Robotic assessment of locomotor recovery in spinal contused rats

The purpose of this study was to investigate the ability of a robotic device, "the rat stepper", to assess intrinsic locomotor recovery following spinal cord contusion injury in adult rats. The device consists of a motorized body weight support mechanism that precisely controls the load to the hindlimbs during stepping, and two small robotic arms that measure and manipulate hindlimb movement. Sixteen rats received a contusion injury to the mid thoracic spinal cord with different severity levels (mild, moderate, severe, and sham). The animals were then evaluated weekly using the rat stepper, beginning one week after injury and continuing for a period of twelve weeks, across a range of body weight support levels. The contused animals demonstrated recovery in a standard locomotor assessment score (the BBB score), with most of the recovery occurring by four weeks post injury. We analyzed fourteen robotic measures of stepping and found that the measures that were most sensitive to intrinsic recovery were step velocity and inter limb coordination. These measures were also significantly correlated with the BBB score. The number of steps taken during testing was not sensitive to intrinsic recovery, nor correlated to the BBB score. These results suggest that step quality, rather than quantity, best reflects recovery after contusion injury in adult, untrained rats. Thus, robotic motion capture of only a few steps can provide a sensitive, valid measure of locomotor recovery after contusion.