Chapter 3 Shoulder Ultrasound
Additional videos for this topic are available online at www.expertconsult.com.
The rotator cuff is composed of four tendons (Fig. 3-1). Anteriorly, the subscapularis with its tendons converges onto the lesser tuberosity. Superiorly, the supraspinatus inserts on the superior aspect of the greater tuberosity; its footprint or attachment averages 2.25 cm anterior to posterior, which covers the superior facet and the anterior portion of the middle facet of the greater tuberosity (Fig. 3-2).1,2 Posterior to the scapula and inferior to the scapular spine, the infraspinatus tendon inserts on the middle facet of the greater tuberosity, and the smaller and more inferior teres minor tendon inserts on the inferior facet of the greater tuberosity. Between the lesser and greater tuberosities anteriorly is the bicipital groove, which contains the long head of the biceps brachii tendon; although not a part of the rotator cuff, its proximal intra-articular portion courses through a space between the supraspinatus and subscapularis tendons, called the rotator interval. At this location, the intra-articular portion of the biceps tendon is stabilized by the biceps reflection pulley made up of the superior glenohumeral ligament and the coracohumeral ligament, which are essentially thickened reflections of the joint capsule. The glenohumeral joint normally communicates with the biceps brachii long head tendon sheath. Several joint recesses also exist and include the axillary recess, which extends inferiorly, and the subscapular recess, which extends medially through the rotator interval to be located inferior to the coracoid process at the superior aspect of the subscapularis tendon in an inverted U shape. The subacromial-subdeltoid bursa is located between the rotator cuff and the overlying deltoid muscle and acromion (see Fig. 3-1). The glenoid labrum represents a rim of fibrocartilage at the periphery of the glenoid.
FIGURE 3-1 Shoulder anatomy.
(A and B, Image courtesy of Carolyn Nowak, Ann Arbor, Michigan. C, From Drake R, Vogl W, Mitchell A: Gray’s anatomy for students, Philadelphia, 2005, Churchill-Livingstone.)
Ultrasound Examination Technique
Table 3-1 is a shoulder ultrasound examination checklist. Examples of diagnostic shoulder ultrasound reports are available online at www.expertconsult.com (see eBox 3-1 and 3-2).
| Step | Structures/Pathologic Features of Interest |
|---|---|
| 1 | Biceps brachii long head |
| 2 | Subscapularis, biceps tendon dislocation |
| 3 | Supraspinatus, infraspinatus |
| 4 | Acromioclavicular joint, subacromial-subdeltoid bursa, dynamic evaluation |
| 5 | Posterior glenohumeral joint, labrum, teres minor, infraspinatus |
eBox 3-1 Sample Diagnostic Shoulder Ultrasound Report
Normal
Examination: Ultrasound of the Shoulder
History: Shoulder pain, evaluate for rotator cuff abnormality
Findings: No evidence of joint effusion. The biceps brachii long head tendon is normal without tendinosis, tear, tenosynovitis, or subluxation/dislocation. The supraspinatus, infraspinatus, subscapularis, and teres minor tendons are also normal. No subacromial-subdeltoid bursal abnormality and no sonographic evidence for subacromial impingement with dynamic maneuvers. The posterior labrum is unremarkable. Additional focused evaluation at site of maximal symptoms was unrevealing.
Impression: Unremarkable ultrasound examination of the shoulder. No rotator cuff abnormality.
eBox 3-2 Sample Diagnostic Shoulder Ultrasound Report
Abnormal
Examination: Ultrasound of the Shoulder
History: Shoulder pain, evaluate for rotator cuff abnormality
Findings: There is a focal anechoic tear of the anterior, distal aspect of the supraspinatus tendon measuring 1 cm short axis by 1.5 cm long axis. The anterior margin of the tear is adjacent to the rotator interval. There is no involvement of the subscapularis, infraspinatus, or rotator interval. A moderate amount of infraspinatus and supraspinatus fatty degeneration is present. There is a small joint effusion distending the biceps brachii tendon sheath and moderate distention of the subacromial-subdeltoid bursa. No biceps brachii long head tendon abnormality and no subluxation/dislocation. Mild osteoarthritis of the acromioclavicular joint. Additional focused evaluation at site of maximal symptoms was unrevealing.
