Gait analysis of C57BL/6 mice with complete Freund's adjuvant-induced arthritis using the CatWalk system

BACKGROUND The CatWalk system, a video based automated gait analysis system developed to evaluate footfall and gait changes in rodents, has been used for studying rodent models of arthritis, mainly the rat model. However, it has not been used to study static and dynamic gait parameters in mice with complete Freund's adjuvant (CFA). CFA is used extensively to induce arthritis in rodents including mice. METHODS The CatWalk system was used to study gait of freely moving mice with CFA-induced monoarthritis and evaluate pharmacological pain relief in this model of arthritis. CFA (20 μl) was injected intra-articularly into the right hind (RH) limb ankle joint through the Achilles tendon of C57BL/6 mice. RESULTS Mice had less regularity in their walking patterns after CFA inoculation compared to baseline walking patterns, which was significant at 2 days post inoculation (dpi). The mice also showed changes in static parameters (paw pressure (light intensity) and print area) as well as dynamic parameters (stance phase duration, swing phase duration and speed, and duty cycle). The ratio of the RH limb (ipslateral) to the left hind (LH) limb (contralateral) for paw pressure, print area, stance phase duration, duty cycle (stance phase duration/sum of stance and swing phase duration), and swing speed were significantly reduced compared to baseline ratios at 1-6 and/or 7 dpi. On the other hand, RH/LH limb ratio of the swing phase duration increased at 3 dpi compared to baseline values. Treatment with indomethacin (10 mg/kg) improved or restored the gait parameters of CFA inoculated mice i.e. similar to baseline values or LH limb. CONCLUSIONS These data show that the CatWalk system can be used to assess static and dynamic gait changes and pharmacological pain relief in freely moving mice with CFA-induced monoarthritis.