An Experimental Study Of Remodeling Process And Reinnervation Of Autogenous Hamstring Graft For Anterior Cruciate Ligament Reconstruction

Objective: We evaluated the remodeling and reinnervation process of free autogenous Hamstring tendon graft for anterior cruciate ligament (ACL) reconstruction.Methods: Free ipsilateral 4-5stands Hamstring tendon biopsy specimens were obtained 18 patients at different time points (from 2 months to 31months) after the anterior crucitate ligament construction during second-look arthroscopy. Morphological observations were made under light microscopy (LM) and electron microscopy (EM), and the maturation of the graft were evaluated quantitatively. In addition, immunohistochemical method was used to detect the neuropeptide nerve fibers in the autograft .The results were correlated with the morphology of normal Hamstring tendons and normal ACL.Results: Our study showed that the 7-month and 13-month grafts were almost the same as the normal ACL mophorlogically by 7 months in the feature of vascularity, cellularity, and fiber pattern, which did not change from 12 to 31months postoperatively. And no other significant differences of the three features except vascularity were noted between the 1-month group and 7-month group. EM study showed that the number of large-diameter fibrils within the autografts had decreased while small-diameter collagen fibrils had increased during the remodeling process. The predominance of small-diameter collagen fibrils persisted in almost all specimens aged from 12 months to 31 months, which was different from either the bimodal distribution of Hamstring tendon or the heterogenous distribution of normal ACL.Immunohistochemistry study confirmed the regrowth of neuropeptidergic nerve fibres into the autograft. Most of them were located in the walls of the vascular in synovial membrane surrounding the autograft. The regrowth of nerve fibres suggested that neuropeptides were actively involved in the early remodeling process and the healing of the autograft.Conclusions: Hamstring tendon autografts remain immature after transplant into the human knee. The autografts have matured and gained the close resemblance to normal ACL by 7 months which are faster than the BPTB grafts. The ultrastructure of grafts is still different from the normal ACL even at 12 months postoperatively. The autonomic nerve fibers found in the walls of the vascular in synovial membrane surrounding the autograft indicated the active role the neuropeptide played in the early stage of ligament remodeling process. No mechanoreceptors are found in the autografts.