The teres minor is a narrow, elongated muscle of the rotator cuff.
Structure It arises from the dorsal surface of the
axillary border of the scapula for the upper two-thirds of its extent, and from
two aponeurotic laminæ, one of which separates it from the infraspinatus
muscle, the other from the teres major muscle.
Its fibers run obliquely upward and laterally; the upper ones end in a
tendon which is inserted into the lowest of the three impressions on the greater
tubercle of the humerus; the lowest fibers are inserted directly into the
humerus immediately below this impression.
= Relations= The tendon of this muscle passes across,
and is united with, the posterior part of the capsule of the shoulder-joint.
= Innervation= The muscle is innervated by the
posterior branch of axillary nerve where it forms a pseudoganglion. A
pseudoganglion has no nerve cells but nerve fibres are present. Damage to the
fibers innervating the teres minor is clinically significant.
= Variation= Sometimes a group of muscle fibres from
teres minor may be fused with infraspinatus.
Function The infraspinatus and teres minor attach
to head of the humerus; as part of the rotator cuff they help hold the humeral
head in the glenoid cavity of the scapula. They work in tandem with the
posterior deltoid to externally rotate the humerus, as well as perform
transverse abduction, extension and transverse extension.
Clinical significance = Injury=
There are two types of rotator cuff injuries: acute tears and chronic tears.
Acute tears occur as a result of a sudden movement. This might include
throwing a powerful pitch, holding a fast moving rope during water sports,
falling over onto an outstretched hand at speed, or making a sudden thrust with
the paddle in kayaking. A chronic tear develops over a period of time. They
usually occur at or near the tendon, as a result of the tendon rubbing against
the underlying bone. = Imaging=
Atrophy of the teres minor muscle is often a consequence of a rotator cuff
tear, but common isolated teres minor atrophies have also been found. A
quadrangular space syndrome causes excessive and or chronically compression
of the structures which pass through this anatomical tunnel. The axillary
nerve and the posterior humeral circumflex artery pass through the
space. People affected note shoulder pain and paresthesia down the arm first
and foremost in abduction, extension, external rotation and overhead activity.
Selective atrophy of the teres minor muscle has been seen and pulled together
directly with compression of the corresponding axillary nerve branch or
posterior humeral circunflex artery. Fibrous bands, cysts of the glenoid
labrum, lipoma or dilated veins can occupy the quadrilateral space
pathologically. Similar symptoms are common with anterior shoulder
dislocation, humeral neck fracture, brachial plexus injury and thoracic
outlet and inlet syndrome. It is important to include those pathologies
for a complete as possible differential diagnosis.
Ultrasonography is a tool to detect a fatty degenerative atrophy of the teres
minor and shows in affected muscles increased echogenicity and betimes a
slight reduction in muscle bulk. MR imaging helps to consolidate the
diagnosis of neurogenic muscle atrophy. Extracellular edema after traumatic
events causing neural damage show an increased signal intensity on
T2-weighted MRI sequences and normal intensity on T1-weighted sequences.
Posterior humeral circunflex artery compression and reduced blood flow in
stressful arm positions and or maneuvers can be diagnosed by a Doppler
ultrasonography. The nerve should be detected adjacent to the vessel. In an
elevated arm position the axillary neurovascular bundle can be seen at the
posterior axillary fold just before it perforates the deltoideus, while the
posterior course is well visible in the neutral position. For a detailed
assessment of the artery, a MR angiography is required. The major task
of an ultrasonographic examination is to rule out any space occupying mass.
Additional electromyography is helpful to reveal any decelerated nerve
conduction velocity, and thus denervation of the concerned muscle.
Additional images See also
Accessory muscles of the scapula References
This article incorporates text in the public domain from the 20th edition of
Gray's Anatomy External links
-1583742916 at GPnotebook Anatomy figure: 03:03-05 at Human
Anatomy Online, SUNY Downstate Medical Center
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