FETAL NERVE HEALING - AN EXPERIMENTAL-STUDY

An experimental study was performed to assess fetal nerve repair and r egeneration both qualitatively and quantitatively. The posterior tibia l nerves in one hindlimb were transected in 16 midgestational fetal la mbs and in their mothers. The nerves were then repaired with epineuria l sutures and allowed to progress to 2, 4, 6, and 8 weeks postinjury. Qualitative assessment was performed through standard nerve histologic staining, including Luxol fast and toluidine blue for myelin and Biel schowsky stain for axons, and quantitative assessment through nerve co nduction velocity studies and morphometry to determine mean myelinated fiber diameter, total fiber number, and density. A frequency histogra m of the distribution of myelinated nerve fibers according to fiber di ameter also was generated. In our model, the subsequent fetal nerve re sponse to injury was characterized by earlier degeneration than in the adult counterparts. Repair and regeneration proceeded with dense coll agenous scar formation in both groups. Electrophysiologic studies show ed nerve impulse conduction across the repair site only at 6 and 8 wee ks postinjury in both fetus and adult. Action potential amplitudes at 6 and 8 weeks were measured at 3 to 5 percent of control nerves in bot h nerve types. No electrophysiologic differences in the recovery of th e injured fetal and adult nerves could be identified. Morphometry reve aled that fetal nerve regeneration appeared to occur at a rate equival ent to that of the adult, although by 8 weeks the total percentage of remyelinated nerves appeared more complete in the fetus than in the ad ult (87 versus 59 percent), suggesting that fetal nerves may have a mo re favorable regenerative capacity than their adult counterparts.