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Body Mechanics
by Joseph E. Muscolino, DC
The name thoracic outlet syndrome (TOS) refers to three
different conditions: anterior scalene syndrome,
costoclavicular syndrome and pectoralis minor syndrome.
The reason that these three conditions are all grouped
together as TOS is that they are all entrapment
syndromes of the brachial plexus of nerves and/or the
subclavian artery/vein in the region where the thorax
outlets into the upper extremity (Figure 1). As a
result, all three types of TOS can result in nerve or
vascular impingement, resulting in symptoms in the upper
extremity.
 Figure 1 is an anterior view illustrating the
relationship of the brachial plexus of nerves and the subclavian artery and vein to adjacent structures. These
nerves and vessels may be impinged in three locations
where the thorax outlets into the upper extremity: 1) between the anterior and middle scalenes, 2)
between the clavicle and first rib and 3) between the
pectoralis minor and the rib cage.
TYPES OF TOS
With all three types of TOS, the name describes the
location of the impingement. In anterior scalene
syndrome, the brachial plexus and subclavian artery run
between the anterior and middle scalene muscles in the
anterolateral neck. If the scalene muscles are tight,
perhaps due to a whiplash accident, impingement may
occur. In costoclavicular syndrome (cost means rib),
the brachial plexus and subclavian artery and vein run
between the first rib and clavicle in the medial
pectoral region. If the posture of the relationship of
the clavicle and first rib changes and they approximate
each otheras often happens with rounded and slumped
shouldersimpingement may occur.
In
pectoralis minor syndrome, the brachialis plexus and
subclavian artery and vein run between the pectoralis
minor muscle and the rib cage in the lateral pectoral
region.
Impingement can also occur if the pectoralis minor is
tight; this often happens with slumped shoulder postures
as well.
THE BRACHIAL PLEXUS
The brachial plexus of nerves is created by a mixing of
the C5, C6, C7, C8 and T1 spinal nerve roots. As a
freedom from thoracic outlet syndrome body mechanics
result of this intermixing, the brachial plexus creates
five major nerves: the median, radial, ulnar,
musculocutaneous and axillary (Figure 2).
 Figure 2 illustrates the brachial plexus. Five major
nerves are formed by the brachial
plexus: the median, radial, ulnar, musculocutaneous and axillary.
These nerves carry both sensory innervation and motor
innervation that supply the upper extremity. Sensory
information travels upward from the upper extremity
through sensory neurons of the brachial plexus nerves
and enters the central nervous system (CNS) to alert us
to the sensations that we feel in the upper extremity.
Motor information travels downward from the CNS through
motor neurons of the brachial plexus nerves and enters
the upper extremity to direct its musculature to
contract as needed.
Therefore, TOS can cause sensory and/or motor symptoms
in the upper extremity depending upon which aspect of a
brachial plexus nerve is impinged. Typical sensory
impingement symptoms include pain (sharp or dull),
numbness and tingling; the typical motor impingement
symptom is weakness of the affected musculature.
Further, because the brachial plexus innervates the
entire upper extremity (arm, forearm and hand), these
symptoms can occur anywhere within the upper extremity.
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