Dance Anatomy & Kinesiology

78 Dance Anatomy and Kinesiology

to the shape and orientation of the ribs, elevation

creates more of an anterior increase in diameter in

the upper ribs and a lateral increase in diameter in

the lower ribs.

Lumbosacral Joint

The lower portion of the spine is specialized for

transference of weight through the pelvis. The joint

between the body of the last lumbar vertebra and

rigid sacrum (L5-S1), called the lumbosacral joint,

is very important for movements of the spine and for

the movements of the pelvis relative to the spine (the

latter are described in chapter 4). In addition to the

regular intervertebral ligaments, this joint receives

further stability from two paired ligaments that span

between the transverse processes of the lower lumbar

vertebrae and the crest of the ilium (iliolumbar liga-

ment) or sacrum (lumbosacral ligament). However,

despite additional ligamental support, due to greater

disc thickness and joint surface area there is much

greater motion possible at the lumbosacral joint than

between the initial lumbar vertebrae. Furthermore,

unlike the gradual transitions seen between the

other regions of the spine, a sharp angle termed the

lumbosacral angle occurs at the lumbosacral joint

as seen in figure 3.9. This sharp angle increases the

tendency for the upper vertebrae to slide forward on

the lower vertebrae (shear forces). The greater shear

FIGURE 3.8 The thoracic cage and selected key joints. (A) Anterior view of key joints, (B) lateral view, and (C) superior

view of joints between ribs and vertebrae.