Gait analysis as an objective measure in a chronic pain model.

The aim of this study was to investigate objective characterisation of gait as a marker of the chronic pain of adjuvant arthritis (AA). Video recorded images of spontaneous rat ambulations were analysed to quantify various temporal and spatial parameters and compare these between the AA and control groups. Changes were also recorded after the administration of a single dose of buprenorphine (15 ?g). Individual temporal parameters were significantly reduced (velocity (P=0.05), stride length (P=0.007), single stance time (P<0.001), swing time (P=0.001)), or increased (dual stance time (P<0.001)) at 10 days in the AA group compared to control. The rear paws showed reduced ground contact and the fore paws an increase in proximal pad and decrease in digit area, although these changes were not all statistically significant. Some of the gait parameters showed significant reversal following administration of buprenorphine (velocity (P<0.001) and stride length (P<0.001) were increased and single stance time (P=0.014) reduced). It is proposed that changes in gait are a marker of AA chronic pain in this model. These behavioural changes were significant at a very early stage (day 10), before the development of physical deformities and increase in paw volume and might permit an earlier detection of pain than other models.