Sacral Spine | Anatomy of the spine

Sacral Spine

The so-called sacrum originally consists of five independent vertebrae. After the birth, however, these merge uniformly to one in the view from the front triangular looking bone. Nevertheless, the sacrum still possesses all characteristics of a vertebra.

The fused vertebrae form four T-shaped bone channels in the upper area, through which the sacral nerves emerge. The fused spinous processes form a jagged bone ridge on the convex posterior surface. At each side of this, the fusion of the transverse processes with the rib rudiments on both sides of the sacrum creates the powerful lateral parts, which carry on their sides ear-shaped joint surfaces for the iliac bones of the pelvis. The sacrum is followed by the coccyx with three to four vertebral rudiments. At least the first coccyx vertebra usually still shows typical structural elements.

Ligamentous apparatus of the spinal column

The spinal ligaments lead to a stable connection of the vertebrae with each other and allow high mechanical loads. Within the ligamentous apparatus, vertebral body ligaments and vertebral arch ligaments can be distinguished from one another. The anterior vertebral ligament runs broadly along the front of the vertebral bodies from the base of the skull to the sacrum.

With its deep fibers, it connects adjacent vertebral bodies; with its superficial portions, it extends over several segments. This ligament is only loosely connected to the intervertebral discs. The posterior ligament of the vertebral bodies runs from the posterior fossa through the back of the vertebral bodies into the sacral canal.

In contrast to the anterior ligament, the posterior ligament is firmly fused with the intervertebral disc. Both ligaments are involved in maintaining the curvature of the spinal column. As the name suggests, the vertebral arch ligaments run between the vertebral arches and also between the spinous and transverse processes, thus creating additional stability.

Range of movement of the spine

The vertebral arch joints (so-called small vertebral joints) are responsible for the mobility of the spine. They are formed by the articular processes of the vertebral arches and are arranged in pairs. Since they are tilted against the horizontal to varying degrees depending on the spinal column section, they have a certain range of motion and special directions of movement (see table). In general, the following movements are possible: The following table shows the extent of movement in the individual sections of the spinal column Cervical spine (cervical): Thoracic spine (thoracic): Lumbar spine (lumbar): Cervical+BWS+ lumbar:

  • Forward flexion (ventral flexion)
  • Backward flexion (dorsal extension)
  • Lateral flexion (lateral flexion)
  • Rotation (Rotation)
  • Forward bending: 65
  • Backward flexion: 40
  • Sideways bending: 35
  • Rotation: 50°.
  • Forward bending: 35
  • Backward bending: 25°.
  • Sideways bending: 20
  • Rotation: 35°.
  • Forward bending: 50
  • Backward bending: 35°.
  • Sideways bending: 20
  • Rotation: 5°.
  • Forward bending: 150
  • Backward bending: 100°.
  • Sideways bending: 75
  • Rotation: 90°