Next, let’s take a look at the segmental
vertebral specification for our lumbar vertebrae.
And once you get into the lumbar area, a most
obvious structural change is that the vertebral
bodies get even larger than what we saw above
this particular segmental level. And the reason
that these vertebral bodies have to become
much more massive is that they are supporting
a greater weight of the body as gravity pulls
those forces inferiorly.
The vertebral foramen, if we look at it, it
tends to be triangular with the base of the
triangle oriented here along the vertebral
body and then the apex forming at the level
of the spinous process. Spinous processes
tend to be short and stout. And we can see
a spinous process at this particular level.
And there are two signature processes that
are associated with lumbar vertebrae.
The first of these are associated with the
superior articular processes. And if we look
here, we see one of these prominences and
we see one on the opposite side. And these
are referred to as mammillary processes. Associated
with the transverse processes, and we can
see one of those here fairly clearly, and
we see another one over here as well and we
see them here anteriorly. These are
accessory processes. And there’s a ligament
that will connect a mammillary process to
an accessory process with two adjacent vertebrae
and mammillary processes also serve as a point
of attachment for a muscle that we find in
the deep back, the multifidus.
Our next stop, segmentally, is to understand
the specification that’s associated with
the sacrum. And here we’re looking at an
adult sacrum where the five sacral vertebrae
have fused. This is a posterior view that
we are looking at. And the first thing that
we should note are these superior structures
here and here. These are superior articular
processes associated with the sacrum. These
then will articulate with the inferior articular
processes of the fifth lumbar vertebra.
If we look right here in the posterior midline,
we see what is referred to as the median sacral
crest. And when we think about the sacral
vertebrae fusing together here in this posterior
orientation, let’s think about the structures
that lie superior to this segment. And in
that posterior midline, we had spinous processes.
So, what happens here in the sacrum is that
spinous processes of adjacent vertebrae will
fuse to produce this median sacral crest.
We also have an intermediate sacral crest
that’s less noticeable, but it’s going
to be produced by articular processes, superior
and inferior sacral articular processes, that
are now fused in this adult form.
And then lastly, we have lateral sacral crests
and these are going to represent the point
of fusion of transverse processes. And we
also then will see here posteriorly, openings
four branches of sacral spinal nerves. And
we have four that come into view here and
we have four that come into view here.
Right in through here, we have the sacral
canal. And so, this results in the individual,
sacral foramina will fuse together. And then,
down below, we see an area that did not fuse
posteriorly and as a result of
the laminae of S5
here failed to fuse and as a result, that
will form the sacral hiatus.
Here’s an anterior view of this sacrum.
The first thing to note is the superior aspect
of the anterior body of S1. This is a very
prominent structure referred to as the sacral
promontory. And it is readily visible, discernible
on radiographs and it helps you identify your
vertebral level very, very readily. These
lateral extensions at this level are wing-like
extensions. In the anatomic terminology that
we’ll utilize for wing-like insections is
We also have these areas here. And these represent
the points of fusion between sacral bodies.
Here is the sacral body at this level, sacral
body here and this represents the point of
fusion between those sacral bodies. Similarly,
this area here is the fusion point between
S1 and S2. These are transverse ridges or
transverse lines. The inferior aspect, so
the inferior most projection of the sacrum
is termed the apex. And then we also have
foramina that are oriented anteriorly. And
these foramina will allow for the transmission
of branches of the typical spinal sacral nerves
at this level.
Here’s a lateral view of the sacrum and
it has a prominent feature that we see here
shaded in blue. Here we have articular cartilage.
And so, this is the articular region of the
sacrum and this point of articulation is with
the ilium. And we would have another articular
surface on the opposite side of the sacrum
to articulate with the opposite ilium.
And then our last segment is the coccyx. Generally,
it will have four fused coccygeal vertebrae,
and that’s exactly what we see in this view.
Here is the first, here’s the second, third
and then here’s our fourth coccygeal vertebra.
But again, there is some anatomic variability.
We may have three, we may have even up to
five. If we focus on the first coccygeal vertebra,
it will have these prominent horn-like projections
and these are referred to as the cornua. And
the cornua will often fuse with the sacrum.