Morphological and functional electrophysiological evidence of relative spinal cord tethering in adolescent idiopathic scoliosis

Study Design. Magnetic resonance ( MR) imaging and multiplanar reconstruction was used to evaluate the morphology and relative position of the spinal cord in adolescent idiopathic scoliosis ( AIS). Objective. To determine the longitudinal and cross-sectional morphology of spinal cord in AIS subjects versus normal controls and their correlation with relative position of cerebellar tonsils and somatosensory cortical evoked potentials ( SSEP). Summary of Background Data. Our previous studies revealed significantly reduced spinal cord to vertebral column length ratios in AIS patients with severe scoliotic curves suggesting the presence of disproportional growth between the neural and skeletal system. A possible neural origin of etiopathogenesis of AIS is suggested. Methods. MR multiplanar reconstruction was performed in 97 adolescent girls ( 35 moderate, 26 severe AIS with right-sided thoracic/thoracolumbar curve, and 36 age-matched controls). Measurements of the ratio of anteroposterior ( AP) and transverse ( TS) diameter of the cord, the concave and convex lateral cord space ( LCS) were obtained at the apical level in AIS subjects. Same parameters were obtained in normal controls at matched vertebral levels. Correlations were made with cord to vertebral column length ratio, cerebellar tonsil position and SSEP findings. Results. AP/TS cord ratio and LCS ratio were increased in AIS subjects in the presence of reduced spinal cord to vertebral length ratio when compared with normal controls ( P < 0.05). The above ratios were exaggerated in AIS subjects with abnormal SSEP findings. The AP/TS cord ratio and LCS ratio were negatively correlated with the cord to vertebral column length ratio ( rho = - 0.410 and - 0.313, P < 0.01) and cerebellar tonsillar level ( rho = - 0.309 and - 0.432, P < 0.01). Conclusion. Our study suggests presence of tethering and increased tension along the longitudinal axis of spinal cord with associated morphologic changes of cross-sectional shape and relative position of the cord.