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Histological comparison of fate of ligamentous insertion after reconstruction of anterior cruciate ligament: autograft vs allograft.

OBJECTIVE
To analyze the histological results and the biological remodeling of ligamentous insertion after the reconstruction of anterior cruciate ligament (ACL) with autograft or allograft tendon.


METHODS
Extensor digitorum tendon was harvested from hind limb as graft material and transplanted to reconstruct the resected ACL in 12 mongrel dogs. Each free tendon end was secured by holding sutures and then the sutures were tied to the post screw at the femoral and tibial bony tunnel outlet after transplantation respectively. Autograft was randomly performed on one side of knee while allograft on the other side of knee. After transplantation, the histological analysis was undertaken at the 6th, 12th weeks and the 6th month using hematoxylin-eosin (HE) stain under light microscope.


RESULTS
The insertion structure of normal ACL typically consisted of four layers, i.e., dense connective tissue, fibrocartilage, mineralized fibrocartilage and bone. There was a distinct regular tidemark line between fibrocartilage and mineralized fibrocartilage. At the 6th week postoperatively, loose connective tissue presented in the interspace between graft and bony tunnel wall in both autograft and allograft groups. At the 12th week postoperatively, the collagenous fibers between autograft and tunnel wall became well organized and the four layers of insertion with discontinuous tidemark line were demonstrated indistinctly in autograft group but not in allograft group. At the 6th month postoperatively, both of a clear and continuous tidemark line and distinct four layers could be seen in autograft group. In allograft group, only a waved discontinuous tidemark line was shown and either the anatomic morphology or the maturity of insertion was inferior to that of autograft group.


CONCLUSIONS
At the 6th month postoperatively, although the ligament-cartilage insertion is primarily formed after ACL reconstruction with autograft or allograft tendon, the histological morphology and the maturation of insertion of autograft tendon are better than those of allograft group, which suggests that postoperative rehabilitation should be paid more attention and could be safer if little delayed during ACL reconstruction with allograft tendon.