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Shoulder Ultrasonography: Performance and Common Findings

Ultrasound (US) of the shoulder is the most commonly requested examination in musculoskeletal US diagnosis. Sports injuries and degenerative and inflammatory processes are the main sources of shoulder pain and functional limitations. Because of its availability, low cost, dynamic examination process, absence of radiation exposure, and ease of patient compliance, US is the preferred mode for shoulder imaging over other, more sophisticated, and expensive methods. Operator dependence is the main disadvantage of US examinations. Use of high range equipment with high resolution transducers, adhering to a strict examination protocol, good knowledge of normal anatomy and pathological processes and an awareness of common pitfalls are essential for the optimal performance and interpretation of shoulder US. This article addresses examination techniques, the normal sonographic appearance of tendons, bursae and joints, and the main pathological conditions found in shoulder ultrasonography.


IntroductIon
Imaging of the shoulder is a common investigation requested in patients presenting with shoulder pain and functional disabilities. A wide variety of etiologies, from rotator cuff pathologies to calcifying tendinosis, synovitis, acromioclavicular arthritis, and cervical radiculopathy may lead to similar symptoms. Shoulder arthrography and magnetic resonance imaging have been the imaging modalities commonly used to distinguish among these conditions. [1][2] The development of musculoskeletal ultrasonography, based on advanced ultrasound (US) capabilities, has enabled this technique to be included as a primary imaging investigation among the battery of available diagnostic tests. [3] Knowledge of optimal techniques, normal anatomy, dynamic maneuvers, and pathological conditions is essential for correct US imaging and interpretation. [4] Shoulder US should strictly adhere to the imaging protocol. [5] Comparison between the damaged and the contralateral sides may aid in reaching diagnostic conclusions.
This pictorial essay aims to illustrate the technical performance, normal anatomy, and main pathologies related to the rotator cuff and beyond, as well as pitfalls in the US examination of the shoulder.

