Mechanical process and growth cartilages. Essential factors in the progression of scoliosis.

This study showed that the worsening of scoliosis was the result of a mechanical phenomenon. The key feature in this mechanical process was the finding that cuneal deformation affects only part of the vertebral body. The onset of scoliotic curvature occurred as a result of intervertebral motions. However, the worsening was essentially caused by deformation of the vertebral bodies. After the onset of scoliosis, the orientations of the vertebrae were modified in all three planes, and as a result, the spine became mechanically unstable. As a result of this mechanical instability, intervertebral pressures no longer were distributed equally but were concentrated at the junction of the growth cartilages of the vertebral body, near the pedicle on the concave side. Osseous growth was perturbed in this area, the vertebra became deformed, and the vertebral body became wedge shaped. These cuneal deformations resulted in a relative change of position between adjacent vertebral bodies and led to a worsening of the scoliotic curve without involving any articular motion. This phenomenon occurred mostly in the apical region because of the geometric shape of the curvature.