a practical approach to imaging of the shoulder with emphasis on mr imaging

MUSCULOSKELETAL IMAGING UPDATE, PART I 0030-5898/97 $0.00 + .20

A PRACTICAL APPROACH TO IMAGING OF THE SHOULDER

WITH EMPHASIS ON MR IMAGING

Phillip F. J. Tirman, MD, Lynne S. Steinbach, MD, John P. Belzer, MD, and Frederic W. Bost, MD

Imaging has a significant role in the diagnosis and treatment of shoulder abnormalities. Numerous complexities unique to the shoulder make diagnosis challenging for both the primary care physician and the accomplished surgeon. The evolving knowledge of shoulder biomechanics, improved anatomic visualization by arthroscopy, and overlapping symptoms with multiple conditions all contribute to the difficulty in clinical diagnosis.

The shoulder is anatomically complex with numerous structures contributing to both the mobility and stability of the joint. Variations of normal anatomy can lead to confusion during arthroscopic diagnosis and treatment. Diag- nostic imaging, especially MR imaging, clari- fies some diagnostically difficult scenarios by demonstrating both intra-articular and extra- articular anatomy. The dynamic elements of glenohumeral and scapulothoracic muscle force couples contribute to shoulder stability and mobility. MR imaging, in particular, provides an accurate assessment of muscle anatomy and status.

A spectrum of disorders of the shoulder with overlapping clinical presentations can be extrinsic and intrinsic to the joint. The accurate diagnosis of pain in the shoulder caused by

cervical spine disease, neurovascular disease, or neoplasm that can mimic intra-articular pathology is often aided by the positive and perti- nent negative findings of imaging.

Arthroscopy often demonstrates multiple pathologic lesions during a single evaluation and treatment. More sophisticated methods of imaging in combination with an accurate history and complete physical examination help to prioritize treatment in situations in which multiple options exist.

Orthopedic treatment sometimes fails to produce predictable results, questioning the accuracy of diagnosis. This underscores the need for improved imaging for diagnosis. This article describes the application of available imaging modalities with an emphasis on MR imaging. A strategy for the appropriate use of these studies and their variations of technique is provided.

PLAIN FILM EVALUATION

Plain film evaluation remains a useful initial tool for the diagnostic work-up of a patient with a shoulder abnormality. For the detection of fractures, dislocations, extra-articular cal-

From the San Francisco Magnetic Resonance Center (PFJT); the Departments of Radiology (PFJT, LSS) and Orthopaedics (JPB, FWB), Musculoskeletal Division (LSS), University of California, San Francisco; St. Francis Memorial Hospital (PFJT); and California Pacific Orthopaedics and Sports Medicine (JPB, FWB), San Francisco, California

ORTHOPEDIC CLINICS OF NORTH AMERICA

VOLUME 28 * NUMBER 4 OCTOBER 1997 483

484 TIRMAN et a1

cium deposits, and the evaluation of glenohumeral arthritis and neoplasm, plain film studies contribute a considerable amount of information. Conventional radiography and arthrography have been disappointing for the detection of pathologic soft-tissue changes of instability and the early diagnosis of impingement syndrome and rotator cuff disease. Sev- eral osseous changes, such as a subacromial enthesophyte, laterally downsloping acromion, and acriomioclavicular (AC) joint undersurface osteophytes, have been implicated in rotator cuff impingement; however, these findings can also be present in the absence of rotator cuff pathology. The conventional ra- diograph is of limited value in the evaluation of rotator cuff tears. Radiographic changes diagnostic of a rotator cuff tear are seen only in advanced disease. These include an acromiohumeral articulation or an acromiohumeral distance of less than 7 mm.

The addition of intra-articular contrast (plain film arthrography) permits a nonspecific diagnosis of rotator cuff tears, some biceps tendon tears, articular cartilage abnormalities, ad- hesive capsulitis, and loose bodies.z6, lol,loz Soft- tissue discrimination and pathophysiologic information, such as the presence of edema, are restricted, which limits the usefulness of arthrography. Arthrographic demonstration of partial-thickness undersurface and full- thickness tears of the rotator cuff is highly sensitive and Arthrography cannot, however, demonstrate partial-thickness tears within the substance (delamination) or bursa1 surface tears of the tendon. A detailed discus- sion of the abnormalities of the shoulder seen on plain films is beyond the scope of this article, and the interested reader is directed to the many available references.z6* lol, loZ

ULTRASONOGRAPHY

Ultrasonography is an operator-dependent technique that can demonstrate abnormalities of the rotator cuff, bursa, and long head of the biceps tendon.6, 8, 16, 43, 45, 91, lO9 It permits the noninvasive evaluation of muscles and tendons of the rotator cuff. Ultrasonography is associated with high sensitivity and specificity when performed and interpreted by a highly experienced sonographer using state-of-the- art equipment. Several groups have published results that demonstrate diagnostic sensitivity and specificity of more than 90% in the detection of partial- and full-thickness rotator cuff tears.Iz* 4z, 463 lo5 It has not been as successful in

the hands of less experienced radiologists and thus is not widely used. Changes in the tendon with shoulder motion can be assessed directly using ultrasound. Ultrasound cannot be used to evaluate many abnormalities of the shoulder that might be causing a rotator cuff tear or contributing to shoulder pain, including lesions associated with instability, such as labral tears and capsular disruption. It has been shown to demonstrate greater tuberosity frac- t u r e ~ ~ ~ but is limited in its ability to evaluate deeper osseous structures. Normal findings on ultrasonography in a patient with impingement symptoms should be followed with further imaging examinations to detect changes associated with the osseous structures of the coracoacromial arch and secondary causes of impingement, including lesions of the labrum and glenohumeral ligaments associated with instability.

COMPUTED TOMOGRAPHY AND CT ARTHROGRAPHY

Computed tomography allows a detailed evaluation of osseous structures and depicts the differences between soft tissues better in comparison with plain films. It is a useful ad- junct for further imaging of bony abnormalities noted on plain films, such as displaced proximal humerus fractures, arthritis, and neoplasms. CT scanning in the evaluation of soft-tissue abnormalities of the shoulder, such as labral lesions, is much less useful.

The addition of air and iodinated contrast material into the joint improves the evaluation of smaller structures in the j0int,7~-~~* 85, 115 and is a valuable tool in the evaluation of glenohumeral instability. CT arthrography is an accurate test for the depiction of capsulolabral disruption (Fig. 1)76, n, 78, 85, 115 and is particularly useful when a fracture of the glenoid is present, revealing the position of a displaced bony fragment (Fig. 2). An additional advantage of CT arthrography over plain films is the ability to demonstrate the capsulolabral structures to- mographically in the axial plane.

CT arthrography demonstrates the joint surfaces outlined with contrast and air. Although this may depict tears accurately, healed resynovialized abnormalities may not be displayed because fibrous tissue and adjacent anatomic structures will be of identical density. Disad- vantages of CT arthrography include the in- ability to display pathophysiologic changes, such as intramuscular or intraosseous edema, to discriminate between various soft-tissue

A PRACTICAL APPROACH TO IMAGING OF THE SHOULDER 485

Figure 1. CT arthrogram of capsulolabral disruption. Single axial image obtained during CT arthrography demonstrates avulsion and medial displacement of labral capsular attachment (arrow). (Courtesy of Mark Percy, Somerset West, South Africa.)

structures (extra-articular cysts versus adjacent muscle) (Fig. 3), and to acquire data in multiple planes.

MR IMAGING

noninvasive imaging technique, an assump- tion that has to some extent proved premature. As shortcomings and pitfalls are being defined, a more realistic pragmatic approach is called for and, by necessity, is currently being debated. MR imaging has the advantages of inherent improved soft-tissue contrast, multi- planar imaging capability, and excellent reso- lution. It allows the visualization of soft-tissue structures, giving unparalleled contrast with inherent pathologic information without the use of ionizing radiation.

