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Chapter 9 Axial Skeleton: Osteology and Arthrology 327
tive bodies would block rotation in the sagittal and frontal
planes—allowing only tipping or translation. Finally, the space (superior) vertebral segment. During C4-C5 axial rotation to
created by the intervertebral discs provides adequate passage the left, for example, a point on the anterior body of C4 rotates
for the exiting spinal nerve roots. to the left, although the spinous process rotates to the right.
Impairments involving the apophyseal or the interbody Arthrokinematics of intervertebral motion describe the rela-
joints can result from trauma, cumulative stress, advanced age, tive movement between articular facet surfaces within the
disease, or combinations thereof. Regardless of cause, impair- apophyseal joints. Most facet surfaces are flat or nearly flat,
ments involving these joints can lead to abnormal and painful and terms such as approximation, separation (or gapping), and
kinematics, distorted posture, and mechanical impingement sliding adequately describe the arthrokinematics (Table 9-5).
of neural tissues. Appreciating the spatial and physical rela-
tionships between the neurology, osteology, and arthrology STRUCTURE AND FUNCTION OF THE APOPHYSEAL JOINTS
of a typical intervertebral junction greatly enhances one’s The vertebral column contains 24 pairs of apophyseal joints.
ability to understand and evaluate many of the approaches Each apophyseal joint is formed between opposing articular
used to treat spinal-related pain and dysfunction. facet surfaces (Figure 9-31). Mechanically classified as plane
joints, apophyseal joints are lined with articular cartilage and
TERMINOLOGY DESCRIBING MOVEMENT enclosed by a synovial-lined, well innervated capsule.
With few important exceptions, movement within any given Although exceptions and natural variations are common, the
intervertebral junction is relatively small. When added across articular surfaces of most apophyseal joints are essentially flat.
the entire vertebral column, however, these small movements Slightly curved joint surfaces are present primarily in the
can yield considerable angular rotation. The osteokinematics upper cervical and throughout the lumbar regions.
across the entire axial skeleton (which includes the vertebral
column and cranium) are described as rotations within the The word apophysis means “outgrowth,” emphasizing the
three cardinal planes. Each plane, or degree of freedom, is protruding nature of the articular processes. Acting as
associated with one axis of rotation, directed approximately mechanical barricades, the articular processes permit certain
through the body of the interbody joint (Figure 9-30).174 By movements but block others. In general, the near–vertically
convention, movement throughout the vertebral column, oriented apophyseal joints within the lower thoracic, lumbar,
including the head on the cervical spine, is described in a and lumbosacral regions block excessive anterior translation
cranial-to-caudal fashion, with the direction of movement of one vertebra on another. Functionally this is important
referenced by a point on the anterior side of the more cranial because excessive anterior translation significantly compro-
mises the volume of the vertebral canal—the space occupied
by the spinal cord or passing spinal nerve roots.
Axial rotation
Medial-lateral Anterior-
axis posterior
axis
Lateral
flexion
Flexion and
extension
Vertical axis
Terminology Describing the Osteokinematics of the Axial Skeleton
Common Terminology Plane of Movement Axis of Rotation Other Terminology
Flexion and extension Sagittal Medial-lateral Forward and backward bending
Lateral flexion to the right or left Frontal Anterior-posterior Side bending to the right or left
Axial rotation to the right or left* Horizontal Vertical Rotation, torsion
*Axial rotation of the spine is defined by the direction of movement of a point on the anterior side of the
vertebral body.
FIGURE 9-30. Terminology describing the osteokinematics of the vertebral column; illustrated for a typical
lumbar intervertebral junction.
