Effects Of Drop Landing Height On Lower Extremity Joint Contact Forces

Abstract

The impact phase of loading has long been associated with osteogenisis and lower extremity skeletal injuries. Although reaction forces increase with drop landing height, they comprise only a small portion of the joint loading environment. The true loading experienced by the joints can only be realized when muscle forces are taken into consideration. PURPOSE: To determine the effects of drop landing height on lower extremity joint contact forces METHODS: Nine subjects completed ten landings from three heights in a random order (26, 39, and 52 cm). Electromyographical, force platform and kinematic data were collected concurrently. Musculoskeletal modeling and computer optimization techniques were used to determine muscle forces of the lower extremity. Electromyographical data were used to validate muscle optimizations, and joint contact forces at the hip, knee, and ankle were calculated by summing the reaction and muscle forces at each joint. Peak instantaneous joint contact forces during the impact phase (200 ms) were determined. Differences in joint contact forces were compared between conditions using a repeated measures ANOVA with Tukey‘s post-hoc tests. RESULTS: The knee and hip contact forces significantly increased with drop height. The ankle contact force during the 52 cm drop height was significantly larger than the 26 cm drop height. Respectively, joint compressive contact forces for the 26, 39, and 52 cm drop heights were as follows: ankle 6.8, 7.7, and 8.7 body weight (BW), knee 9.5, 10.5, 12.1 BW, hip 8.6, 9.9, 11.8 BW. Ground reaction forces contributed 20 to 28% of joint contact forces during drop landings. CONCLUSION: The results show an evident increase in ground reaction forces and joint contact forces with an increase in drop landing height. However, ground reaction forces account for only a small portion of joint loading during drop landings. Muscle forces substantially contribute to the joint loading environment. The results suggest that conventional methods using external forces and ground reaction forces may drastically underestimate force experienced by the joint.