Patient-reported outcomes are increasingly used in evaluations of joint replacement surgery, but it is unclear if symptoms of osteoarthritis (i.e., pain and dysfunction) influence health perceptions similarly before and after surgery.
In this prospective study based on a hospital-based arthroplasty registry, patients with primary total hip or knee arthroplasty (THA, N = 990, and TKA, N = 907) completed the WOMAC Pain and Function scales, and the SF12 Physical and Mental Component Scores (PCS and MCS), before surgery and one year later. Associations between WOMAC and SF12 scales were examined using mixed linear regression models.
All patient-reported outcomes improved following total joint arthroplasty, but the associations between symptom scales and global health perceptions were altered. Mental health scores at a given level of pain or function were lower after surgery than before, by about 4-5 points, a clinically meaningful and statistically significant difference. In contrast, the associations between WOMAC scales and the PCS remained stable. These findings were observed in both cohorts of patients.
After total joint arthroplasty, mental health scores were lower than would have been expected given the symptomatic improvement. This suggests that relationships between patient-reported outcomes are context-dependent, and that care should be exerted when interpreting changes in patient-reported outcomes over time.