The pathogenesis of idiopathic scoliosis.

1. Scoliosis has four fundamental characteristic features as seen in the roentgenograms: Penetration or a transverse shift of the spine into the space surrounding it, contracture of the spine, rotation of the vertebrae, and compressions of the vertebrae on the concave side of the curve. 2. Penetration and compression are the essential scoliotic signs and are not encountered under physiological conditions. 3. The prevention of penetration is physiologically carried out by a passive mechanism. 4. The universal mechanical factor of all forms of acquired scoliosis is human gait, which in the presence of a definite pathological process brings about the deformity. 5. Rotation of the shoulders and of the trunk, or of the pelvis, is accompanied by rotation of the spine in the opposite direction. 6. The compression on the concave side is a primary characteristic of idiopathic scoliosis in the thoracic spine. 7. The vertebra is protected against undue compression by the disc, by the cartilaginous plate, and by the vertebral cortex which is composed of the end plates covering the upper and lower surfaces, of the circular bony hull, and of the epiphyseal ring. 8. The separation of the vertebral cortex from the intravertebral system, notably the separation of the epiphyseal ring and its partial displacement, represents the basic pathological process of idiopathic scoliosis in the thoracic spine. Separation is preceded by the infantile (juvenile) form of osteoporosis of the spine. 9. Postero-anterior roentgenograms reveal the presensce of channels crossing the vertebrae in a frontal direction. 10. The compressed vertebrae, as seen in the early stages, consist of two distinct portions: One is an ossified and porotic part, the core; the other, surrounding it or lying beside it, is a poorly or non-calcified, still more or less cartilaginous, portion. 11. In a typical case, idiopathic scoliosis of the thoracic spine starts in the cervicothoracic segment, and several years may pass before the middle and lower thoracic regions become involved. The process in the uppermost region presumably begins in the first four years of life. 12. Penetration and lateral movements, to the extent observed in scoliosis, are caused partly by subluxation in the articulations between the vertebrae. 13. Since idiopathic scoliosis of the lumbar spine is essentially of a rotatory nature without compression, a distinction is made between idiopathic scoliosis of the thoracic and lumbar spine. 14. Idiopathic scoliosis of the lumbar spine is made possible by congenital anomalies in the articular system of this region. The disappearance or decrease of the lumbar lordosis materially contributes to the development of the deformity. 15. Extrusion of the epiphyseal ring, if it occurs at all, is mostly a late phenomenon in the lumbar region. 16. The lumbar type of idiopathic scoliosis is characterized by rotation in the same direction of all vertebrae involved. The lumbar type is prognostically more favorable than the type involving the thoracic spine. 17. The prognostically most serious cases are those in which the congenital anomalies in the lumbar segment are combined with the pathological process encountered in the thoracic type of the deformity.