76 Dance Anatomy and Kinesiology
possible between adjacent vertebrae and tend to vary
significantly in different regions of the spine as seen
in figure 3.6. For example, in the lumbar region, the
more vertical alignment of the facet joints limits
the degree of possible rotation (figure 3.6C), while
in the thoracic (figure 3.6B) and cervical regions
(figure 3.6A) the facet orientation allows more free
rotation. While the forces on the facet joints are rela-
tively small in standing and sitting, during bending
and lifting the lumbar facets take on a greater role in
spinal stability by helping prevent one vertebra from
sliding forward on another (Fiorini and McCam-
mond, 1976). These facet joints can also undergogreater forces with hyperextension, lateral flexion,
and rotation; they have been shown to provide about
40% of the spine’s ability to resist rotational torsion
and must withstand 30% of the compression forces
accompanying hyperextension (Hall, 1999).
The facet joints are given further support by a
thin articular capsule and by more distant ligaments
of varying width and strength as seen in figure 3.4.
These ligaments span between adjacent transverse
processes (intertransverse ligaments [L. inter,
between]), laminae (ligamentum flavum), deeper
portions of the spinous processes (interspinous
ligaments), and tips of the spinous processes (supra-
spinous ligament [L. supra, above]). In the neck
region, the supraspinous ligament merges with the
ligamentum nuchae (L. nucha, back of the neck)
and actually provides a site for muscle attachment
(Moore and Agur, 1995). The ligamentum flavum
(L. flavus, yellow) also is unique in that its relatively
high elastic content (giving rise to its yellowish color)
allows it to aid with straightening the spine after it
has been flexed.
The various ligaments of the spine, including those
between the bodies and vertebral arches, have been
shown to be under tension during erect positions
and are very important for helping provide stability
to the vertebral column as a whole. The pre-tension
of these ligaments, in conjunction with the presence
of the intervertebral discs, helps resist the tendency
for the vertebral column to collapse. In addition,
the muscles, discussed shortly, are fundamental for
integrity as well as movements of the spine.Specialized Vertebral Joints
There are some specialized joints associated with the
vertebral column. These joints help link the head,
ribs, and pelvis to the spine.Craniovertebral Joints
The craniovertebral joints (G. kranion, skull)—the
atlanto-occipital and atlantoaxial joints—involve the
skull and the two most superior cervical vertebrae
(C1 and C2). These two uppermost vertebrae lack
an interposed intervertebral disc, are not typical in
shape, and are specialized to meet their function of
helping support and move the head. The first cervi-
cal vertebra is ringlike, without a body or spinous
process, as seen in figure 3.7A. Because it receives
the weight of the head, C1 is called the atlas (after
the mythical giant who is said to have supported the
pillars of heaven). Its superior concave, oval articular
facets join with two rockerlike projections located
on the lower skull (occipital condyles) to form theFIGURE 3.6 The role of the facet joints in spinal move-
ment (lateral view). Orientation of facets in (A) cervical
and (B) thoracic regions allows for more free rotation,
while (C) orientation in the lumbar region limits rotation.