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Ultrasound examination of the shoulder should be done in a systematic way.
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During examination of the rotator cuff, attention should be paid to pitfalls due to anisotropy and calcifications.
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Thorough knowledge of acoustic windows is required to recognize pathology, e.g., the posterior acoustic shadow from the bony coracoid may mask a distended subcoracoid bursa or superior subscapular bursa.
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Effusion in the glenohumeral joint spills into other recesses or pockets of the shoulder capsule, including the long head of the biceps tendon cul-de-sac, and the superior and inferior subscapularis bursa.
Shoulder pain is a common complaint in the general population and among patients with rheumatic diseases. Full-thickness tears, which are often asymptomatic, occur in up to 25% of the general population. Cadaver studies have shown a significant age-related increase in the incidence of partial- and full-thickness tears.
In the rheumatic diseases, shoulder involvement is part of the clinical spectrum, and the rotator cuff, bone, entheseal structures, and synovial elements may be affected. About three fourths of patients with rheumatoid arthritis develop shoulder pain, and more than 20% develop moderate or severe glenohumeral joint destruction within 15 years of disease onset. Among those with rheumatoid arthritis, rotator cuff disease may develop in up to 50% of patients, further deteriorating shoulder function. Rotator cuff disease also contributes to the significantly poorer functional results and greater postoperative pain after shoulder replacement surgery in rheumatoid arthritis patients. Acromioclavicular osteoarthritis is found in patients with ankylosing spondylitis, and acromial entheseal edema in the deltoid origin has been observed only in the shoulders of these patients.
In patients with rheumatic diseases, the spectrum of shoulder abnormalities includes bony lesions, bursal inflammation, and tendon disease. The classic radiographic sign of long-standing rheumatoid shoulder disease is medialization and upward migration of the humeral head, as well as glenohumeral joint space narrowing with cyst formation and erosions of the humeral head. There is a significant correlation between bony erosions and rotator cuff disease. For end-stage shoulder disease, shoulder replacement surgery may provide pain relief, but it fails to restore shoulder function. Shoulder involvement must be diagnosed earlier to provide better care and better outcomes.
Imaging often is done with some combination of conventional radiography, ultrasonography, computed tomography (CT), and magnetic resonance imaging (MRI). Each of these techniques has strengths and weaknesses. Ultrasound can provide information about the rotator cuff, biceps tendon, joints, and bone. Ultrasound of the shoulder was first evaluated for diagnosis of rotator cuff tears.
Ultrasound examination of the shoulder is difficult because of the complex anatomy of the joint. Elements such as the bursae, ligaments, muscles, tendons, bones, fibrocartilage, and synovium may obscure scanning and produce artifacts that resemble pathology. Because a thorough understanding of anatomy, sonoanatomy, procedural pitfalls, and technical restrictions is required for an accurate examination, superior outcomes demand experienced ultrasonographers.
Ultrasound Equipment
The shoulder joint is examined with a linear-array transducer, which is a broadband-frequency probe of 7.5 to 12 MHZ. In very obese patients, frequencies lower than 7.5 MHz may be required. The lower frequencies can also be used to view the deep-seated anterior and posterior recesses of the shoulder. Curved-array transducers play a limited role in ultrasound of the shoulder. Higher frequencies are used to depict the superficial structures, such as the acromioclavicular joint. Standardized ultrasound examination requires bilateral shoulder scanning. The power Doppler mode can be used to detect hyperemia in synovial structures, including the subacromial-subdeltoid (SASD) bursa and the various recesses. Doppler also can differentiate blood vessels, cysts, and nerves. Standoff pads are not used in the evaluation of the shoulder.
Patient Position
There are two ways to perform an ultrasound examination of the shoulder. First, the patient is seated upright on a revolving stool opposite the examiner. The examiner sits slightly higher than the patient to prevent injury. The ultrasound machine is positioned adjacent to the patient, and the screen and console face the examiner ( Fig. 20-1 ). For examination of the right shoulder, the examiner faces the machine, and the patient’s back is directed toward the machine, and for examining the left shoulder, the examiner and patient face the machine. The examiner also can stand behind the seated patient ( Fig. 20-2 ). This position enables the examiner to perform all the necessary dynamic maneuvers for a complete assessment. Because dynamic examination is important, the supine position is not optimal.
Shoulder Anatomy and Sonoanatomy
Several scanning protocols have been published for ultrasound examination of the shoulder. A standard scanning protocol includes multiplanar, dynamic, and bilateral assessments. As a rule of thumb, if an abnormality is suspected, the probe should be rotated 90 degrees to confirm the finding in a second, perpendicular plane. Performing a routine ultrasound shoulder protocol takes about 10 to 15 minutes. Reference values are used for tendon thicknesses.
A good starting point for ultrasound examination of the shoulder is the anterior side ( Figs. 20-3 and 20-4 ). The patient’s arm is resting comfortably at the iliac crest, and the elbow is flexed 90 degrees. The forearm is supinated. The probe is placed horizontally (transverse view) over the anterior side of the shoulder, where the long head of the biceps tendon should be identified.
