There is a lack of research on the biomechanical properties of the spinal cord in scoliosis specimens. Dr Chu and colleagues have a biomechanical model in hand to test the asynchronous neuro-osseous growth concept of AIS. There is research on the biomechanical properties of the normal spinal cord in relation
in vivo kinematics caused by spinal movements [
16,
17,
46‐
50], viscoelastic properties [
51‐
56] and, some evidence for the development of an
anterior component of force in spinal forward flexion [
16]; the latter which may be relevant to scoliosis pathogenesis is not debated in this EFG.
From the biomechanical standpoint the
continuous axial neural tract (neuraxis) of pons, medulla oblongata, spinal cord and cauda equina is a functional unit between mesencephalon and lumbo-sacral ganglia [
17,
47]. When the normal adult spinal canal is elongated by forward flexion, the
neuraxis is axially stretched between its cranial and caudal points of fixation and, when backward extended, is slackened [
16,
17,
46‐
49]. Breig [
17] examined cadavers and living subjects and found that in
spinal flexion/extension the spinal cord: 1) unfolds and folds; 2) does not move up and down axially in the spinal canal but adapts to the varying length of the canal by
plastic deformation – lengthening in flexion and shortening in extension; 3) cross-sectional area decreases in flexion and increases in extension (Figure
2); and 4) resistance to further cord elongation in pronounced flexion is taken up primarily by pia mater and to a lesser extent by cord substance. In
lateral flexion, both spinal canal and
neuraxis elongate on the convexity and shorten on the concavity. During spinal flexion, or lateral flexion, there is slight elastic tension with cord lengthening limited by an unyielding pia mater. Breig [
17] suggested that processes which increase axial tension in the neuraxis namely,
changes in relative lengths of spinal canal and cord, can lead to
pathologic axial tension and damage the cord and spinal nerves by overstretching. In health, cord function, synaptic transmission, and metabolism all continue undisturbed within dynamically changing cord tissue [
46,
50].