Aims: Gait abnormalities have been suggested to provide an objective measure for joint pain in animal models of polyarthritis. Here, we aimed to assess whether measures of gait analysis correlate with measures of pain-related behaviour in experimental monoarthritis and how this association might be influenced by tumour necrosis factor-a (TNF-a) neutralizing compounds.

Methods: 

Antigen-induced arthritis was induced in the left knee joints of 53 female Lewis rats, of which 20 were treated with the TNF-a-neutralizing compound etanercept. During the course of arthritis, paw print analysis was performed on days 1, 3, 7, 14 and 21 after induction. At the same time points, measures for direct mechanical hyperalgesia at the knee joint and mechanical and thermal secondary hyperalgesia at the paw were obtained. On days 3 and 21 of the experiments, knee joints were scored histologically for signs of inflammation and cartilage or bone destruction. Data were compared to those obtained from 28 immunized control rats.

Results: 

Arthritic rats showed distinct asymmetric gait abnormalities. In the acute stage of antigen-induced arthritis (days 1 and 3 after induction), but not in the chronic phase (starting day 7), there is a significant correlation between gait parameters and measures of primary and secondary hyperalgesia. However, in the chronic stage, measures of gait abnormalities mainly correlate with joint destruction as assessed using histology and only to a minor degree with pain-related behaviour. Anti-TNF-a therapy showed pronounced antinociceptive effects, but did not alter the correlation pattern between gait and pain-related behaviour.

Conclusions: 

Gait abnormalities may represent a good measure for arthritis pain in acute inflammation. However, in the chronic phase, joint deformation as indicated by cartilage and joint destruction increasingly influences locomotion. Thus, gait abnormalities may not be suitable for objective pain assessment in all stages of experimental arthritis unless being adjusted for joint deformation.