The Shoulder

The shoulder is a combination of joints including the glenohumeral and acromioclavicular joints. The glenohumeral joint has the greatest range of motion of any joint in the body and, because of its unique design, is subject to dislocation more often than any other joint in the body. The arrangements of muscles, tendons, and ligaments around the shoulder account for the range of motion and protection against inherent dislocation. Knowledge of the anatomy is crucial in understanding the pathology and mechanism of injury, which will aid the clinician in treatment of the patient. As discussed with other joints, utility of fat suppression and fluid-sensitive sequences is helpful in identifying areas of edema or abnormal fluid collections. Imaging in oblique sagittal, oblique coronal, and axial planes is critical for evaluating the anatomy around the shoulder joint. Because the labrum is such a small structure, the selected field of view is key in being able to evaluate this structure. Generally 12 to 14 cm is reasonable.1,2 Oblique sagittal imaging allows for evaluation of the rotator cuff muscles, and when considering sequence design, T1-weighted imaging will give an idea of muscle bulk as well as evidence of atrophy. The bone marrow can also be evaluated for abnormal signal intensity. Fluid-sensitive sequences as mentioned previously will allow for identification of abnormal fluid collections as well as foci of edema. Occasionally, an entire muscle belly may demonstrate abnormal T2 signal indicating pathology. The pattern of abnormal signal can lead to specific diagnoses in some cases. The acromioclavicular joint is also well imaged in the oblique sagittal plane. Oblique coronal imaging is aligned along the plane of the supraspinatus. A fluid-sensitive sequence should be performed in this plane allowing for ease of diagnosis of muscle and tendon pathology as it relates to the rotator cuff. The deltoid muscle and acromioclavicular joint are also well visualized. The small structure of the superior labrum is also visualized in the oblique coronal plane. Finally, the articular cartilage within the glenohumeral joint is nicely visualized in this plane, and an echo time (TE) that is midrange (40–60 milliseconds) is more apt to demonstrate the articular cartilage distinctly from the underlying cortical bone. The axial images allow for visualization of the anterior and posterior labrum, biceps tendon, and subscapularis tendons. Evaluation of the coracohumeral interval is also readily appreciated in this plane of imaging. Evaluation of the articular cartilage can also be accomplished in this plane, keeping in mind that an intermediate-weighted TE will allow for discrimination of the labrum and articular cartilage as they will demonstrate different signal characteristics. The longer the TE, the more the cartilage will resemble the labrum, and areas of pathology may be more challenging to evaluate. Magnetic resonance (MR) arthrography with intra-articular gadolinium contrast injection can assist in evaluation of labral and capsular injuries.3 Because labral pathology predominates in younger patients, MR arthrography is generally reserved for evaluation of patients with clinical instability or in patients younger than 40 years presenting with shoulder pain.4 For rotator cuff pathology, in most circumstances, noncontrast MR imaging (MRI) is sufficient for diagnosis. This chapter will focus on anatomy and pathology as it relates to sports medicine. Understanding the anatomy cannot be underestimated when interpreting a shoulder MRI. Patterns of injury yield clues to mechanism of injury that assists with treatment plan. ROTATOR CUFF The rotator cuff is composed of 4 tendons—supraspinatus, infraspinatus, teres minor, and subscapularis. The tendons of the cuff interdigitate with each other as they attach to the greater and lesser tuberosity of the humerus. These tendons do not have a synovial sheath or a paratenon. Therefore, tenosynovitis is not a finding in the rotator cuff tendons. The supraspinatus tendon is located deep to the undersurface of the acromion and superficial to the humeral head. If the undersurface of the acromion is prominent or irregular or the space between the humeral head and acromion is narrowed, the supraspinatus tendon can become trapped or continually irritated. This may cause irritation of the overlying subacromial-subdeltoid bursa leading to inflammation and a bursitis. While the diagnosis of rotator cuff “impingement” is made on clinical examination, there are MRI findings that can support the diagnosis. These findings include a narrow space within the subacromial location and increased T2 signal in the region of the bursa. Impingement can be related to acromial development or acquired spurs at the inferior margin5,6 (Fig. 1). Overall shape of the acromion is no longer considered to be significant. However, an acromion that slopes downward laterally is developmentally predisposed to causing outlet impingement. Often in this situation the anterolateral