Histomorphometric studies in patients with facial palsy treated by functional muscle transplantation: new aspects for the surgical concept

Whenever it was possible, muscle and nerve biopsies were performed in patients with irreversible, unilateral facial palsy treated by cross-face nerve grafting and free gracilis muscle transplantation with microneurovascular anastomoses. Planimetric analyses of cross-sections showed the following, to some extent, surprising, results: (1) Independent of the final functional result, approximately the same number of regenerated, thin nerve fibers (100-200) were found in the distal end of the cross-face nerve graft at the time of muscle transplantation. These are approximately 20% of the nerve fibers counted in the branches of the facial nerve at the healthy side used for reinnervation. (2) There is no correlation between the number or diameter of the nerve fibers in the distal end of the cross-face nerve graft and the functional recovery of the transplanted muscle, but there is good correlation between the morphology of the fibers of the muscle graft and the functional result. (3) Different portions of slow-contracting and fast-contracting muscle fibers in the reinnervated muscle grafts showed the strong influence of the quality of the nerve used for the crossover innervation. If a facial nerve branch innervating the slow buccinator muscle was used, the originally fast gracilis muscle was transformed to a slow muscle by this kind of reinnervation. These important findings are the basis of a new view of surgery in the treatment of irreversible facial palsy by functional free-muscle transplantation.