Intraoperative long-latency reflex activity in idiopathic scoliosis demonstrates abnormal central processing. A possible cause of idiopathic scoliosis.

Segmental reflex regulation in 37 patients with idiopathic scoliosis and 8 patients with nonidiopathic scoliosis was studied by recording evoked reflex muscle potentials from four muscle groups in each lower extremity during partial neuromuscular blockade. Effects on reflex activity mediated through descending systems arising in the brain stem were investigated by recording from proximal-distal and flexor-extensor muscles. Ipsilateral and contralateral long-latency complex polysynaptic activity was present in all 37 patients with idiopathic scoliosis. This reflex activity was absent in eight nonidiopathic scoliosis patients. Long-latency reflex activity may represent segmental disinhibition. The presence of long-latency reflex activity in patients with idiopathic scoliosis and the absence of this activity in nonidiopathic scoliosis patients with curves of equal magnitude demonstrates that the curve per se is not responsible for the activity. This would imply that abnormal reflex processing may play a role in the development of the spinal deformity in patients with idiopathic scoliosis.