F-wave amplitudes indicate evolving spinal autonomy during spontaneous recovery of hindlimb function in rat spinal cord contusion

Study design: Experimental rat model of spinal cord contusion. Objectives: To reveal the extent of spinal autonomy contributing to recovery of hindlimb function. Setting: Experimental laboratory of a neurosurgical university department. Methods: F-wave amplitudes as a probe for spinal cord excitability were recorded from both sciatic nerves (lumbar segments L2-L5) before and after an experimental spinal cord contusion performed in the lower thoracic spinal cord. Additionally, transcranial electrically motor evoked potentials from the hindlimbs and cerebral somatosensory potentials evoked by sciatic nerve stimulation were recorded. Clinical evaluation of hindlimb function was done regularly for survival periods of 3 and 50 days, respectively. Electrophysiological testing was performed immediately prior and after lesioning of the cord and at the endpoint of survival periods. Results: Hindlimb function recovered from a mean Basso-Beattie-Bresnahan score of 5.6 on day 1 to 9.2 on day 3 (3-day-survivors) and from 7.7 to 17.2 on day 50 (50-day-survivors). This was accompanied by a significant increase of F-wave amplitudes on day 50 compared to baseline values, whereas amplitudes of somatosensory and motor-evoked potentials remained significantly depressed. Conclusion: Recovery of hindlimb function may at least in part be attributed to evolving spinal autonomy, which can be assessed by F-wave amplitudes.