Page 80 - ASOP ROT Study Guide

14 . 4 Sacrum and Coccyx

The sacrum consists of a triangular shaped bone which is really five vertebral segments fused to
form one irregular bone. There is of course no movement at the sacrum itself because it is made of
fused segments. Like the other vertebrae it also has nerves coming out of it. The junction between
the sacrum and the lumbar spine is very mobile and so is a site prone to wearing diseases
The sacrum not only forms part of the spine but it also forms one of the three bones of the pelvic
ring, as described in Unit 2A. Its principal role is to provide a link between the pelvic girdle and
the lumbar spine. The coccyx is a primitive residue of our tail! There are no nerves associated
with coccygeal segments.

15. THE VERTEBRAE

15 . 1 Typical Vertebra

The spine is made up of a stack of vertebrae, which are irregular bones. Each vertebra consists
of a cylindrical shaped bony body, which is separated from the adjacent vertebrae at the front by an
intervertebral disc, which will be described in detail later.

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At the rear of the spine there is an arch of bone (the neural arch) on each vertebra which abuts
onto similar arches on adjacent vertebrae forming a tunnel or conduit, known as the spinal
foramen, down which the spinal cord and nerves pass.

On either side of the arch on each vertebra is a pair of synovial joints known as facet joints. The
upper facet of a vertebra articulates with the lower facet of the vertebra above. The lower facet
articulates with the upper facet of the vertebra below.

Each vertebra has three bony bars projecting from it. The one at the back is the spinous process
and the ones on either side are the transverse processes. They are anchorage sites for ligaments
and muscles which stabilize and move the spine.