MR imaging of the d m ~ ~ l d e r was initially greeted With m ~ c h a-d~usiasm as an accurate

General Principles

MR imaging refers to the generation of images through the phenomenon of nuclear magnetic resonance (NMR). Protons (tiny magnets) in the body orient or align themselves with the axis of an external magnetic field (MR scanner). With the addition of FM radio- waves, the protons become excited and as- sume a different orientation with the external magnetic field. After the radiowave is discon- tinued, the protons again align themselves with the external magnetic field and in the process of doing so emit a radiowave. This radiowave emission is detected by a radio an- tenna located in the scanner, and images are built from the collected data after complex computer Once the protons are excited after the exposure to radiowave% they relax by two primary methods while emitting

Figure 2. Bony Bankart fragment. CT arthrogram obtained through the inferior portion of the joint demonstrates a displaced fragment of bone (arrow). The patient had a Bankart labral capsular disruption as the result of an anterior dislocation. (Courtesy of Mark Percy, Somerset West, South Africa.)

486 TIRMAN et a1

Figure 3. Limitations of CT arthrography. A, CT arthrogram through the midportion of the joint demonstrates a small posterior labral tear (arrows). B, A small accumulation of contrast (arrow) is seen in the region of the spinoglenoid notch. No evidence of a cyst is seen, as the cyst is of the same intensity as adjacent muscle. C, MR image through the inferior portion of the joint demonstrates a small cyst extending from a posterior labral tear (arrow). 0, The cyst is larger (arrow) in this image, which is slightly more superiorly located. The posterior labral tear (long arrow) is still seen. €, A large, lobulated cyst (arrow) is seen in the spinoglenoid notch. (Courtesy of Gabrielle Bergman, MD.)

their own radiowave-T1 and T2 relaxation. By taking advantage of these different types of relaxation, anatomy can be displayed in two predominate modes referred to as T1- weighted and T2-weighted spin echo images. On T1-weighted images, fatty tissues are bright in signal intensity, and water is dark (Fig. 4). On T2-weighted images, water is bright, and fat is less bright (Fig. 5). T2- weighted images generally take a long time to obtain, approximately 15 to 16 minutes for a set of images. Fast spin-echo (FSE) techniques are frequently four to five times faster. To increase the sensitivity of FSE T2-weighted images, one can selectively rid the image of the signal from fatty tissue, leaving water (edema) to be very conspicuous. These are termed fa t - saturated images. Because the important finding in many disease processes is edema (e.g., in the rotator cuff), the FSE sequence is very useful and has become a mainstay in MR imaging (Fig. 6). Gradient echo produces another type of image in which water tends to be bright in signal intensity, but it is fraught with technical artifact. Edematous lesions, such as bone edema in the setting of trauma, may be hidden with the sole use of gradient echo images (Fig. 7). However, these images may be useful in demonstration of the glenoid labrum when MR arthrography is not available.

Technique Considerations: Type of Study

The technique of MR evaluation employed is dependent on the clinical history (Table 1). Conventional MR imaging allows direct visualization of most of the important anatomic structures of the shoulder, such as in the older patient in whom rotator cuff disease is suspected. The limitation of coventional MR imaging is that small intra-articular structures, such as the glenoid labrum, glenohumeral ligaments, and articular surface of the rotator cuff can be difficult to evaluate in the absence of a joint effusion.

Magnetic resonance arthrography improves the diagnostic accuracy of the examina- ti~n.’~, 31, loo The anterior capsule will fold on itself in the neutral position and become closely applied to the anterior labrum in the absence of a joint effusion. Additionally, a MR imaging phenomenon called the ”magic angle artifact” affects the collagenous tissues present in the shoulder joint, especially in the anteroinferior region of the glenoid and the critical zone of the rotator cuff. These are the two areas of the shoulder where accurate imaging is essential. Many abnormalities leading to continued subluxation or dislocation are located in the anteroinferior quadrant, thus accurate de-


Figure 3 (Continued)

piction of the anatomy is essential and best accomplished by arthrography (Fig. 8).68,70,98,100 In the younger patient with chronic recurrent instability, MR arthrography is the method of choice to avoid a misdiagnosis.68, 70, 99, loo

The spectrum of lesions associated with instability can be subtle as the result of partial healing, which adds to the difficulty of diagnosis. The joint may resynovialize the injury, making it potentially occult both at imaging and surgery.61 Placing stress on the stabilizing structures of the shoulder may bring out an otherwise undetected lesion. Abduction and external rotation stresses the inferior glenohumeral labral-ligamentous complex and "opens up" some partially healed or healed and incompetent labral-ligamentous attachments to

the underlying glenoid (Fig. 9). Therefore, the authors recommend MR arthrography using the standard position coupled with imaging in the abducted externally rotated (ABER) position for adequate visualization of this region.14, 98, 99

ROTATOR CUFF DISEASE

Rotator cuff disease can be related to several factors. Impingement within the coracoacromial outlet, trauma, aging, underlying disorders that weaken the tendon, including diabetes, arthritis, steroid use, and smoking, as well as athletic and occupational activities can contribute to rotator cuff pathology.

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Figure 4. T1-weighted image. Note that the fatty bone marrow has increased in signal intensity, as has the subcutaneous fat.

Impingement

The impingement syndrome is a progres- sively painful compression of the supraspinatus tendon, subacromial-subdeltoid bursa, and long head of the biceps tendon between the humeral head and the coracoacromial arch. The coracoacromial arch is comprised of the undersurface of the anterior third of the acro-

Figure 5. T2-weighted image. There is a slight decrease in signal intensity of fatty tissues. T2-weighted images tend to be grainy.

Figure 6. Fast spin-echo T2, with fat saturation. Notice that the fatty tissues (marrow and subcutaneous fat) are of decreased signal intensity owing to the nullifying fat- saturation pulse. Note the irregular undersurface partial tear of the supraspinatus (small arrows) and the humeral head chondromalacia and irregularity (large arrow).

mion, the coracoacromial ligament, the anterior third of the coracoid process, the AC joint, and the distal clavicle. The pain occurs when the arm is forward elevated.54 Impingement is common in persons with occupations that require overhead motion and in older individuals with degenerative changes of the coracoacromial arch.

There are several forms of impingement. Classic primary extrinsic impingement results from entrapment of the supraspinatus tendon by the coracoacromial arch caused by variations in the architecture of the coracoacromial arch, including one or more of the following: a subacromial enthesophyte, anteriorly hooked acromion, downsloping or low-lying acromion, inferior AC joint osteophytes, or a thickened coracoacromial ligament. Secondary extrinsic impingement can be caused by inferior narrowing of the coracoacromial outlet from glenohumeral or scapulothoracic instability. Posterosuperior glenoid impingement is an internal form of impingement of the undersurface of the posterosuperior rotator cuff on the posterosuperior glenoid labrum. This form of impingement can produce shoulder pain and lead to tears (often partial-thickness) of the undersurface of the rotator cuff. A prominent greater tuberosity caused by fracture or mal- union and supraspinatus muscle hypertrophy


Figure 7. Advantage of fast spin-echo with fat saturation over gradient echo in a patient with reverse Hill-Sachs lesion. A, Gradient echo image demonstrates irregularity of the medial humeral head (arrow) in a patient who had suffered an acute posterior dislocation. This irregularity represented a reverse Hill-Sachs lesion. B, Fast spin-echo T2-weighted image with fat saturation, obtained in greater degree of external rotation during arthrography, demonstrates a bone trabecular injury (small arrows) not visualized on the gradient echo image. The reverse Hill-Sachs lesion (large arrow) is again seen.

