Paw Print Gait Analysis in Rats with Spinal Cord Injury

Recovery of locomotion following spinal cord injury (SCI) in the rat may be tracked by different approaches to gait analysis, such as open field locomotor scoring and automated paw print analysis. Until recently, both of these approaches allowed the animal to walk at a self-selected speed. To further characterize gait recovery, the DigiGait system was developed to obtain video of paw prints through a clear plastic treadmill that may be set at various speeds. The DigiGait allowed the variability in gait parameters due to changes in speed to be characterized and controlled to mitigate effects of speed on these parameters. The purpose of the first study presented in this paper was to conduct a small preliminary study that uses the DigiGait with the rat model and to further characterize gait at multiple standardized treadmill speeds. A minimum treadmill speed of 10 cm/s was determined for use with the Long-Evans rat because at this speed, the rats were able to run without frequent acceleration or deceleration and it was attainable by all of the subjects by two weeks after SCI. Statistical analysis of the data was ongoing during the writing of this paper, and as a result the focus in this paper was to examine trends in the data. With increasing treadmill speed from 10 cm/s to 25 cm/s, hindlimb stride length and stride frequency were increased in injured animals by 1.3-fold and 1.9-fold, respectively; whereas, stance width was unaffected, and stance/swing ratio and hindlimb shared stance time were decreased by 1.6-fold and 2.4-fold, respectively. This study showed that certain gait parameters vary with a change speed. This variability may be reduced in future studies of gait parameters by using standardized speeds.
The second study was performed three years prior to the DigiGait study. At that time, results from the DigiGait system had not yet been published. A device called the CatWalk was available for acquiring video of rats crossing a clear walkway. Analysis software for the CatWalk existed but was not available commercially. The purpose of the second study was to design software that partly automates paw print analysis of video of rats using the CatWalk. The goal of this software was to measure the same gait measures as the CatWalk analysis software. These parameters included stride length, stance width, paw print area, swing duration, and interlimb coordination. The Java computer programming language was used to incorporate open-source image analysis tools available through the National Institution of Health's (NIH) ImageJ, which is a set of Java-based plug-ins. The software was able to analyze sequential series of frames that were extracted from video clips by third party software. A proof of concept study showed that this paw print analysis software was able to identify each paw in an image as left hindpaw, right hindpaw, left forepaw, or right forepaw. The software was then able to automatically measure and save the contact area of paws and the distance between paws. Additional gait parameters may be added to this software in the future. Both of these studies contributed to the overall goal of better characterizing the efficacy of treatments that lead to improved locomotor function after SCI in the rodent model and that eventually may be used for human subjects with gait dysfunction due to SCI.