Advanced Trauma Life Support ATLS Student Course Manual 2018

ANATOMY AND PHYSIOLOGY 131
B
A
n FIGURE 7-1 The Spine. A. The spinal column, right lateral and posterior views. B. A typical thoracic vertebra, superior view.
incidence of thoracic fractures is much lower. Most
thoracic spine fractures are wedge compression
fractures that are not associated with spinal cord injury.
However, when a fracture-dislocation in the thoracic
spine does occur, it almost always results in a complete
spinal cord injury because of the relatively narrow
thoracic canal. The thoracolumbar junction is a fulcrum
between the inflexible thoracic region and the more
mobile lumbar levels. This makes it more vulnerable
to injury, and 15% of all spinal injuries occur in
this region.
Spinal Cord Anatomy
The spinal cord originates at the caudal end of the
medulla oblongata at the foramen magnum. In adults,
it usually ends near the L1 bony level as the conus
medullaris. Below this level is the cauda equina, which
is somewhat more resilient to injury. Of the many tracts
in the spinal cord, only three can be readily assessed
clinically: the lateral corticospinal tract, spinothalamic
tract, and dorsal columns. Each is a paired tract that can
be injured on one or both sides of the cord. The location
in the spinal cord, function, and method of testing for
each tract are outlined in n TABLE 7-1.
When a patient has no demonstrable sensory or motor
function below a certain level, he or she is said to have
a complete spinal cord injury. An incomplete spinal cord
injury is one in which some degree of motor or sensory
function remains; in this case, the prognosis for recovery
is significantly better than that for complete spinal
cord injury.
Dermatomes
A dermatome is the area of skin innervated by the
sensory axons within a particular segmental nerve
root. The sensory level is the lowest dermatome with
normal sensory function and can often differ on the
two sides of the body. For practical purposes, the
upper cervical dermatomes (C1 to C4) are somewhat
variable in their cutaneous distribution and are not
commonly used for localization. However, note that the
supraclavicular nerves (C2 through C4) provide sensory
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