Table 1. MR OF THE PAINFUL SHOULDER: ALGORITHM, ADVANTAGES, AND SHORTCOMINGS OF THE VARIOUS TECHNIQUES

Recommended Clinical Problem MR Imaging Study Information Gleaned Shortcomings

Routine rotator cuff Conventional MR irnaaina Rotator cuff status. osseous lnabilitv to reliablv - - evaluation including impingement (generally, after age 40 years)

Trauma and instability after Conventional MR imaging age 40 years

Instability before age 40 MR arthrography including years ABER position

Acute athletic injuries before Conventional MR imaging age 40 years

Chronic athletic injuries MR arthrography before age 40 years

acromial outlet anatomy, occasional mimic ke rs (i . e . , labral cyst compression of the suprascapular netve)

Distinguish between cuff tear, greater tuberosity fracture, and subscapularis avulsion, helping direct therapy

Bankart, PerIhes, and ALPSA, and HAGL lesions; demonstrates communication of joint with labral cysts

Wide range of abnormalities of the rotator cuff and capsulolabral structures, especially if effusion is present

Wide range of abnormalities of the rotator cuff (including posterosuperior impingement) and capsulolabral structures

Distinguish between

distiiguish between full- and partial-thickness rotator cuff tears; may not display instability lesion leading to cuff disease

May not accurately display labral abnormality if one exists

May not provide reliable assessment of capsular stretching as a cause of subluxation or recurrent dislocation

Small labral tears and hyaline cartilage abnormalities

May not provide reliable assessment of capsular stretching as a cause of subluxation or recurrent dislocation

490 TIRMAN et a1

Figure 8. Benefit of arthrography. A, Gradient echo axial image through the inferior portion of the joint in an asymptomatic volunteer demonstrates a generalized increase in signal intensity and indistinctness of the capsulolabral complex (arrow). This patient was an asymptomatic volunteer with no clinical symptoms or evidence of instability. The “magic angle” artifact leads to an increase in signal intensity such as this. 6, Gradient echo axial image through the inferior portion of the joint in a multiple dislocator demonstrates a similar increase in signal intensity (arrow) of the capsulolabral complex. The patient had a healed ALPSA lesion proven in surgery. C, Gradient echo axial image through the inferior portion of the joint again demonstrates indistinctness of the capsulabral complex (arrow). 0, Same patient as in Figure 8C. Arthrogram demonstrates good visualization of the insertion of the inferior glenohumeral ligament onto the labrum (arrow).

can also lead to narrowing of the coracoacromial outlet with subsequent impingement.

Stages of Impingement

In 1972 Neer described the technique of anterior acromioplasty to relieve the symptoms of im~ingement.~~ He hypothesized that abnormalities of the anterior third of the acromion and excessive traction by the coracoacromial ligament resulted in a progression of

degenerative changes of the supraspinatus tendon.

The area of the tendon that is most frequently affected by impingement is termed the critical zone,l’ a hypovascular area approximately 1 cm from the tendon insertion on the greater tuberosity. Mechanical impingement to the critical zone is thought to lead to inflammatory tendinitis that represents the first stage of the degenerative process.

Neer subsequently described three stages of im~ingernent.5~ The first stage is reversible


Figure 9. Benefit of imaging in abduction and external rotation (ABER). A, Normal ABER image. The insertion of the inferior glenohumeral ligament onto the labrum (arrow) is well seen. 6, Multipledislocator. Axial MR arthrogram demonstrates a normal appearance to the anterior glenoid labrum (arrow). C, Same patient as seen in Figure 9B, imaged in the ABER position. Note that the capsulolabral complex (arrow) is pulled away from the underlying glenoid (arrowhead). A large labral detachment was confirmed at surgery.

edema and hemorrhage usually seen in patients less than 25 years of age. The second stage is fibrosis and tendinitis resulting from chronic trauma. The third stage is degeneration and rupture of the supraspinatus tendon, often associated with osseous changes, usually seen in patients more than 40 years of age.

Neer postulated that as many as 95% of rotator cuff tears result from chronic impingement.55 Others believe that degeneration with aging is perhaps the most important cause,'l. 66 followed by impingement, acute trauma, overuse, and chronic inflammatory disease.

MR Imaging Evaluation

MR imaging demonstrates osseous and soft-tissue abnormalities of the shoulder in any plane with high soft-tissue contrast. The status of the muscles, marrow, and labrocapsular structures can also be assessed. Normal tendons and those with a full- thickness tear are easily identified on routine noncontrast MR imaging. The most sensitive and specific study, especially for partial undersurface tears of the rotator cuff, is MR arthrography. Conventional MR imaging may be of limited use for this evalua-

492 TIRMAN et a1

Figure 10. Small subacromial enthesophyte (arrows) pro- jects inferiorly from the undersurface of the acromion on this coronal image.

tion if fluid is not present in the glenohumeral joint.

Osseous Abnormalities Associated with Primary Extrinsic Impingement

MR imaging can aid in detecting osseous and soft-tissue abnormalities that may predispose a shoulder to rotator cuff im~ingement.~~, 83

These include morphologic changes of the acromion, AC joint, and coracoacromial ligament. Many of these changes are more appro-

priately evaluated by plain film radiography as discussed previously. Many of these anatomic features may be present in asymptomatic shoulders, and clinical correlation is i m p e r a t i ~ e . ' ~ ~ ~ ~ ~ ~ ~ ~ ~ ~ , ~ ~ The diagnosis of impingement should be based on clinical criteria not made from static MR imaging studies.

Acromion and Acromioclavicular Joint

Osseous changes that may lead to primary extrinsic impingement include subacromial enthesophytes and osteophytes and capsular hypertrophy along the inferior aspect of the AC joint54,'08 (Fig. 10). Anteriorly hooked, anteroinferior and inferolaterally downsloping, and low-lying acromions are believed to predispose the shoulder to impingement by narrowing the acromiohumeral di~tance.'~, 51 An 0s acromiale can also predispose the shoulder to im~ingement .~~ It is helpful to correlate the MR imaging findings with conventional radiographs when the diagnosis is uncertain.

In 1986, Bigliani and co-workers4 studied the shape of the acromion in 140 cadaveric shoulders to determine the relationship of acromial configuration with full-thickness rotator cuff tears. They defined three different acromial shapes. A type I configuration with a flat undersurface was present in 18.6% of cases; 42% had a type I1 acromion with a curved undersurface; and 38.6% had a type I11 acromion with an anterior hook (Fig. 11).

Figure 11. Type 111 acromion. Sagittal T1-weighted image demonstrates a hook of the anterior acromion (arrow). Note the thickened coracoacromial ligament (thin arrow). Thickening of the coracoacromial ligament is a subjective determination.


Figure 12.0s acromiale. A, Axial image obtained through the superior portion of the joint demonstrates a separate ossification center (arrows), representing an 0s acromiale. The remainder of the acromion (open arrow) and the distal clavicle (curved arrow) are shown. 6, Sagittal image demonstrates an 0s acromiale (arrow).

Many investigators have found that supraspinatus tendon tears are frequently associated with the anteriorly hooked (type 111) acromion. In their studies correlating acromial shape with surgical or arthrographic results, Mor- rison and Bigliani demonstrated that 70% and 8O%, respectively, of the rotator cuff tears were associated with type I11 acr~mions.~, 51 The remaining patients with rotator cuff tears had a type I1 acromion. Only 3% of type I acromions were associated with a rotator cuff tear.

correlation between morphology identified during radiographic and MR assessment.

Osteophytes and osseous or fibrous callus under the AC joint may predispose the shoulder to (see Fig. 10). AC joint osteoarthrosis is not specific for im~ingement .~~

The 0s acromiale is an accessory ossification center along the outer aspect of the acromion that has failed to fuse to the acromion by the age of approximately 25 years (Fig. 12). It is

The shape of the acromion can be determined on sagittal oblique MR images located lateral to the AC joint (see Fig. 11). In one study of acromial morphology on sagittal oblique MR images, patients with rotator cuff tears had a significantly increased prevalence of hooked acromions when compared with control patients (62% versus 13%, P < 0.001), and there was a greater prevalence of hooked acromions in the group with impingement (30%, P = 0.17).19 Farley and colleaguesz1 also found a correlation between the anteriorly hooked acromion seen on MR imaging and the presence of clinical impingement.

