Specific Overground Walking Kinematic Measures are Related to Degree of Spinal Injury in the Rat

After incomplete spinal cord thoracic injury (iSCI) rodents retain locomotor capability. We tested the hypothesis that the degree of retained function would be related to the sparing of spinal tissue. Hindlimb stance width, hindfoot rotation, stride length, and velocity during overground walking and qualitative Basso, Beattie, and Bresnahan (BBB) locomotor scores were obtained in 5 rats with mild-moderate iSCI (T10 injury caused by 10 gm, 2 mm New York University impactor probe dropped from 12.5 mm). The extent of injury was estimated from histological sections stained for myelin by calculating percent volumes of gray matter (%GM) and white matter (%WM) spared for a 9 mm cord section. The white and grey matter volumes were 19.6+/-3.9 (mean+/-SD) and 4.5+/-1.8 cubic mm respectively. This resulted in 47.6+/-6.5 %WM and 10.9+/-4.0 %GM being spared. Kinematic measures of stance width and hindfoot limb rotation showed a significant negative correlation with %WM spared (r=-0.924 and -0.87 8). All other measures did not show significant correlation. BBB showed a significant positive correlation with %WM spared (r=0.93). None of the measures showed significant correlations with %GM spared. The data indicate that impairment of specific features of overground walking is related to the loss of axonal connections after iSCI.