The peak and impulse of patellofemoral joint force during running are not associated with pain severity or duration in adolescents with patellofemoral pain: An exploratory cross-sectional study

OBJECTIVES: Examine the association between the peak and impulse of patellofemoral joint force during running and the severity and duration of pain in adolescents with patellofemoral pain. DESIGN: Exploratory cross-sectional. PARTICIPANTS: Fifty-one physically active adolescents with patellofemoral pain (12-19 years). MAIN OUTCOME MEASURES: Kinematic, kinetic, and electromyography data were collected, and PFJ force (N) and impulse (N*s) during stance were estimated using an EMG-informed neuromusculoskeletal model. Pain was assessed as: (i) worst pain in the previous week (11-point numerical rating scale [NRS]), (ii) pain immediately after running (NRS), (iii) KOOS-Child pain (0-100), and (iv) pain duration (months). Associations were examined using linear regression adjusted for age, sex, and body mass. RESULTS: Each 100-N increase in peak patellofemoral joint force was associated with trivial changes of -0.01 (95% CI -0.03 to 0.01) in worst pain in the previous week, -0.02 (-0.05-0.01) in pain immediately following running, 0.01 (-0.19-0.21) in KOOS-Child pain, and -0.20 (-0.64-0.24) in duration of pain. Findings were similar for patellofemoral joint force impulse. CONCLUSION: These exploratory findings suggest the peak and impulse of patellofemoral joint force during running may not be important cross-sectional associates of pain severity or duration in adolescents with patellofemoral pain.