EFFECT OF QUADRICEPS OR HAMSTRING CONTRACTION ON THE ANTERIOR SHEAR FORCE TO ANTERIOR CRUCIATE LIGAMENT FAILURE - AN IN-VIVO STUDY IN THE RAT

We studied the effect of quadriceps or hamstring contractions on the a nterior tibial shear load to anterior cruciate ligament failure in an in vivo rat model. in both knees of 20 Wistar rats the joint capsule a nd ligaments, except the anterior cruciate ligaments, were cut and the menisci resected. In 10 rats the right ligament was loaded to failure by anterior translation of the tibia relative to the femur in a testi ng device during hamstring contraction induced by electrical stimulati on of the ischiatic nerve. In the other 10 rats, the right ligament wa s loaded to failure correspondingly during quadriceps contraction indu ced by electrical stimulation of the femoral nerve. The loading rate w as 2.5 mm s(-1) (similar to 0.6(-1)). The knee flexion during testing was 30 degrees. As control, the anterior cruciate ligament of the left knee was loaded correspondingly with relaxed muscles. The ultimate lo ad for the ACL tested during hamstring contraction was 1.5 times highe r than when tested with the hamstrings relaxed, more than double the e nergy was absorbed at failure and the linear stiffness was 1.2 times h igher. During testing with quadriceps contraction, no differences in t he structural properties were found, compared to testing with the quad riceps relaxed. Our findings show that hamstring contraction helps to resist anterior tibial shear force at 30 degrees knee flexion in rats thus protecting the anterior cruciate ligaments. Quadriceps contractio n in this situation does not affect anterior shear force to ligament f ailure.