Is quadriceps strength associated with patellofemoral joint loading after anterior cruciate ligament reconstruction?

Objective: To test whether quadriceps strength is associated with measures of patellofemoral (PF) joint loading during running and hopping in people after an anterior cruciate ligament reconstruction (ACLR). Design: Cross-sectional study. Setting: Biomechanics laboratory. Participants: Sixty-five participants (24 women; 41 men) 1–2 years post-ACLR. Main outcome measures: Peak isometric quadriceps strength for the surgical limb was measured using a dynamometer. Motion analysis and ground reaction force data were combined with musculoskeletal modelling to measure PF joint loading variables for the reconstructed knee (peak knee flexion angle; peak/impulse of the PF joint contact force; time to peak PF joint contact force) during the stance phase of running and during the landing phase of a standardised forward hop. Linear regression analysis (adjusting for age and sex) assessed the association between quadriceps strength and PF joint loading variables. Results: Two significant, albeit modest, associations were revealed. Quadriceps strength was associated with the time to peak PF joint contact force during running (β = −0.001; 95%CI -0.002 to −0.000; R² = 0.179) and the impulse of the PF joint contact force during hopping (β = 0.014; 95%CI 0.003 to 0.024; R² = 0.159). Conclusions: A strong link between quadriceps strength and PF joint loading was not evident in people 1–2 years post-ACLR.