Page 352 - Kinesiology of the musculoskeletal system foundations for physical rehabilitation

328 Section III Axial Skeleton

TABLE 9-5. Terminology Describing the Arthrokinematics at the Apophyseal Joints

Terminology Definition Functional Example

Approximation of joint surfaces An articular facet surface tends to move closer to Axial rotation between L1 and L2 typically
its partner facet. Joint approximation is usually causes an approximation (compression)
Separation (gapping) between caused by a compression force. of the contralateral apophyseal joint
joint surfaces
An articular facet surface tends to move away from Therapeutic traction as a way to
Sliding (gliding) between joint its partner facet. Joint separation is usually decompress or separate the apophyseal
surfaces caused by a distraction force. joints

An articular facet translates in a linear or curvilinear Flexion-extension of the mid to lower
direction relative to another articular facet. cervical spine
Sliding between joint surfaces is caused by a
force directed tangential to the joint surfaces.

Posterior view

Superior articular Mammillary 45Њ
facet process C6

20Њ 20Њ

Transverse Axis
process

Intertransverse Apophyseal joint
ligament L2 (opened)

Apophyseal 15Њ L2
joint capsule T4
L3 Interspinous
ligament

Supraspinous ligament

FIGURE 9-31. A posterior view of the second and third lumbar 25Њ 25Њ
vertebrae. The capsule and associated ligaments of the right apophy-
seal joint are removed to show the vertical alignment of the joint FIGURE 9-32. Spatial orientations are displayed for a typical set of
surfaces. The top vertebra is rotated to the right to maximally expose superior articular facet surfaces (of apophyseal joints) from cervical,
the articular surfaces of the right apophyseal joint. Note the slight thoracic, and lumbar vertebrae. The red line indicates the plane of
gapping within the right apophyseal joint. the superior articular facet, measured against a vertical or horizontal
reference line.
The orientation of the plane of the facet surfaces within
each joint strongly influences the kinematics at different Anatomically, this joint is classified as a cartilaginous synar-
regions across the vertebral column. As a general rule, hori- throsis (see Chapter 2).
zontal facet surfaces favor axial rotation, whereas vertical facet Structural Considerations of the Lumbar Intervertebral Discs
surfaces (in either sagittal or frontal planes) block axial rotation. Most of what is known about the structure and function of
Most apophyseal joint surfaces, however, are oriented some- intervertebral discs is based on research performed in the
where between the horizontal and vertical. Figure 9-32 shows lumbar region.23 The research focus reflects the region’s dis-
the typical joint orientation for superior articular facets in the proportionately high frequency of disc degeneration, espe-
cervical, thoracic, and lumbar regions. The plane of the facet cially in the lower vertebral segments.
surfaces explains, in part, why axial rotation is far greater in
the cervical region than in the lumbar region. Additional A lumbar intervertebral disc consists of a central nucleus
factors that influence the predominant motion at each spinal pulposus surrounded by an annulus fibrosus (Figure 9-33).
region include the sizes of the intervertebral discs (relative to The nucleus pulposus is a pulplike gel located in the mid-to-
the associated vertebral bodies), the overall shape of the posterior part of the disc. In youth the nucleus pulposus
vertebrae, local muscle actions, and attachments made by within the lumbar discs consists of 70% to 90% water.188 The
ribs or ligaments. hydrated nucleus allows the disc to function as a modified
STRUCTURE AND FUNCTION OF THE INTERBODY JOINTS hydraulic shock absorption system, capable of continuously
From C2-C3 and L5-S1, 23 interbody joints can be found in dissipating and transferring loads across consecutive verte-
the spinal column. Each interbody joint contains an interver- brae. The nucleus pulposus is thickened into a gel-like con-
tebral disc, vertebral endplates, and adjacent vertebral bodies. sistency by relatively large branching proteoglycans. Each