Changes in conduction, blood flow, histology, and neurological status following acute nerve-stretch injury induced by femoral lengthening

The effects of an acute stretch on evoked potential, blood flow, histologic al change, and clinical neurological state were studied in a rat model of a cute nerve stretch induced by femoral lengthening. The purposes of this stu dy were to assess, in a model of acute limb lengthening, the safe limits of nerve stretch for nerve function, the pathogenesis of nerve dysfunction, t he sensitivity of spinal somatosensory evoked potential, and one of the pro posed criteria for irreversible compromise of the sciatic nerve. Thirty-two rats were assigned to one of four groups defined by the degree of acute fe moral lengthening (8, 16, 24, and 32%). Spinal somatosensory evoked potenti al at L5/6 following stimulation of the sciatic nerve was recorded before, immediately after, and 30 minutes after Lengthening. Sciatic nerve blood fl ow was measured by laser Doppler flowmetry at the stretched site before and after lengthening. One week after the operation and without further length ening, clinical neurological status was evaluated by the functional index o f the sciatic nerve and histological examination was performed. At the meas urement immediately after the procedure, amplitude changed significantly in all groups except for the group with 8% lengthening. In all groups, sciati c nerve blood flow also dropped significantly compared with values for the control side. Moreover, a greater percent age increase in acute lengthening corresponded with more marked changes in spinal somatosensory evoked poten tial and sciatic nerve blood flow. The groups that underwent acute lengthen ing of 24 and 32% had significant neurological deficits and histological ch anges and demonstrated a significant and profound (50%) drop in amplitude a nd blood flow. We concluded that spinal somatosensory evoked potential is v ery sensitive and may serve as an effective tool for the early detection of impending acute nerve-stretch injury and that a 50% reduction in amplitude indicates irreversible damage.