In spite of the cumulating evidence for the prognostic relevance of illness perceptions regarding the course of disease and recovery of hip and knee joint patients, there are still no studies that examine the effects of these perceptions on postoperative functioning as assessed by clinical ratings. The aim of this inception cohort study was to describe the course of functioning following a hip or knee joint replacement over a period of one year and to analyse moderator-type effects of illness perceptions in order to develop strategies for preoperative counselling and postoperative rehabilitation.
The course of functioning following a hip joint replacement was assessed by the Harris hip score (HHS), the course of functioning following a knee joint replacement by the American Knee Society score (AKSS). Illness perceptions were assessed by the brief illness perception questionnaire. Due to the non-linear relationship of time and functional outcome, time was transformed using a log transformation. Moderator-type effects were analysed by interaction terms of log time and illness perceptions.
For 135 patients the course of the HHS was analysed, for 127 patients the course of the AKSS. Results after one year confirmed a successful treatment for 82.3 % of the hip patients and 70.6 % of the knee patients. Hip patients expecting an enduring illness had lower scores on the HHS after one year (p = 0.026). The expectation that the treatment will be helpful was associated with a better outcome (p = 0.002). The outcome of knee patients was moderated by the degree how concerned they were about their illness (p = 0.016).
The results confirmed the prognostic relevance of illness perceptions for the functional outcome and indicate the importance of preoperative counselling and the potential benefit of patient-oriented education that is aimed at modifying illness perceptions.