Allograft anterior cruciate ligament reconstruction in a sheep model

Abstract

The purpose of this study was to assess the effect of synthetic augmentation of a bone-patellar tendon-bone allograft on the basis of biomechanical, morphologic, and histologic evaluation. The anterior cruciate ligament was reconstructed in the left knee of 66 adult sheep. Half the knees received bone-patellar tendon-bone grafts alone, while the other half were augmented. All of the knees, including the contralateral controls, had gross and histologic examination, hydroxyproline assay for collagen content, and biomechanical testing in groups at 0, 4, 16, and 52 weeks postoperatively. Biomechanical testing included anteroposterior trans lation, ultimate tensile strength, energy to failure, stiff ness, and mode of failure. Eight fresh bone-patellar tendon-bone allografts were compared to eight cryo preserved bone-patellar tendon-bone allografts for baseline data on the effects of the cryopreservation. Cryopreservation did not have any effect on graft characteristics. Gross and histologic examination did not reveal any significant difference between the aug mented and nonaugmented groups at any of the time periods. In addition, hydroxyproline content of the al lograft was not altered by augmentation throughout the study period. Biomechanical laboratory evaluation dem onstrated the augmented group had significantly re duced anteroposterior translation (P < 0.05) at 52 weeks compared to the nonaugmented group. The ultimate tensile strength was significantly higher (P < 0.05) in the augmented group at 4 weeks, but at 52 weeks both groups had attained only 50% of the normal anterior cruciate ligament strength. Stiffness and en ergy to failure were similar in both groups at all time periods. From the results of this study, synthetic augmentation appears to improve initial strength and prevent late allograft laxity while allowing normal remodeling proc esses to occur in the bone-patellar tendon-bone allo graft anterior cruciate ligament reconstruction.