IN-VIVO FORCES DURING REMODELING OF A 2-SEGMENT ANTERIOR CRUCIATE LIGAMENT GRAFT IN A GOAT MODEL

An existing goat model was used to measure in vivo graft forces during walking, to determine if the forces set at surgery change over time u nder the same external load and if the forces in the graft during in v ivo function can be dictated by the forces set at surgery The anterior cruciate ligament was reconstructed in 12 goats with use of a composi te graft consisting of a bone-patellar tendon-bone autograft and a syn thetic augmentation segment. The forces in the graft segments were est ablished intraoperatively by a force-setting technique. In five animal s, the tendon segment was set to carry 90% of the total graft force, a nd in the seven other animals, the augmentation segment was set to car ry 90% of the total force. The total graft force was the same in all a nimals. Graft forces due to anterior tibial loads of 67 N were measure d before and after fixation and 6 weeks after surgery with the use of buckle transducers mounted extra-articularly over the anterior tibia. They were also measured during straight, level walking at 6 weeks. The forces changed significantly from just after surgery to 6 weeks later , such that the initially set load-sharing was eliminated by 6 weeks. At 6 weeks, a relatively smooth gait had been achieved, and the maximu m total graft force in each animal during walking averaged 35 N and wa s of similar magnitude to forces generated by the anterior tibial load s of 67 N with the animal anesthetized. After fixation, forces in the tendon graft segments were significantly different between the group w ith high set forces and that with law set forces. At 6 weeks, when fun ctional joint loads were approaching normal levels, the graft segment forces for the two groups were not significantly different. Load-shari ng between tendon and augmentation segment and load in the tendon segm ent at 6 weeks could not be dictated at surgery.