The spinal column (spine or backbone) consists of multiple bones that mechanically connect the upper and lower portions of the body. As a unit, the spine enables movement in three rotational degrees of freedom including forward/backward bending, bending to the side, and twisting about the axis of the spine.
The spine is divided into the cervical, thoracic, lumbar, sacral, and coccyx regions. The sacral and coccyx are fused and are also part of the pelvic girdle. The spinal column supports weight and other forces between the upper and lower portions of the body, and it protects the spinal cord. The cervical, thoracic, and lumbar spine consist of a stack of individual vertebrae separated by intervertebral discs and held together by strong ligaments. Each functional spinal unit, consisting of two adjacent vertebrae and the intervertebral discs, contributes toward overall spinal movement.
Biomechanically, the spine may be modeled in a variety of different ways. Lower-order models are appropriate for small movements and often include a single pivot point in the lumbar or cervical spine. Higher-order models take into account individual vertebrae as well as the spinal curvature associated with larger movements.
The upper spine connects to the occipital bone at the base of the skull through the atlanto-occipital joint. This joint, in combination with the other joints in the cervical spine, enables the head to move in a variety of different ways. Injury, disease, or inflammation can result in neck pain. The thoracic spine connects to the ribs to form the rib cage. The lumbar spine connects the trunk to the pelvic girdle at the lumbosacral joint. This joint in combination with the other joints in the lumbar spine enables movement in three rotational degrees of freedom (range of motion varies). Injury, disease, or inflammation can result in low back pain, a common medical condition affecting four out of five people at some point within their lifetimes.