acromial undersurface acquires a broad, flat spur resembling an “elephant’s foot.” Other subacromial spurs develop at the anterior acromion, at the insertion site of the coracoacromial ligament. Another source for impingement is an os acromiale. During development, the anterior portion of the acromion may fail to fuse, resulting in an ossicle with a fibrous synchondrosis to the remaining acromion. The anterior fibers of the deltoid muscle deflect the ossicle into the rotator cuff, leading to impingement. In later stages, the synchondrosis can break, with intervening fluid signaling transformation into a pseudarthrosis.FIGURE 1: Acromial factors associated with impingement of the rotator cuff. A, Coronal oblique T1-weighted image shows lateral down-sloping of the acromion with a broad, flat lateral subacromial spur (arrow) that can be associated with impingement. B, Axial proton-density fat-suppressed image shows an os acromiale (long arrow) attached with a synchondrosis (arrowheads) to the scapula. Note anterior fibers of the deltoid muscle (short arrows) attaching to the ossicle.The normal appearance of the rotator cuff tendons is low signal on T1- and T2-weighted imaging sequences. Diffusely increased signal on T1- and T2-weighted images (but lower T2 signal than fluid) is termed tendinopathy or tendinosis presuming a pathologic diagnosis of degeneration of the tendon5–7 (Fig. 2). The term tendinitis has fallen out of favor because it implies an inflammatory etiology. Foci of black signal may be seen in the tendons or bursa representing calcific tendinosis/bursitis.FIGURE 2: Rotator cuff tendinosis. A, T1-weighted coronal oblique image shows diffuse increase in signal within the supraspinatus tendon (arrows) representing tendinosis. B, T2-weighted coronal oblique image demonstrates a thin rim of fluid signal extending along the subacromial/subdeltoid bursa (short arrows) representing bursitis. Diffuse intermediate signal (arrowheads) extends through the tendon with associated thickening, consistent with tendinosis. A cyst is present in the greater tuberosity (long arrow). C, Coronal oblique T2-weighted fat-suppressed image reveals a focus of low signal (arrows) in the subacromial-subdeltoid bursa representing calcific bursitis.When the signal within a tendon is isointense to fluid on T2-weighted images, it is reported as a tear.5–7 The dimensions of the tear should be measured in anteroposterior and medial-lateral dimension. Rotator cuff tears are described in terms of full thickness (ie, extending from the bursal surface to undersurface), interstitial (along the central tendon fibers with preservation of bursal and articular surfaces), or partial thickness (partially extending through the tendon substance: isolated to the bursal or articular surface). Bursal-sided partial-thickness tears are less common than undersurface tears. Tears at the far anterior aspect of the supraspinatus may be difficult to identify on oblique coronal images and may be best seen on axial or oblique sagittal images (Fig. 3).FIGURE 3: Rotator cuff partial-thickness tears. A, Coronal oblique T2-weighted fat-suppressed image shows an undersurface (articular surface) partial-thickness tear of the supraspinatus tendon (arrows). Note intact superficial fibers (arrowheads). B, Coronal oblique T2-weighted fat-suppressed image shows a bursal surface partial-thickness supraspinatus tear (arrow). Note intact deep fibers (arrowhead). C, Interstitial tear of the supraspinatus (arrow) on coronal oblique T2-weighted fat-suppressed image, with intact deep and superficial fibers (arrowheads).A full-thickness tear is diagnosed by recognizing a gap in the tendon with fluid extending through the entire “footprint” of the rotator cuff insertion, extending through the deep and superficial fibers5–7 (Fig. 4). It is important to describe the tendon quality (ie, whether the tendon is thickened, thinned, frayed) and whether the myotendinous junction (normally positioned at 12 to 1 o’clock on the humeral head) is retracted. Muscle fatty infiltration may also be recognized on T1-weighted images allowing for determination of chronicity of the tendon tear. Large size of the tear, poor tendon quality, retraction, and muscle atrophy are all bad prognostic indicators for surgical repair. The supraspinatus is the most commonly torn rotator cuff tendon. Often when the tear increases in size, it will extend posteriorly to involve the infraspinatus. The teres minor tendon rarely tears; however, muscle atrophy may occur idiopathically in the teres minor muscle. Subscapularis tears are also fairly common, often presenting as interstitial tears allowing for subluxation or dislocation of the long head of the biceps tendon.7–9FIGURE 4: Rotator cuff full-thickness tear. Coronal oblique T2-weighted fat-suppressed image through the supraspinatus shows a full-thickness tear (arrows) with fluid signal extending from the joint to the bursa.BICEPS TENDON The biceps tendon is best recognized on the axial images as a low-signal, round or oval