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Ultrasound of the Shoulder

Anatomy

Understanding the complex three-dimensional anatomy of the rotator cuff is crucial to successful rotator cuff sonography. The limited acoustic window, due to adjacent bone structures, is an additional factor making sonographic evaluation technically difficult. For this reason, comprehensive understanding of normal anatomy gained in the anatomy laboratory or operating room is essential for mastering this technique and accelerating the learning curve.

Figure 2. Anterior (left) and posterior (right) views of the bone structures of the left shoulder are shown.

Figure 3. Anterior (left) and posterior (right) views of the muscular origins and insertions of the left rotator cuff are shown.

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Figure 4. General surface anatomic landmarks have been sketched on this healthy volunteer. The lateral photograph shows the bone structure, which limits the acoustic window for examination of the cuff. Sup = supraspinatus muscle and tendon, I = infraspinatus muscle and tendon, arrowheads = scapular spine; arrows = acromion, H = humerus.

Ultrasound of the Shoulder

| Intro | Why do US? | Anatomy | Technique | Cuff Tears | PostOp | Trauma | Tendinitis | Arthritis | Biceps Tendon | Conclusion |

US Technique

The relevant patient history is obtained, eliciting information regarding any antecedent trauma, underlying arthritides, previous diagnostic studies (plain radiography, arthrography, MR imaging, US, etc), and previous surgery or procedures (including direct steroid injection).

Technique: Equipment

In initial reports of rotator cuff sonography, mechanical sector scanners with frequencies of 5-10 MHz were used. While these transducers produce high-quality images, their utility is limited by suboptimal superficial resolution due to near-field artifact and a narrow superficial image field. In addition, the specular reflection condition can be met by only a small portion of the parallel tendon fibers at the center of the image, which may create an artifactually heterogeneous appearance of tendons.

The introduction of high-resolution linear-array transducers has greatly expanded our diagnostic capabilities in examination of the shoulder and other musculoskeletal areas. Clinical experience has demonstrated that 7- or 10-MHz transducers are preferable to those of lower frequency. These transducers demonstrate marked improvement in near-field resolution compared with other devices. In addition, the broad superficial field of view is helpful in evaluating superficial abnormalities. The specular reflection condition can be met with a greater portion of the parallel tendon fibers. When lower-frequency transducers (5 MHz) must be used in patients with excessive fat or soft tissue, an acoustic standoff pad may be helpful in improving the near-field image.

Technique: Mechanics

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The patient is scanned while seated on a revolving stool that permits easy positioning during the scanning of both shoulders. The examiner is also seated on a stool, preferably with wheels to enhance mobility. Increased transducer stability is provided by holding the transducer so that the examiner's hand is resting on the skin surface (15). Both shoulders are examined, starting with the less symptomatic side. This allows comparison views and the detection of asymptomatic tears, which are fairly frequent in an older population. We always attempt to visualize normal and abnormal anatomy in two orthogonal planes.

The following technique for the evaluation of the rotator cuff is the one used at the University of Washington (12, 17-19). Although film-recording preferences are individualized and it must be stressed that diagnosis is made in real time and not from hard-copy images, I have marked the basic set of images that we permanently record from each patient with the word Image. This convention allows a single 15-on-1 sheet of film for each shoulder and a final sheet with the direct bilateral comparison images, perfusion images, and optional images, for a total of three sheets of film per patient. A standardized process such as this promotes learning and understanding of the technique among trainees, and makes the examination easier to understand for the referring clinician. Recorded images are oriented on the film as if one is facing the patient.

Technique: Specifics

Biceps Tendon: Transverse View

The examination begins with a transverse image of the bicipital groove, which serves as an anatomic landmark for differentiating the subscapularis from the supraspinatus. The patient's arm should be resting comfortably in his lap. Supination of the hand with slight external rotation of the shoulder improves visualization of the bicipital groove. The groove appears as a concavity in the bright echoes originating from the surface of the humerus. The tendon of the long head of the biceps is visualized as a hyperechoic oval structure within the bicipital groove. This view is important for detecting intraarticular fluid that, even when present in small amounts, may be seen surrounding the biceps tendon (13). One should scan 1.5-3 cm distal to the transverse humeral ligament and take care to ensure that excessive transducer pressure does not compress a fluid-filled tendon sheath.

