INTRAOPERATIVE FORCE-SETTING DID NOT IMPROVE THE MECHANICAL-PROPERTIES OF AN AUGMENTED BONE-TENDON-BONE ANTERIOR CRUCIATE LIGAMENT GRAFT INA GOAT MODEL

It has been hypothesized that load affects the mechanical properties o f an anterior cruciate ligament graft while it remodels. The goal of t his study was to use an existing goat model to evaluate the effect of intraoperative set force on the postoperative mechanical properties of an autograft that had been augmented with a synthetic segment. The fo llowing questions were addressed. Do augmented autografts set with a h igh force intraoperatively have improved structural and material graft properties and lower anterior-posterior knee laxity at 3 months after surgery, compared with autografts set with a low intraoperative force ? How do the structural and material properties of these implanted aut ografts compare with the mechanical properties of an intact anterior c ruciate ligament or an unimplanted control autograft? The anterior cru ciate ligament was reconstructed in seven goats with use of a composit e graft consisting of a bone-patellar tendon-bone autograft and a synt hetic augmentation device. A force-setting technique was used intraope ratively to establish the load-sharing between the autograft and augme ntation segments such that the autograft carried either a high (16.5 N in four animals) or low (1.5 N in three animals) level of force, whil e the total force in the composite graft remained constant. Tensile te sting was performed at 3 months after surgery to determine the materia l and structural properties of the autograft, the intact anterior cruc iate ligament from the normal contralateral knee, and a control bone-p atellar tendon-bone graft of similar size that was harvested from the contralateral knee at the time of necropsy and had never been implante d in the joint. The structural and material properties of the autograf ts initially set to high or low loads at surgery were not significantl y different after 3 months of implantation. The strength and stiffness of the implanted tendons were an average of 24 and 20% of the strengt h and stiffness of the normal anterior cruciate ligament and 31 and 62 % of the control tendons, respectively. Intraoperative set force in an augmented anterior cruciate ligament graft at the levels chosen in th is study did not significantly affect weakening of the autograft at 3 months.