Impression: Focal or incomplete full-thickness tear of the supraspinatus tendon with infraspinatus and supraspinatus muscle atrophy.
General Comments
For ultrasound examination of the shoulder, the patient sits on a stool with low back support but without wheels, and the sonographer sits on a stool with wheels to allow easy maneuvering. For examination of the patient’s left shoulder, the patient faces the ultrasound machine, with the sonographer sitting somewhat between the patient and ultrasound machine if the sonographer is right-handed (Fig. 3-3A, online). For examination of the patient’s right shoulder, the patient turns toward the left and faces the sonographer (see Fig. 3-3B, online). The transducer frequency for the shoulder is generally at least 10 MHz, although one may need to use a lower frequency in evaluation of the deeper structures such as the posterior glenoid labrum or if the patient has a large body habitus. It is important to follow a sequence of steps to ensure a complete and thorough evaluation.3 Although a targeted approach is often used in other peripheral joints, this is not recommended with the shoulder because pain is often diffuse or referred. It is recommended, however, that every sonographic evaluation be followed by targeted evaluation over any area with point tenderness or focal symptoms.
Position No. 1: Long Head of Biceps Brachii Tendon
The patient places the hand palm up in supination on his or her leg (Fig. 3-4A). This position rotates the bicipital groove anteriorly, an important bone landmark. The transducer is placed in the transverse plane on the patient, and the long head of the biceps brachii tendon is seen within the bicipital groove in short axis (see Fig. 3-4) (Video 3-1). 
Because the distal biceps tendon courses deep, tendon obliquity to the transducer sound beam commonly creates anisotropy and an artifactual hypoechoic appearance of the normal tendon (see Fig. 3-4C). This is corrected by toggling the transducer inferiorly to aim the sound beam superiorly (Video 3-2).
A hyperechoic and well-defined humeral cortex in the floor of the bicipital groove indicates that the sound beam is perpendicular to the overlying biceps tendon. The biceps brachii tendon is evaluated in short axis from proximal to distal. It is important to evaluate the most proximal aspect where the biceps tendon courses over the humeral head because this is a common site for tendon pathology.4 Evaluation is also continued inferiorly to the level of the pectoralis tendon (see Fig. 3-4D) to assess the pectoralis and biceps because complete biceps brachii long head tendon tears may retract to this level. The transducer is then turned 90 degrees to visualize the tendon in long axis from the humeral head to the pectoralis tendon (Fig. 3-5A) (Video 3-3).
Asymmetrical pressure on the distal aspect of the transducer (or heel-toe maneuver) is typically needed to bring the biceps tendon fibers perpendicular to the transducer sound beam to eliminate anisotropy (see Fig. 3-5B and C) (Video 3-4).
An additional method to visualize the biceps tendon in long axis is to identify the characteristic pyramid shape of the lesser tuberosity (see Fig. 3-5D); movement of the transducer laterally from this point will visualize the bicipital groove and biceps long head tendon (Video 3-5).
Position No. 2: Subscapularis and Biceps Tendon Dislocation
The transducer is placed in the transverse plane, as before, to visualize the bicipital groove and to center the field of view over the lesser tuberosity (see Fig. 3-4A). In this neutral position, although the subscapularis tendon can be seen in long axis, there is significant anisotropy (Fig. 3-6A). Ask the patient to rotate the shoulder externally (see Fig. 3-6B), and this will bring the subscapularis tendon fibers into view perpendicular to the transducer sound beam and will eliminate anisotropy (see Fig. 3-6C) (Video 3-6).
It is important to move the transducer superiorly and inferiorly over the lesser tuberosity to ensure complete evaluation of the subscapularis tendon. The transducer should also be moved laterally over the bicipital groove to evaluate for potential biceps brachii tendon subluxation or dislocation, which may be present only in external rotation (see Biceps Tendon, Subluxation and Dislocation).5 Center the transducer over the distal subscapularis tendon again, rotate the transducer 90 degrees, and assess the subscapularis tendon in short axis (Fig. 3-7A and B). In this view, it is common to see vertical hypoechoic striations of muscle or interfaces between the several tendon bundles, especially when spatial compound sonography is not used (see Fig. 3-7C) (Video 3-7).