Several studies have found MR imaging assessment of acromial shape to be confusing. Haygood and co-workersz9 showed significant variability in the interpretation of images by different clinicians in identifying a particular acromial morphology. These investigators did not use a routine location for the assessment of acromial shape. A more recent study by Peh and co-workers73 that apparent acromial shape is sensitive to minor changes in the MR section viewed. There was a poor

Figure 13. Cystic humeral head changes as a result of posterosuperior glenoid impingement. Image obtained in the ABER position demonstrates cystic changes within the posterosuperior humeral head (short arrows). Note the small laminar tear (long arrow) of the infraspinatus in this young baseball pitcher.

494 TIRMAN et a1

seen in 1% to 15% of the population. It is not known how many of these are symptomatic.', 18, 38, @ Contraction of the deltoid muscle can pull down on the lateral aspect of the 0s acromiale, creating a hinge effect that narrows the subacromial outlet with resultant impingement. Tears of the rotator cuff are postulated to be a result. Simply identifying the 0s acromiale does not implicate it as the source of shoulder pain or rotator cuff disease. This ossification center may be difficult to find on conventional radiographs', 18, 38, 44 but is well-seen on axial

MR images if the images begin adequately cephalad to visualize the acromion.

Soft-Tissue Abnormalities Associated with Impingement

A thickened coracoacromial ligament has been associated with the impingement syndrome'07 (Fig. 11). Some believe that it is a cause of impingement: whereas others postu- late that it is thickened as a result of alteration

Figure 14. Posterosuperior glenoid impingment. Benefit of ABER imaging. A, ABER image demonstrates a small tear of the posterosuperior glenoid labrum (arrow). B, Arthroscopic image of the posterosuperior portion of the joint demonstrates the labral tear (arrow). Note the long head of the biceps (open arrows). C, ABER image demonstrates a dissecting flap tear of the infraspinatus. The flap component is identified along the articular surface of the joint (small arrows). Contrast (long arrow) insinuates between the flap and the remainder of the tendon. 0, Arthroscopic image demonstrates the large flap tear (arrows).


of the soft-tissue structures from the impingement process.82 The criteria for determining thickening of the ligament on MR imaging are subjective, and no reproducible measurement has been reported.

Treatment Correlation of Primary Extrinsic Impingement

The findings on MR imaging may be used as the basis for planning conservative treatment versus surgical repair. The type of impingement determined clinically and radiographically and the severity of tendon disease as determined by MR imaging may suggest the need for prophylactic coracoacromial arch de- compression before the development of irre- versible cuff pathology. Decisions should be based on careful evaluation of the MR findings with close clinical correlation.

Other Causes of Impingement

Other causes of impingement syndrome include secondary extrinsic impingement (due to an unstable glenohumeral joint), posterosuperior glenoid impingement, supraspinatus

muscle hypertrophy, post-traumatic remodel- ing of the proximal humerus (following greater tuberosity fracture), and a prominent greater tuberosity.33, 34, 41, 47, *06, 113 The last three are not discussed herein as the diagnosis is usually made by clinical criteria, and a role for imaging is not defined. The exception is characterization of fracture healing causing visible compression of the rotator cuff which may be directly observed with MR imaging.

Secondary forms of impingement are treated in a different manner than primary extrinsic impingement, with attention directed toward the primary problem rather than the coracoacromial structures.

Secondary Extrinsic Impingement

Caused by glenohumeral instability, secondary extrinsic impingement produces narrowing of the coracoacromial outlet as the result of abnormal superior migration of the humeral head.34 Secondary extrinsic impingement may also result from scapulothoracic instability. Di- agnosis is by clinical criteria, with MR imaging potentially having a confirmatory role demonstrating the primary abnormality. In this setting, MR arthrography is more helpful in the younger patient.

Figure 15. Normal rotator cuff. A, T1 -weighted image demonstrates a morphologically normal supraspinatus tendon. Note the increased signal (arrow) within the critical zone, consistent with the “magic angle” artifact. 6, Fast spin-echo T2-weighted image with fat saturation demonstrates a normal appearance of the rotator cuff. Note the increased signal intensity within the distal clavicle as a component of reactive post-traumatic change.

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Posterosuperior Impingement

Internal impingement of the rotator cuff on the glenoid rim may produce shoulder pain and can lead to partial-thickness tears of the undersurface of the rotator cuff. This form of impingement was first described by Walch and then J ~ b e ~ ~ in overhead athletes'06 and more recently has been recognized in nonathletes who frequently rotate the shoulder into the extremes of abduction and external rotation.33

The mechanism that leads to this form of impingement involves superior or posterosuperior angulation of the humerus with respect to the glenoid. The articular side of the rotator cuff tendons and the greater tuberosity are compressed against the posterosuperior glenoid labrum, resulting in partial-thickness tendon tears, especially the posterior articular surface of the supraspinatus and the infraspinatus, a degenerative tear of the posterior surface of the posterosuperior labrum or underlying gle-

Figure 16. Severe tendinosis. A, T1 -weighted image demonstrates thickening and diffuse increased signal intensity within the supraspinatus tendon (arrow). T1 -weighted images are unreliable for characterization of rotator cuff disease and are useful for morphologic observations. 6, Fast spin-echo T2- weighted image with fat saturation demonstrates diffuse increased signal intensity within the mildly thickened rotator cuff tendon, consistent with severe tendinosis (arrow). A small partial tear cannot be excluded. C, Interstitial laminar tear. Fast spin-echoT2-weighted image with fat saturation demonstrates fluid intensity within the distal supraspinatus tendon (shortarrow). Fluid is present within the subacromial bursa, but no communication was found at surgery. The fluid in the bursa likely indicated bursitis.


noid, and osteochondral irregularity (chronic repetitive trauma) in the region of the greater tuberosity of the humeral head (which can simulate a Hill-Sachs lesion) (Fig. 13). The inferior glenohumeral ligament and adjacent labrum may also be injured. Anterior instability may be causative, although this aspect is under debate. The abnormalities of posterosuperior glenoid impingement are well seen on MR arthrograms, especially those including the ABER position97 (Fig. 14). Treatment is directed at controlling extremes of shoulder elevation and abduction external rotation by exercise or surgery and at repair of the injured structures.

Evaluation of the Rotator Cuff Tendon on MR Imaging

A normal supraspinatus tendon is, for the most part, decreased in signal intensity on T1- and T2-weighted images. The magic angle artifact may lead to mild increased signal in the critical zone on the T1-weighted image, but the morphology of the tendon remains normal (Fig. 15). Mild increase in signal may also result from interdigitation of muscle fibers, which varies from patient to patient. When a tendon has a signal intensity abnormality without focal disruption or associated findings to suggest a partial-thickness tear, the terms tendinosis or tendinopathy have been used to signify an underlying tendon degeneration or inflamrnati~n.~~ These terms suggest that there is a chronic, often preexisting degenerative process. In general, the signal intensity of the lesion is not as marked as that of a tear on T2- weighted images.

The presence of tendinous enlargement and heterogenity of signal which is predominately increased on T2-weighting is seen in patients with tendinosis'O8 75, lo4, 114 (Fig. 16B). This same appearance could represent severe degeneration or a partial tear, and close clinical correlation is needed.

Partial- Thickness Tears

Partial-thickness tears of the rotator cuff can be seen inferiorly at the articular surface, superiorly at the bursa1 surface, or within the tendon substance (Fig. 16C). Tears at the articular surface are the most common.94 These are the only types of partial-thickness tears demonstrated by conventional shoulder arthrography.

Several abnormalities are seen on MR imaging in association with partial-thickness rotator cuff tears. Increased signal intensity extending through a portion of a nonretracted tendon is suggestive of a partial-thickness tear (Fig. 17). These tears are often difficult to distinguish from tendinosis or nondisplaced full- thickness tears if they are elevated in signal intensity on all imaging sequences. The authors routinely offer the differential diagnosis of severe tendinosis versus partial tear as it is often difficult to differentiate between the two. Identification of the abnormality should lead the surgeon to appropriate therapy when closely correlated with the clinical presentation. FSE T2-weighted images with fat suppression have a higher sensitivity for the diagnosis of partial-thickness tears of the rotator

Figure 17. Partial tear. A, Fast spin-echo T2-weighted image demonstrates fluid intensity consistent with an undersurface partial tear (arrow). This was proved at surgery. B, MR arthrogram demonstrates a small undersurface partial tear of the rotator cuff (arrow).

