How the Vertebrae Are Grouped
The vertebral column consists of 33 vertebrae located in five regions. The cervical, thoracic, lumbar and cervical regions are well known, but there is a coccygeal region too with 4 vretebrae. The vertebrae in these spinal regions all have unique characteristics.
Fractures of the vertebrae are often due to forceful compression and/or flexion as a result of a traumatic accident such as a bad car accident. Diving into a shallow pool or lake can result in a compression fracture when the diver hits his or her head on the pool floor or lake bottom.
Cervical, thoracic, and lumbar vertebrae
The seven cervical vertebrae (C1–C7) are found in the posterior region of the neck and include two atypical and five typical vertebra. Twelve thoracic vertebrae (T1–T12) form the most posterior part of the thoracic cage, and five lumbar vertebrae (L1–L5) form the lower back:
Atypical cervical vertebrae (C1–C2): These vertebrae are also called the atlas (C1) and the axis (C2).
The atlas doesn’t have a vertebral body or a spinous process; it has two lateral masses connected by a posterior arch and an anterior arch. The superior portion of each lateral mass has an articular surface that articulates (forms a joint) with the skull and a similar surface inferiorly that articulates with the axis.
The axis has a superiorly pointing projection called the odontoid process (or sometimes called the dens). The atlas pivots around the odontoid process.
Typical cervical vertebrae (C3–C7): These vertebrae have bodies that are smaller than the other types, and the vertebral foramina are large and triangular in shape. The spinous processes are shorter and bifid (split into two projections) on the 3rd, 4th, and 5th vertebrae. The superior facets face upward and backward, and the inferior facets face downward and forward. Each transverse process includes a foramen transversarium, which allows passage of the vertebral artery and vein.
Thoracic vertebrae (T1–T12): These 12 vertebrae have medium-sized bodies that are heart shaped with small vertebral foramina. The spinous processes are quite long; in fact, some slope inferiorly to the level of the vertebra below. Most thoracic vertebrae have costal facets on the transverse processes that articulate with the ribs, with the exception of T11 and T12, which don’t have those facets. The superior facets face backward but more laterally than the cervical vertebrae. The inferior facets face forward and medially.
Lumbar vertebrae (L1–L5): These vertebrae are large and have kidney-shaped bodies with short, rectangular spinous processes. The transverse processes are long and slender. The superior facets face medially, and the inferior facets face laterally.
The sacrum and the coccyx
Five partial vertebrae (S1–S5) in the sacral region fuse to form the wedge-shaped sacrum. The broad superior surface serves as a base of the vertebral column. The narrow inferior surface of the sacrum forms a joint with the coccyx. What’s that, you ask? The coccyx, or tailbone, hangs inferiorly from the sacrum. It’s formed from the fusion (or partial fusion) of three to five small vertebrae.
The median sacral crest is formed by the fused spinous processes and is palpable under the skin. The sacral canal is formed from the vertebral foramina of the sacral segments and contains the sacral and coccygeal spinal roots.