Understanding Anterior Cruciate Ligament Injury Due to Drop Landing: Effects of Different Landing Techniques and Muscles' Action at the Knee Joint

Jumping and subsequent landing was found to be one of the most injurious maneuvers to the anterior cruciate ligament (ACL). The ability to predict ACL susceptibility to injury is extremely difficult due to the complex interaction between the lower extremity joints and the surrounding musculoskeletal structure. While muscles play an important role, whether they act to prevent ACL injury during drop landing is still debatable. Our objective is to quantify and compare the muscles recruitment and actions for different drop landing methods, which include single and double leg landing. We hypothesized that: I.) recruitment of antagonist muscles (Quadriceps force (Q) and Hamstrings force (H)) differs between the two different drop landing methods; 2.) a linear relationship exists between Q/H ratio and Ground Reaction Force (GRF), independent of drop landing height and landing methods. Lower extremity muscles' force were calculated and compared. Vertical GRF was found to increase in single leg landing. GRF and Q/H ratio were inversely proportional at the time of peak GRF. We concluded that muscles' force ratio around knee joint in conjunction with GRF and knee flexion angle are important parameters affecting the risk of ACL injury during drop landing.