Figure 5. Tendon anatomy and surface landmarks: biceps, transverse view.

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Figure 6. Annotated (left) (arrows = bicipital groove; D = deltoid; B = echogenic oval biceps tendon) and example (right) (Image 1) sonograms in two different patients illustrate the transverse view of the biceps tendon.

Biceps Tendon: Longitudinal View

The transducer is then turned 90° so that the biceps tendon is viewed parallel to its axis. Care should be taken to have the transducer parallel to the tendon, or portions of this structure will appear artifactually hypoechoic. As is the case when this tendon is viewed transversely, small effusions may be seen as fluid surrounding the hyperechoic biceps tendon.

Figure 7. Tendon anatomy and surface landmarks: biceps, longitudinal view.

Figure 8. Longitudinal view of the biceps tendon with the correct transducer orientation (left) (Image 2) and a view of the same normal biceps tendon with the transducer improperly oriented in a

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nonspecular fashion (right). Note how a nonparallel appearance of the fibers may incorrectly suggest tendon damage or fluid.

Subscapularis: Longitudinal View

The transducer is then moved medially along the humerus relative to the biceps tendon groove to visualize the subscapularis tendon, which appears as a band of medium-level echoes deep to the subdeltoid bursa. The subdeltoid bursa is seen as a thin, convex echogenic line. Tears of the subscapularis are uncommon. This tendon is rarely torn in isolation except after severe trauma. Subscapularis tears are more common in elderly patients with recurrent shoulder dislocation or in patients with massive cuff tears. The subscapularis tendon is best seen when the arm is externally rotated to the maximum extent and slightly abducted (34).

Figure 9. Tendon anatomy and surface landmarks: subscapularis, longitudinal view.

Figure 10. Annotated (left) and example (right) (Image 3) sonograms from two different patients illustrate longitudinal views of the subscapularis tendon. The tendon (SUB) is a band of soft tissue deep to the subdeltoid bursa (arrows) and medial to the biceps tendon (B). The bone contour of the lesser tuberosity (LT) is also noted. D = deltoid muscle.

Subscapularis: Transverse View

Turning the transducer 90° allows it to scan perpendicularly to the axis of the subscapularis tendon. This view may be helpful in patients with chronic anterior dislocation.

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Figure 11. Tendon anatomy and surface landmarks: subscapularis, transverse view.

Figure 12. Annotated (left) and example (right) (Image 4) sonograms from two different patients illustrate transverse views of the subscapularis tendon (SUB). Arrows = humerus, D = deltoid muscle.

Supraspinatus: Longitudinal View

One of the most important aspects of the sonographic examination of the rotator cuff is adequate visualization of the "critical zone" (or "crucial zone"), which is that portion of the supraspinatus tendon that begins 1 cm posterolateral to the biceps tendon. The critical zone is the portion of the tendon that is most susceptible to injury. Failure to adequately visualize this area can cause a false-negative result. To view the supraspinatus, the transducer is moved posterolaterally from the biceps tendon groove so that the tendon is viewed parallel (longitudinal) to its axis. The patient's arm should be hanging comfortably by his side for these views of the supraspinatus, infraspinatus, and teres minor.

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Figure 13. Tendon anatomy and surface landmarks: supraspinatus, longitudinal view.

The tendon appears as a beak-shaped structure of medium-level echogenicity extending from under the acromion, which casts an acoustic shadow, to its attachment along the greater tuberosity. The bright linear echoes from the subdeltoid bursa identify the superficial margin of the supraspinatus tendon. The articular cartilage may be seen as a hypoechoic band just superficial to the bone cortex. Scanning further laterally (distally) in the same plane may be helpful in visualizing small bursal effusions. Again, be careful about using excessive transducer pressure: Small amounts of fluid may be compressed and thus not visualized.

Figure 14. Annotated (left) and example (right) (Image 5) sonograms from two different patients illustrate longitudinal views of the supraspinatus tendon. SUP = supraspinatus tendon, D = deltoid, solid arrows = subdeltoid bursal complex, open arrow = acromion, GT = greater tuberosity.

Supraspinatus: Transverse View

The supraspinatus tendon is then scanned perpendicularly to its axis (transversely) by rotating the transducer 90°. The sonographic window is very narrow, limited by the acromion, and careful transducer positioning is essential.

