The Spine 79FIGURE 3.9 The lumbosacral angle (lateral view). (A) Normal, (B) increased, (C) decreased.
and greater motion associated with the lumbosacral
joint and lower lumbar spine markedly increase the
risk for injury, and approximately 75% (Grabiner,
1989) of all serious back injuries occur at the L4-L5
and L5-S1 levels.
The lateral portions of the sacrum join with the
pelvis via the paired sacroiliac joints. These joints
will be discussed in chapter 4.
Movements of the Vertebral Column
Movements of the vertebral column can be described
relative to the spine as a whole or relative to a given
motion segment (segmental movement). A motion
segment is composed of two adjacent vertebrae and
their related soft tissue, including the interposed
intervertebral disc. Segmental movement varies
markedly by region (figure 3.10) (White III and Pan-
jabi, 1978), but in general, movements of the verte-
bral column are more free in the cervical and lumbar
region. In contrast, they are more limited (except for
rotation) in the thoracic region due to their struc-
tural linking to the relatively rigid rib cage.
In terms of specific joint movements, flexion is
greatest in the cervical region followed by the lumbar
region. It is more limited in the thoracic region due
to the presence of the ribs. Extension is most free in
the cervical and lumbar regions. It is more limited in
the thoracic region due to the longer, vertical spinous
processes and the orientation of the thoracic curve
(convex posteriorly). Lateral flexion is greatest in the
cervical and lumbar regions. It is more limited in the
thoracic region due to the ribs. Rotation is free in
the upper cervical region (atlantoaxial joint) and
the thoracic region. Rotation is more limited in the
lumbar region due to the more vertical orientation
of the facet joints that resist such motion. It is help-
ful to keep these movement ranges in mind when
one is analyzing and teaching the desired execution
of dance movements. For example, given the large
potential extension in the lower lumbar vertebrae
and the relatively low amount of extension in the
thoracic region, it is easy to see why many dancers
excessively arch the low back and do not achieve the
desired extension higher in the spine in movements
such as port de bras to the back.
While describing movements at individual motion
segments is key for research, injury prevention, and
rehabilitation, description of movements of the ver-
tebral column as a whole is important for movement
analysis and description of the actions of muscles.
And although movements between individual ver-
tebrae are relatively small and include only gliding
and cartilaginous joints, the summation of all of these
small movements produces a considerable range of
motion of the spine as a whole, more comparable to
that seen with a triaxial joint. Movements of the spine
(also termed trunk) include flexion-extension in the
sagittal plane, right lateral flexion-left lateral flexion
primarily in the frontal plane, and right rotation-left
rotation primarily in the transverse plane as seen in
figure 3.11.
However, in functional movement, due to various
factors, including the presence of the anteroposte-
rior curves of the spine and the facings of the facet
joints, movements of the spine often involve small
subtle movements in planes in addition to the plane
of the primary movement. For example, rotation is
generally associated with slight lateral flexion at the
segmental level. This consistent linking of motion