Nerve biomechanics and features of gait are altered in rats after mild crush injury to the sciatic nerve

Abstract

Purpose To investigate biomechanical properties of the rat sciatic nerve and characteristics of gait in the early healing period after a mild crush injury to the nerve. Methods Mild crush injury was achieved through a weight drop onto the left sciatic nerve of Sprague Dawley rats. In uninjured controls, sham-injured and injured rats, gait kinematics and timing variables were measured using a novel pressure mapping system and nerve stiffness under tensile loading was measured periodically for 21 days after injury. Nerve sections were evaluated on post injury days 7 and 21. Results The hind limb force (L:R ratio) was significantly less in the injured and sham-injured groups (injured, day 1, p=0.009, day 3, p=0.003; sham-injured, day 1, p<0.001) compared to controls. The L:R hind limb pressure ratio was also less in the injured and sham-injured groups (injured, day 3, p<0.001; sham-injured, day 1, p=0.019). Although the hind limb stride length and stance time ratios were not different from controls, the force and pressure data indicate that weight was shifted to the non-injured hind limb. Under tensile load, the slope of the stress-strain curve was significantly lower for injured nerves (day 3, p=0.044; day 7, p=0.046), indicating less stiffness compared to sham-injured and control nerves. Macrophage infiltration and edema were apparent by post injury day 7. Conclusions This is the first study to document both mechanical changes in gait and biomechanical changes in nerve stiffness in the early period after a mild nerve crush injury. BB is supported by a Kean Fellowship in the UCSF/SFSU Graduate Program in Physical Therapy.