Position No. 3: Supraspinatus and Infraspinatus
The goal when imaging the supraspinatus is to evaluate the tendon in long and short axis. This will avoid numerous diagnostic pitfalls and is an indicator that the operator has a thorough understanding of anatomy and shoulder ultrasound technique. The key to obtaining such images is to understand the anatomy of the greater tuberosity and the effects of various shoulder positioning. If one wanted to assess the supraspinatus tendon in long axis with the shoulder in neutral position, the transducer would be placed in the coronal place over the greater tuberosity; however, in this position, much of the tendon is hidden beneath the acromion, which could hide more proximal cuff tears (Fig. 3-8). One way to correct this is to ask the patient to place the back of his or her ipsilateral hand in the lower lumbar region and to keep the elbow close to the body (called the Crass position) (Fig. 3-9).6 In this position, the humerus is rotated internally such that the greater tuberosity is located anteriorly on the patient. By placing the transducer in the sagittal plane on the patient over the greater tuberosity, a long axis view of the supraspinatus tendon is demonstrated. Rotating the transducer 90 degrees (or transverse on the patient) will produce a short axis image of the supraspinatus. The Crass position is helpful when one is first learning shoulder ultrasound technique in that a long and short axis views are easily obtained; however, the significant disadvantages of this position include limited view of the rotator interval (see later) and, often, significant patient discomfort. Because of this, the modified Crass position is used (I primarily use the modified Crass position and uncommonly the Crass position for problem solving) (Fig. 3-10).7 To obtain the modified Crass position, the patient is asked to place his or her hand on the ipsilateral hip area. The elbow should be pointed posteriorly to ensure some degree of shoulder external rotation compared with the Crass position; otherwise, the rotator interval may not be visible. The greater tuberosity is now located between the locations in the neutral and Crass positions; therefore, to obtain a long axis view of the supraspinatus tendon, the transducer is placed over the greater tuberosity and pointed superior and oblique toward the patient’s ear. Usually, the axis of the transducer is parallel to the proximal biceps tendon and humeral shaft regardless of each position when imaging the supraspinatus in long axis. The transducer is then turned 90 degrees to evaluate the supraspinatus tendon in short axis.
Regardless of patient positioning in the Crass or modified Crass position, supraspinatus evaluation begins with evaluation in long axis because this important view allows visualization of the three surfaces of the supraspinatus tendon. In long axis, the normal supraspinatus will appear hyperechoic and fibrillar, with a convex superior margin (Fig. 3-11) (Video 3-8).
The thin hypoechoic layer over the curved humeral head represents the hyaline articular cartilage. At times, a thin hypoechoic layer over the greater tuberosity, which represents the fibrocartilage transition zone between the tendon and bone at the enthesis, may be seen and should not be confused with hyaline articular cartilage over the rounded humeral head. One must be aware that the distal fibers of the tendon curve downward at the greater tuberosity near the articular surface, and the transducer orientation should be adjusted using the heel-toe maneuver to eliminate anisotropy (Fig. 3-12A and B) (Video 3-9).
A hyperechoic and well-defined humeral head cortex indicates that the sound beam is perpendicular to the bone and overlying tendon. The footprint of the supraspinatus tendon inserts over approximately 2.25 cm of the greater tuberosity shelf, so the transducer should be moved anterior and posterior over the greater tuberosity (or medial and lateral on the patient in the modified Crass position), to ensure complete evaluation.2 It is important to continue scanning anteriorly along the greater tuberosity until the intra-articular portion of the biceps tendon is seen because this would indicate that the full anterior extent of the supraspinatus was evaluated, a location where supraspinatus tendon tears commonly occur.8,9 Including a long axis image of the intra-articular portion of the long head biceps brachii tendon will document that the most anterior aspect of the supraspinatus was evaluated (see Fig. 3-11B). As the transducer is moved posteriorly over the middle facet of the greater tuberosity, the infraspinatus is also evaluated (see Fig. 3-11C). At the middle facet, the angle between the greater tuberosity and the articular surface of the humeral head flattens, and alternating hypoechoic linear areas representing anisotropy of the infraspinatus tendon fibers can be seen over the supraspinatus tendon (Video 3-10).
