AUTHOR AND EDITOR INFORMATION

Section 1 of 6  

• Authors and Editors
• Introduction
• Differentials
• MRI
• Multimedia
• References

INTRODUCTION

Section 2 of 6  

• Authors and Editors
• Introduction
• Differentials
• MRI
• Multimedia
• References

Background

Shoulder pain is a common complaint by patients during physician visits, and it can be due to a variety of causes. The major cause of shoulder pain in patients older than 40 years is rotator cuff impingement and tears. With the development of new arthroscopic techniques for treating rotator cuff disorders, magnetic resonance imaging (MRI) has played an increasingly important role as a noninvasive test for determining which patients may benefit from surgery.

For excellent patient education resources, visit eMedicine's Breaks, Fractures, and Dislocations Center. Also, see eMedicine's patient education articles, Shoulder Dislocation, Shoulder Separation, and Magnetic Resonance Imaging (MRI).

Pathophysiology

The 2 potential etiologies of rotator cuff pain are mechanical causes, such as a flap of tendon that catches under the acromion, and biologic causes, such as synovitis. Although the rotator cuff is innervated, the subacromial bursa has 20 times the number of free nerve endings compared with the rotator cuff tendon. Compression of the subacromial bursa or catching of redundant synovium may cause much of the pain in patients with rotator cuff impingement.

Rotator Cuff Tears

There are 3 main mechanisms involved in the development of RCTs:

• Extrinsic compression of the cuff


• Intrinsic tendon degeneration


• Muscle imbalance

Charles Neer was the first to popularize the theory that RCTs in older patients were primarily the result of extrinsic compression by the anterior acromion process, coracoacromial ligament, and acromioclavicular joint¹—the structures that make up the coracoacromial arch (see Image 1). Until then, most surgical procedures had only involved repairing the rotator cuff, without decompressing the roof of the arch; unfortunately, these procedures often failed to provide patients with long-term pain relief.

Neer's technique of decompression of the coracoacromial arch along with repair of the rotator cuff was extremely successful, with a 90% success rate reported by most surgeons.² However, surgeons have since modified portions of Neer's original theory. For example, they now believe that most anterior subacromial spurs are coracoacromial ligament enthesophytes caused by chronic impingement. Yet over 3 decades after Neer's study, decompression of the arch with rotator cuff repair remains the standard surgical treatment of rotator cuff impingement pain and RCTs.

Despite the surgical success of subacromial decompression, several authors have stressed the role of intrinsic tendon degeneration as the main etiology in the development of RCTs. Rathburn and Macnab demonstrated a zone of relative hypovascularity in the supraspinatus tendon approximately 1 cm from the insertion onto the greater tuberosity, which corresponded with the critical zone where most RCTs were noted to occur.³ Rothman and Parke had previously shown that degeneration occurred in these same hypovascular areas of the cuff.⁴

Lohr and Uhthoff⁵ and Clark and Harryman⁶ took this a step further, noting that the articular side of the rotator cuff has a sparse blood supply relative to the bursal surface. Multiple studies have revealed that most partial-thickness tears of the rotator cuff involve the articular surface, which would be unusual if chronic impingement from a hooked acromion or acromioclavicular joint osteophyte was the dominant cause of the tears. In addition, Nakajima et al⁷ and Lee et al⁸ showed that although the bursal surface bundles are able to elongate with a tensile load, the articular-surface fibers do not stretch and therefore tear more easily.

Kjellin et al reported that partial RCTs originated from areas of advanced degeneration and that there was no vascular ingrowth around the tears to indicate active inflammation.⁹ Many authors now believe that chronic tendon overload leads to degeneration in the hypovascular region of the rotator cuff because of poor healing and that these areas can eventually progress to RCT.

Burkhart has refined this theory with 2 observations: he noted that this hypovascular region does not involve the anterior and posterior edges of the supraspinatus tendon and that a "cable" of thicker, better-perfused tissue connects these edges more medially (see Image 2).¹⁰ This thickened tendon "cable" separates the musculotendinous junction from a crescent-shaped area of the lateral aspect of the supraspinatus tendon, where most RCTs occur.

Although the rotator cuff "cable" is seen histologically, it is not normally identifiable on MRIs. Several authors now believe that even full-thickness tears isolated to this crescent-shaped portion of the rotator cuff can solely be debrided and that patients will do well without significant loss of rotator cuff function.

Finally, muscle imbalance and scapular dyskinesis may also lead to impingement syndrome and RCTs. Strengthening of the humeral head depressors and of the muscles involved in reestablishing normal scapular motion is important in the nonoperative treatment of rotator cuff impingement syndrome.

