ABSTRACT
Pain in the musculoskeletal system is of major clinical importance because it is frequent and often chronic. In general, the deep somatic tissue is a major site of injury, acute and chronic inflammatory processes, and degenerative disease. Inflammatory conditions cause similar pain symptoms in all somatic deep tissues, namely hyperalgesia with increased responses to noxious stimuli and occurrence of pain upon innocuous mechanical stimulation. Pain during degenerative osteoarthritis shows similarities and differences to inflammatory arthritic pain. Joints are supplied by branches descending from main nerve trunks or their muscular, cutaneous, and periosteal branches. Muscle nerves contain axons from motoneurons, sensory neurons, and postganglionic sympathetic neurons. In muscle nerve, inflammation enhances the proportion of Aδ-fibers showing resting discharges, as well as the discharge rate in spontaneously active fibers. Neurons with input from joint and muscle are located in the superficial and deep dorsal horn. Central sensitization has been observed during peripheral inflammation and in models of neuropathic pain.