Minimal thinning of the cuff over this region may be seen.10 In addition, the rotator cable may be seen as a distinct hyperechoic structure (see Fig. 3-15).
After assessment of the supraspinatus in long axis, the transducer is turned 90 degrees to evaluate the tendon in short axis (Fig. 3-13) (Video 3-11).
First, beginning over the proximal aspect of the supraspinatus, the humeral head should be seen as a round echogenic line with overlying hypoechoic hyaline cartilage (see Fig. 3-13A). The transducer should be toggled until the bone cortex and overlying tendon are hyperechoic and well defined to eliminate anisotropy (see Fig. 3-12C and D). At this level, the rotator cuff should be of fairly uniform thickness, similar to a tire on a wheel, measuring on average 6 ± 1.1 mm.11 This appearance indicates that the transducer is in the true short axis plane relative to the supraspinatus tendon and not in an oblique plane. The transducer is then moved distally relative to the supraspinatus tendon. As the hyaline cartilage disappears from view, the round humeral head surface will be replaced with the angulated surface of the greater tuberosity facets. At this point, the tendon uniformly becomes thinner, an indication that the transducer position is now beyond the articular surface. The facets of the greater tuberosity from anterior to posterior appear as three flat surfaces: the superior, middle, and inferior facets.1 The supraspinatus tendon inserts on the superior facet and the superior half of the middle facet, the infraspinatus inserts on the middle facet (overlapping the supraspinatus tendon superficially), and the teres minor inserts on the inferior facet.1 At this point, both the distal supraspinatus and infraspinatus are assessed. Similar to long axis imaging, alternating hypoechoic lines are seen over the middle facet, which represent anisotropy of the infraspinatus tendon fibers over the supraspinatus (Video 3-12).
As the transducer is moved more distally, the greater tuberosity becomes somewhat square, and the rotator cuff thins even more and eventually disappears as the transducer moves beyond the greater tuberosity and beyond the rotator cuff (see Fig. 3-13C and D). Similar to evaluation of the supraspinatus tendon in long axis, it is critical that the intra-articular portion of the biceps tendon (the rotator interval) is identified to indicate that the most anterior aspect of the supraspinatus tendon is evaluated. This is one of the advantages of the modified Crass position because this important landmark is well visualized. In addition, the biceps reflection pulley is identified with the superior glenohumeral ligament seen at the subscapularis aspect of the biceps tendon adjacent to the humerus, and the coracohumeral ligament is identified over the biceps tendon as it courses lateral to merge with the supraspinatus tendon (Fig. 3-14).12
Another structure of the rotator cuff is the rotator cable, which may be identified by its characteristic shape and position (Fig. 3-15).13 The rotator cable has a U shape, with each limb attaching to the greater tuberosity. The curved aspect of the U is visualized with its fibers perpendicular to the supraspinatus at the articular surface. The rotator cable is more prominent in some individuals (termed cable dominant) and outlines an area of the rotator cuff within the U, termed the rotator crescent.
Position No. 4: Acromioclavicular Joint, Subacromial-Subdeltoid Bursa, and Dynamic Evaluation
The acromioclavicular joint can be located with palpation of the clavicle and placement of the transducer in the coronal-oblique plane over the distal clavicle (Fig. 3-16) or by moving the transducer superiorly in the transverse plane from the bicipital groove region. The acromioclavicular joint is identified by the bone landmarks and hypoechoic joint space, although a hyperechoic fibrocartilage disk may be seen.14 If the acromioclavicular joint is widened, the patient can place his or her hand on the opposite shoulder to assess for acromioclavicular joint widening or, conversely, narrowing, which may be associated with pain.15 The transducer is then moved laterally in the coronal place over the proximal humerus beyond the greater tuberosity to assess for fluid within the dependent portion of the subacromial-subdeltoid bursa (see Fig. 3-16C).