structure within the bicipital groove.10,11 It has a tendon sheath that is contiguous with the joint. Therefore, it is not unexpected to identify a distended biceps tendon sheath in the setting of a joint effusion. However, isolated fluid in the tendon sheath without the presence of a joint effusion is suggestive of a biceps tenosynovitis, which can result in anterior shoulder pain (Fig. 5). The long head of the biceps tendon originates from the glenoid rim adjacent to the superior labrum (together known as the “biceps anchor”). It is occasionally torn in the setting of chronic rotator cuff impingement as its location under the supraspinatus tendon makes it vulnerable to injury. The torn tendon may retract to the upper arm, resulting in an “empty biceps groove.” As noted above, subscapularis tears can result in subluxation or dislocation of the tendon from the bicipital groove; initially, the biceps enters the substance of the subscapularis tendon, eventually tearing through the superficial fibers or the deep fibers. In the latter circumstance, the biceps displaces into the anterior glenohumeral joint (Fig. 5).FIGURE 5: Biceps tendon pathology. A, Axial proton-density fat-suppressed image demonstrates prominent fluid signal within the biceps long-head tendon sheath (arrow) representing tenosynovitis. Thickening of the tendon (arrowhead) consistent with tendinosis. B, Subluxation of the long head of the biceps tendon (long arrow) from the bicipital groove (short arrow) into a subscapularis tendon tear (arrowheads) depicted on an axial proton-density fat-suppressed image.Abnormalities of the superior labrum can also involve the attachment of the biceps tendon as an extension of the superior labral tear.10,11 This will be discussed in more detail. GLENOHUMERAL LIGAMENTS, ROTATOR CUFF INTERVAL, AND FROZEN SHOULDER The glenohumeral ligaments represent thickenings of the joint capsule. Three ligaments, the and inferior glenohumeral ligaments, have all at the anterior aspect of the glenohumeral (Fig. These ligaments a with the superior and inferior ligaments and the extending and along the anterior glenoid is some in the appearance of the ligaments, the glenohumeral ligament. The glenohumeral ligaments to the of the shoulder in a of The superior glenohumeral the long head of the biceps In with the the glenohumeral to anterior the inferior glenohumeral anterior and posterior joint is the shoulder is and and posterior is when the shoulder is ligaments and A, oblique T1-weighted MR image shows normal anatomy of the capsular coracohumeral superior glenohumeral glenohumeral inferior glenohumeral B, oblique T1-weighted image shows synovial (arrows) in the rotator cuff interval representing rotator cuff interval is the space within the glenohumeral joint between the supraspinatus and subscapularis tendons. The intra-articular portion of the long head of the biceps tendon through the interval it within the biceps The intra-articular portion is in by the coracohumeral and superior glenohumeral to capsular ligaments, associated with rotator cuff tear, can result in synovial within the interval on MRI as edema and of fat signal in this often with (Fig. may be associated edema of the inferior as This is known as or patients present with pain and of range of commonly patients are can present in any often by injury. generally a of joint injection under has previously with AND The labrum is composed of that to the rim of the glenoid of the with 1 to the glenoid It also as the attachment of the long head of the biceps tendon as well as the glenohumeral The labrum as well as glenohumeral ligaments are low in signal on all sequences. The superior labrum and inferior labrum are best evaluated on oblique coronal images (Fig. the anterior labrum and posterior labrum are visualized on the axial images (Fig. articular cartilage may be seen between the labrum and the underlying The articular cartilage is best on intermediate-weighted images from the adjacent low signal the TE is the articular cartilage lower in signal and is difficult to from the adjacent labral A, Coronal oblique T2-weighted fat-suppressed image shows a with a rim of fluid signal (arrow) extending under the superior labrum at the biceps B, on an axial proton-density fat-suppressed Note fluid extending under the labrum (arrow). C, on an axial T1-weighted fat-suppressed MR Note a glenohumeral (arrow) with labrum glenoid are a normal that are important to in to not labral The labrum is most often in may occasionally be round or in the labrum as it to the glenoid may have articular cartilage The superior labral attachment can be allowing for fluid to extend under the labral known as a labral are present at the A can be present at the labrum a (Fig. and the labrum may be with of the glenohumeral known as a (Fig. The labrum may be or The MRI for a labral tear include fluid signal within the substance of the labrum or of the or an small labrum, and of the labrum from the glenoid keeping in mind normal described of the labrum other than at the