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Figure 15. Tendon anatomy and surface landmarks: supraspinatus, transverse view.

Figure 16. The supraspinatus tendon is visualized as a band of medium-level echoes deep to the subdeltoid bursa and superficial to the bright echoes originating from the bony surface of the greater tuberosity. Annotated (left) (SUP = supraspinatus tendon, D = deltoid, arrows = subdeltoid bursal complex, C = humeral articular cartilage, B = biceps tendon, HH = humeral head) and example (right) (Image 6) sonograms from two different patients illustrate transverse views of the supraspinatus tendon.

Infraspinatus: Longitudinal View

By moving the transducer posteriorly, the infraspinatus tendon is visualized. It appears as a beak-shaped soft-tissue structure as it attaches to the posterior aspect of the greater tuberosity. Passive internal and external rotation may be helpful in examination of the infraspinatus. At this level, a portion of the posterior glenoid labrum is seen as a hyperechoic triangular structure. The articular cartilage of the humeral head is imaged as a thin, hypoechoic layer superficial to the high-level echoes originating from the bone surface.

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Figure 17. Tendon anatomy and surface landmarks: infraspinatus, longitudinal view.

Figure 18. Annotated (left) and example (right) (Image 7) sonograms from two different patients illustrate longitudinal views of the infraspinatus tendon. In the annotated sonogram, note the dual image of the infraspinatus tendon (INF) in internal (INT) and external (EXT) rotation. Arrows = humeral surface, D = deltoid, arrowheads = posterior glenoid labrum.

Teres Minor: Longitudinal View

By moving the transducer distal along the humerus, the teres minor is visualized as a trapezoidal structure. It is differentiated from the infraspinatus by its oblique internal echoes. Although the teres minor tendon is rarely torn, some reports have demonstrated that very small intraarticular effusions may be best visualized at this level (35). Visualization of the teres minor tendon ensures that the entire infraspinatus has been scanned.

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Figure 19. Tendon anatomy and surface landmarks: teres minor, longitudinal view. These images represent positioning for infraspinatus (INF) visualization, but it is easily seen from the left image

that the teres minor can be visualized by moving the transducer distally along the humerus.

Figure 20. Annotated longitudinal views of the teres minor tendon in two different patients. TM = teres minor, D = deltoid, arrows = humerus, H = humeral head.

Dynamic Scanning

One of the major advantages of US relative to MR imaging is its real-time ability. At a minimum, we obtain two routine dynamic image sets and will often visualize the motion of the patient's arm in any of the sonographic positions to assess the validity of findings.

Figure 21. When the subscapularis is viewed parallel to its axis, scanning during passive internal and external rotation may be helpful in assessing its integrity. This dual image (Image 8) shows the subscapularis tendon (SUB) parallel to its axis (longitudinal) in internal and external rotation, seen

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as a band of medium-level echoes deep to the subdeltoid bursa (arrowheads). D = deltoid muscle, B = biceps tendon, arrows = humeral surface.

Figure 22. Movie clip of subscapularis tendon during internal and external rotation (1.5 Mb).

The movie clip above nicely demonstrates the unique attributes of real-time, dynamic sonography. This longitudinal view of the subscapularis tendon during internal and external rotation shows the normal appearance of the tendon during movement. Note how this also shows the changing specular reflections of the tendon as different fibers become parallel to the ultrasound beam. This is a normal finding and not to be confused with true changes in tendon echogenicity.

Figure 23. Passive abduction-adduction with the transducer in a longitudinal orientation is often helpful in assessing the integrity of the supraspinatus tendon. Annotated (left) and example (right) (Image 9) sonograms from two different patients illustrate dynamic longitudinal views of the supraspinatus tendon. Dual-image scans with the right arm in adduction (ADD) and abduction (ABD) demonstrate the supraspinatus tendon as a beak-shaped soft-tissue structure (SUP) extending out from the acoustic shadow caused by the acromion (arrows). Its superficial margin is formed by the subdeltoid bursa (arrowhead). GT = greater tuberosity, D = deltoid muscle.

Figure 24. Movie clip of supraspinatus tendon during passive abduction and adduction (2.3 Mb).

