Curvature And Movements Of The Vertebral Column
The spine (also called the vertebral column or spinal column) is composed of a series of bones called vertebrae stacked one upon another. There are four regions of the spine, and they are:
- cervical (neck region)
- thoracic (chest/trunk)
- lumbar (low back region)
- sacral (pelvic), all four of which, correspond to the four curvatures of the vertebral column
The vertebral curvatures provide a flexible support (shock-absorbing resilience) for the body. The thoracic and sacral (pelvic) curvatures are concave anteriorly and are referred to as kyphoses (singular: kyphosis). They appear during the fetal period of embryonic development, hence they are also termed primary or developmental curvatures.
The primary curvatures are retained throughout life as a consequence of differences in height between the anterior and posterior parts of the vertebrae.
The cervical and lumbar curvatures are concave posteriorly and convex anteriorly, being referred to as lordoses (singular: lordosis). They appear later (although before birth) and are accentuated in infancy by support of the head and by the adoption of an upright or erect human posture. As a result, they are termed secondary or acquired curvatures.
Secondary curvatures are maintained by differences in thickness between the anterior and the posterior parts of the intervertebral discs (IV discs). The cervical curvature becomes fully evident when an infant begins to raise (extend) its head while prone and to hold its head erect while sitting. The lumbar curvature becomes apparent when an infant begins to assume the upright posture, while standing and walking. The lumbar curvature is more pronounced in females and ends at the lumbosacral angle formed at the junction of L5 vertebra with the sacrum. The sacral curvature also differs in males and females. That of the female is reduced so that the coccyx protrudes less into the pelvic outlet.
Spinal curvatures are classified as a spinal disease or dorsopathy when they are exaggerated in an individual. It includes the following abnormal curvatures:
- Excess Thoracic Kyphosis is an exaggerated kyphotic (concave) curvature in the thoracic region, also called hyperkyphosis. This produces the so-called "humpback" or "dowager's hump", a condition commonly resulting from osteoporosis.
- Excess Lumbar Lordosis as an exaggerated lordotic (convex) curvature of the lumbar region, also known as "lumbar hyperlordosis" or "swayback". Temporary excessive lordosis is common during pregnancy.
- Scoliosis, or a lateral curvature of the spine, is the most common abnormal curvature, occurring in 0.5% of the population. It is more common among females and may result from unequal growth of the two sides of one or more vertebrae, so that they do not fuse properly. It can also be caused by pulmonary atelectasis (partial or complete deflation of one or more lobes of the lungs) as observed in asthma or pneumothorax.
The range of movement of the vertebral column varies according to the region and the individual. Movements are extraordinary in some people, such as acrobats who begin to train in early childhood. The mobility of the vertebral column results primarily from the compressibility and elasticity of the IV discs. The following movements of the vertebral column are possible: flexion, extension, lateral flexion and rotation (torsion). The range of movement of the vertebral column is limited by the:
- Thickness, elasticity, and compressibility of the IV discs
- Shape and orientation of the facet joints
- Tension of the articular capsules of the zygapophysial joints
- Resistance of the back muscles and ligaments (such as the ligamenta flava and the posterior longitudinal ligament).
The back muscles produce movements of the vertebral column, but the movements are not produced exclusively by the back muscles. They are assisted by gravity and the action of the anterolateral abdominal muscles. Movement of the vertebral column are more free in the cervical and lumbar regions than elsewhere.