Patellofemoral cartilage stresses are most sensitive to variations in vastus medialis muscle forces

Abstract

The purpose of this study was to evaluate the effects of variations in quadriceps muscle forces on patellofemoral stress. We created subject-specific finite element models for 21 individuals with chronic patellofemoral pain and 16 pain-free control subjects. We extracted three-dimensional geometries from high resolution magnetic resonance images and registered the geometries to magnetic resonance images from an upright weight bearing squat with the knees flexed at 60°. We estimated quadriceps muscle forces corresponding to 60° knee flexion during a stair climb task from motion analysis and electromyography-driven musculoskeletal modelling. We applied the quadriceps muscle forces to our finite element models and evaluated patellofemoral cartilage stress. We quantified cartilage stress using an energy-based effective stress, a scalar quantity representing the local stress intensity in the tissue. We used probabilistic methods to evaluate the effects of variations in quadriceps muscle forces from five trials of the stair climb task for each subject. Patellofemoral effective stress was most sensitive to variations in forces in the two branches of the vastus medialis muscle. Femur cartilage effective stress was most sensitive to variations in vastus medialis forces in 29/37 (78%) subjects, and patella cartilage effective stress was most sensitive to variations in vastus medialis forces in 21/37 (57%) subjects. Femur cartilage effective stress was more sensitive to variations in vastus medialis longus forces in subjects classified as maltrackers compared to normal tracking subjects (p = 0.006). This study provides new evidence of the importance of the vastus medialis muscle in the treatment of patellofemoral pain.

Keywords:

• Patellofemoral pain
• patellofemoral stress
• vastus medialis
• quadriceps force
• finite element modelling
• probabilistic modelling

Acknowledgements

We thank Christine Draper for help with data collection. This work was supported by the National Institutes of Health under grants EB0002524 and EB005790; U.S. Department of Veterans Affairs, Rehabilitation Research and Development Service under grants Merit Review Project A2592R and Pilot Project I01 RX000590-01. The contents of this publication do not represent the views of the U.S. Department of Veterans Affairs or the United States Government.

Disclosure statement

The authors have no conflict of interest to disclose related to this manuscript.