Idiopathic scoliosis and the central nervous system: a motor control problem. The Harrington lecture, 1983. Scoliosis Research Society.

An etiologic concept linking an impaired axial motor control system to the structural deformity of idiopathic scoliosis (ISc) is proposed. Postural studies reveal that during quiet stance, adaptation is marked in conditions associated with visual control of sway, particularly of lateral sway; during imposed perturbations of the body, destabilized postural reactions are pronounced in tests requiring visual-vestibular coupling. Observations of visual and/or vestibular generated eye movements indicate ocular instability among a high proportion of the ISc. Previously, the authors argued that a direct relationship exists between visual and/or vestibular functioning and a disordered axial motor system. This was attributed to an aberrant brain stem mechanism. In this presentation, however, we propose that a higher level CNS disturbance may be responsible for reports of EEG abnormalities, visuo-spatial impairment, motor adaptation, and learning deficits. Among the wide range of visual-vestibular variables studied, those representing processing of vestibular signals within the CNS yield the highest degree of correlation with the magnitude of the curve. Moreover, differences in vestibular processing between two subsets of ISc, namely ISc with (70%) and without (30%) normal academic achievement are significant. Variables referable to both vestibular and visual processing correctly classify 87% of the ISc with normal academic achievement and 100% of the ISc with a history of academic problems. The association between learning deficits, altered processing of vestibular information, and ISc suggest a unique syndrome complex, and an important role of cortical structures in the etiology of this disorder. The presence of a visuo-spatial perceptual impairment may be the common feature of ISc. In an attempt to restore perceptual dysfunction (by rearrangement), the ISc adopts a new axial and vestibular motor control strategy based upon recalibration or reinterpretation of proprioceptive signals arising from the axial musculature.