Study design: Gait analysis and immunohistological analysis in a rat model of myofascial inflammation in low back.
Objective: To investigate gait in a rat model of myofascial inflammation using the CatWalk gait analysis system.
Summary of background data: There are few reports examining low back pain behavior in animal models. The CatWalk is a computer-assisted gait analysis system that provides an automated way to assess gait function and this behavior during pain.
Methods: In a myofascial inflammation group, 0.5 mL of 4% paraformaldehyde buffer and 0.5 mL of 5% Fluoro-Gold (FG) buffer were injected into bilateral multifidus muscles of rats. In a control group, FG buffer alone was injected. Five days after surgery, the gait of rats in both groups was investigated using the CatWalk system. In the present study a total of 36 gait parameters were quantified and used to judge pain-related behavior. Bilateral dorsal root ganglia (DRGs) from L1 to L6 levels were resected, and immunostained for calcitonin gene-related peptide (CGRP).
Results: In the myofascial inflammation group, the mean duty cycle (duration of paw contact divided by time between consecutive paw contacts) of each paws (front and hind) were significantly higher and mean stride length (the distance between successive placements of the same paw) of each paws were significantly shorter compared with the control group. Furthermore, mean minimum contact intensity of the complete paw and mean contact intensity of each paws in the myofascial inflammation group were significantly higher compared with the control group. The proportion of CGRP-immunoreactive FG-labeled neurons among all FG-labeled DRG neurons in the myofascial inflammation group was significantly higher than the proportion in the control group.
Conclusion: These results suggest that myofascial inflammation in low back caused the changes to the rat's gait, including long stands, short stride, and strong paw contact.