Pathophysiology of joint pain.

The diversity of symptoms experienced by patients with musculoskeletal pain is in stark contrast to the relative paucity of effective treatment. The intensity and character of symptoms vary considerably and may be independent of the underlying disease. In some patients, pain may occur in the absence of demonstrable pathology, whereas in others obviously damaged joints may be relatively symptom free. The past few decades have seen a move away from the concept of a 'fixed' pain pathway towards acceptance of a more flexible system capable of a wide range of responses to varied stimuli. It is now appreciated that tissue injury and inflammation produce prolonged changes in the function and activity of the nervous system. This review will focus first on peripheral events leading to sensitisation and abnormal excitation of sensory nerves, and second on central mechanisms resulting in enhanced transmission in the dorsal horn of the spinal cord and elsewhere. While many aspects of clinical pain remain unclear, the relevance of these mechanisms to symptoms arising as a consequence of musculoskeletal disease will be explored.