Objective: To evaluate the effect of pre-intervention factors in patient-reported outcomes at 6 months post-operatively following total knee replacement.
Methods: A prospective observational study was carried out using two questionnaires sent to patients while they were on the waiting list for surgery: a generic questionnaire, the Medical Outcomes Study Short Form-36 (SF-36), and a specific questionnaire, the Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC). Six months after intervention, patients again received the same questionnaires. The dependent variables were the scores of the three domains of the WOMAC and the eight domains of the SF-36.
Results: We recruited 640 patients. The mean age was 71 yrs and 73.6% of the patients were females. The multivariate analysis, in which the pre-intervention scores for each domain were added as covariates, showed that the most significant pre-intervention predictors were the baseline scores of each domain. Besides that, the social support, low back pain and the baseline score of the mental health domain (SF-36) were the pre-intervention predictors in the three WOMAC domains. With regard to the SF-36 domains the main predictors were the baseline mental health score, comorbidities, low back pain and social support.
Conclusions: The main predictor of outcome at 6 months post-operatively in all eleven domains was the pre-intervention score of each domain. Presence of social support, absence of low back pain and higher baseline SF-36 mental health score were related to the improvement in the health-related quality of life post-operatively.