SENSORY RECOVERY IN MYOCUTANEOUS, NONINNERVATED FREE FLAPS - A MORPHOLOGIC, IMMUNOHISTOCHEMICAL, AND ELECTRON-MICROSCOPIC STUDY

The aim of this study was to clarify the following questions: (1) Do n ewly sprouting axons use the empty neurilemmal sheaths of a flap as co nduits? (2) To what extent can sensibility recover? (3) Does sensory r ecovery occur at the margins of the flap or at its center? (4) Doe's c hemotaxis influence the regeneration process? In 16 free myocutaneous flaps (12 latissimus dorsi, 4 rectus abdominis) we investigated pain ( pinprick), constant touch, temperature, 30- and 256-Hz vibration, and static and moving two-point discrimination between 1 1/2 and 8 years a fter surgery. Four flaps were anesthetic, eight recovered partly, and four had six or more modalities present all over the flap; six of ten flaps with poor recovery showed better sensitivity close to the anasto mosis. Nine patients agreed to have two punch biopsies (6 mm) taken fr om their flaps (seven from areas with different degrees of sensory rec overy and two from the center and the periphery when recovery was homo geneous). Biopsies from the areas with better sensory recovery showed slightly more nerves than the other punches in five instances, showed no difference between the two biopsies in one instance, and seemed to have more nerves in the biopsy from the area with less recovery in the last instance. The two pairs of biopsies from the homogeneously recov ered flaps showed similar amounts of nerves. S-100 protein-positive ne ural structures (Schwann cells) were found in 13 biopsies, and neuron- specific enolase-positive nerve fibers (nerve axons) were found in 10 biopsies. Electron microscopy showed mainly unmyelinated fibers, alway s adjacent to vessels and sometimes with regenerative phenomena. We be lieve that sprouting axons probably grow into a flap attracted by chem otaxis from hair follicles, the basement membrane, and the laminin con tained in the sheath. We recommend maximum scar excision at the recipi ent site to enhance sensory recovery in flaps. We conclude that (1) th e sprouting axons primarily use the empty neurilemal sheaths as condui ts, (2) sensory recovery can reach two-point discrimination equal to t he donor site of the flap, and (3) sensory recovery occurs mainly from the margin of the flap but also from the bed.