Freeze dried anterior cruciate ligament allografts: Preliminary studies in a goat model

Abstract

One ACL in each of 11 mature goats was replaced with a freeze dried bone-ACL-bone allograft. One year fol lowing implantation the goats had their knees evaluated biomechanically and for microvascularity and histologic changes. The reconstructed knees had a significantly greater total AP laxity (3.8 ± 0.6 mm) (mean and SEM) than the controls (1.0 ± 0.1 mm). Differences in primary AP laxity were responsible for 81 % of the difference in total laxity, with only a 0.4 mm difference in secondary laxity. Neutral stiffness in the reconstructive knee was 17% of control. while stiffness at 30 newtons (N) of anterior force was approximately 50% of controls. Lig ament stiffness in the linear region for the ACL allograft was 35% of the control value of 686 N/mm. The maxi mum load of the allografts was 571 ± 45 N, or 25% of the contralateral ACL control strength (2301 ± 155 N). Five of the seven allografts failed at the femoral inser tion. Both elongation (83%) and energy (21 %) to max imum load were less for allografts than controls. His tologic evaluation of the allografts revealed the pres ence of a regular oriented dense connective tissue which resembled a normal ligament. Microangiography revealed a periligamentous and endoligamentous vas cular pattern reminiscent of a normal ACL and complete revascularization of the bone plugs.