57 Lumbar Spine

Marcos Gridi-Papp

Lumbar Vertebrae9

Lumbar vertebrae carry the greatest amount of body weight and are thus characterized by the large size and thickness of the vertebral body (Figure). They have short transverse processes and a short, blunt spinous process that projects posteriorly. The articular processes are large, with the superior process facing backward and the inferior facing forward.

Lumbar Vertebrae

This image shows the location and structure of the lumbar vertebrae. The left panel shows the location of the lumbar vertebrae (highlighted in green) along the vertebral column. The right panel shows the inferior articular process and the major parts are labeled.Lumbar vertebrae are characterized by having a large, thick body and a short, rounded spinous process.

Sacrum and Coccyx

The sacrum is a triangular-shaped bone that is thick and wide across its superior base where it is weight bearing and then tapers down to an inferior, non-weight bearing apex (Figure). It is formed by the fusion of five sacral vertebrae, a process that does not begin until after the age of 20. On the anterior surface of the older adult sacrum, the lines of vertebral fusion can be seen as four transverse ridges. On the posterior surface, running down the midline, is the median sacral crest, a bumpy ridge that is the remnant of the fused spinous processes (median = “midline”; while medial = “toward, but not necessarily at, the midline”). Similarly, the fused transverse processes of the sacral vertebrae form the lateral sacral crest.

The sacral promontory is the anterior lip of the superior base of the sacrum. Lateral to this is the roughened auricular surface, which joins with the ilium portion of the hipbone to form the immobile sacroiliac joints of the pelvis. Passing inferiorly through the sacrum is a bony tunnel called the sacral canal, which terminates at the sacral hiatus near the inferior tip of the sacrum. The anterior and posterior surfaces of the sacrum have a series of paired openings called sacral foramina (singular = foramen) that connect to the sacral canal. Each of these openings is called a posterior (dorsal) sacral foramen or anterior (ventral) sacral foramen. These openings allow for the anterior and posterior branches of the sacral spinal nerves to exit the sacrum. The superior articular process of the sacrum, one of which is found on either side of the superior opening of the sacral canal, articulates with the inferior articular processes from the L5 vertebra.

The coccyx, or tailbone, is derived from the fusion of four very small coccygeal vertebrae (see Figure). It articulates with the inferior tip of the sacrum. It is not weight bearing in the standing position, but may receive some body weight when sitting.

Sacrum and Coccyx

This figure shows the structure of the sacrum and coccyx. The left panel shows the vertebral column with the sacrum and coccyx highlighted in pink. The middle panel shows the anterior view and the right panel shows the posterior view of the sacrum and coccyx.

The sacrum is formed from the fusion of five sacral vertebrae, whose lines of fusion are indicated by the transverse ridges. The fused spinous processes form the median sacral crest, while the lateral sacral crest arises from the fused transverse processes. The coccyx is formed by the fusion of four small coccygeal vertebrae.

Marcos Gridi-Papp, Human Anatomy. OpenStax CNX. Mar 1, 2018. http://cnx.org/contents/c29920ff-cf11-4c44-a140-046fb0e6e1f0@2.57


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Introduction to Exercise Science for Fitness Professionals Copyright © 2021 by Marcos Gridi-Papp is licensed under a Creative Commons Attribution 4.0 International License, except where otherwise noted.

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