Sportorthopädie - Sporttraumatologie

Savio L-Y. Woo, R. J. Fox, M. Sakane, G. A. Livesay, Th. W. Rudy, Th. J. Runce, G. Li, Chr. R. Allen, F.H. Fu.


Injury of the anterior cruciate ligament (ACL) can lead to knee instability and an associated risk of degenerative joint disease. We have developed an innovative approach to measure multiple degree-of-freedom (DOF) knee kinematics as well as to determine the in situ forces within the ACL using a 6-DOF robotic manipulator and a universal force-moment sensor (UFS). The primary advantage of this system is that forces can be obtained in a non-contact manner while allowing a series of experiments to be performed on the same knee. This manuscript briefly describes the verification of the robotic/UFS testing system and presents a series of studies conducted to provide insight into the function of the ACL and ACL grafts. Beginning with a procine model, we detailed significant increases in anterior tibial translation under anterior tibial loading when knee motion was unconstrained, as compared to when it was constrained to 1-DOF motion. Significant changes in the direction of the in situ forces in the ACL and the distribution of these forces between the anteromedial (AM) and posterolateral (PL) bundles were also noted. In the human knee, we examined the effect of knee flexion angle and anterior tibial loads on the in situ forces in the ACL and its AM and PL bundles during unconstrained knee motion. Interestingly the PL bundle carried significantly greater in situ forces than the AM bundle at flexion angles less than 45°. These data suggest that the PL bundle plays a significant role in resisting anterior tibial translation. Finally, we compared the performance of bone-pateller-bone (BPTB) and quadruple semitendinosus/gracilis (QST/G) grafts for ACL reconstruction. The robotic/UFS system has the advantage of testing the intact ACL and performing both reconstructions within the same knee to minimize interspecimen variability and also utilize the intact ACL as the "gold standard" for reconstruction. We found that although both reconstructions effectively reduced anterior tibial translation compared to the ACL-deficient knee, the in situ forces in the QST/G graft more closely approximated those for the intact ACL.