To dynamically assess for subacromial impingement, the transducer is positioned in the coronal or coronal-oblique plane to visualize the lateral border of the acromion and the adjacent greater tuberosity (Fig. 3-17). The examiner assesses the supraspinatus tendon and subacromial-subdeltoid bursa dynamically first by passively abducting the arm (with or without elbow flexion). This allows the examiner to slow or stop the patient’s movement if the bone landmarks are not visualized to allow repositioning of the transducer and also trains the patient to abduct the arm at a particular speed. The movement is then repeated actively (see Fig. 3-17C and D). Subsequent pooling of fluid in the subacromial-subdeltoid bursa indicates subacromial impingement, although more advanced cases can show additional upward movement of the humeral head.16,17 The finding of incomplete sliding of the supraspinatus beneath the acromion during this dynamic maneuver indicates adhesive capsulitis.18 When assessing for subacromial impingement, the transducer should also be moved anterior to the acromion to assess the region of the coracoacromial ligament for abnormal distention of the subacromial-subdeltoid bursa as well.
Position No. 5: Infraspinatus, Teres Minor, and Posterior Glenoid Labrum
The patient rotates on the stool to permit visualization of the posterior structures of the shoulder; initially, the patient keeps his or her hand palm up on the thigh. Place the transducer in the oblique axial plane angled superiorly toward the humeral head parallel and just inferior to the scapular spine (Fig. 3-18). Position the transducer to visualize the well-defined central tendon of the infraspinatus tendon within the infraspinatus muscle at the musculotendinous junction posterior to the glenoid to ensure an imaging plane that is long axis to the infraspinatus (see Fig. 3-18B). The infraspinatus tendon can then be followed distally to its insertion on the middle facet at the posterior aspect of the greater tuberosity. Evaluation of the distal infraspinatus tendon supplements earlier evaluation from the modified Crass position (see Figs. 3-11 and 3-13). If the infraspinatus tendon is not visible because of shadowing beneath the acromion (which is not common), then the patient can place the hand on the opposite shoulder to improve visualization; this maneuver is less ideal because the infraspinatus tendon, seen linear and perpendicular to the sound beam in neutral shoulder position, becomes curved, introducing anisotropy. The transducer can then be moved inferiorly to visualize the smaller teres minor, with its tendon more superficial over the muscle compared with the infraspinatus tendon (see Fig. 3-18C). The transducer is then turned 90 degrees to evaluate the infraspinatus and teres minor in short axis (Fig. 3-19). An alternate approach in identification of the infraspinatus and teres minor is to palpate the scapular spine, place the transducer sagittal on the patient over the scapular spine, and then move the transducer inferiorly. The first structure identified inferior to the scapular spine is the infraspinatus. Once the infraspinatus and teres minor are identified, the transducer is turned long axis to the infraspinatus tendon to evaluate the hyperechoic triangle-shaped posterior glenoid labrum (see Fig. 3-18B). It is important to slide the transducer medially from the glenohumeral joint to assess the spinoglenoid notch, a site where paralabral cysts may be found. The patient can actively internally and externally rotate the shoulder to assess the infraspinatus tendon and posterior glenoid labrum dynamically (Video 3-13).
This maneuver is also important in the evaluation for posterior glenohumeral joint recess fluid, which also facilitates evaluation of potential paralabral tears (see Glenoid Labrum and Paralabral Cyst). In shoulder external rotation, the suprascapular vein may dilate, and this can simulate a paralabral cyst (see Glenoid Labrum and Paralabral Cyst) (Video 3-14).
