A critical review of the evidence for a pain-spasm-pain cycle in spinal disorders.

The existence of a pain-spasm-pain cycle in musculoskeletal disorders has been debated for over 40 years. This paper reviews critically the evidence for such a cycle in patients with back pain. Clinical studies indicate that a substantial proportion of patients with back pain have muscle spasm. Patients with acute back pain have increased muscular activity on electromyography (EMG). EMG studies of patients with chronic back pain show, on the whole, an increase in activity in static postures, and a reduction of muscle activity during movement. Experimental evidence shows that pain may cause muscle spasm and that muscular activity can be painful. Further evidence for the existence of a pain-spasm-pain cycle comes from studies which show that analgesics can reduce muscle spasm, and that a variety of muscle relaxant techniques can reduce pain. There are substantial methodological problems in many of the studies cited, but the evidence reviewed provides general support for the existence of a pain-spasm-pain cycle. However further work is required to determine the nature of spasm and to evaluate methods for its detection, particularly in acute back pain syndromes. The value of therapeutic intervention may then be assessed.