Curvature and movements of the vertebral column
The vertebral column, also known as the spine, is composed of a series of bones called vertebrae, which are stacked one upon another and interconnected by cartilaginous intervertebral discs to form a column. It forms the skeleton of the neck and back and is divided into five regions based on structure and location of the vertebrae. The alignment of the vertebrae within the vertebral column results in the formation of the four normal curvatures.
The vertebral column is largely flexible and capable of a range of motions and movements, such as flexion, extension, lateral flexion and rotation and thus, plays an important role in body posture and movement. The major functions of the vertebral column are to protect the spinal cord and spinal nerves particularly from mechanical trauma, and to support the weight of the body above the pelvis.
Cervical spine: C1 - C7 (C1= atlas, C2= axis)
Thoracic spine: T1 - T12
Lumbar spine: L1 - L5
Sacral spine: S1 - S5, fused into unique bone → sacrum
Coccyx: 3 - 5 fused vertebrae that form the tailbone
Cervical curve (C2-T2): convex anteriorly → cervical lordotic curve
Thoracic curve (T2-T12): concave anteriorly → thoracic kyphotic curve
Lumbar curve (T12 - sacrovertebral angle): convex anteriorly → lumbar lordotic curve
Sacral curve (sacrovertebral articulation - coccyx): concave anteriorly → sacral kyphotic curve
|Movements||Flexion, extension, lateral flexion, rotation (torsion)|
|Clinical significance||Dorsopathies, osteoporosis, fractures, dislocations of vertebrae|
This article will discuss the anatomy and function of the vertebral column as well as relevant clinical relations.
- Clinical correlation
The vertebral column is composed of 33 vertebrae separated by fibrocartilaginous intervertebral discs (IV discs) that unite to form a single unit supported by strong joints and ligaments. It extends from the base of the skull to the pelvis, with the vertebra generally increasing in size moving caudally, to support increasing amounts of the body’s weight which is ultimately transferred from the sacrum to the pelvic girdle. From here, it subsequently reduces in size towards the apex of the coccyx.
The vertebral column is grouped into five regions. Craniocaudally, these include seven cervical vertebrae between the skull and the thorax, twelve thoracic vertebrae which articulate with the ribs, five lumbar vertebrae, five fused sacral vertebrae which form the sacrum and 3-4 fused coccygeal vertebrae that form a single triangular bone called the coccyx. In the adult, the vertebral column has four normal curvatures, the cervical, thoracic, lumbar and sacral curvatures. These curvatures are more evident from a lateral view of the vertebral column. Their main function is to provide a flexible and dynamic support (shock-absorbing resilience) for the body and to protect the vertebral column from injury.
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. As a consequence of differences in height between the anterior and posterior parts of the vertebrae, the primary curvatures are preserved throughout life. It is important to note that the sacral curvature differs in males and females; the latter is less pronounced so that the coccyx protrudes less into the pelvic outlet, making it suitable for childbirth.
The cervical and lumbar curvatures are concave posteriorly and convex anteriorly, being referred to as lordoses (singular: lordosis). These curvatures arise as a consequence of extension from the flexed fetal position. Although they begin to appear before birth, they are not apparent until later in infancy when they are accentuated 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.
The cervical curvature becomes apparent when an infant begins to raise the head while prone and to maintain the head erect when sitting. The lumbar curvature becomes more evident when an infant begins to stand and walk in an upright posture. The lumbar curvature is more pronounced in females and ends at the lumbosacral angle which is formed at the junction of L5 vertebra with the sacrum. Differences in thickness between the anterior and the posterior parts of the intervertebral discs are mainly responsible for maintaining these secondary curvatures.
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The range of motion of the vertebral column depends on the specific region involved and the individual performing the movement. Some acrobats who start their training at a young age are capable of extraordinary movements. Although very little movement is permitted between any two adjacent vertebrae, movement of the vertebral column typically involves a number of segments acting as a unit. The summation of the relatively small movements results in a considerable range of movement of the entire vertebral column or specific regions of it.
The principal movements permitted by the vertebral column are: flexion (bending forward), extension (bending backwards), lateral flexion (bending right/left), and rotation (torsion/twisting). The thickness, compressibility and elasticity of the IV discs are features that primarily permit movements of the vertebral column. Thus, the extent to which the IV discs are deformed significantly affects the range of movements at each region. In addition to this, there are other anatomical constraints that may limit the range of motion depending on the specific region of the vertebral column. These include the:
- Shape and orientation of the zygapophyseal (facet) joints
- Tension of the articular capsules of the zygapophyseal (facet) joints
- Attachment to the thoracic (rib) cage
- Resistance of the back muscles and ligamentous complexes (such as the ligamenta flava and the posterior longitudinal ligament)
- Surrounding soft tissue bulk
The various movements of the vertebral column are produced by the action of the back muscles, anterolateral abdominal muscles and the muscles of the neck with assistance by gravity. These movements are much easier and freer in the cervical and lumbar regions than other regions such as the thoracic region, which is relatively stable due to its attachment to the thoracic (rib) cage.
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Abnormal or exaggerated curvatures of the spine (also called spinal disease or dorsopathy) 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.
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 posterior curvature of the vertebral column. 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 at the hip joints (the upper sacrum tilts anteroinferiorly), producing an abnormal increase in the lumbar curvature, causing 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 the most common abnormal curvature, occurring in 0.5% of the population and is more common among females. The condition 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.
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.
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