The biomechanics of anterior cruciate ligament rehabilitation and reconstruction

The rehabilitation of knee injuries involving the anterior cruciate ligament (ACL) is controversial. This paper describes strain in the normal and reconstructed ACL during a series of passive and active tests of knee flexion with and without varus, valgus, and axial rotation torques on the tibia. Strain in the human knee ACL was significantly different depending on whether the knee flexion angle was changed passively or via simulated quadriceps contraction. The knee joint capsule was found to be important for strain protection of the ACL. Quadriceps activity did not strain the normal or recon structed ACL when the knee was flexed beyond 60°, but significantly strained the tissue from 0 to 45° of knee flexion. Immobilization may not protect the ACL if isometric quadriceps contractions are allowed to occur. Properly placed reconstructions exhibited strain behav ior which closely followed the anteromedial band of the ACL.