Singleton, S., Nefla, M., Dennison, N. et al. 2020. Assessing pain in models of rheumatoid arthritis. Animal Technology and Welfare 19(2), 149-152.

A hallmark symptom of rheumatoid arthritis in humans is painful swollen joints. Pain can manifest before any inflammation is noticeable as well as persist long after inflammation has resolved. In rodent models of arthritis, ankle or footpad width is a commonly used surrogate marker of pain. Measuring footpad width assumes that increased swelling is proportional to enhanced pain. A mild arthritis phenotype in which there is minimal swelling may therefore inaccurately reflect the extent of pain and discomfort. We aimed to determine how well pain correlated to footpad widths using the collagen antibody arthritis mouse model. We found that footpad widths poorly reflect pain experienced in arthritis models. Observing the posture and activity of an animal might better indicate whether or not they are in pain. Qualitative and semi-quantitative measures of affective pain can be useful in determining when an animal should receive analgesia. Further qualitative refinements should be added to identify better humane endpoints.