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 (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.