An ap internal rotation projection of the shoulder demonstrates what anatomical part in profile?

5

The scapula, classified as a flat bone, forms the posterior part of the shoulder girdle (Figs. 5-3 and 5-4). Triangular in shape, the scapula has two surfaces, three borders, and three angles. Lying on the superoposterior thorax between the second and seventh ribs, the medial border of the scapula runs parallel with the vertebral column. The body of the bone is arched from top to bottom for greater strength, and its surfaces serve as the attachment sites of numerous muscles. The flat aspect of the bone lies at about a 45- to 60-degree angle in relation to the anatomic position (see Fig. 5-2).

The costal (anterior) surface of the scapula is slightly concave and contains the subscapular fossa. It is filled almost entirely by the attachment of the subscapularis muscle. The anterior serratus muscle attaches to the medial border of the costal surface from the superior angle to the inferior angle.

The dorsal (posterior) surface is divided into two portions by a prominent spinous process. The crest of spine arises at the superior third of the medial border from a smooth, triangular area and runs obliquely superior to end in a flattened, ovoid projection called the acromion. The area above the spine is called the supraspinous fossa and gives origin to the supraspinatus muscle. The infraspinatus muscle arises from the portion below the spine, which is called the infraspinous fossa. The teres minor muscle arises from the superior two thirds of the lateral border of the dorsal surface, and the teres major arises from the distal third and the inferior angle. The dorsal surface of the medial border affords attachment of the levator muscles of the scapulae, greater rhomboid muscle, and lesser rhomboid muscle.

The superior border extends from the superior angle to the coracoid process and at its lateral end has a deep depression, the scapular notch. The medial border extends from the superior to the inferior angles. The lateral border extends from the glenoid cavity to the inferior angle.

The superior angle is formed by the junction of the superior and medial borders. The inferior angle is formed by the junction of the medial (vertebral) and lateral borders and lies over the seventh rib. The lateral angle, the thickest part of the body of the scapula, ends in a shallow, oval depression called the glenoid cavity. The constricted region around the glenoid cavity is called the neck of the scapula. The coracoid process arises from a thick base that extends from the scapular notch to the superior portion of the neck of the scapula. This process projects first anteriorly and medially and then curves on itself to project laterally. The coracoid process can be palpated just distal and slightly medial to the acromioclavicular articulation.

The proximal end of the humerus consists of a head, an anatomic neck, two prominent processes called the greater and lesser tubercles, and the surgical neck (Fig. 5-5). The head is large, smooth, and rounded, and it lies in an oblique plane on the superomedial side of the humerus. Just below the head, lying in the same oblique plane, is the narrow, constricted anatomic neck. The constriction of the body just below the tubercles is called the surgical neck, which is the site of many fractures.

The lesser tubercle is situated on the anterior surface of the bone, immediately below the anatomic neck (Figs. 5-6 and 5-7; see Fig. 5-5). The tendon of the subscapular muscle inserts at the lesser tubercle. The greater tubercle is located on the lateral surface of the bone, just below the anatomic neck, and is separated from the lesser tubercle by a deep depression called the intertubercular (bicipital) groove. The superior surface of the greater tubercle slopes posteriorly at an angle of approximately 25 degrees and has three flattened impressions for muscle insertions. The anterior impression is the highest of the three and affords attachment to the tendon of the supraspinatus muscle. The middle impression is the point of insertion of the infraspinatus muscle. The tendon of the upper fibers of the teres minor muscle inserts at the posterior impression (the lower fibers insert into the body of the bone immediately below this point).

Bursae are small, synovial fluid–filled sacs that relieve pressure and reduce friction in tissue. They are often found between the bones and the skin, and they allow the skin to move easily when the joint is moved. Bursae are found also between bones and ligaments, muscles, or tendons. One of the largest bursae of the shoulder is the subacromial bursa (Fig. 5-8). It is located under the acromion process and lies between the deltoid muscle and the shoulder joint capsule. The subacromial bursa does not normally communicate with the joint. Other bursae of the shoulder are found superior to the acromion, between the coracoid process and the joint capsule, and between the capsule and the tendon of the subscapular muscle. Bursae become important radiographically when injury or age causes the deposition of calcium.

The scapulohumeral articulation between the glenoid cavity and the head of the humerus forms a synovial ball-and-socket joint, allowing movement in all directions (Figs. 5-9 and 5-10). This joint is often referred to as the glenohumeral joint. Although many muscles connect with, support, and enter into the function of the shoulder joint, radiographers are chiefly concerned with the insertion points of the short rotator cuff muscles (Fig. 5-11). The insertion points of these muscles—the subscapular, supraspinatus, infraspinatus, and teres minor—have already been described.

Fig. 5-10 A, Coronal MRI of shoulder. Note articular cartilage around humeral head and muscles closely surrounding bone. B, Axial CT of shoulder, mid-joint. Note position of bones relative to each other and articular cartilage in glenoid cavity. gc, glenoid cavity; h, humerus; sn, scapular neck. (From Kelley LL, Petersen CM: Sectional anatomy for imaging professionals, ed 2, St Louis, 2007, Mosby.)

An articular capsule completely encloses the shoulder joint. The tendon of the long head of the biceps brachii muscle, which arises from the superior margin of the glenoid cavity, passes through the capsule of the shoulder joint, goes between its fibrous and synovial layers, arches over the head of the humerus, and descends through the intertubercular (bicipital) groove. The short head of the biceps arises from the coracoid process and, with the long head of the muscle, inserts in the radial tuberosity. Because it crosses with the shoulder and elbow joints, the biceps help synchronize their action.

The interaction of movement among the wrist, elbow, and shoulder joints makes the position of the hand important in radiography of the upper limb. Any rotation of the hand also rotates the joints. The best approach to the study of the mechanics of joint and muscle action is to perform all movements ascribed to each joint and carefully note the reaction in remote parts.

NOTE: Do not have the patient rotate the arm if fracture or dislocation is suspected.

Image receptor: 10 × 12 inch (24 × 30 cm) crosswise

Collimation:

• Adjust to 10 × 12 inches (24 × 30 cm) on the collimator.

Use of a specially designed compensating filter for the shoulder improves the quality of the image. These filters are particularly useful when digital imaging (CR or DR) systems are used for this projection.

Structures shown: The image shows the bony and soft structures of the shoulder and proximal humerus in the anatomic position (Figs. 5-14 to 5-16). The scapulohumeral joint relationship is seen.

External rotation: The greater tubercle of the humerus and the site of insertion of the supraspinatus tendon are visualized (see Fig. 5-14, A).

Neutral rotation: The posterior part of the supraspinatus insertion, which sometimes profiles small calcific deposits not otherwise visualized (see Fig. 5-14, B), is seen.

Internal rotation: The proximal humerus is seen in a true lateral position. When the arm can be abducted enough to clear the lesser tubercle of the head of the scapula, a profile image of the site of the insertion of the subscapular tendon is seen (see Fig. 5-15).

Only gold members can continue reading. Log In or Register to continue