Anatomy of the Back and Vertebral Column

Overview of Back

• The back is the posterior aspect of the trunk, inferior to the neck and superior to the buttocks.
• It comprises skin, subcutaneous tissue, muscles, vertebral column, ribs, spinal cord, and meninges.
• The back is the region where the head, neck, and limbs are attached.

Overview of Vertebral Column

• The vertebral column is the skeleton of the neck and back that forms the axial skeleton.
• It extends from the cranium to the apex of the coccyx, approximately 72-75 cm long.
• The vertebral column:
  • Protects the spinal cord and spinal nerves.
  • Supports the weight of the body superior to the level of the pelvis.
  • Provides a partly rigid and flexible axis for the body.
  • Plays an important role in posture and locomotion.

Vertebrae

• There are 33 vertebrae in an adult, arranged in five regions: 7 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 4 coccygeal.
• Significant motion occurs only between the 25 superior vertebrae.
• The vertebrae gradually become larger as the vertebral column descends to the sacrum and then become progressively smaller towards the apex of the coccyx.
• The vertebral column is flexible due to the many small bones separated by resilient intervertebral discs.

Structure and Function of Vertebrae

• A typical vertebra consists of a vertebral body, vertebral arch, and seven processes.
• The vertebral body is the more massive, roughly cylindrical, anterior part of the bone that gives strength to the vertebral column and supports body weight.
• The size of the vertebral bodies increases as the column descends, most markedly from T4 inferiorly, as each bears progressively greater body weight.
• The vertebral body consists of vascular, trabecular (spongy, cancellous) bone enclosed by a thin external layer of compact bone.

Sacrum

• The sacrum provides strength and stability to the pelvis and transmits the weight of the body to the pelvic girdle.
• The sacral canal is the continuation of the vertebral canal in the sacrum, containing the bundle of spinal nerve roots arising inferior to the L1 vertebra.
• There are four pairs of sacral foramina on the pelvic and posterior surfaces of the sacrum for the exit of the posterior and anterior rami of the spinal nerves.
• The sacrum is tilted so that it articulates with the L5 vertebra at the lumbosacral angle, which varies from 130° to 160°.

Movements of the Vertebral Column

• The range of movement of the vertebral column varies according to the region and the individual.
• The vertebral column is capable of flexion, extension, lateral flexion, and rotation (torsion).
• The range of movement is limited by the:
  • Thickness, elasticity, and compressibility of the intervertebral discs.
  • Shape and orientation of the zygapophysial joints.
  • Tension of the joint capsules of the zygapophysial joints.
  • Resistance of the back muscles and ligaments.
  • Attachment to the thoracic (rib) cage.
  • Bulk of surrounding tissue.

Nerves of Vertebral Column

• As the spinal nerves exit the intervertebral foramina, most of the meningeal branches run back through the foramina into the vertebral canal.
• Some branches remain outside the canal and are distributed to the anterolateral aspect of the vertebral bodies and intervertebral discs.
• The nerves also supply the periosteum, annuli fibrosi, and anterior longitudinal ligament.
• Inside the vertebral canal, transverse, ascending, and descending branches distribute nerve fibers to the:
  • Periosteum.
  • Ligamenta flava.
  • Anuli fibrosi of the posterior and posterolateral aspect of the intervertebral discs.
  • Posterior longitudinal ligament.
  • Spinal dura mater.
  • Blood vessels within the vertebral canal.