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Figure 18. Partial tear. Benefit of ABER imaging. A, T2-weighted image demonstrates no abnormality of the rotator cuff (arrow). B, MR arthrographic image obtained in the ABER position demonstrates a large undersurface flap tear (arrows).

cuff in comparison with the same sequence without fat suppression.88 MR arthrography has been shown to be more accurate than conventional MR imaging for the evaluation of partial tears, especially those located on the undersurface of the rotator cuff.24, 30, 67 Addi- tional characterization of undersurface tears can be accomplished if the arm is placed in the ABER position during the e~aminat ion~~

(Fig. 18). Abduction of the arm allows the undersurface to be depicted free from the superior surface of the humerus and also promotes spreading of the frayed and torn edges of the inferior surface.97, lo6 Fluid accumulation in the subacromial-subdeltoid bursa, common with full-thickness rotator cuff tears, may be seen in patients with all types of partial-thickness tears or even with bursitis in the absence of

Figure 19. Full-thickness tear. Fast spin-echo T2-weighted image with fat saturation demonstrates a full-thickness rotator cuff tear with retraction of the tendon edge medially (arrow). Note a small remnant of degenerated tendon remaining on the greater tuberosity (open arrow).


Figure 20. Superior surface rotator cuff tear and fluid within the subacromial bursa. Fast spin-echo T2-weighted image demonstrates marked irregularity of the superior surface of the supraspinatus (heavy arrows) and a large amount of fluid within the subacromial bursa (small arrows), indicating reactive bursitis. The rotator cuff tear was confined to the superior surface.

tears. Increased intra-articular fluid may also be found in the setting of a partial- or full- thickness rotator cuff tear, often as the result of synovitis.

Full-Thickness Tears

A full-thickness rotator cuff tear involves a complete disruption of the tendon from the articular to the bursa1 surface (Fig. 19). MR imaging findings in full-thickness rotator cuff tears include one or more of the following signs: disruption of the low-signal intensity tendon by an area of high-signal intensity on T2-weighted images; tendon retraction; muscle atrophy and fatty replacement; absence of the tendon; fluid in the subacromial- subdeltoid bursa; and, in advanced cases, acromiohumeral articulation.

Full-thickness tears of the rotator cuff tendons can be accurately identified using conventional nonarthrographic MR imaging with high sensitivity and specificity.8, 20, 35, 80, lo4 In- creased signal intensity extending from the inferior to the superior surface of the tendon on all imaging sequences is an accurate sign of a full-thickness rotator tear.37 Use of a fat- saturation technique can improve the detection of both full-thickness and partial- thickness tears in comparison with standard spin echo imaging techniq~es .~~ Sometimes,

the muscles may be atrophied and fatty re- placed, which may be shown as an increase in signal on T1-weighted images. Recognition of atrophy of the rotator cuff muscles is important preoperative information for determining the success of operative repair.

Fluid in the subacromial-subdeltoid bursa is a common but relatively nonspecific finding in patients with rotator cuff tears.20 The fluid may be present on the basis of “reactive” subacromial bursitis (Fig. 20) or may escape from the glenohumeral joint through a tear of the rotator cuff into the bursa (Fig. 21). Small amounts of fluid in the bursa can be seen as

As many as 10% of partial- and full- thickness tears do not demonstrate high-signal intensity on long TE (T2-weighted) images.” This may be due, in part, to the fact that chronic tears fill in with fibrous or granulation tissue that is low-signal intensity on T2-weighting. In such cases, one can look for abnormal tendon morphology, such as attenuation or irregularity of the rotator cuffy5 or rely on arthrography or MR arthrography for the diagnosis.

If there is any question concerning the dis- tinction of a full- and partial-thickness tear, MR arthrography is recommended, particularly if the abnormal signal intensity extends from the undersurface of the tendon.67 When gadolinium is injected into the glenohumeral

an isolated finding.lO, 35,39, 49,50.56

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Figure 21. Arthrography demonstrating full-thickness tear. A, T2-weighted image demonstrates increased signal within the undersurface of the distal supraspinatus tendon (black arrow). The superior surface (white arrows) appears intact. A partial tear was diagnosed. B, Same patient during MR arthrography. Dilute gadolinium extends into the subacromial bursa (arrow), indicating a full-thickness component to the tear.

joint, it will fill a defect in the rotator cuff that extends to the articular surface, including partial-thickness undersurface tears. It will not demonstrate a partial tear in the substance or at the superior surface (Fig. 20) of the rotator cuff tendons. The addition of fat-suppressed T2-weighted images will detect these abnormalities. Gadolinium may be imbibed at frayed friable tendon margins during arthrog-

r a ~ h y . ~ ~ If the tear is full-thickness, the contrast material will enter the subacromial-subdeltoid bursa (Fig. 21). The subacromial-subdeltoid bursa must be carefully evaluated for the presence of contrast in patients with equivocal full- thickness tears. Fat suppression should be employed to decrease the signal from fat without affecting the high-signal intensity of the gadolinium on T1-weighted images.67

Figure 22. Isolated infraspinatus tear. Sagittal image demonstrates fluid intensity within the tendon of the infraspinatus (heavy arrow). Note the normal appearing supraspinatus tendon (thin arrow). The coracoid process (open arrow) can be seen anteriorly.


Figure 23. Isolated subscapularis rupture. A 35-year-old patient after anterior dislocation. MR arthrogram demonstrates rupture of the subscapularis tendon with medial displacement (arrowhead). The orientation of the subscapularis (long arrow) is more anterior than usual. Note the dislocated biceps tendon (open arrow).

Infraspinatus, Teres Minor, and Subscapularis Tears

An isolated tear of the infraspinatus tendon is un~ommon.~ However, increasing evidence supports this tendon as a source of symp- t o m ~ . ~ ~ Tears of the infraspinatus are more common in younger overhead athletes, most likely as a result of posterosuperior glenoid

impingement syndrome. Tears of this tendon are well seen in all three imaging planes (Fig. 22).

Subscapularis tendon tears usually present in middle-aged and older patients with shoulder dislocation (Fig. 23) or in association with massive tears of the other rotator cuff ten- d o n ~ . ~ ~ , ~ ~ , ~ ~ Tears may also be seen following direct trauma to the anterior aspect of the shoulder joint and with hyperextension or external rotation of the adducted arm.27 Down- ward sloping of the coracoid may cause impingement and eventual tear of the superior aspect of the subscapularis tendon.l5. 28 A portion of the coracoid can be excised in such cases. On MR imaging, subscapularis tears can be identified using the same criteria as for tears of the supraspinatus. There is an associated abnormality in the long head of the biceps tendon in many of these patients, including medial tendon dislocation.

Teres minor tendon tears are rare (Fig. 24). Posterior dislocation is a mechanism for tear of this tendon. The posterior labrocapsular structures should be checked for abnormalities when such a tear is present.

Rotator Interval Lesion Figure 24. Isolated teres minor tear. TP-weighted axial image demonstrates disruption of the teres minor tendon (arrow) posteriorly in this bicycle courier who suffered a Dosterior dislocation. NO evidence of a Dosterior labral tear

h o t h e r type of tear involves the rotator The coracohumeral ligament lies su-

perficially and the biceps tendon more deeply was found. this region. Lesioncof the rotator interval

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are most commonly associated with enlargement or tearing from a shoulder dislocation; however, a group of individuals with abnormalities in the region do not have glenohumeral in~tability.~~ The supraspinatus and subscapularis tendons may be torn in association with the rotator interval tear. Isolated tears of the rotator cuff interval are thin and longi- tudinal and are not associated with muscle re t ract i~n.~~ A tear of the rotator interval produces communication with the subacromial- subdeltoid bursa, and fluid or intra-articularly injected contrast may be seen in this bursa (Fig. 25). T2-weighted sagittal oblique MR images are particularly useful for demonstrating these tears as a region of high-signal intensity, often in association with biceps tendon and coracohumeral ligament abnormalities.

