Quantitative metrics of spinal cord injury recovery in the rat using motion capture, electromyography and ground reaction force measurement

Abstract

Toward improving the quantitative tools available for evaluation of locomotion after a spinal cord injury, we characterized selected biomechanical and physiological parameters that could be used to assess the level of recovery of locomotion after a mid-thoracic spinal cord lateral hemisection. Specifically we defined quantitative measures of muscle activation and coordination, body weight support, propulsive force, and pre-toe contact activation. Generation of this ensemble of recovery measures was based on kinematics, ground reaction forces, and EMG in rats from the hindlimb ipsilateral to the hemisection during quadrupedal running on a trackway. We derived muscle activation levels using inverse dynamics and static optimization applied to a model of the hindlimb musculoskeletal system. Rats exhibited a phased recovery pattern: progressive recovery of general muscle activity beginning within 2-3 days post-injury, followed by recovery of propulsive force and intralimb coordination of antagonistic muscles 12-13 days post-injury. Even at 12-13 days post-injury however, body weight support and the normal pre-paw contact EMG burst were significantly impaired. These data are consistent with a differential rate of recovery of general motor pool recruitment, and coordination among motor pools. The results demonstrate the discriminative potential of these physiologically based measures in quantifying the progressive recovery of gait performance after a lateral spinal cord hemisection.