Innervation of skin grafts over free muscle flaps

Skin grafts regain their sensory innervation from the graft bed by the rege neration of nerve endings. Although some clinical studies report sensory re covery in skill grafts implanted on fi ce muscle naps, the mechanism of rec overy is obscure. The purpose of this study was to investigate nerve regene ration in experimental skill grafts on free muscle naps to elucidate this p henomenon. Thirty-eight male Sprague-Dawley rats, weighing 450-550 g were used in the study. The rat gracilis muscle flap was the free flap model transferred fro m one groin to the other using microvascular anastomoses. Full-thickness sk in grafts harvested from the abdomen were used to cover the free muscle fla ps after transfer. Four study groups were formed: Group I (n = 10): free muscle flaps were tra nsferred without any nerve anastomosis, Group II (n = 10): Free naps transf erred with the anastomosis of the muscle's motor nerve to a sensory nerve a t the recipient site: Group III (n = 10): Free flaps transferred with the a nastomosis of the muscle's motor nerve to a motor nerve at the recipient si te: Group IV (n = 8). Skin grafts were placed directly on the fascia layer over the medial hindlimb muscles and served as controls. The specimens were harvested for histologic examination after 12 weeks Hist ologic examination was performed to visualise regenerating nerve endings us ing H&E, S100, Luxol Fast Blue and tyrosine hydroxylase staining. The speci mens were categorically scored according to the staining pattern of neural structures around pilosebaceous units and statistical comparisons were perf ormed by using paired t-test. Skin grafts in both Group II and Group III markedly received tyrosine hydro xylase at the base of their pilosebaceous units in many of the specimens an d functional nerve twigs could also be traced from the muscle layer to the overlying skin graft. In contrast, the skin grafts in Group I did not show any nerve function in the central parts. The overall staining scores of Gro ups II. III and IV were significantly higher than Group I (P <0.05; P < 0.0 01: P < 0.05, respectively). There was no statistically significant differe nce between other groups. No myelinated nerve fibres could be detected in a ny of the skin grafts with Luxol Fast Blue technique. It was concluded in the present study that skin grafts over reinnervated fr ee muscle flaps can develop significantly better innervation than skin graf ts over non-innervated muscle flaps. However the activity in skin appendage s indicating serve regeneration may only imply a gross sensation and in the absence of any myelinated nerve fibres transmission of finer sensation can not be expected in ally of the study groups. (C) 2000 Harcourt Publishers L td.