The bicipital groove appears as a semicircular impression on the anterior axial scan (transverse view) between the medially located lesser tuberosity and the lateral greater tuberosity. Along with the long head of the biceps tendon, the bicipital groove represents the most important landmark in shoulder sonography. The biceps tendon is seen as an echogenic, circular structure within the groove ( Fig. 20-5 ). Medial to the bicipital groove, the subscapularis tendon is identified ( Fig. 20-6 ); lateral to it is the supraspinatus tendon ( Figs. 20-7 and 20-8 ). Anterior to the biceps tendon, the examination identifies the transverse ligament (i.e., fused fibers from the supraspinatus tendon and some fibers from the subscapularis, forming the roof of the bicipital groove). The superior part of the subscapularis passes under the biceps tendon to join with fibers from the supraspinatus tendon to form the floor of the sheath. More posteriorly, the biceps tendon passes into the joint capsule, and this region is called the rotator cuff interval . In the rotator cuff interval, the roof of the rotator cuff interval is formed by a slip of the supraspinatus along with the coracohumeral ligament, and the floor is formed by fibers of the subscapularis. The coracohumeral ligament can sometimes be visualized by ultrasound as a thin, hyperechoic band.
Long Head of the Biceps Tendon
The long head of the biceps tendon should be examined along its full course in two perpendicular planes (i.e., axial and sagittal images). The axial or short-axis scan confirms the tendon’s presence within the groove, detects fluid around the tendon, and 3 to 4 cm distally, shows the musculotendinous junction. The scanhead should be gently tilted so that the biceps tendon appears hyperechoic. Lateral to the tendon within the groove, power Doppler examination reveals the lateral branch of the anterior circumflex humeral artery. This arterial branch should appear as a small, circumscribed focus of flow.
The sagittal or long-axis scan shows the typical fibrillar pattern, consisting of long, parallel and linear fibers, and it may show partial or complete tears. It may also show synovial tissue or calcifications. The mean thickness of the long head in the axial view is 5.0 mm (range, 2.9 to 7.1 mm), and it is 2.6 mm (range, 1.2 to 4.0 mm) in the sagittal plane. At the distal end, there may be a small amount of fluid, which is physiologic. The long head of the biceps tendon may subluxate, usually toward the medial side under the subscapularis tendon.
Subscapularis Tendon
Starting at the bicipital groove, the horizontally held scanhead is moved a few centimeters medially. This plane yields a long-axis view of the subscapularis tendon. The mean thickness is 4.2 mm (range, 2.6 to 5.8 mm). A dynamic examination of the tendon insertion on the lesser tuberosity should be performed by gentle internal and external rotation of the shoulder. The probe should be moved superiorly and inferiorly to ensure visualization of the entire tendon. On the 90-degree transverse scan, the multipennate pattern of the subscapularis tendon is usually striking. Anteromedial impingement can be detected by internal rotation of the arm, and the subscapularis should easily disappear under the coracoid process. The subscapularis tendon is infrequently involved in a rotator cuff tear, but the tendon insertion at the lesser tuberosity may tear, allowing the biceps tendon to subluxate medially.
Supraspinatus Tendon
In the neutral position, the supraspinatus tendon is obscured by the acromion. Optimal imaging of the supraspinatus tendon requires the shoulder to be extended and maximally endorotated; this is the hyperextended internal rotation view first described by Crass. With the shoulder internally rotated, the greater tuberosity is directed anterior, with the supraspinatus medial and the infraspinatus lateral to the midpoint of the greater tuberosity. The patient is asked to extend the arm with the elbow flexed and pointed laterally (not posteriorly) and the hand placed on the buttock or the iliac wing.
The scan should be performed in two planes by moving the probe from medial to lateral. The fibers of the supraspinatus tendon do not run exactly in the coronal or sagittal plane, but in a plane about 45 degrees between the coronal and sagittal planes. The probe should be placed in this plane to obtain a longitudinal image and rotated 90 degrees to examine the tendon in the transverse plane ( Fig. 20-9 ).
Most supraspinatus tears occur in the anterior portion, near the biceps tendon. The long-axis view is most accurate for viewing tears. It shows the tendon gap and the accompanying fluid. Mean thickness of the supraspinatus is 4.6 mm (range, 2.7 to 6.5 mm).
Infraspinatus Tendon
The infraspinatus and teres minor tendons are visualized on posterior scans. Their fibers are deep to the deltoid muscle, which inserts on the acromion. To enhance the visualization, the arm is externally rotated. The probe is then placed in a transverse plane, just inferior to the lateral ridge of the scapular spine for a long-axis view of the tendons. The tendons have a triangular shape in the transverse plane.
The infraspinatus and teres minor tendons cannot be differentiated by ultrasound. The infraspinatus tendon is 2 to 3 cm superior to the smaller teres minor. The infraspinatus tendon usually shows a large aponeurosis, and the mean thickness is 3.8 mm (range, 2.0 to 5.6 mm), which is less than that of the supraspinatus.
The posterior labrum is evaluated in the transverse posterior plane. The posterior labrum is positioned between the infraspinatus and the glenoid, and it is hyperechoic. Moving the transducer medial to the labrum in a transverse plane, the examiner can visualize the spinoglenoid notch.
Glenohumeral Joint
The glenohumeral joint can be assessed on posterior and axillary views ( Fig. 20-10 ). The posterior view allows scanning of a portion of the posterior recess and the posterior labrum. The axillary scan may be more difficult to obtain, because patients must be able to lift the arm ( Fig. 20-11 ). Effusion of the glenohumeral joint distends the capsule posteriorly and anteriorly. The mean distance between the anterior humeral shaft and capsule is 2.4 mm (range, 1.9 to 2.9 mm). Effusion makes the anterior and posterior labra more visible.