To complete the posterior shoulder examination, the transducer is turned 90 degrees and moved medial to assess the infraspinatus and teres minor in short axis globally at the musculotendinous junctions for atrophy or fatty degeneration; the infraspinatus muscle should be nearly twice the size of the teres minor over the scapular body, with normal muscle appearing relatively hypoechoic compared with hyperechoic tendon (see Fig. 3-19B). At this site, a ridge is often seen in the scapula, which forms a concave surface beneath each muscle and aids in their identification. The transducer can be moved superiorly to similarly assess for atrophy of the supraspinatus muscle. An extended field of view image may be considered (if available on the ultrasound machine) (see Fig. 3-19E).19
Rotator Cuff Abnormalities
Supraspinatus Tears and Tendinosis
General Comments
Most rotator cuff tears involve the supraspinatus tendon, although they may extend posterior to involve the infraspinatus and anterior to involve the biceps reflection pulley and subscapularis tendons.8 The anterior aspect of the distal supraspinatus is a common site of tear, often near the rotator interval, although a more posterior location near the supraspinatus-infraspinatus junction has been described with degenerative cuff tears.20 Most tendon tears are the result of chronic attrition and possible superimposed injury, and they typically occur after the age of 40 years. Such chronic supraspinatus tears occur distally and are associated with cortical irregularity of the greater tuberosity, an important indirect sign of supraspinatus tendon tear.21,22 Acute tears may occur more proximally and may or may not have associated cortical irregularity, depending on the age of the patient and the state of the underlying rotator cuff. Accurate localization of a tendon tear is essential to classify the tear properly (Fig. 3-20). For example, partial-thickness tears could involve either the articular or bursal surface of the tendon. A tear that is localized within the tendon or that extends only to the greater tuberosity surface (or footprint) of the supraspinatus attachment is called an interstitial or intrasubstance tear because it would not be visible at arthroscopy or bursoscopy.2,8 A tear that extends from articular to bursal surfaces is a full-thickness tear. Correct description and nomenclature are also essential. A full-thickness tear may be focal or incomplete, whereas a full-thickness tear that involves the entire width of a tendon can be termed a complete or full-width full-thickness tear. Initial evaluation in long axis of the supraspinatus is ideal in that the three surfaces of the rotator cuff (articular, bursal, greater tuberosity) are visible and easily identified.23 Most tears are anechoic or hypoechoic. As a supraspinatus tendon tear becomes larger, tendon retraction and volume loss of the tendon occur, with loss of the normal superior convex shape. Ultrasound and magnetic resonance imaging (MRI) have comparable accuracies in detection and measurement of rotator cuff tears.24 A meta-analysis of 65 articles has also shown that ultrasound and MRI are comparable in sensitivity and specificity for the diagnosis of rotator cuff tear.25
Partial-Thickness Tear
Partial-thickness supraspinatus tendon tears are characterized by a well-defined hypoechoic or anechoic abnormality that disrupts the tendon fibers.21,26 Such tears may be articular-side or bursal-side partial-thickness tears determined by which surface of the tendon is involved. An intrasubstance or interstitial tear may also be considered a form of partial-thickness tear, but one that does not extend to the articular or bursal surface.
Articular-side partial-thickness tears most commonly involve the supraspinatus anteriorly and distally at the greater tuberosity and are seen with increased frequency in patients younger than 40 years.8,9 A mixed hyperechoic-hypoechoic appearance may be present, which represents hypoechoic fluid that surrounds the hyperechoic torn tendon stump (Figs. 3-21, 3-22, and 3-23).26 Cortical irregularity of the greater tuberosity immediately adjacent to the tendon tear is common, related to the chronic cuff attrition at the site of the tear.21,22 An acute tear of a previously normal cuff or a proximal tear (see Fig. 3-23) does not demonstrate cortical irregularity and more likely appears anechoic from fluid, although these types of tears are less common. With an articular-side partial-thickness tear, the superior surface of the tendon remains convex because global tendon volume loss is usually absent. Articular surface extension of a tear is suggested when the tear is in direct contact with the hypoechoic hyaline cartilage. The hyperechoic interface between the tendon tear and the hyaline cartilage may be accentuated in this situation (called the cartilage interface sign).27 The terms rim-rent tear and PASTA (partial articular-sided supraspinatus tendon avulsion) lesion are used specifically to describe a far-distal articular-side partial-thickness tear, immediately adjacent to the greater tuberosity surface (Video 3-15).8,9 
A bursal-side partial-thickness supraspinatus tendon tear is also hypoechoic or anechoic, but it is localized to the bursal surface (Figs. 3-24, 3-25, 3-26, and 3-27).21 Tear extension from the bursal surface to the greater tuberosity surface (or tendon footprint), without extension to the articular surface, is still considered a bursal-side partial-thickness tear. Because of the superficial location of the tear, tendon thinning and volume loss of the cuff are usually present. This situation results in loss of the normal superior convexity of the supraspinatus tendon surface, with dipping of the deltoid muscle and subacromial-subdeltoid bursa into the torn tendon gap. Similar to other supraspinatus tendon tears, greater tuberosity cortical irregularity is typically present because the tear extends from the bursal surface to the greater tuberosity surface. If adjacent subacromial-subdeltoid bursal synovial hypertrophy is present, hypoechoic or isoechoic synovial tissue may fill the torn tendon gap, making the tear and tendon thinning less conspicuous (see Fig. 3-27) (Video 3-16).
