Subscapularis Muscle

The scapulothoracic plane separates the body of the scapula and the subscapularis muscle from the thoracic surface, consisting of the superficial aspect of the serratus anterior muscle which overlies the ribs. This gliding plane allows the scapula and the glenoid cavity to tilt anteriorly and posteriorly around the rib cage during shoulder movements. In addition, the scapulothoracic articulation has an important role in shoulder abduction. 

The capsule of the glenohumeral joint is loose and pleated. The ligaments, which are merely thickenings in the capsule, provide little support. The major support of the humerus into the fossa is provided by the rotator cuff muscles, which hold the head into the fossa. These muscles include the supraspinatus, infraspinatus, teres minor, and subscapularis. Abduction-adduction and axial and horizontal rotations are coupled in that angular motions are accompanied by translatory slides. The caudal slide of the humeral head with abduction confers increased freedom of motion on the supraspinatus tendon beneath the coracoacromial ligament. 

From the anatomic point of view, the muscles of the shoulder may be subdivided into two main groups intrinsic musdes (subscapularis, supraspinatus, infraspinatus, teres minor, teres major and deltoid), which originate and insert on the skeleton of the upper limb, and extrinsic muscles, which join the upper limb with either the spine (trapezius, latis-simus dorsi, levator scapulae and rhomboid) or the thoracic wall (serratus anterior, pectoralis minor... 

Considered as a whole, the tendons of the rotator cuff muscles are broad and relatively flat, somewhat similar to belts, and converge toward the lesser and greater tuberosity to create a hood - commonly referred to as the rotator cuff - that covers the humeral head anteriorly, superiorly and posteriorly (Fig. 6.7). The subscapularis tendon is sepa-... 

Fig. 6.19a,b. Clinical tests for assessing the strength of rotator cuff muscles, a Supraspinatus strength is tested with the patient s arm in a position of 60° of forward elevation with the shoulder internally rotated and the elbow extended. A downward force (arrow) applied by the examiner is resisted by the patient, b A lift-off test is performed to evaluate subscapularis strength. The patient is asked to actively lift (arrow) the hand off of the lumbar region... 

When examined onits short axis, the multipennate structure of the normal subscapularis tendon creates a series of hypoechoic clefts among the fascicles that should not be confused with tendon tears (Fig. 6.26). In fact, these cleft are related to muscle fibers interposed with tendon fascicles. On short-axis scans, the lesser tuberosity has a flat appearance ending in a smooth downsloping contour located just caudal to the tendon insertion (Fig. 6.26). Such a bony landmark would be helpful when assessing partial tears... 

Fig. 6.27a,b. Normal subscapularis tendon, a Transverse 12-5 MHz US image over the long axis of the subscapularis tendon (arrowheads). This tendon lies deep to the anterior deltoid muscle and just superficial to the humeral head. It has a convex shape and a well-defined fibrillar echotexture. Note the relatively small area (dashed line) of the lesser tuberosity (LT) on which the tendon inserts, b Schematic drawing of a coronal view through the anterior shoulder illustrates the examination technique. Due to the tendon s broad insertion, the transducer should be swept (arrows) up and down to cover its full width. The insert at the upper left side of the figure indicates probe positioning... 

Fig. 6.28a,b. Short head of the biceps tendon, coracobrachialis and pectoralis minor. a,b Transverse 12-5 MHz US images obtained a at the level of the coracoid process of the scapula and b approximately 2 cm caudal to it. In a, the relationship of the coracoid (Co) with the humeral head (HH), the subscapularis tendon (SubS) and the deltoid muscle are illustrated. The coracoid is easily identified with US owing to its medial position relative to the humeral head and the curvilinear hyperechoic appearance of its bony surface. In b, three individual structures are seen arising from the coracoid. From lateral to medial, they are the hyperechoic tendon of the short head of the biceps (curved arrow), the hypoechoic myotendinous junction of the coracobrachialis (straight arrow) and that of the pectoralis minor (arrowheads)... 

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