Background: The origin of joint pain involves the activation of terminals of slowly conducting C and A-delta afferent fibres. The aim of this study was to characterize the slowly conducting nerve fibres supplying the rat knee joint and to illustrate the usefulness of this model for objective studies of the pathophysiological aspects of articular nociception and pain.
Material and methods: Using an in vivo model, single afferent fibres innervating normal and inflamed knee joints were isolated and electrophysiologically characterized. Responses of these fibres were examined after local mechanical stimulation (von Frey hairs) and rotations consisting of inward and outward rotations of the knee joint within (non-noxious) and outside (noxious stimuli) its normal working range. The chemosensitivity of afferent fibres was tested by applying excitatory and sensitizing agents.
Results: The nerve fibres supplying the rat knee joint responded to mechanical and chemical stimuli (bradykinin, capsaicin). Bradykinin, substance P and prostaglandin E2 sensitized a considerable percentage of nerve fibres to mechanical stimuli.
Conclusions: The rat knee joint is a useful model to study nociception and inflammatory processes in an objective way. It can also be successfully used to study aspects of pain modulation.