superior or glenoid is considered a labral and The is the most common injury an anterior dislocation of the glenohumeral joint. It is a or tear of the anterior inferior labrum from the glenoid (Fig. may be as a of the glenoid It is important to the bone injury If more than of the rim of the glenoid is the injury is to be and anterior injury may be on the termed a (Fig. Therefore, recognizing a bone or in this location should a evaluation of the anterior inferior The may be however, without an associated A is termed a this of tear is difficult to and may not be without MR have a sequence with the in in to on the labrum for this labral tear. A, Axial proton-density fat-suppressed image fluid signal under the labrum (arrowhead) representing a Note bone (arrow) at the posterior humeral head related to dislocation. B, as A a (arrow) at the aspect of the humeral head with cortical and adjacent bone marrow edema on an axial proton-density fat-suppressed C, with of anterior dislocation. of the glenoid rim long arrow) is depicted on this axial T1-weighted fat-suppressed MR of the anterior (arrowheads) and a body in the posterior (short labrum with intact has termed an anterior labral or This is important to Because the the can retract and in a that will lead to instability (Fig. A chronic injury may resemble an injury as may develop around the torn labrum resembling a These can be difficult for an to and on the signal of the will more intermediate in signal than the normal labrum on an intermediate-weighted TE axial may not extend into this on MR labrum A, Axial T1-weighted fat-suppressed MR image labrum (arrow) with attached (arrowheads). B, with injury and Axial T1-weighted fat-suppressed MR image of the labrum (arrows) to the anterior glenoid with intermediate This the labrum with to the posterior labrum are not as as The for pathology are the as for an anterior inferior labral tear. A posterior dislocation of the shoulder is a result of with the in and This mechanism of injury can be seen in as well as and an in Magnetic resonance imaging is more helpful than in the diagnosis. Occasionally, the may and identification of the may be Magnetic resonance imaging will the of the posterior labrum and associated glenoid injury The humeral injury can also be readily appreciated on MRI This injury has also to as a (Fig. labral tear. Axial proton-density fat-suppressed image in a with posterior dislocation. A posterior labral tear (arrow) is noted with bone marrow edema at the anterior humeral head (arrowheads) representing a of findings at the shoulder or previously in (Fig. The acromion is of the to presenting with shoulder pain occasionally edema at the acromial representing injury. This has in and development of os in can also result in of the posterior glenoid leading to a appearance glenoid This may represent a allowing for increased range of however, it can lead to posterior labral tear and cartilage with posterior can also from a known as This of injury to the undersurface of the as well as the posterior superior The pathology is a result of and of the humeral head within the glenoid the motion on the or The of the and the posterior superior glenoid trapped between the glenoid and humeral head. Magnetic resonance imaging findings include undersurface partial-thickness tearing of the as well as tearing of the posterior superior is often noted at the humeral head. Another in has termed glenohumeral presenting with pain on the of This is related to of the posterior from on leading to of of the humerus. Magnetic resonance imaging shows of the posterior in with other posterior glenoid findings associated with noted A finding can include posterior glenoid Magnetic resonance imaging findings in A, Axial proton-density fat-suppressed image of a with pain The acromial shows edema (arrows) with B, Axial T1-weighted fat-suppressed MR image of a Note of the posterior glenoid (arrow) associated with posterior labral degeneration and tear (arrowhead). C, impingement in a with pain in Coronal oblique T1-weighted fat-suppressed MR image demonstrates an undersurface partial-thickness tear of the tendon (arrow) as well as a tear of the labrum (arrowhead). with pain on is on this axial proton-density fat-suppressed image as posterior capsular (arrowhead). Note of the posterior glenoid commonly seen in posterior labral that may be chronic in is that which is associated with the of and the The posterior glenohumeral joint in the extension of This to increased along the posterior glenohumeral joint space and at the the glenoid attachment can and the labrum can signal is recognized at the and the labrum may be or abnormal in signal (Fig. Finally, may also occur at the superior The superior labrum is unique because of the insertion of the long head of the biceps tendon on the superior Therefore, to the superior labrum may also involve the biceps as it to the superior A labrum anterior to is a term for a tear that is in an and at the attachment site of the biceps (Fig. The term is out of in patients may have