Gait Analysis

1. How does the DigiGait system compare to other gait analysis systems?

The DigiGait system does not require external reflective markers to be attached to the animal for Digigait1gait analysis, whereas other systems may require markers. DigiGait directly collects digital video images of the underside of animals, whereas other systems may use a mirror to reflect the ventral view of the animal to a camera. As a consequence, image clarity, color, and shades are best preserved by DigiGait. The DigiGait system enables the user to select a range of walking speeds, whereas other systems expect the animal to walk [or not walk] at its preferred walking speed. This feature of DigiGait is important since there may be no gait abnormalities at a slow walking speed, but a high walking speed may demonstrate important differences. Moreover, even subtle differences in walking speed may have profound effects on gait indices. DigiGait empowers the user to study uphill and downhill walking, as subtle phenotypes might be highlighted with incline and decline locomotion. Standard errors are lower, repeatability is higher, throughput is higher, and data is more relevant from DigiGait.


2. Why is temporal resolution important in gait analysis?

Rodents may walk at speeds exceeding 90 cm/s. Mice walking at such speeds recruit their limbs DigiGait-2-300x100more than 10 times each second. All the kinematic parameters are shortened at such a high speed. The braking duration of the forelimbs, for example, can be shorter than 40 ms. High temporal resolution, therefore, is important to provide exact information about subtle gait abnormalities.


3. What is the spatial resolution of the DigiGait system?

The spatial resolution of the DigiGait system exceeds 5,000 pixels per cm2.


4. How does the DigiGait system determine the correct swing time?

The treadmill belt of the DigiGait system is transparent, so that the high resolution digital video camera is able to image the ventral view of the paws even when they are not in contact with the treadmill belt. Among the thousands of lines of code and artificial intelligence algorithms within the DigiGait software are functions that detect not only the spatial coordinates of a pixel, but also its direction. An image pixel of a paw that has a linear direction parallel to the treadmill belt is in the stance phase of a stride. An image pixel of a paw that has a direction different from the direction of the belt is in the swing phase of stride.


5. How often does the treadmill belt need to be replaced?

One of the first DigiGait treadmills has been in service at the Pfizer Pharmaceutical Company for over 5 years, and the treadmill belt has been changed once. The belt can be exchanged in <10 minutes. The belt material has good transparency without comprising the animals’ tactile walking comfort. The belt can be cleaned with most laboratory cleaning agents, including ethanol.


6. Can spinal cord injured animals walk on the treadmill?

Spinal cord injured rodents are able to execute stepping on the treadmill. In animals with total hemisection, the forelimbs of the animals attempt to compensate for hind limbs paralysis. The DigiGait system is able to quantify the asymmetry between forelimb and hind limb stepping as the animals recover from spinal cord injury. Several gait metrics are of interest in spinal cord injured animals, including phase dispersion, paw placement angle, and toe spread.


7. How do the metrics of the DigiGait system compare to the BBB score?

The DigiGait system objectively reports over 30 metrics of posture and locomotion at a range of walking speeds. There are likely some functional measures of the Basso-Beattie-Bresnahan (BBB) score that relate to the DigiGait system’s quantitative metrics. However, most gait metrics are very sensitive to walking speeds, and walking speeds usually differ between animals in the open field. Stride lengths, for example, of a group of mice with cerebral infarction, may be significantly different at walking speeds of 20 cm/s vs. 25 cm/s, a velocity difference imperceptible to the eye. The DigiGait system also reports phase dispersion values that quantify interlimb coordination, differences which are relevant when animals are studied at comparable walking speeds.


8. Does the DigiGait system measure ground reaction forces?

The DigiGait system does not measure ground reaction forces. Only a system that includes force transducers can measure ground reaction forces. The qualitative shape and quantitative timings of gait signals obtained by the DigiGait system, however, have been shown to correlate to force development in rodents. For example, the protracted braking durations of forelimbs compared to hind limbs, and the briefer propulsion durations of hind limbs compared to forelimbs, indicate hind limb vs. forelimb functional differences in loading and force development. DigiGait, moreover, has demonstrated significant differences in several gait metrics in hamsters with muscular dystrophy that may be attributable to their muscle weakness.


9. Why did you patent the DigiGait system?

Scientists and engineers from Mouse Specifics, Inc. and The CuraVita Corporation invented the technology and analysis software for imaging small mammals’ gait from underneath a transparent treadmill belt, for which a United Sates patent was issued [US Patent (#6,899,686), Method and Apparatus for Monitoring Locomotion Kinematics for Ambulating Animals]. The system provides not only two-dimensional topography, but also three-dimensional kinematics from one camera placed ventrally. The patent exemplifies not only the system’s utility and novelty, but also our commitment to scientific leadership in the field. Imitators of our patented technology do not adhere to the same rigor in ensuring instrument accuracy or sensitivity, especially when most motor defects are subtle.