Influence of Thigh Muscle Forces on Anterior Cruciate Ligament Forces during Single-Leg Landing from Three Different Heights
Over 200,000 anterior cruciate ligament (ACL) injuries occur every year amounting to billions of dollars being spent on the ACL annually. While the quadriceps muscle produces an anterior shear force on the tibia that causes the ACL to strain, the hamstrings muscle can protect the ACL by producing a posterior shear force to the tibia reducing the strain. When the hamstrings contract simultaneously with the quadriceps, ACL strains are considerably less compared to isolated quadriceps forces, thus the balance of hamstring and quadriceps muscle forces play a critical role in determining the forces on the ACL. During dynamic landing tasks, quadriceps demands increase as the landing height increases, which may cause the ACL to be more susceptible to injury. The purpose of this study was to determine the relationship of the quadriceps and hamstring muscle forces on ACL forces during single-leg landing from three different heights. We hypothesized that the ratio between hamstrings and quadriceps muscle forces would be negatively correlated to peak ACL forces during landing from three different heights. We anticipated that the hamstring to quadriceps ratio would decrease as landing height increased primarily due to the increased quadriceps demands. Three males with an average height of 1.75±0.07m with an average mass of 74.08±8.66kg and three females with an average height of 1.70±0.04m and an average mass of 55.93±6.83kg landed on their right leg from three different heights, 15cm, 30cm, and 45cm. Musculoskeletal modeling was used to estimate muscle forces. Regression analyses predicted the ACL forces from all three heights, and the heights pooled together. The results showed that the quadriceps muscles forces were strongly positively correlated to the peak ACL force while the hamstrings muscle forces were not significantly correlated to peak ACL force. Linear analysis showed the hamstring to quadriceps ratio to be moderately negatively correlated with peak ACL force (r[superscript]2 = 0.278), but nonlinear curve analysis showed a stronger relationship between these variables (r[superscript]2 = 0.425). However, as the landing height increased, these linear and nonlinear relationships both decreased. This signifies that another factor was contributing to the peak ACL force especially at higher heights. The combined influence of ground reaction forces and the hamstring to quadriceps ratio revealed that as landing height increased the ground forces became more of a factor in predicting peak ACL forces compared to the hamstring to quadriceps ratio being the dominant predictor at the lowest heights. In conclusion, the data support our hypothesis the hamstring to quadriceps ratio was inversely related to the peak ACL force although the strength of this relationship was height dependent. Further, as landing height increases, the ground reaction forces become the stronger predictor of peak ACL forces compared to the hamstring to quadriceps force ratio.
Biomechanics, Health Sciences, Rehabilitation and Therapy
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