Abstract
Background: The objective of this study was to investigate dynamically the load on the cruciate ligaments and the effect of simulated co-contraction of the hamstrings muscles on quadriceps force and load on the cruciate ligaments.
Methods: Load transducers were fixed in the fibers of the anterior and posterior cruciate ligament of seven knee specimens. Isokinetic extension motions applying an extension moment of 31 Nm, representing an extension moment capable by healthy human volunteers in isokinetic extension tests, were simulated in a knee simulator from 120° to full knee extension. Quadriceps force and load on the cruciate ligaments were measured in the absence and presence of a 200 N hamstrings co-contraction.
Results: Quadriceps force significantly (p=0.04) increased under the application of hamstrings co-contraction. Anterior cruciate ligament load significantly increased below 20° knee flexion up to 161 N and was significantly (p=0.04) reduced to 29 N under hamstrings co-contraction at full knee extension. Posterior cruciate ligament load without hamstrings co-contraction showed a maximum load at 112° knee flexion of 38 N, reducing to knee extension and was not significantly increased(p=0.20) under hamstrings co-contraction, showing a maximum load of 66 N near knee flexion.
Conclusions: This dynamic in vitro study revealed the dependency of anterior cruciate ligament load on knee flexion angle during an isokinetic extension cycle. With a co-contraction of hamstring muscles the peak load on the anterior cruciate ligament was significantly decreased in knee extension with a non significant concomitant increase of posterior cruciate load at knee flexion. These findings have implications for graft donor site selection and postoperative rehabilitation, e.g. after anterior cruciate ligament reconstructions.