Long-segment nerve allograft regeneration in the sheep model: experimental study and review of the literature

Experimental work in the field of nerve allotransplantation has dealt with the feasibility of nerve allografts reconstructing nerve gaps. In the majority of studies, the nerve gap studied has been short, and some degree of regeneration has been achieved, even in the untreated allograft. To better approximate clinical nerve-allograft reconstruction, a series of long-segment (8-cm) nerve allografts were performed in the ovine model. Twenty outbred ewes were randomized into two experimental groups with four experimental conditions. Animals received nerve allografts treated under one of the following conditions: fresh nerve autograft, fresh nerve allograft, cold-preserved nerve autograft, or cold-preserved nerve allograft. The nerve grafts were examined and compared at 6 and 10 months, using histological, morphometric, and electro-physiologic analyses. The results of the study demonstrated that, while excellent regeneration occurred across the nerve autograft, the long nerve allograft could not support axonal elongation. Similarly, cold nerve preservation did not enhance regeneration. The sheep animal model allows for investigation of the long nerve gap and may be beneficial in a better correlation of experimental nerve transplantation with clinical conditions.