Performance protocol and normal anatomy
Modern US systems, offering high resolution multifrequency linear array transducers ranging from 4 to 7, 3 to 9, 5 to 12 and 5 to 17 MHz, and color Doppler capabilities, enable optimal definition of anatomical structures. Bone surface, tendons, bursae, ligaments, and muscles can be clearly demonstrated. A checklist protocol is proposed for a systematic shoulder US examination [ Table 1].
Shoulder ultrasound starts by examining the bicipital groove (BG) and long head of the biceps brachii tendon. The patient is seated facing the operator in a neutral position, his/her hand placed palm up on the thigh. A short axis image is performed by positioning the transducer over the proximal humeral metaphysis perpendicular to the humerus. The long axis image of the tendon is obtained by rotating the transducer to a position parallel to the humeral shaft [ Figure 1]. Then, the subscapularis tendon is examined. Patient's arm is fixed on the flank and the forearm abducted in external rotation. Long and short axis views of the tendon are performed [ Figure 2]. The infraspinatous and teres minor tendons are examined from a posterior view of the shoulder The patient is rotated 90°, his/her hand placed over the opposite shoulder and the transducer oriented in the axial plane over the head of the humerus [ Figure 3]. The glenohumeral joint and the spinoglenoid notch are also examined on a posterior view of the shoulder. The transducer is now moved medially and caudally in the transverse plane until the posterior margin of the glenohumeral joint is seen and then, further medially to show the spinoglenoid notch [ Figure 4]. The supraspinatous tendon is scanned on an anterior view of the shoulder. The patient is seated facing the operator. Patient's arm is placed in a posterior position, the dorsal hand on the opposite iliac wing or the palmar hand on the ipsilateral iliac wing. Long and short axis views of the supraspinatous tendon are obtained. Scanning of the rotator cuff is then performed during dynamic      b a maneuvers. The transducer is placed over the acromion. Patient's arm is abducted with the elbow flexed to 90°, or/ and the arm is extended anteriorly [ Figure 5]. Finally, the acromioclavicular joint is scanned. Patients hand is placed palm up on the thigh. The transducer is positioned over the shoulder top in a coronal plane [ Figure 6].
Tendons are seen as a fine fibrillar echogenic structure. Examiners must be aware of anisotropy-a common artifact and potential pitfall in US of tendons, making them appear hypoechoic when the incident ultrasound beam angle is not perpendicular to the tendon. This phenomenon can be avoided by ensuring that the transducer is correctly positioned. [5][6] rotator cuff pathologies Rotator cuff tears are the most common pathology found in shoulder US examinations. [7] The incidence of tears increases with age. Tendon tears may be classified according to the extent of fiber failure, ranging from complete tears [ Figure 7], full-thickness tears [ Figures 8,9], partial-thickness tears [ Figures 10-12], and intrasubstance tears [ Figure 13]. An acute tear is usually accompanied by joint or bursal effusion [ Figure 12]. [7][8][9] Absence of effusion is usually related to chronic tears. [9] In a meta-analysis on the accuracy of MRI, MR arthrography, and US in the diagnosis of rotator cuff tears, US offered high sensitivity and specificity for the assessment of full-thickness rotator cuff tears (92.3 and 94.4%, respectively) with 85.1% and 92%, respectively for all tears. [7] Partial thickness tear appears as a hypoechoic defect or cleft in the tendon, affecting only part of its thickness, while a full-thickness tear extends from the bursal to the articular surface of the tendon. A complete tear is a full-thickness tear affecting the full width of the tendon. The tendon retracts medially, the amount of retraction depending on the age of the tear. In chronic ruptures, the tendon dissapears beneath the coracoacromial arch, leaving the humeral head uncovered by the supraspinatous, the so-called "naked head" sign.  US findings include nonvisualization of the tendon and herniation of the deltoid muscle. Intrasubstance tears remain localized in the tendon without involvement of its margins. Intrasubstance and partial-thickness tears may be difficult to differentiate from focal tendinopathy.        The most commonly found nontear-related pathologies of the rotator cuff are rotator cuff tendinosis [ Figure 14], rotator cuff calcifying tendonitis [ Figure 15], and subacromial tendon impingement [ Figure 16]. It is worthwhile noting that in such cases, tears may develop due to tendon weakness [ Table 2]. [7,9] Rotator cuff tendinosis or tendinopathy presents as swelling of the tendon with a heterogeneous hypoechoic tendon echotexture. Rotator cuff calcifications appear as hyperechoic foci, either with welldefined posterior shadowing (Type I) or with a faint (Type II) or absent (Type III) shadow. Type I corresponds to the formative phase and Types II and III to the resorptive phase, in which they change to semi or totally liquid deposits of calcium. In subacromial impigment, tendon gliding in the subacromial space during abduction and anterior elevation of the arm is absent. Figure 15: Rotator cuff calcifying tendonitis. Extensive foci of calcifications in the supraspinatous tendon. The image shows calcium deposition as intrasubstance hyperechoic foci with posterior acoustic shadowing (arrows) Type I calcific tendonitis. [9] non-rotator cuff pathologies Gleno-humeral joint effusion [ Figure 17], subacromialsubdeltoid bursa effusion [ Figure 18], calcifying bursitis [ Figure 19], acromio-clavicular joint arthropathies and dislocation [ Figure 20], biceps tendon tear [ Figure 21], synovitis [ Figure 22], and dislocation [ Figure 23] are the main nonrotator cuff-related pathologies seen in shoulder US [ Table 3]. [8][9] US is sensitive for the detection of glenohumeral joint effusion and subacromial subdeltoid bursal effusion, even in small amounts. Fluid aspiration          b a capsule and ligament. Rupture of the long head of the biceps brachii tendon typically generates a lump in the anterior arm, known as "Popeye sign". Tendon disruption occurs usually at the intrarticular level with distal retraction, leaving an empty groove. In acute tears the tendon stump appears surrounded by fluid. Medial biceps tendon dislocation is diagnosed with US on transverse scans, which depict the bicipital sulcus and the tendon overlying the lesser tuberosity.

Shoulder uS-guided interventions
Beyond the benefits of US as a diagnostic tool, interventional procedures under US guidance, such as local anesthetic and steroid injection therapy, fluid aspiration in synovial processes, and biopsies of masses, may be accurately performed. US guidance allows precise needle location thus avoiding the risks of intratendinous steroid injection [ Figure 24-26]. [10] concluSIonS Shoulder US has become the modality of choice for the diagnosis of rotator cuff and non-rotator cuff pathologies, offering a high level of diagnostic specificity and sensitivity along with significant benefits to the examiner and the patient, assuming the study is performed by an experienced examiner with high-capacity equipment. US is noninvasive, relatively inexpensive and allows for easy comparison between the affected shoulder and the contralateral side. Strict compliance with procedure protocol, and a comprehensive knowledge of shoulder anatomy, pathologies, and potential technical pitfalls are all needed to make accurate diagnoses. Dynamic imaging and color/