Factors affecting graft force in surgical reconstruction of the anterior cruciate ligament

The effect of the maximum unloaded graft length (Lo) and femoral fixation hole location on graft force with the knee under anteriorly directed tibial loads was measured in five fresh cadaver knees with a reconstruction of the anterior cruciate ligament (ACL). The reconstruction was performed using a composite graft consisting of the semitendinosus and gracilis tendons augmented with the Kennedy ligament augmentation device (LAD). Buckle transducers were used to measure ligament and graft forces. The total graft force was adjusted to match the intact ACL at 30° flexion using a force-setting method so that a standardized reference configuration could be repeatedly obtained. The graft force was highly sensitive to L0, typically changing by 50% with a change in L0 of 3 mm. Variation in femoral hole location of 5 mm anterior, posterior, proximal, and distal to the anatomic position produced changes in graft force, particularly at 60° and 90° flexion; however, these changes were not statistically significant. The effect of femoral hole location varied considerably between knees. This variability makes predicting proper hole placement difficult, and suggests the need to adjust each knee at surgery to account for this variable femoral hole position sensitivity.