PASSIVE MUSCLE TENSION AUGMENTS THE ANTERIOR CRUCIATE LIGAMENT - AN IN-VIVO STUDY IN THE RAT

The contribution by passive muscle tension to the structural load-bear ing capacity of the anterior (cruciate) ligament in the anesthetized r at was investigated. Using a stereomicroscope, the joint capsule and l igaments of the right knee, except the anterior ligament, were cut and the menisci removed leaving the anterior ligament and the tendons of the denervated muscle to constrain the knee. The ligament was tested i n tension until failure, using a loading rate of 2.5 mm s(-1) (similar to 0.6 s(-1)). As a control, the femur-anterior ligament-tibia comple x of the left knee was tested. The mean ultimate tensile load on the a nterior ligament augmented by muscle tendons was 48 percent higher. Th e energy absorption at failure was 84 percent higher; and the stiffnes s 26 percent higher. The deformation remained unchanged. This investig ation suggests that, when the strain rate is high, muscle may be passi vely stretched and thus absorb energy and increase the force needed to rupture the anterior ligament.