Adjuvant Monoarthritis at the Tibio-Tarsal Joint in the Rat: A Model for Investigating the Mechanism of Pain in Chronic Inflammation

The animal models of polyarthritis, induced by the injection of complete Freund's adjuvant (CFA) into the rat's tail, have been extensively used to study the mechanism of chronic pain. However, since the animals suffer severe physical distress in this model, a new model that induces chronic pain without endangering the animal's health has been sought. In this study, CFA solution was injected into the tibio-tarsal joint of the rat. Monoarthritis was observed only near the injection site and lasted at least four weeks. As a result, the animals showed an increased response to mechanical stimulation with von Frey hairs to the hairy skin of the hind paw. This monoarthritis hardly aggravates the physical condition of the animals compared to the polyarthritis, suggesting that this model is useful for investigating the mechanism of chronic pain.