The weight-bearing knee after anterior cruciate ligament rupture. An in vitro biomechanical study.

Unilateral weight bearing was simulated on 12 cadaver knees to quantitate anterior tibial translation (ATT) after anterior cruciate ligament (ACL) transection and to asses the role of the posteromedial structure and the hamstrings in controlling laxity. With the ACL intact, ATT was 3.5 +/- 2.8 mm in extension and 4.3 +/- 3.6 mm at 60 degrees flexion. After sectioning the ACL, ATT was 6.5 +/- 4.7 mm in extension and 17.5 +/- 10 mm at 60 degrees flexion (P = 0.001). Applying a force in the hamstrings was unable to correct the pathological ATT observed after ACL section. Partial medial meniscectomy did not increase ATT after the ACL section. Disinsertion of the posterior horn of the medial meniscus and total medial meniscectomy increased ATT significantly compared to isolated ACL section. After ACL transection, sectioning the meniscotibial fibers or posteromedial capsule significantly increased ATT (6.5 +/- 0.5 mm in extension). Section of the postero-oblique ligament or popliteus tendon had no effect on ATT.