Internal impingement

Another cause of RCTs is internal, or posterosuperior, impingement. During abduction and external rotation, the undersurface of the supraspinatus and infraspinatus tendons may normally lie between the greater tuberosity and the posterosuperior glenoid. In the throwing athlete, this normal physiologic phenomenon may result in pathologic internal impingement pain.

• Articular-surface tears at the posterior margin of the supraspinatus tendon and/or the anterior aspect of the infraspinatus tendon


• Posterosuperior labral tears


• Cystic change of the humeral head at the insertion of the rotator cuff

Identification of this constellation of findings by MRI should alert the radiologist and arthroscopist to the diagnosis of internal impingement.

In 1998, Tuite et al identified the fact that patients with clinically diagnosed internal impingement of the rotator cuff had thickening of the posteroinferior labrocapsular complex as well as a more shallow posterior capsular recess.¹¹ These observations may prove useful in identifying patients who are at risk for internal impingement; diagnosis by MRI is helpful in this subset of patients, as nonoperative therapy with selective stretching of the posterior inferior labrum may decrease symptoms. In those in whom conservative measures fail, a posterior capsulotomy may be of benefit. 

Frequency

United States

Shoulder pain is one of the most common reasons patients give for a physician visit, third only to headache and back pain.¹² The incidence of rotator cuff disease increases as people age, although RCTs may not always be symptomatic. Sher et al obtained MRI scans for 46 asymptomatic individuals who were older than 60 years and found that 54% had either a partial-thickness or full-thickness RCT.¹³ Another study found that only 28% of all RCTs are painful and that many full-thickness tears are asymptomatic.¹⁴

International

See US Frequency.

Mortality/Morbidity

Although RCTs can be asymptomatic, these injuries can also be quite painful, with many affected patients describing the pain as one that awakens them at night. A functioning rotator cuff is also necessary for many activities of daily living, such as brushing one’s hair. There is significant job-related disability for individuals who have to lift or perform activities at the shoulder level.

Race

No race predilection has been observed.

Sex

A slightly higher incidence of RCTs in men has been reported in cadaver studies, but the difference is not significant.

Age

Most RCTs occur in older individuals, although they can also occur in younger individuals who are active in sports that involve overhead movements. Sher et al found the average age of patients with full-thickness tears was greater than that of those with partial-thickness tears.¹³ Because some patients with chronic RCTs and supraspinatus tendon atrophy are not surgical candidates, the true average age of those in the general population who have a full-thickness tear is probably higher as well.

Anatomy

The rotator cuff is made up of tendons from 4 muscles: the supraspinatus, infraspinatus, teres minor, and subscapularis. The tendon fibers of the supraspinatus, infraspinatus, and teres minor blend 1.5 cm from their lateral margins before they insert onto the greater tuberosity, with the bulk of the supraspinatus fibers inserting onto the superior facet of the greater tuberosity, whereas the infraspinatus and teres minor tendon fibers insert along the posterior aspect. The subscapularis tendon inserts independently onto the lesser tuberosity.

The rotator cuff interval, or anterior interval, separates the supraspinatus and subscapularis tendons. This gap between the tendons contains the coracohumeral ligament and superior glenohumeral ligament, as well as allows the long head of the biceps tendon to pass from the bicipital groove through the glenohumeral joint before inserting onto the superior glenoid.

The supraspinatus tendon is clinically the most important rotator cuff tendon because it is involved, either alone or in combination with 1 or more additional tendons, in 95% of cuff tears.¹⁵ The main tendon of the supraspinatus forms within the mid portion of the muscle, but as the supraspinatus courses laterally, the tendon lies progressively more anteriorly within the muscle. The supraspinatus tendon follows the curvature of the superior humeral head and curves caudally to insert onto the superior facet of the greater tuberosity. The supraspinatus tendon is approximately 9-11 mm thick at dissection but usually appears thinner (approximately 6-8 mm) on oblique coronal MRIs in patients who are positioned with the affected arm adducted and the rotator cuff under tension.

Histologically, Clark and Harryman described 5 layers that make up the rotator cuff.⁶ The 2 layers that form the bursal one third of the tendon contain closely packed, well-organized tendon fibers, as does the layer forming the articular surface of the cuff. In the center of the rotator cuff are 2 layers that contain less-organized fibers mixed with loose connective tissue. On fat-suppressed, T2-weighted MRI, this central third of the tendon can have an intermediate signal intensity in normal individuals, whereas the outer portions of the cuff should show low signal intensity (see Image 3).

