Arthroscopy

John W. Xerogeanes, M.D., Yoshitsugu Takeda, M.D., Glen A Livesay, M.S., Yasuyuki Ishibashi, M.D., Hyoung-Soo Kim, M.D., Freddie H. Fu, M.D., Savio L-Y. Woo, Ph.D.


This study was conducted to evaluate the effect of applied load on the magnitude, direction and point of tibial intersection of the in-situ forces of the anteromedial (AM) and posterolateral (PL) bands of the human anterior cruciate ligament (ACL) at 30* and 90* of knee flexion. An Instron was used to apply a 100 N anterior shear force to 11 human cadaver knees, 6 at 30* of knee flexion and 5 at 90* of knee flexion. A Universal Force Sensor (UFS) recorded the resultant 6 degree-of-freedom (DOF) forces/moments. Each specimen then underwent serial removal of the AM and PL bands. With the knee limited to 1 DOF (anteroposterior), tests were performed before and after each structure was removed. Because the path was identical in each test, the principle of superposition was applied. Thus, the difference between the resultant forces could be attributed to the force carried by the structure just removed. The magnitudes of force in the ACL at 30* and 90* of knee flexion were 114.1±7.4 N and 90.8±8.3 N, respectively (P<.05). At 30*, the AM and PL bundles carried 95% and 4% of the total ACL force, respectively. At 90*, the AM and PL bands carried 85% and 13% respectively (P<.05). The direction of the in-situ force in the whole ACL as well as its two bands correlated with the anatomic orientation of the ligament. The resultant total ACL force intersected the tibial plateau at the posterolateral aspect of the AM band's insertion at 30* of knee flexion, while at 90*, the force intersection moved posteriorly to the AM/PL border. This research provides new insight into the fundamental force relationships of the ACL and its bundles. In response to an anterior tibial shear force, the AM band of the ACL was the predominant load carrier at both 30* and 90* of knee flexion. However, contrary to earlier reports, the in-situ force carried in the PL band increased as knee flexion increased. Further, the tibial intersection of the resultant ACL force moved laterally with knee flexion. These findings confirm that the ACL is a dynamic structure that in itself has no isometricity and also may mean that there is no ideal location in which to place a replacment graft. The use of this methodology with more physiologic unconstrained motion should lead to more definitive clinical conclusions.