Structural assessment of rat sciatic nerve following tourniquet compression and vascular manipulation

In a recent study (Nitz et al., Exp Neurol 94:264-279, 1986) the validity of a rat animal model to examine effects of tourniquet compression and vascular occlusion on limb motor function, leg girth, and electrophysiologic changes was established. Here we report observations on sciatic nerve morphologic and morphometric alterations of these same animals. The hindlimbs of 90 rats were compressed by a pneumatic tourniquet at clinically relevant pressures (200 to 400 mm Hg) for 1 to 3 hours, and the sciatic nerve was assessed by light and electron microscopy at 1, 3, and 6 weeks post compression. The nerves were also examined from five additional animals at each of these time intervals following arterial ligation and sciatic nerve epineurectomy (30 rats). Percentage of degenerating myelinated nerve fibers and volume fraction of mast cells and fibroblasts were quantified morphometrically. The percentage of degenerating myelinated nerve fibers after moderate to severe tourniquet compression and vascular manipulation was similar and ranged from 15% to 45%. Tourniquet compression, but not vascular occlusion, resulted in an increase of mast cells and fibroblasts and disruption of endothelial cells of endoneurial vessels. The results suggest that clinically relevant tourniquet compression causes a secondary increase in vascular permeability, intraneural edema, and subsequent prolonged tissue ischemia, resulting in nerve degeneration.