CAPSULOLABRAL ABNORMALITIES

Glenohumeral Instability

Classification and Anatomic Considerations

The shoulder is considered the most unstable joint in the body.13, 65, 89 The clinical defini-

Figure 25. Rotator interval lesion. Sagittal T i -weighted MR arthrographic image demonstrates fluid within the subacromial bursa (short arrows). The thickened coracohumeral ligament (curved arrow) is shown, which was found to be incomplete at surgery. Notice the “ghost-like” biceps tendon imbibing a large amount of contrast (thin arrow). For orientation purposes, the subscapularis tendon is shown anteriorly (open arrow).

tion of shoulder instability is slipping of the humeral head out of the glenoid socket during activities causing symptoms. Varying degrees of instability are recognized, ranging from subluxation to dislocation.

Instability is classified according to the tem- poral relationship of antecedent trauma (acute first-time versus recurrent) and degree (subluxation versus dislocation). Instability is further defined according to direction, such as unidirectional (anteroinferior or posterior) or multidirectional (i.e., gross instability). Pa- tients can be classified into two broad categories: (1) those with traumatic unidirectional anteroinferior instability with a Bankart lesion (referred to by the acronym TUBS for traumatic, unidirectional, Bankart, surgical) and (2) those with atraumatic, multidirectional, bilateral instability or AMBRI pathology.40, 86, 87

Patients with TUBS are usually surgical candi- dates if the dislocation is recurrent, whereas patients with AMBRI are usually not.40, 86, 87

Most commonly, the dislocation occurs during a fall on the outstretched externally rotated, abducted arm. These patients (post- traumatic) fit into the TUBS category and usually have a capsulolabral disruption (Bankart or Bankart variation lesion). Imaging beyond plain films is rarely required as the patients usually are initially treated conservatively. Pa- tients may describe traumatic episodes during which they believe the shoulder popped out and came back in, but the dislocation is difficult to document clinically and is not docu- mented radiographically. Some of these episodes represent true dislocations, and some are severe subluxations.86 Imaging may be required to document the damage done and to plan further therapy. This is especially true in the older patient, as the spectrum of lesions resulting is generally quite different from a typical capsulolabral disruption (Bankart le- ~ i o n ) . ~ ~ , 6o

The anatomic causes of recurrent dislocation are varied. The cause of instability in these patients may be hypermobility or laxity, as a result of stretching of the supporting structures from overuse. Reliable standards of normal have not yet been defined with imaging.

Recurrent instability in patients with TUBS is anteroinferior, resulting from previous dislocation. To understand the cause of recurrent instability, it is useful to consider the stabilizing structures of the shoulder as the unit termed the anterior capsular mechanism. That mechanism consists of the capsule and capsular ligaments (glenohumeral ligaments), the


Figure 26. Partial labral capsular avulsion, leading to subluxation. A, Axial arthrographic image demonstrates a small amount of contrast underlying the free edge of the glenoid labrum. No definite labral capsular disruption can be diagnosed from this image. B, ABER image demonstrates the small divot of the hyaline cartilage and partial tear of the capsulolabral attachment (arrow). The patient repeatedly subluxed. The findings were confirmed at surgery.

glenoid labrum, subscapularis muscle, and tendon. The most important structure stabilizing the shoulder and limiting gross anteroinferior subluxation and dislocation is the inferior glenohumeral labral-ligamentous complex (IGHLC).I3* lo3 The ligament is a thickening of the inferior capsule and is lax when the humerus is in the neutral position, allowing normal shoulder motion. The ligamentous complex becomes taut in abduction and external rotation (ABER) and stabilizes the joint at the end range of shoulder movement in this direction. The threshold of restraint of the ligamentous complex is exceeded during a dislocation, which leads to tears with or without stretching of the IGHLC. This, in turn, may lead to laxity and symptomatic instability.'OO

The components of the anterior capsular mechanism are all important stabilizing structure~.'~, *03 Any or all of these structures may be injured after dislocation, leading to a spectrum of abnormalities that may be shown with MR imaging. Usually, and especially in the younger patient, a labral ligamentous avulsion (Bankart lesion) is the most common lesion resulting from a dislocation.

The radiologist must know the history of the patient before the imaging examination is interpreted, as the spectrum of lesions differs depending on the age of the patient and the mechanism of injury. Several types of lesions may result in continued instability. Sometimes neither the patient nor the orthopedist knows

for certain what the exact mechanism of injury was and whether the patient has dislocated the shoulder or not. It should be determined whether the injury is of a repetitive nature. At the author's center, technologists are encour- aged to ask historical questions and to document these on the intake requisition for additional information.

Figure 27. Bankart lesion. Axial arthrographic image dern- onstrates a detached anterior labrum (long arrow) and disrupted capsular attachment (arrowhead). The lesion was described as a Bankart at surgery.

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Figure 28. Bankart lesion. A, Axial arthrographic image demonstrates a chondral defect (heavy arrow) and extravasation of contrast through a detached labrurn (smallarrow). B, Imaging in the ABER position demonstrates detachment of the capsulolabral complex (heavy arrow) and anterior translation of the humerus (thin arrow), leading to a contact point (open arrow) of the humerus and glenoid labrum, more anteriorly placed than is usually seen.

Instability Lesions

Subluxation

Abduction external rotation injury resulting in a subluxation of the shoulder may result in a partial tear of the capsule, labrum, or both, or may stretch the capsule. These lesions may lead to repeated subluxation. The abnormalities may be difficult to diagnose by conventional MR imaging, and MR arthrography may provide more useful information (Fig. 26). Subluxation resulting from a stretched capsule in the absence of a labral tear is a diagnosis of exclusion as no reproducible imaging criteria have been developed to characterize this abnormality.

Post-Traumatic Anterior Dislocation

The types of lesions that occur after anterior dislocation can be conveniently divided into two broad categories based on the patient’s age at time of first dislocation. MR arthrography helps in the evaluation of the younger patient with glenohumeral instability.

Adolescence to 40 Years

Bankart Lesion. Damage to the anteroinferior glenoid labrum and inferior glenohumeral ligament (labral-ligamentous complex) is the most common injury after anterior shoulder dislocation in the younger age g r ~ u p . ~ , ~ , ~ Typi- cally, these patients have a labral-ligamentous

avulsion with a disrupted scapular periosteum (Bankart lesion) (Fig. 27). The Bankart lesion represents a detachment of the inferior glenohumeral labral-ligamentous complex from the anteroinferior glenoid with or without a fracture of the bony glenoid. Findings of MR imaging include labral/capsular tear seen as increased signal intensity through the substance of the labrum (see Fig. 27). If the dislocation is recent, an effusion is often present, and one may visualize detachment or pulling away of the labral-ligamentous complex. Usually, the tear is large enough to involve not only the labrum where the anterior band of the inferior glenohumeral ligament inserts but also the middle and sometimes superoanterior labrum as the avulsion dissects upward. This lesion is sometimes visualized using a conventional (nonarthrographic) technique, especially in the acute setting. There is often surrounding soft- tissue edema in the region, and bone marrow edema or fracture may be present, increasing the likelihood of detection. In the chronic case, healing of the lesion may take place, which involves fibrosis and resynovialization. If the lesion does not heal correctly, the shoulder will continue to be unstable. If the lesion heals or partially heals, it is difficult to demonstrate fully using conventional MR imaging and MR arthrography including the ABER position is helpful (Fig. 28).