degeneration of the labrum in this The 12 on tear pattern and It is more important to be and an in the biceps labral The described 4 1 a labrum with a is to be the most common of superior labral tear a of the superior labrum from the underlying is as a tear of the superior labrum without of the biceps and 4 the attachment of the long head of the biceps with a tear of the superior in mind that the can a tear, and it is important to identify fluid signal extending into the labral labral tears are best diagnosed on coronal fluid-sensitive sequences. The diagnosis is made MR arthrography is labrum anterior to posterior tear. Coronal oblique T1-weighted fat-suppressed MR image shows contrast the substance of the superior labrum (arrow) representing a superior labral to labral pathology, capsular may of the inferior has termed an of the glenohumeral a considering that the tear from the humeral attachment and can be present along the inferior capsule. this injury can be seen as of the inferior or extension of fluid contrast an MR from the joint into the (Fig. of the glenohumeral Coronal oblique T1-weighted fat-suppressed MR image shows contrast from the joint through an inferior capsular tear (arrow) into the should be from fluid signal adjacent to the glenoid that result from a tear in the are important to as presence underlying labral tear or a narrow extends to the labral tear. These can be located around the labrum are most common and (Fig. a cyst from a superior labral tear extends into the or in this location can lead to of the that the supraspinatus and muscle. on the can lead to pain a rotator cuff tear. edema is as increased T2 signal the muscle which can be from muscle injury seen as a pattern of edema. The most common location for a cyst is adjacent to the inferior glenoid related to an inferior labral tear. A cyst in this location can cause on the space and impingement on the that the teres minor and posterior deltoid muscle. to above, in can be seen on MRI in this known as space Muscle on MRI presenting without impingement should for an A, Coronal oblique T2-weighted fat-suppressed image shows a cyst (arrow) extending into the Note narrow (arrowheads) to the a labral tear is not on this image, is to be B, Coronal oblique T2-weighted fat-suppressed image an inferior cyst (arrows). a (arrowhead) extends to the inferior labrum a tear is C, oblique T2-weighted image shows atrophy of the muscle (arrows) with diffuse signal related to impingement the by a cyst (arrowheads) in the articular cartilage injury may result from an injury and can be isolated in its may not lead to However, of an articular cartilage injury may assist with treatment The from of the humeral head against the articular surface of the glenoid with the in and is often the clinical than a of may also occur to the glenohumeral articular cartilage resulting in and development of The is most recognized on axial and occasionally coronal images by recognizing the articular cartilage with fluid (Fig. It is important to and the articular cartilage within the cartilage are not isolated to can be seen with rotator cuff pathology, and the presence of cartilage may have an on surgical for cuff cartilage A, Axial T1-weighted fat-suppressed MR image a cartilage (arrow). Note adjacent labral tear (arrowhead). B, Axial T1-weighted fat-suppressed MR image shows a focus of cartilage (arrows) at the posterior aspect of the Tears of the muscle most often occur in of the tear treatment of the injury. The muscle is composed of the and which as they insertion on the at the bicipital Tears may be partial or and may occur in the muscle or at the attachment of the tendon to the humerus. is generally performed for at the treatment is for to the muscle or The axial images as well as far anterior coronal images will the muscle to best Tears have the appearance as in all other The appearance on the and whether is If is this can be recognized as increased The location of the fluid signal with treatment of increased T2 signal at the attachment of the than within the muscle belly is of an surgical (Fig. tear. A, Axial proton-density fat-suppressed image of a with injury. is seen at the insertion of the tendon (arrowheads) on the humeral representing a tear at the a surgical Note associated of the muscle belly (arrow). B, Axial image of a different a tear at the myotendinous junction this injury is Note intact tendon at the are to seen as of the articular surface of the at the acromioclavicular joint on and bone marrow edema on fluid-sensitive MRI sequences. the are or on the and or on the acromial is that the a related to on the articular surface (Fig. Axial T2-weighted fat-suppressed image through the acromioclavicular joint shows bone marrow edema isolated to the (arrow). Note low signal (arrowhead) representing the chapter the more commonly in sports as well as the clues the pattern that can to the mechanism of injury leading to more and treatment for the patient. of are more readily appreciated by the at than can be appreciated at