Short
Scapular Muscles Anatomy
These
short muscles, the four rotator cuff muscles and teres major, span the shoulder
(glenohumeral) joint, attaching to the scapula and to the proximal part of the
humerus (Figs 3.59 & 3.62).
This important group of
muscles, namely subscapularis, supraspinatus, infraspinatus and teres minor, is
intimately related to the shoulder joint.
By attaching not only to the tubercles of the humerus but also to the capsule
of the joint, they hold the humeral head firmly in the glenoid fossa and help
stabilize the joint.
Subscapularis
Subscapularis (Fig. 3.60) attaches proximally
to the medial part of the costal surface of the scapula. Its tendon, separated
from the neck of the scapula by the subscapular bursa, is attached to the
lesser tubercle of the humerus. The muscle is supplied by the subscapular
nerves from the posterior cord of the brachial plexus. Subscapularis produces
medial rotation of the arm at the shoulder joint.
Supraspinatus (Fig. 3.61) attaches to the
supraspinous fossa of the scapula and to the superior facet of the greater
tubercle of the humerus (Fig.
3.62). The subacromial bursa lies above the tendon of supraspinatus,
separating the tendon and the capsule of the shoulder joint from the
coracoacromial arch. The muscle initiates abduction of the shoulder joint.
Tendinitis results in an arc of painful movement from about 60° to 120° of
abduction. Complete rupture may lead the patient to develop a trick movement in
which the body is tilted so that the limb abducts passively until deltoid can
abduct the joint actively.
Infraspinatus (Fig. 3.63)
arises from the infraspinous fossa, and its tendon inserts into the middle
facet of the greater tubercle of the humerus. The muscle is covered by a strong
fascial membrane. A bursa some-times separates the tendon from the neck of the
scapula.
Supraspinatus and
infraspinatus are supplied by the suprascapular nerve, which arises from the
upper trunk of the brachial plexus and passes beneath the suprascapular
ligament (Fig. 3.59).
Teres minor (Fig. 3.63) attaches to the
posterior surface of the scapula along the upper part of the lateral edge and
to the inferior facet of the greater tubercle of the humerus. It is supplied by
the axillary nerve.
Both infraspinatus and teres
minor laterally rotate the humerus at the shoulder joint. Fractures of the
greater tubercle of the humerus may detach infraspinatus and teres minor from
the humerus, allowing muscle spasm to produce medial rotation at the shoulder joint.
Teres major (Fig. 3.64) is a short bulky
muscle, which attaches to the lower part of the posterior surface of the
scapula. Laterally, the muscle attaches below the lesser tubercle of the
humerus to the medial lip of the intertubercular sulcus (Fig. 3.59). Teres
major is supplied by the lower subscapular nerve and adducts and medially
rotates the humerus at the shoulder joint.
The axillary nerve and
posterior circumflex humeral vessels pass between the teres minor and major
muscles, lateral to the long head of triceps, through the quadrangular space (Fig. 3.64). Near the space,
the axillary nerve and the posterior circumflex humeral artery are closely
related to the surgical neck of the humerus, and fracture of the neck may
damage both structures.
