Neurobiological basis of painful, function-disturbed joints

Joints are innervated by nociceptive nerve fibres (nociceptors), which are only activated by tissue-damaging stimuli. This activation causes pain in conscious humans. The sensory terminals of many nociceptors in the tissue are sensitized by inflammatory processes. Under these conditions, normally innocuous and non-painful stimuli are sufficient to activate nociceptors and to elicit pain. The effect of inflammatory mediators such as bradykinin and prostaglandins is important for the process of sensitization. In addition to their sensory function, many nociceptors have an efferent function. They evoke a neurogenic inflammation by the release of neuropeptides such as substance P and calcitonin gene-related peptide into the tissue. The efferent function of nociceptors contributes to the generation of inflammatory lesions of the tissue.