A tendon tear that does not contact the articular or bursal side of the supraspinatus is termed an intrasubstance or interstitial tear.8,9 Such tears may be anechoic or hypoechoic, located within the tendon substance or in contact with the greater tuberosity surface (Fig. 3-28). Cortical irregularity is often seen in the latter situation. Volume loss of the tendon is absent. Extensive intrasubstance tears may either represent or be precursors of a more extensive delamination tear. The presence of a well-defined anechoic cyst within the rotator cuff is usually associated with a supraspinatus articular-side tear (Fig. 3-29).28
Full-Thickness Tear
A full-thickness supraspinatus tendon tear is characterized by a well-defined hypoechoic or anechoic abnormality that disrupts the hyperechoic tendon fibers and extends from the articular to bursal surfaces of the tendon (Figs. 3-30 through 3-38).21,24 Anterior and distal location is common, although degenerative supraspinatus tears may be isolated more posterior at the supraspinatus-infraspinatus junction.8,20 Associated cortical irregularity of the adjacent greater tuberosity surface is usually present at a supraspinatus tear in patients older than 40 years. Identification of a hyperechoic interface between the hypoechoic hyaline cartilage and anechoic or hypoechoic tendon tear (cartilage interface sign) assists in the identification of the articular extent.27 This finding is only seen when the sound beam is perpendicular to the hyaline cartilage; the heel-toe maneuver when imaging the tendon in long axis and toggling the transducer while in short axis is helpful (see Chapter 1). Small full-thickness tears may not be associated with volume loss of the tendon, especially if filled with fluid. Narrow longitudinal tears are best visualized with the tendon in short axis (see Fig. 3-31). As a tear becomes larger, flattening or concavity of the superior supraspinatus tendon surface with volume loss is typical (Video 3-17). 
Acute tears may occur more proximally, and more commonly they are anechoic and are filled with fluid (see Fig. 3-34).29 An acute tear in a patient younger than 40 years or a proximal tear does not demonstrate cortical irregularity, although these types of tears are less common. It is important to describe the location of the tendon tear, the dimensions of the tear in long axis and short axis, and extension to other adjacent tendons. A full-thickness tear that is focal may be termed an incomplete full-thickness tear, whereas a tear that involves the entire width of a tendon may be termed a complete or full-width full-thickness tear. Chronic tears may be associated with extensive remodeling of the greater tuberosity, and the distal torn tendon may be tapered without adjacent fluid but possibly with isoechoic or hyperechoic synovial hypertrophy (see Fig. 3-38). With regard to tear extension to other tendons, a supraspinatus tear that extends posterior to the rotator interval beyond 2.5 cm involves the infraspinatus tendon.2 In addition, imaging the cuff in short axis over the greater tuberosity facets assists in this determination because a tear that extends over the posterior aspect of the middle facet indicates infraspinatus involvement as well. A supraspinatus tendon tear may also extend anteriorly through the rotator interval to involve the cephalad fibers of the subscapularis tendon (see Subscapularis Tears and Tendinosis). A bicep reflection pulley tear and long head of biceps brachii tendon subluxation or dislocation may also occur in this situation (Fig. 3-39) (Video 3-18).12
It is also important to assess for supraspinatus and infraspinatus atrophy in the setting of a rotator cuff tear because this finding is associated with poor surgical outcome after repair (see Rotator Cuff Atrophy).30
