Self-Reported and Performance-Based Functions Differ for People With Tibiofemoral and Patellofemoral Osteoarthritis

To investigate compartment-specific concordance between self-reported measures (SRM) and performance-based measures (PBM) of physical function, and to compare the functional outcomes between isolated patellofemoral joint osteoarthritis (PFJ OA) and tibiofemoral joint osteoarthritis (TFJ OA) subgroups.

This cross-sectional study recruited 168 adults (45-65 years) with radiographically confirmed knee osteoarthritis (KOA). Participants were stratified into PFJ OA (n = 83) or TFJ OA (n = 85) using Multicenter Osteoarthritis Study (MOST)-adapted radiographic criteria and symptom profile. Self-reported function was measured using the Gujarati modified WOMAC (mWOMAC) physical function subscale. Performance-based functions were assessed with the OARSI minimum core set: 30-s Chair Stand Test (30-s CST), 40-m Fast-Paced Walk Test (40-m FPWT), and 11-step Stair Climb Test (11-step SCT). Pearson's correlations evaluated within-group associations; unpaired t-test compared groups.

TFJ OA participants reported significantly greater functional limitation on mWOMAC (45.8 ± 17.1) than the PFJ OA group (35.9 ± 12.8) (p < 0.001) despite objectively superior performance on 30-s CST (9.0 ± 2.2 vs. 7.4 ± 1.1 repetitions; p < 0.001) and 40-m FPWT (1.4 ± 0.4 vs. 0.9 ± 0.1 m/s; p < 0.001). Stair-climb time was comparable between groups (p = 0.969). Within-group correlations revealed task-specific patterns: PFJ OA showed strong correlation only with 11-step SCT (r = 0.589, p < 0.001), whereas TFJ OA exhibited moderate-to-strong correlations with 11-step SCT (r = 0.366) and 40-m FPWT (r = 0.646; both p < 0.001).

TFJ OA exhibits a striking paradox of greater perceived disability despite objectively better performance on the OARSI minimum core set. These findings highlight the limitation of relying on single assessment methods. A comprehensive assessment approach incorporating both self-reported and performance-based measures is recommended. Additionally, adopting an integrated compartment-specific evaluation framework is strongly advocated to facilitate precise clinical interpretation and optimise rehabilitation planning.