Movements of the spine occur primarily in the upper three regions. Spinal flexion, extension and hyperextension occur freely in all three regions . Lateral flexion occurs freely in the cervical and lumbar regions but is limited in the thoracic region by the rib attachments.
Rotation is freest at the top of the spine and least free at the bottom in the lumbar vertebrae.
With correct posture, there is a slight lordotic curve in the cervical region, a kyphotic curve in the thoracic region and a greater lordotic curve in the lumbar region. An abnormal posture with an exaggerated curvature of the spine in the thoracic region is called kyphosis and resembles a hunch back posture while excessive curvature in the lumbar region is called lordosis and resembles a sway back posture. A third abnormal posture, scoliosis , is evidenced by an S-shaped curvature of the spine when viewed from the back. The spine may be divided further into single functional units that consist of two vertebrae and the disk that separates them. The anterior portion of the vertebral functional unit is the weight bearing portion and is ideally constructed with two rounded vertebrae with flattened ends.