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.
Abnormal curvatures in some people results from developmental anomalies; in others, the curvatures result from pathological processes. The most prevalent metabolic disease of bone occurring in the elderly, especially in women, is osteoporosis. It is characterized by net demineralization of the bones caused by a disruption of the normal balance of calcium deposition and resorption. As a result, the quality of bone is reduced and atrophy of skeletal tissue occurs. Although osteoporosis affects the entire skeleton, the most affected areas are the:
- neck of the femur (thigh bone)
- the vertebrae
- the metacarpals (bones of the hand)
- the radius (of the forearm)
These bones become weakened and brittle, and are subject to fracture.
Fractures and Dislocations of the Vertebrae
Fractures, dislocations, and fracture-dislocations of the vertebral column usually result from sudden forceful movement e.g. a forceful flexion of the vertebral column, as occurs in automobile accidents or from a violent blow to the back of the head. The following are some common types:
- Compression/Wedge fracture - Compression/Wedge fracture can result from excessive flexion of the vertebrae leading to fractures affecting the anterior part of the vertebra. This also causes a slight abnormal bending anteriorly.
- Axial burst fracture - This is also caused by an excessive flexion, resulting from accidents like a fall from a height. However in this case, the vertebra loses height on both the anterior and posterior sides.
- Flexion/distraction (Chance) fracture - This fracture may result from accidents causing a vertebra to pull apart or become distracted from an adjacent vertebra due to forceful excessive flexion.
- Transverse process fracture - An excessive rotation or extreme lateral flexion may cause this form of fracture. However, this fracture is uncommon and when it does occur, it does not affect stability.
- Fracture-dislocation - This condition results in an unstable injury to the bone and some associated soft tissues of the vertebra involved. It is characterized by a displacement of the vertebra from alignment with an adjacent vertebra, causing serious spinal cord compression.
Excess Thoracic Kyphosis
This is clinically shortened to kyphosis, although this term actually applies to the normal curvature here, and is colloquially known as humpback or hunchback. It is characterized by an abnormal increase in the thoracic curvature, resulting in the vertebral column to curve posteriorly. This abnormality can result from erosion of the anterior part of one or more vertebrae (e.g., caused by osteoporosis). Dowager’s hump is a colloquial name for excess thoracic kyphosis in older women resulting from osteoporosis. However, excess kyphosis also occurs in the elderly men.
Osteoporosis especially affects the horizontal trabeculae of the trabeculae (spongy) bone of the vertebral body. The remaining unsupported vertical trabeculae are less able to resist compression and sustain compression fractures, resulting in short and wedge-shaped thoracic vertebrae. Progressive erosion and collapse of vertebrae also results in an overall loss of height, and the excess kyphosis leads to an increase in the anteroposterior (AP) diameter of the thorax.
Excess Lumbar Lordosis
This abnormality is clinically shortened to lordosis, although once again this term actually describes the normal curvature here. Colloquially, excess lumbar lordosis is known as hollow back or sway back. It is characterized by an anterior rotation of the pelvis (the upper sacrum tilts anteroinferiorly) at the hip joints, producing an abnormal increase in the lumbar curvature, resulting in the vertebral column to curve more anteriorly.
This abnormal extension deformity is often associated with weakened trunk musculature, especially the anterolateral abdominal muscles. To compensate for the alterations to their normal line of gravity, women develop a temporary excess lumbar lordosis during late pregnancy. This lordotic curvature may cause low back pain, but the discomfort normally disappears soon after childbirth. Obesity in both sexes can also cause excess lumbar lordosis and low back pain because of the increased weight of the abdominal contents (e.g., “potbelly”) anterior to the normal line of gravity. Loss of weight and exercise of the anterolateral abdominal muscles facilitate correction of this type of excess lordosis.
This can also be referred to as crooked or curved back. It is characterized by an abnormal lateral curvature that is accompanied by rotation of the vertebrae. The spinous processes turn toward the cavity of the abnormal curvature, and when the individual bends over, the ribs rotate posteriorly (protrude) on the side of increased convexity. Scoliosis is the most common deformity of the vertebral column in pubertal girls (ages 12-15 years).
Asymmetrical weakness of the intrinsic back muscle (myopathic scoliosis), failure of half of a vertebra to develop (hemivertebra), and a difference in the length of the lower limbs are causes of scoliosis. If the lengths of the lower limbs are not equal, a compensatory pelvic tilt may lead to a functional static scoliosis. When a person is standing, an obvious inclination or listing to one side may be a sign of scoliosis that is secondary to a herniated IV disc.
Habit scoliosis is supposedly caused by habitual standing or sitting in an improper position. When the scoliosis is entirely postural, it disappears during maximum flexion of the vertebral column. Sometimes there is kyphoscoliosis, excess thoracic kyphosis combined with scoliosis, in which an abnormal AP diameter produces a severe restriction of the thorax and lung expansion.