Page 336 - Kinesiology of the musculoskeletal system foundations for physical rehabilitation

312 Section III Axial Skeleton
Posterior end Inferior view
Articular tubercle Angle
for transverse Neck Costal groove
process
Articular facet for Head
vertebral body
Body
A Anterior end
FIGURE 9-6. A typical right rib. A, Inferior view. B, Posterior view.
The lateral edge of the body of the sternum is marked by
a series of costal facets that accept the cartilages of ribs 2 to 7. The human vertebral column consists of a series of reciprocal
The arthrology of the sternocostal joints is discussed in greater
detail in Chapter 11, within the context of ventilation. The
xiphoid process is attached to the inferior end of the body of
the sternum by the xiphisternal joint. Like the manubriosternal
joint, the xiphisternal joint is connected primarily by fibrocar-
tilage. The xiphisternal joint often ossifies by 40 years of age.188 anteriorly and concave posteriorly, exhibiting an alignment
Vertebral Column as a Whole
The vertebral (spinal) column consists of the entire set of verte-
brae. The word “trunk” is a general term that describes the
body of a person, including the sternum, ribs, and pelvis but
excluding the head, neck, and limbs.
The vertebral column usually consists of 33 vertebral bony
segments divided into five regions. Normally there are seven
cervical, twelve thoracic, five lumbar, five sacral, and four coc-
cygeal segments. The sacral and coccygeal vertebrae are usually
fused in the adult, forming individual sacral and coccygeal
bones. Individual vertebrae are abbreviated alphanumerically;
for example, C2 for the second cervical, T6 for the sixth
thoracic, and L1 for the first lumbar. Each region of the
vertebral column (e.g., cervical and lumbar) has a distinct
morphology that reflects its specific function and movement
potential. Vertebrae located at the cervicothoracic, thoraco-
lumbar, and lumbosacral junctions often share characteristics
that reflect the transition between major regions of the verte-
bral column. It is not uncommon, for example, for the trans-
verse processes of C7 to have thoracic-like facets to accept a
rib, or L5 may be “sacralized” (i.e., fused with the base of the
sacrum).
Posterior view
Neck
Posterior end
Head
Articular tubercle for
transverse process
Angle
Costal groove
B
NORMAL CURVATURES WITHIN THE VERTEBRAL COLUMN
curvatures within the sagittal plane (Figure 9-8, A). These
natural curvatures contribute to “ideal” spinal posture while
one is standing. The curvatures also define the neutral position
of the different regions of the spine. In the neutral (anatomic)
position, the cervical and lumbar regions are naturally convex
called lordosis, meaning to “bend backward.” The degree of
lordosis is usually less in the cervical region than in the
lumbar region. The thoracic and sacrococcygeal regions, in
contrast, exhibit a natural kyphosis. Kyphosis describes a curve
that is concave anteriorly and convex posteriorly. The ante-
rior concavity provides space for the organs within the tho-
racic and pelvic cavities.
The natural curvatures within the vertebral column are not
fixed but are dynamic and change shape during movements
and adjustment of posture. Further extension of the vertebral
column accentuates the cervical and lumbar lordosis but
reduces the thoracic kyphosis (see Figure 9-8, B). In contrast,
flexion of the vertebral column decreases, or flattens, the
cervical and lumbar lordosis but accentuates the thoracic
kyphosis (see Figure 9-8, C). In contrast, the sacrococcygeal
curvature is fixed, being concave anteriorly and convex
posteriorly.
The embryonic vertebral column is kyphotic throughout
its length. Lordosis in the cervical and lumbar regions occurs
after birth, in association with motor maturation and the
assumption of a more upright posture. In the cervical spine,
extensor muscles pull on the head and neck as the prone-lying
infant begins to observe the surroundings. More caudally, the