Persistence of Axial Rotation in Idiopathic Scoliosis Due to the Structural Changes of the Intervertebral Disc

There is some research about the morphological changes, spinal instability and causal factors influencing the mechanism of idiopathic scoliosis, however, there remains some controversy about its aetiology and pathogenesis [

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] and complementary research is required to better identify the causal factors and pathologic mechanism(s) involved in the initiation and development of idiopathic scoliotic deformities of spine. In this study, a validated three-dimensional, anatomically accurate, mathematical model of the mid-thoracic motion segment (T7-T8), which consists of all bony element, soft tissues and articular contact surfaces is utilized, enabling investigation the influence of collagen deficiency in the initiation and progression of idiopathic scoliosis deformity. Alteration in the structure of the intervertebral disc is applied to the model and the resulting geometrical changes together with the coupling behaviour are computed.

The results of the model demonstrate the significance of annulus fibrosus collagen fibre imbalance in developing a rotational effect in a motion segment, such as occurs in spinal deformities of idiopathic scoliosis. The structural changes of the annulus fibrosus alter the load displacement pattern of the motion segment and substantially provide the spine with a pattern of deformity under various loading conditions. It is observed that the subtle change in the pattern of collagen network structure results in a flexional rotation (coupled rotational and lateral displacements) due to the involvement of the posterior elements of the thoracic spine particularly during axial rotation. This continuous coupling effect, mainly flexional rotation can, in the long term, cause the morphological changes of the spine with characteristics of scoliotic deformity (axial rotation and lateral bending). The enhanced knowledge of aetiology of the idiopathic scoliosis, throughout understanding the functional characteristics of the annulus fibrosus and articular facets of the thoracic spine, together with the underlying clinical biomechanics and deformation mechanisms, may result in improved treatment of the spinal deformity through less invasive means.