The histology of the rotator cuff contributes to one of the difficulties of rotator cuff MRI interpretation, the magic-angle effect or angular anisotropy. This effect is an MRI artifact in which normally low-signal structures that are made of organized collagen fibers appear as a higher signal intensity on images that are obtained with a short echo time (TE). The artifact occurs when the long axes of the collagen fibers are oriented at 55° to the main magnetic field. In most high-field MRI scanners, the main magnetic field is oriented along the direction of the bore (the central tunnel where the patient lies). The well-organized collagen fibers in the outer portions of the rotator cuff are organized longitudinally; therefore, these normally low-signal fibers have increased signal intensity on short-TE images as the fibers curve and become oriented at the magic angle.

Clinical Details

The classic clinical presentation of rotator cuff impingement pain is a chronic ache in the lateral aspect of the shoulder, aggravated by attempts to abduct the arm and often worse at night. Patients typically have a severely painful arc from 60-120° of abduction and forward flexion. Weakness during abduction or forward flexion also may be present, particularly in patients who have an RCT.

Two physical examination techniques are commonly used to confirm rotator cuff impingement as the source of pain in the affected shoulder. The Neer, or impingement, test involves forward flexion of the arm, with the elbow extended; pain is elicited at maximal elevation. The Hawkins/Jobe test begins with the shoulder flexed forward at 90° and the elbow bent. The shoulder is then internally rotated and further abducted/flexed forward in an attempt to elicit pain. In addition, lidocaine injection into the subacromial bursa that results in decreased pain during the impingement tests is further evidence that impingement is the cause of the shoulder pain.

Preferred Examination

Conventional MRI with T2-weighted images in both the oblique coronal and oblique sagittal planes is the preferred technique for imaging the rotator cuff. Most authors have found that fat-suppressed, FSE, T2-weighted images are the most accurate for detecting RCTs; a sensitivity of 84-100% and a specificity of at least 77-97% for full-thickness tears can be expected with this pulse sequence.^{16, 17, 18, 19, 20, 21}

Although most RCTs can be seen on oblique coronal images, Patten et al reported that oblique sagittal images provide approximately a 10% improvement in accuracy for detecting RCTs, although this was not stastically significant.²² The authors found that oblique sagittal images are especially helpful for identifying tears involving the anterior edge of the supraspinatus (see Images 4a-d).

Magnetic resonance arthrography

Some people prefer to perform either direct or indirect MR arthrography for imaging the rotator cuff. The advantage of direct MR arthrography relative to MRI is that it distends the joint, thus forcing the contrast agent into a small defect. T1-weighted images, which are faster to acquire and have a superior signal-to-noise ratio, can also be used instead of T2-weighted images. The disadvantages of direct MR arthrography are that it is mildly invasive and may require imaging guidance to place a needle into the glenohumeral joint capsule. In addition, bursal-surface partial-thickness tears are not directly opacified.

Several authors have reported that direct MR arthrography is close to 100% sensitive and specific for full-thickness and articular-surface partial-thickness RCTs.²³ A full-thickness tear will demonstrate the gadolinium contrast solution extending first through a defect in the cuff and then into the subacromial-subdeltoid bursa (see Image 5). Articular-surface partial-thickness tears show a focal extension of the contrast solution into the substance of the tendon (see Image 6). When performing direct MR arthrography, it is important to use fat-suppression to decrease the signal intensity of the peribursal fat plane around the subacromial-subdeltoid bursa; without fat-suppression, the fat plane can mimic the contrast agent and lead to a false interpretation of an RCT.

Indirect MR arthrography requires only an intravenous (IV) injection, but this modality has a disadvantage in that it does not distend the joint. As in direct MR arthrography, short scanning time T1-weighted images can be used instead of T2-weighted images. Several authors have shown that compared with conventional MRIs of the rotator cuff, RCTs are better characterized on indirect MR arthrography and there is better correlation with surgical findings. One study reported that 2 radiologists improved their accuracy for detecting RCTs from 67% and 62% with conventional MRI to 92% and 96%, respectively, with indirect MR arthrography.²⁴ Again, use of fat suppression is important, but exercising the joint does not appear to improve accuracy.

Despite these studies, MR arthrography has not been as widely accepted for evaluating the rotator cuff as it has been for imaging the glenoid labrum. Direct MR arthrography does improve the depiction of posterior articular-surface partial-thickness tears that are observed in overhead-throwing athletes, particularly if the shoulder is scanned in abduction and external rotation. However, most authors have found that fat-suppressed, FSE, T2-weighted images obtained with a quality shoulder coil are fairly accurate for most RCTs and that conventional MRI is adequate for routine imaging of the rotator cuff.

Limitations of Techniques

MRI is contraindicated in patients who have a cardiac pacemaker, ferromagnetic foreign bodies (particularly in the orbit), and some cochlear implants. Some patients are extremely claustrophobic in high-field-strength MRI scanners, although many of these patients can be scanned in open MRI scanners after administration of a mild sedative.