Bankart Variation Lesions: Avulsion with an Intact Periosteum

The Bankart lesion results in a disrupted scapular periosteum (Fig. 29). In 1906, prior


i A C

Figure 29. Capsulolabral disruptions. A, Normal attachment of the inferior glenohumeral labroligamentous complex (IGHLC). Axial plane diagram through the anterior-inferior joint demonstrates that the labroligamentous complex (arrow) inserts at the apex of the curve of the anterior glenoid (open arrow). B, Bankart lesion. Note that the IGHLC is avulsed from the glenoid and that the scapular periosteum (arrow) is disrupted. C, Perthes lesion. The IGHLC (arrow) is resting in a relatively normal position. It may appear deceptively normal at arthroscopy. The stripped scapular periosteum (curved arrow) is seen medially. D, Detached Perthes lesion. Note that the detached IGHLC is displaced anteriorly in the direction of the arrow. The stripped periosteum is shown (curved arrow). €, ALPSA lesion. The IGHLC (heavy arrow) has rolled medially in a sleeve-like fashion up the periosteum. Note that there has been fibrous tissue deposition (thin arrows) around the displaced IGHLC. Synovial tissue from resynovialization (healing) sits on top of the fibrous tissue and forms a crevice.

to Bankart's description, Perthes described a labral-ligamentous avulsion in which the scapular periosteum remained intact but was stripped medially, creating a potential space of variable size anterior and medial to the scapula between the scapula and stripped per io~teum~~ (see Fig. 29). This variant has been termed the Perthes lesion. The labrum may reapproximate its normal position and partially heal and resynovialize in place. In this situation, the scapular periosteal anchor may be incompetent and result in recurrent instability. Perthes recommended a finger probe by the surgeon to un- cover this lesion as it may be occult at

This has potential dramatic implications for imaging as well. The lesion may appear deceptively normal on standard MR imaging and MR arthr~graphy.'~, 22, 98 Because the

labral-ligamentous avulsion may reapproximate its normal position during healing and resynovialization, anatomic closure of the labrocapsular tear results. This phenomenon may prevent contrast material from entering the potential tear and make it invisible to MR arthrography, conventional MR imaging, and to arthroscopy. If the labrum has partially healed, it may regain normal signal intensity. In this situation, imaging in the ABER position significantly increases lesion dete~tion'~, 22, 74, 98

(Fig. 30) in comparison with conventional MR arthrography obtained in the neutral position.14 The MR imaging findings in a Perthes lesion range from normal (false-negative study) to those seen with a Bankart lesion to visualization of the torn detached labrum and periosteum.

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Figure 30. Perthes lesion. A, Axial arthrographic image demonstrates a normal-appearing anterior glenoid labrum (arrow). 13, ABER image demonstrates a detached capsulolabral complex (heavy arrow). Note the contrast (thin arrow) between the capsulolabral complex and the glenoid. C, Arthroscopic image demonstrating a labral tear (thin arrow). Note the humeral head (curved arrow).

Another variation of the labrocapsular disruption is termed the anterior labroligamentous periosteal sleeve avulsion (ALPSA) lesion described by Neviaser in 1993. The ALPSA lesion is an avulsion of the anteroinferior glenoid labrum with an intact scapular periosteum in which the labral-ligamentous complex "rolls up" in a sleevelike fashion and becomes displaced medially and inferiorly. Using this analogy, the labrum/ligament is the shirtcuff and the periosteum the long sleeve, such as when one rolls the sleeve up on a hot day. The ALPSA has also been called a "medialized" Bankart lesion, emphasizing the characteristic that the lesion is "tacked down" in a medially displaced location.61 The labrum and capsule do not heal in an anatomic position as a result.61 The shoulder may heal by fibrosis and granulation tissue heaping up over the displaced la-

'

bral-ligamentous complex; the region is then resynovialized.61 The lesion may become difficult to identify in the chronic state on arthroscopy.61 Awareness of the possibility of the lesion is desirable because the surgery to correct an ALPSA lesion is different from a typical Bankart lesion repair.61 MR arthrography helps delineate the anteroinferior region to best advantage, demonstrating the ALPSA lesion and alerting the surgeon to probe the region and to discover the potentially occult abnormality (Fig. 31).

Patients Aged More Than 40 Years

Rotator Cuff Tears and Greater Tuberosity Fractures. The clinical presentation of an older patient after first-time anterior glenohumeral dislocation may be confusing and misleading.


Figure 31. ALPSA lesion. A 1 9-year-old multiple dislocator. ABER image demonstrates medial displacement of the capsulolabral attachment (shortarrow). The normal capsulolabral attachment is positioned at the anterior tip of the glenoid (thin arrow). Please see Figure 9A for comparison.

These patients are often diagnosed with axil- lary neuropraxia, nerve tear, or rotator cuff (supraspinatus) disr~pt ion.~~, Awareness of the mechanism of injury and correlation with radiologic findings are desirable so that the correct diagnosis can be made, allowing for appropriate treatment and the avoidance of continued anterior instability. The injuries oc- curring in the older patient can be divided into

three groups.5, 59, 6o One third of patients tear the supraspinatus tendon.5* 59, 6o Another third sustain a fracture of the greater tuberosity (es- sentially, a cuff-tuberosity avulsion or large Hill-Sachs fracture) (Fig. 32).5, 59, The final third avulse the subscapularis and anterior capsule from the h u m e r ~ s ~ , ~ ~ , ~ ~ (Fig. 23). This last subset may have continued anterior instability as the glenohumeral capsule and subscapularis tendon together are considered important anterior stabilizing structures. This is generally considered a surgical lesion, whereas the fracture may be treated conservatively. The supraspinatus tear may be treated conservatively or surgically depending on the size of the tear and the clinical symptoms. MR imaging may have a pivotal role in distinguishing between the lesions and directing patient therapy. The findings will depend on the injury sustained. In general, conventional technique in these patients will suffice.

Miscellaneous Anterior Instability Abnormalities

Avulsion of the IGHLC from the hu- merus92, 111,112 ha s also been described [humeral avulsion of the glenohumeral ligament (HAGL)] resulting from dislocation. MR arthrography helps with the diagnosis. Arthrographic findings include visualization of contrast material extravasating from the joint through the capsular disruption at its humeral insertion (Fig. 33).

Figure 32. Greater tuberosity fracture as the result of anterior dislocation. A, T1-weighted image demonstrates marked irregularity and decreased signal intensity of the greater tuberosity (arrows) in a patient who suffered a recent dislocation. 19, Fast spin-echo TPweighted image with fat saturation demonstrates increased signal intensity representing the bone trabecular injury as a component of the nondisplaced fracture. Conventional radiography was negative.

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Figure 33. HAGL lesion. Gradient-echo saline arthrographic image of the inferior portion of the joint demonstrates a disrupted inferior capsule (arrow). A pool of saline (curved arrows) lies anterior to the joint.

The inferior glenohumeral ligament may tear in its midsubstance. This is thought to be rare or, at least, rarely diagnosed with imaging, and may also be an arthrographic diagnosis.

Posterior Instability

Posterior instability results from excessive force directed at the shoulder when the arm is adducted and internally rotated. This is the position of function of the posterior capsule (the posterior portion of the inferior glenohumeral ligament). When the arm is adducted and internally rotated, the posterior capsule is tight, and injury in this position leads to

Figure 34. Reverse Bankart. T1 -weighted arthrographic image demonstrates medial displacement of a torn posterior labrum (arrow).

dysfunction of the capsule and labrum with resultant posterior instability. These instability lesions carry the familiar eponyms associated with anterior instability except with the word reverse added to them. A reverse Bankart lesion refers to a labrocapsular disruption of the posterior labrum resulting from a posteriorly dislocated humerus. The resultant impaction fracture of the anterosuperior humerus is known as a reverse Hill-Sach's lesion. Findings and MR imaging include visualization of the labral/capsular tear, bony injury to the posterior glenoid, and an anterior humeral injury (lesser tuberosity) (Fig. 34). The subscapularis may partially or completely tear.

Multidirectional Instability

Imaging is often not employed in cases of multidirectional instability, except when the diagnosis is in question or the multidirectional instability is associated with shoulder pain and is of unknown cause (Fig. 35). MR imaging may also be used in the patient with multidirectional instability to rule out conventional causes of the instability, such as a labral abnormality.

