Strategies for Attachment Site Locations and Twist of the Intraarticular Anterior Cruciate Ligament Graft

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Abstract
We modeled an intraarticular anterior cruciate ligament graft and investigated the effects of attachment orien tation and twist of the graft on its isometry during quadriceps muscle loading. Physiologic levels of quad riceps muscle loads were applied to 15 intact cadaveric knees. We measured the changes in distance between points on the tibia and femur for knee flexion angles between 0° and 120° using a three-dimensional digi tizer. Selected points on the tibia and femur, represent ing graft attachment sites, allowed us to model the graft as a broad band. Distance was used to approximate graft fiber length. A 180° twist in the graft significantly reduced the maximal range of changes in distance when the graft was attached in the anteroposterior direction. Range is defined as the difference between the largest and smallest changes in distance among the fibers of the graft for a given angle of flexion. This reduction enhanced isometry among the fibers of the graft. Enhanced isometry would be expected to en hance load sharing among these fibers, thereby in creasing the overall strength of the graft. For a graft 10 mm wide and 4 mm thick, the dimensions of a typical patellar tendon graft, the best overall isometry was found when the breadth of the graft was attached to the tibia in the mediolateral direction, to the femur along the most isometric line, and with a 180° twist in the graft.