Relative shortening and functional tethering of spinal cord in adolescent scoliosis – Result of asynchronous neuro-osseous growth, summary of an electronic focus group debate of the IBSE

Abstract

There is no generally accepted scientific theory for the causes of adolescent idiopathic scoliosis (AIS). As part of its mission to widen understanding of scoliosis etiology, the International Federated Body on Scoliosis Etiology (IBSE) introduced the electronic focus group (EFG) as a means of increasing debate on knowledge of important topics. This has been designated as an online Delphi discussion. The Statement for this debate was written by Dr WCW Chu and colleagues who examine the spinal cord to vertebral growth interaction during adolescence in scoliosis. Using the multi-planar reconstruction technique of magnetic resonance imaging they investigated the relative length of spinal cord to vertebral column including ratios in 28 girls with AIS (mainly thoracic or double major curves) and 14 age-matched normal girls. Also evaluated were cerebellar tonsillar position, somatosensory evoked potentials (SSEPs), and clinical neurological examination. In severe AIS compared with normal controls, the vertebral column is significantly longer without detectable spinal cord lengthening. They speculate that anterior spinal column overgrowth relative to a normal length spinal cord exerts a stretching tethering force between the two ends, cranially and caudally leading to the initiation and progression of thoracic AIS. They support and develop the Roth-Porter concept of uncoupled neuro-osseous growth in the pathogenesis of AIS which now they prefer to term 'asynchronous neuro-osseous growth'. Morphological evidence about the curve apex suggests that the spinal cord is also affected, and a 'double pathology' is suggested. AIS is viewed as a disorder with a wide spectrum and a common neuroanatomical abnormality namely, a spinal cord of normal length but short relative to an abnormally lengthened anterior vertebral column. Neuroanatomical changes and/or abnormal neural function may be expressed only in severe cases. This asynchronous neuro-osseous growth concept is regarded as one component of a larger concept. The other component relates to the brain and cranium of AIS subjects because abnormalities have been found in brain (infratentorial and supratentorial) and skull (vault and base). The possible relevance of systemic melatonin-signaling pathway dysfunction, platelet calmodulin levels and putative vertebral vascular biology to the asynchronous neuro-osseous growth concept is discussed. A biomechanical model to test the spinal component of the concept is in hand. There is no published research on the biomechanical properties of the spinal cord for scoliosis specimens. Such research on normal spinal cords includes movements (kinematics), stress-strain responses to uniaxial loading, and anterior forces created by the stretched cord in forward flexion that may alter sagittal spinal shape during adolescent growth. The asynchronous neuro-osseous growth concept for the spine evokes controversy. Dr Chu and colleagues respond to five other concepts of pathogenesis for AIS and suggest that relative anterior spinal overgrowt...

Variation in Anisotropy and Diffusivity along the Medulla Oblongata and the Whole Spinal Cord in Adolescent Idiopathic Scoliosis: A Pilot Study Using Diffusion Tensor Imaging

“…10 Geissele et al 31 following the curve of scoliosis on T2-weighted MR imaging. In previous works, 7,8,30 significantly reduced ratios of spinal cord to vertebral column were found in patients with AIS by using multiplanar reformatted MR imaging. All the above observations were based on conventional MR imaging, which only revealed macroscopic information of the brain stem and spinal cord.…”

“…29,30 MR imaging has long been used for assessment of the brain and spinal cord in AIS in view of its high resolution and excellent soft-tissue contrast. 10 Geissele et al 31 following the curve of scoliosis on T2-weighted MR imaging.…”

Adolescent Idiopathic Scoliosis: Etiological concepts and implication for treatment

“…The authors speculate that the initiation and progression of AIS result from vertebral column overgrowth through a lordoscoliotic maladaptation of the spine to the subclinical tether of a relatively short spinal cord. This interpretation accommodates both the lordotic and the dorsal shear force concepts for the pathogenesis of AIS 3,4 . Although functional tethering of the spinal cord is partly accepted as a concept of AIS aetiology restriction of neck flexion -a possible sign for tethering ( Figure 1) -with AIS has not been reported except for a special group of boys 5,6 .…”

“…neuromuscular, congenital, due to certain syndromes or tumours), the majority of the patients with scoliosis (80-90%) are 'idiopathic' as a certain underlying cause is not apparent 1,2 . In the absence of any accepted scientific theory for the aetiology of idiopathic scoliosis, treatment remains pragmatic with a very incomplete scientific basis 3 . In severe adolescent idiopathic scoliosis (AIS) compared with normal subjects, the thoracic vertebral column is significantly longer without detectable change in spinal cord length evaluated as cord-to-vertebral length ratios 4 .…”

“…Although functional tethering of the spinal cord is partly accepted as a concept of AIS aetiology restriction of neck flexion -a possible sign for tethering ( Figure 1) -with AIS has not been reported except for a special group of boys 5,6 . The hypothesis of asynchronous neuro-osseous growth 3 proposes that the relative short cord can lead to hypokyphosis in the thoracic area and hence curve initiation with or without progression of the scoliosis. Therefore, it might be the starting point as well as an aggravating factor in the 'vicious cycle' hypothesis of Dr Stokes 7 .…”