Functional assessment in the rat by ground reaction forces

Although the rat sciatic nerve model is used extensively in the investigation of repair techniques, and a variety of evaluation methods utilized to assess the results, a means to measure directly and accurately the return of function in these animals is absent. Histologic, histomorphometric, and electrophysiologic methods can be reliable indicators of nerve regeneration but do not correlate to functional recovery. The purposes of this study were to develop apparatus to continuously measure ground reaction forces (GRF) and use GRF parameters in the assessment of gait parameters in normal rats preoperatively and following peripheral nerve severance and repair. Three neurorrhaphy methods: direct sciatic nerve repair, direct tibial nerve repair and double sciatic nerve repair simulating autograft, as well as a non-repaired tibial nerve transection were evaluated. The testing apparatus was designed to measure the spontaneous and voluntary effort of the rat with objective data. Three orthogonal components - vertical, craniocaudal (braking and propulsion), and mediolateral - of the ground reaction force were measured. Preoperative data showed that vertical forces were comparable among the four limbs but propulsion and braking forces displayed significant differences. At 12 weeks, functional recovery was most evident in the direct tibial nerve repair group and absent in the non-repaired tibial defect group. Direct sciatic nerve repairs and sciatic nerve grafts resulted in lesser degrees of improvement. Results indicated that the propulsive force is the optimal GRF parameter for evaluating recovery of useful function.