The longitudinal relationship between physical capacity and self-perceived physical functioning after total hip and knee arthroplasty.

Objective: To examine longitudinal within-person effects between capacity and self-perceived performance during postoperative physiotherapy in patients with total hip and knee arthroplasty (THA/TKA). Methods: We performed a secondary analysis of a cluster randomized controlled trial on physiotherapy after THA and TKA using random intercept cross lagged panel models. Capacity was assessed with the 40-m fast-paced walk test (40 m FPWT) and the 30-s chair-stand test (30-s CST), and self-perceived performance with the Oxford Hip/Knee Score functioning subscale (OHS/OKS) and the Hip disability/Knee injury and Osteoarthritis Outcome Score-Physical function Short form (HOOS-PS/KOOS-PS). Assessments were performed preoperatively and at 3 and 12 months postoperatively. Results: 312 THA (mean age 66, SD: 9; 53% female) and 312 TKA (mean age 67, SD: 8; 55% female) were included. From pre-surgery to 3 months, no effects were found between capacity and self-perceived performance in either THA or TKA.From 3 to 12 months, in THA, 40 m FPWT performance at 3 months had a positive effect (β 0.34, 95% CI 0.05-0.63 Conclusion: From pre-surgery to 3 months, capacity and self-perceived performance showed no effects within individuals. However, during the early postoperative phase, gait speed may be a relevant treatment target to improve long-term self-perceived performance.