NONlNSTABlLlTY ANTERIOR LABRAL ABNORMALITIES

If an injury occurs that results in a torn labrum, the shoulder may or may not be unstable as a result. Pappas described a functional instability of the shoulder caused by damage confined to the glenoid labrum,7l which may result from such an injury. The lesion may


Figure 35. Multidirectional instability. A 36-year-old female with bilateral shoulder laxity and recent trauma of uncertain mechanism and marked shoulder pain. A, Fast spin-echo T2-weighted coronal image demonstrates bone trabecular injury (arrow) within the anterior humerus, most likely representing a reverse Hill-Sachs. Close questioning of the patient revealed a mechanism compatible with transient posterior dislocation, although the history was not certain. No evidence of labral abnormality was anteriorly or posteriorly seen. B, Sagittal arthrographic image demonstrates a capacious capsule, especially in the region of the rotator interval (curved arrow). This portion was tightened at surgery, and the patient has not suffered recurrent instability. Reliable capsular measurements indicating instability have not been defined.

result in mechanical locking of the joint because of torn labral fragments between the ar- ticulating surfaces. Although the patient has anterior shoulder pain, the shoulder is not unstable in the classical sense, and, therefore, the term instability is somewhat misleading. MR arthrography may help define the lesion (Fig. 36). Similarly, Neviaser described glenolabral articular disruption, the GLAD lesion, which refers to a partial labral tear associated with an articular (hyaline) cartilage divot.62 He pos-

tulated that the injury resulted from a forced adduction." Again, the lesion is found in a stable shoulder, may be subtle, and may be mistaken for an instability lesion by the radiologist. MR arthrography helps define the lesion to best advantage.

Anatomic variations of the labrum may mimic an anterior labral abnormality. This variation occurs in the anterosuperior quadrant, whereas the labrum may be detached or absent and be normal.96, 110 A detached labrum

Figure 36. GLAD lesion. A, T1-weighted arthrographic image demonstrates a small pool of contrast (large arrow) within a hyaline cartilaginous divot. The free edge of the labrum overlies the divot. Compare this to the normal-appearing, intermediate signal-intensity hyaline cartilage (short arrow). B, Sagittal image in the same patient demonstrates the chondral defect (arrow).

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Figure 37. Anatomic variations of the anterior-superior labrum, which may mimic abnormalities. A, Sublabral hole. Axial MR arthrographic image through the superior portion of the joint demonstrates a detached anterior-superior labrum (thin arrow) with contrast (short arrow), extending beneath the labrum and underlying glenoid. This was originally diagnosed as a labral detachment. A sublabral hole was found at arthroscopy. B, Buford complex. Axial arthrographic image through the midjoint shows a normal anterior labrum (open arrow) and a cord-like middle glenohumeral ligament (arrow). C, Buford complex. Axial arthrographic image through the upper joint, superior to Figure 378, demonstrates absence of labral tissue anterosuperiorly (open arrow) with the cord-like middle glenohumeral ligament mimicking a torn detached labrum. 0, Arthroscopic demonstration of the Buford complex. The posterior portal demonstrates the absence of the anterior-superior labrum (small arrows). Note the biceps tendon (arrow) and cord-like middle glenohumeral ligament (arrowhead) superiorly. The humeral head is to the right of the photograph (curved arrow). (Courtesy of Gary Perlmatter, Boston, MA.)

is referred to as a sublabral hole. An absent labrum is termed a Buford complex as it is found in combination with a cordlike middle glenohumeral ligament (Fig. 37). The history of the patient is critical, as differentiation between an anatomic variation and an isolated anterosuperior labral injury is difficult.

Superior Labral Abnormalities

Snyder and colleaguesg0 described superior labral tears anterior and posterior to the attach-

ment of the biceps tendon to the supraglenoid tubercle. These lesions are not thought of as being associated with classical instability when they are by themselves even though the biceps tendon may be an important anterior stabi- lizer.*l Snyder described four types ranging from fraying and fragmentation to a bucket handle tear.g0 MR arthrography may lift the torn labrum from the attachment to the glenoid, and show insinuation of contrast material into the torn biceps anchor (Fig. 38). In the case of the bucket handle variety of SLAP lesion,


Figure 38. Large SLAP lesion. A, Normal biceps anchor for comparison. Note the biceps tendon (crossedarrow) and biceps anchor (thin arrow). A small recess (arrow) undermines the superior labrum and is a normal finding. B, In a patient with an arthroscopically confirmed type II SLAP lesion, a large amount of contrast is demonstrated within the biceps anchor. Reliable diagnostic criteria (in a large amount of patients) have yet to be described for SLAP lesions in radiologic literature.

contrast may help define the fragment by lift- ing it from the remainder of the torn biceps anchor. Care must be taken to avoid interpre- ting a sublabral hole as a SLAP lesion. Good communication between the orthopedist and the radiologist is helpful in avoiding this potential pitfall.

Glenoid Labral Cysts

Cysts about the shoulder joint are often associated with labral tears and with in~tability.~~ In this way, they are analogous to meniscal cysts of the knee which originate with tears of the meniscus. Cysts in the posterior and anterior paralabral region are associated with posterior and anterior instability, respec- t i ~ e l y . ~ ~ Cysts seen superiorly are associated with SLAP lesions and may or may not be seen with in~tabili ty~~ (Fig. 39). Findings of MR imaging include visualization of a mass with fluid signal intensity usually, but not always, intimately related to a labral tear. Occasionally, at arthrography, the cyst may demonstrate communication with the joint (Fig. 3). Cysts may arise from a region of age-related degeneration with or without dehiscence. Unlike in the knee meniscal cyst, in the shoulder, the tears may completely or partially heal, pre- venting communication with the joint. This ac- counts for the detection of labral cysts in loca- tions associated with instability in shoulders that are currently stable. Arthroscopic evaluation of these patients usually demonstrates evi-

dence of prior capsulolabral disruption with fibrous healing.

The cysts may cause problems secondary to mass effect. If the cyst arises from a break in the integrity of the posterosuperior joint (a common location), it may extend into the spinoglenoid notch, posterior to the scapula between the scapular spine and the glenoid. The suprascapular nerve passes through this notch and may be compressed, resulting in a denervation syndrome. The suprascapular nerve innervates the supraspinatus and infraspinatus and provides some pain fibers to the shoulder joint. Denervation results in weak- ness in those muscles and pain simulating impingement syndrome, which may accompany a rotator cuff tear. MR imaging may be the only method capable of revealing the true cause of symptoms in these cases.

CONCLUSIONS AND RECOMMENDATIONS

Suggested indications for conventional MR

1. Insidious onset of shoulder pain, especially in patients aged more than 40 years.

2. Impingement. 3. Trauma, including dislocation in patients

aged more than 40 years. 4. Initial evaluation of a patient with sus-

pected suprascapular nerve dysfunction. 5. AC joint evaluation.

imaging include the following:

512 TIRMAN et a1

Cla vide

I Figure 39. Labral cyst resulting from SLAP lesion. A, T2-weighted coronal image demonstrates a bilobed cyst (arrows) sitting on top of the glenoid. B, Coronal image demonstrates fluid (arrow) within the superior labrum, indicating the SLAP tear. C, Diagram of proposed mechanism for paralabral cyst formation from labral capsular disruption. In this case, the labral abnormality is a SLAP lesion.

6. Suspected muscle dysfunction (i.e., deltoid)

Suggested indications for MR arthrography

1. Chronic recurring instability, especially if damage to the IGHLC is suspected. CT arthrography may be helpful.

2. Partial rotator cuff tear versus tendinitis. Arthrography may not be necessary if a change in treatment does not result from a differentiation between the two.

are as follows:

3. Postoperative rotator cuff. 4. Further imaging evaluation of suspected

abnormality on conventional MR imaging.

5. Evaluation of labral cysts to determine the patency of a suspected cyst-labral tear communication. CT arthrography may be helpful.

6 . Labral variants-sublabral hole versus a SLAP lesion on conventional MR imaging. CT arthrography may also be helpful.

7. Biceps anchor visualization.

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