECTIVES

To examine the existence, direction, and effect of response shift as measured by the total score of Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) and SF-36 physical and mental component score domains at 6 months and 1 year after primary total knee arthroplasty (TKA).

STUDY DESIGN AND SETTING

Consecutive candidates participated in the study. In line with the Then-test design, two sets of questionnaires were completed at 6 months and 1 year postoperatively. Patients were divided into three groups on the basis of minimal clinically important differences (MCIDs). Parametric and nonparametric statistics and generalized mixed effects models were used.

RESULTS

Two hundred and thirty-six patients completed the study. The magnitude of response shift increased over time for SF-36 physical and mental component scores. The traditional unadjusted presurgical and 1-year postsurgical assessment failed to reveal any mental health improvement, whereas the adjusted treatment effect demonstrated statistically significant changes.

CONCLUSION

Response shift phenomenon increases with time in patients undergoing orthopedic interventions. The traditional pre- and post-assessment of joint replacement surgery may be confounded by a change in perspective and in internal standards of measurement in patients undergoing surgery. Response shift has substantial impact on measuring recovery in this population.