Patient characteristics modify the effects of education plus exercise on patellofemoral joint loading: a secondary effect-modifier analysis of a randomized controlled trial

Patellofemoral pain (PFP) is a multifactorial condition closely associated with deficits in knee and hip muscle strength, aberrant movement patterns, and psychological factors. These factors not only contribute to the onset and recurrence of pain but also influence patients’ responsiveness to rehabilitation interventions. This study aimed to evaluate how patients with PFP characterized by different baseline profiles respond to a combined intervention of patient education and exercise (EDU + EX) compared with exercise alone (EX). The findings are expected to provide empirical evidence supporting the precision and personalization of PFP rehabilitation strategies, while reducing unnecessary intervention costs associated with the indiscriminate implementation of patient education programs. Participants were randomly assigned to either the EDU + EX group or the EX group for an 8-week rehabilitation intervention, followed by a 20-week post-intervention assessment. The primary outcome measure was patellofemoral joint load. Potential effect modifiers included body mass index, Anterior Knee Pain Scale score, pain catastrophizing, fear of movement, hip–knee kinematic parameters, and hip and knee muscle strength. A linear mixed-effects model was employed to examine how these patient-specific characteristics influenced responsiveness to the EDU + EX and EX interventions. Compared with baseline, patellofemoral joint load was significantly reduced after 8 weeks of intervention in both the EDU + EX group (3.46, P = 0.0013) and the EX group (3.38, P < 0.001). Patients with PFP exhibiting gluteus minimus strength < 8.37 N/kg (2.93, 95% CI: − 6.28 to 0.42), gluteus medius strength < 16.82 N/kg (–3.46, 95% CI: − 7.14 to 0.50), vastus lateralis strength < 44.87 N/kg (1.86, 95% CI: − 5.03 to 1.31), or a Tampa Scale for Kinesiophobia score > 37 (–11.45, 95% CI: − 15.47 to − 2.13) were more likely to benefit from the EDU + EX intervention. In contrast, PFP patients with gluteus minimus strength > 8.37 N/kg (3.29, 95% CI: − 0.58 to 7.15) or vastus lateralis strength > 44.87 N/kg (4.15, 95% CI: 1.37 to 6.93) demonstrated greater improvement following the EX intervention. For PFP patients with hip muscle weakness, knee muscle imbalance, or elevated fear of movement, the EDU + EX intervention demonstrates superior comprehensive benefits by improving postural control and cognitive–behavioral adaptation, thereby enhancing rehabilitation outcomes. In contrast, for patients with sufficient hip and knee strength and stable psychological profiles, the EX intervention alone appears adequate to meet rehabilitation demands. This stratified intervention strategy may enhance the efficiency of resource utilization while maintaining therapeutic effectiveness.