Abstract
Background and purpose of the study: the anterior cruciate ligament (ACL) is a continuum of fibres which are differently recruited through range of motion. Two main functional bundles can be identified: the postero-lateral bundle (PLB) which is taut exclusively towards extension and the anteromedial bundle (AMB) which is taut through full range of motion. The purpose of this investigation was to assess the relative contribution of the bundles to intact knee kinematics.
Material and methods: fourteen intact cadaver knees were instrumented in a non-ferromagnetic rig and six degrees of freedom kinematics through flexion-extension was recorded with an electromagnetic device under the application of a 90N anterior force or a 5Nm internal rotation torque. The AMB and PLB were alternatively cut first in each knee and knee kinematics was recorded. The other bundle was then dissected and ACL deficient knee kinematics tested.
Results: when the AMB was cut anterior tibial translation increased and no effects on rotations were recorded. When the PLB was first cut no significant effects on anterior laxity were observed. Different rotational responses were observed in different knees. After the section of both bundles a larger increase in anterior laxity was observed. The changes in rotation differed from knee to knee.
Discussion: The AMB is a primary restraint against anterior tibial translation and has a small and variable effect on rotations. The PLB is a secondary restraint against anterior tibial translation in extension and maintains normal rotational laxity in AMB deficient knees. Therefore, reconstruction of both bundles is theoretically advantageous to restore both intact knee anteroposte-rior and rotational laxity.
Correspondence should be addressed to: Tim Wilton, BASK, c/o BOA, The Royal College of Surgeons, 35–43 Lincoln’s Inn Fields, London WC2A 3PE.