The movie clip above shows the normal appearance of the supraspinatus tendon during passive abduction and adduction. Note how the supraspinatus retracts under the acromion during abduction. In the setting of a massive tear, the deltoid muscle may appose to the humeral head and mimic rotator cuff tendon on isolated static images. However, dynamic views in that setting will fail to demonstrate significant motion of the deltoid with abduction. The apparent subdeltoid effusion is merely an artifact of the video process.

Internal Rotation and Extension

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As stressed by Crass et al (36), scanning the supraspinatus tendon with the arm in extension and internal rotation is an important and integral portion of every rotator cuff evaluation. This is best achieved by placing the patient's arm behind his back. The supraspinatus may then be scanned perpendicular and parallel to its fibers. In this position, tendons that were obscured by a laterally placed acromion may be visualized. Small tears and effusions may also be accentuated with this maneuver. Although all positions are important in the sonographic evaluation of the shoulder, we have found these views with the arm in extension and internal rotation to be some of the most crucial for diagnosis.

Figure 25. Paired longitudinal supraspinatus (SUP) view in neutral (left) and extension with internal rotation (right) positions demonstrates improved visualization of the supraspinatus tendon (arrow).

Supraspinatus, Transverse View: Internal Rotation and Extension

Figure 26. Tendon anatomy and surface landmarks of supraspinatus, transverse view: internal rotation and extension.

Figure 27. Transverse views of the supraspinatus tendon in extension with internal rotation. Left image (Image 10) shows the mid supraspinatus. Right image (Image 11) was obtained more anteriorly and medially to include the critical zone.

Supraspinatus, Longitudinal View: Internal Rotation and Extension

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Figure 28. Tendon anatomy and surface landmarks of supraspinatus, longitudinal view: internal rotation and extension.

Figure 29. Longitudinal views of the supraspinatus tendon in extension with internal rotation. Left image (Image 12) shows the mid supraspinatus. Right image (Image 13) was obtained more anteriorly to include the critical zone.

Images 14 and 15 are used to better document particular areas of interest from any part of this portion of the study.

Remaining Images

• Second sheet of film (15 images): Repeat above examination on the contralateral (symptomatic) shoulder .

• Third sheet of film (total of 10 images, leaving five discretionary spaces on the film sheet). • Direct comparison (six images).

Figure 30. Biceps tendon, paired transverse views of the right (left) and left (right) shoulders (Image 1) (note the incidental small biceps tendon effusion on the right shoulder in this asymptomatic athlete).

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Figure 31. Supraspinatus (arm hanging), paired longitudinal views (as in Fig 30) (Image 2).

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Figure 32. Supraspinatus, internal rotation and extension, paired transverse views (as in Fig 30). Images were obtained at two slightly different areas of the tendon. Image 4 (b) is obtained further anterior than Image 3 (a), allowing visualization of the biceps tendon as an echogenic structure at the medial edge of each arm.

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Figure 33. Supraspinatus, internal rotation and extension, paired longitudinal views (as in Fig 30). Image 5 (a) and Image 6 (b) were obtained at two slightly different areas of the tendon.

• • Perfusion Imaging (four images).

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Figure 34. Gray-scale image (left) (Image 7) and power Doppler image (topographic mode) (right) (Image 8) of the right supraspinatus demonstrate the normal, essentially avascular appearance of the tendon.

Figure 35. Gray-scale image (left) (Image 9) and power Doppler image (topographic mode) (right) (Image 10) of the left supraspinatus demonstrate the normal, essentially avascular appearance of the tendon.

We use power Doppler technology to maximize slow-flow detection. Images are longitudinal supraspinatus views obtained in internal rotation and extension, with one image of each shoulder obtained with and without topographic mapping (vide infra).

N.B. The above filming sequence for the entire study is just a suggestion that provides a systematic approach to performing and documenting the examination. However, there are wide variations in what each examiner chooses to record, and, therefore, the filming sequence may be individualized with practice. For example, there is nothing particularly magical about obtaining the power Doppler images in the topographic mode. From a practical standpoint, we find this display mode useful because it records perfusion information in a black-and-white format, thus permitting the entire study to be documented on the black-and-white film used for the remainder of the examination, reducing film costs and clutter. However, others choose to film the power images in color or choose not to perform them at all.