Paper 203: Contributions of the Posterolateral Bundle of the Anterior Cruciate Ligament to Anterior-Posterior Knee Laxity and Ligament Forces

Abstract

The purpose of this study was to measure changes in anterior-posterior laxity and graft forces after cutting the posterolateral (PL) bundle of the anterior cruciate ligament (ACL). Twelve fresh frozen cadaveric knees underwent anterior-posterior (AP) laxity testing at + 100N of applied tibial force. Resultant forces in the ACL were recorded during passive extension from 120° to 0° with no tibial force, 100N anterior tibial force, 100N quadriceps force, and 5 N-m internal tibial torque. The femoral origin of the PL bundle was identified, the ligament fibers were dissected from bone, and tests were repeated. Cutting the PL bundle significantly increased mean laxity +1.3 mm (at 0°), +1.1 mm (at 10°), and +0.5 mm (at 30°). For the passive knee extension tests, cutting the PL bundle significantly decreased mean ACL force at 0° for all loading modes; mean decreases were 31N (no tibial force), 50N (100N anterior force), 33N (100N quadriceps force), and 40N (5 N-m internal torque). The decreases in ACL force at 0° from cutting the PL bundle are consistent with the commonly accepted view that the PL bundle tightens with knee extension. Cutting the taut PL bundle did significantly increase AP laxity between 0° and 30°, but the increases were relatively small. Therefore we conclude that the PL bundle plays a relative minor role in controlling anterior tibial translation.