Robotic gait analysis of bipedal treadmill stepping by spinal contused rats: characterization of intrinsic recovery and comparison with BBB.

There is a critical need to develop objective, quantitative techniques to assess motor function after spinal cord injury. Here, we assess the ability of a recently developed robotic device (the "rat stepper") to characterize locomotor impairment following contusion injury in rats. In particular, we analyzed how the kinematic features of hindlimb movement during bipedal, weight-supported treadmill stepping change following contusion, and whether these changes correlate with the recovery of open field locomotion. Female, Sprague-Dawley rats (n=29, 8 weeks of age) received mid thoracic contusion injuries of differing severities (11 mild, nine moderate, nine severe, and four sham). In a first experiment, 16 of the animals were evaluated weekly for 12 weeks using the robotic stepping device. In a second experiment, 17 of the animals were evaluated every other day for 4 weeks. The contused animals recovered open field locomotion based on the Basso, Beattie, and Bresnahan Scale (BBB) analysis, with most of the recovery occurring by 4 weeks post-injury. Analysis of 14 robotic measures of stepping revealed that several measures improved significantly during the same 4 weeks: swing velocity, step height, step length, hindlimb coordination, and the ability to support body weight. These measures were also significantly correlated with the BBB score. The number of steps taken during testing was not directly related to intrinsic recovery or correlated to the BBB score. These results suggest that it is the quality of weight-supported steps, rather than the quantity, that best reflects locomotor recovery after contusion injury, and that the quality of these steps is determined by the integrity of extensor, flexor, and bilateral coordination pathways. Thus, by measuring only a few weight-supported steps with motion capture, a sensitive, valid measure of locomotor recovery following contusion injury can be obtained across a broad range of impairment levels.