Experimental ligament reconstruction by allogeneic tendon graft in a canine model

The revascularization and remodelling of fresh-frozen allografts used to replace the anterior cruciate (ACL) and medial collateral ligaments (MCL) of the knee were studied by microangiographic, histological and biomechanical methods. The allografts were produced from the patellar tendons of dogs. No bone was attached on either end. The tissue was frozen and thawed immediately before grafting. The grafts were shaped to either 4 to 4.5 mm (for ACL or MCL) or 8 to 9 mm wide (for ACL), and fixed into the drill holes made in the femur and tibia with sutures and buttons after excision of the original ligaments. The animals were sacrificed from 3 to 52 weeks postoperatively. Microangiographically, the ACL and MCL allografts were revascularized from the sixth postoperative week, and later developed an intrinsic vascular pattern similar to that of a normal ACL or MCL. Histologically, both the allografts regained a fibrous framework similar to that of normal ligaments, and showed no evidence of immunological rejection. Biomechanical tests on the ACL allografts showed that their mean maximum tensile loads at 52 weeks were 36% of those for the control ACLs, or 27% of those for the allografts before reconstruction. The tests on the MCL allografts showed that their maximum tensile loads at 52 weeks were 73% of those for the normal MCLs, or 60% of those for the allografts before reconstruction.