Sagittal plane biomechanics cannot injure the ACL during sidestep cutting.

BACKGROUND Knee joint sagittal plane forces are a proposed mechanism of anterior cruciate ligament injury during sport movements such as sidestep cutting. Ligament force magnitudes for these movements however, remain unknown. The need to examine injury-causing events suggests elucidation via model-based investigations is possible. Using this approach, the current study determined whether sagittal plane knee loading during sidestep cutting could in isolation injure the anterior cruciate ligament. METHODS Experiments were performed on subject-specific forward dynamic musculoskeletal models, generated from data obtained from 10 male and 10 female athletes. Models were optimized to simulate subject-specific cutting movements. Random perturbations (n=5000) were applied to initial contact conditions and quadriceps/hamstrings activation levels to simulate their effect on peak 3D knee loads. Injury via the sagittal plane mechanism was based on the criterion of an anterior drawer force greater than 2000 N. FINDINGS Realistic neuromuscular perturbations produced significant increases in external knee anterior force and valgus and internal rotation moments. Peak anterior drawer force never exceeded 2000 N in any model, and thus failed to cause anterior cruciate ligament injuries. Valgus loads reached values that were high enough to rupture the ligament, occurring more frequently in females than in males. INTERPRETATION Sagittal plane knee joint forces cannot rupture the anterior cruciate ligament during sidestep cutting. The interaction between muscle and joint mechanics and external ground reaction forces in this plane, places a ceiling on ligament loads. Valgus loading is a more likely injury mechanism, especially in females. Modifying sagittal plane biomechanics will thus unlikely contribute to the prevention of anterior cruciate ligament injuries.