IN-VIVO FORCES IN THE ANTERIOR CRUCIATE LIGAMENT - DIRECT MEASUREMENTS DURING WALKING AND TROTTING IN A QUADRUPED

In vivo forces in the anterior cruciate ligament (ACL) were measured i n three adult goats during quiet standing and during gait (walking or trotting). A modified pressure transducer (MPT) was implanted within t he anteromedial band of the ligament to make direct measurements of AC L force. One or two days following implantation, measurements were mad e of ACL force, knee joint flexion angle, ground reaction forces, and speed of locomotion. MPT calibration was performed in vitro using ante roposterior displacement tests at six flexion angles. The ACL was load ed during quiet standing (30-61 N) and during the stance phase of gait . Peak ACL forces were achieved within the first 40% of stance, with m agnitudes ranging from 63 to 124 N during walking and from 102 to 150 N during trotting. The average ACL force during the stance phase range d from 34 to 68 N while walking and from 46 to 69 N while trotting. Th e partial correlations between peak ACL force and speed, and between a verage ACL force and speed, were both statistically different from zer o (p < 0.01). ACL forces dropped to zero during the swing phase in all trials. ACL forces were less than 15 N throughout swing in two of the animals, both of which did not extend their knees during gait beyond 20 degrees from full extension. In the animal which did show knee exte nsion beyond 40 degrees (20 degrees from full extension), ACL loading occurred during late swing. The magnitude of the peak ACL force during late swing was significantly correlated with the extent of knee exten sion in this animal.