Fig. 3

Cluster analysis of mechanical withdrawal threshold in rats aged P21 following monoarthritis revealed three distinct clusters (a). These could be related to differing pain trajectories with mechanical hypersensitivity (a reduction in mechanical withdrawal threshold) lasting different lengths of time (p < 0.001): 3 days for animals with low sensitivity to inflammatory pain (n = 7, blue; p < 0.001), 7 days for animals with a medium sensitivity to inflammatory pain (n = 9, green; p < 0.001), and 10 days for animals with a high sensitivity to inflammatory pain (n = 9, orange; p < 0.001). Weight bearing also differed between the sensitivity groups with animals with low sensitivity having a smaller reduction in weight bearing post-CFA compared to animals with medium or high sensitivity (p = 0.012, b). Females were more likely to have medium or high sensitivity (p < 0.001, c). These differing sensitivities to inflammatory pain were despite no difference in joint inflammation between the three groups (p = 0.89, d). * p < 0.05 between baseline mechanical threshold (0 day time-point) and indicated time-points for each sensitivity group as shown by the line colour. ⁺ p < 0.05 between indicated groups