MR arthrography is mildly invasive, and because the off-label use of gadolinium is not currently approved by the US Food and Drug Administration (FDA) for intra-articular injection, it may require written, informed patient consent. Imaging is also usually necessary to correctly position the arthrogram needle within the joint capsule. Fluoroscopy is the most common method of imaging guidance, but needle placement also can be performed under CT scanning, by ultrasound, or within the MRI scanner. Conventional arthrography is also mildly invasive and has the limitation of not being a tomographic technique.

Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble moving  or  straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.

DIFFERENTIALS

Section 3 of 6  

• Authors and Editors
• Introduction
• Differentials
• MRI
• Multimedia
• References

Other Problems to Be Considered

Instability with secondary impingement
Calcific tendinitis
Tendinopathy
Rotator cuff strain
Posterolateral impingement syndrome

MRI

Section 4 of 6  

• Authors and Editors
• Introduction
• Differentials
• MRI
• Multimedia
• References

Findings

Full-thickness tears

For many orthopedic surgeons, the main role of shoulder MRI is to detect a full-thickness RCT. The most common appearance of a full-thickness tear is high signal intensity on a T2-weighted image that extends from the articular surface of the rotator cuff to the subacromial-subdeltoid bursa (see Image 2). Rafii et al reported that high signal was observed in approximately 90% of full-thickness tears proven at surgery.²⁵ In chronic RCTs in which the shoulder joint has little or no effusion, the humeral head may be high riding, such that not much high signal is seen at the tear site (see Image 3).

Most small full-thickness tears arise in the anterior aspect of the supraspinatus tendon in the critical zone (see Images 4-5).

Partial-thickness tears

Partial-thickness tears can be classified as articular, bursal, or intratendinous. Intratendinous tears may be a cause of shoulder pain, but they are not observed at routine arthroscopy and are rarely treated surgically. Articular-surface partial-thickness tears are more common than bursal-surface tears (at an approximately 3:1 incidence rate).^{26, 27} Many patients with a bursal-surface tear also have an articular-surface tear.

The accuracy of MRI for partial-thickness tears is lower than that for full-thickness tears. Although some authors have reported a sensitivity greater than 0.90 for partial-thickness tears, others have reported sensitivities as low as 0.17-0.56.^{18, 21, 25, 28, 29} Reinus et al were unable to correctly identify the side of the affected rotator cuff (articular vs bursal) in 50% of their patients with a partial-thickness tear.¹⁶ One reason for the low accuracy is that a high-signal defect on T2-weighted images is a less common finding in partial-thickness tears than in full-thickness tears; in a study by Rafii et al, this high-signal defect was seen in only 7 of 16 cases of partial-thickness tears.²⁵

Partial-thickness tears often appear on MRI as only an intermediate signal, isointense to muscle, which disrupts the normal low-signal surface of the rotator cuff (see Image 6). Absence of fluid in an RCT on MRI may be from the presence of a poor-quality scar or granulation tissue within the defect, and this can be difficult to distinguish from tendon degeneration or a healed RCT. Partial-thickness tears may also have smooth margins that taper gradually so that the rotator cuff appears to be only somewhat thinned (see Image 7).

Although most partial-thickness tears occur in the critical zone of the supraspinatus tendon, some RCTs occur in less common locations. In younger patients, a small articular-surface avulsion-type partial-thickness tear can occur adjacent to the greater tuberosity; this is termed a rim-rent tear (see Image 8). Tears isolated to the infraspinatus tendon occur in 1-7% of patients with RCTs, but these tears are more common in athletes who perform overhead activities.¹¹ MR arthrography in which the patient is positioned with the arm in abduction and external rotation is the best technique for identifying these infraspinatus articular-surface partial-thickness tears, which often are associated with adjacent glenoid labral fraying.

Although the most important MRI criterion of a partial-thickness tear is the presence of an increased signal that disrupts the normally low-signal surface of the rotator cuff, some authors have described some secondary signs that may be helpful in improving the accuracy of MRI. Sanders et al demonstrated that an intramuscular cyst, typically in the supraspinatus muscle, is always associated with articular-surface involvement by a tear.³⁰ The authors suggested that when such cysts are present, associated rotator cuff pathology should be investigated.

Inferiorly directed acromioclavicular joint osteophytes, a hooked anterior acromion, and an os acromiale have all been associated with a higher incidence of RCTs; therefore, these findings should prompt a careful evaluation of the rotator cuff. Subacromial-subdeltoid fluid is common in full-thickness tears, but a small amount can be observed in patients without a bursal-surface tear; thus, the presence of this fluid is not an accurate secondary sign of a bursal-surface partial-thickness tear.

Degree of Confidence

Many studies investigating the use of fat-suppressed, FSE imaging have reported a sensitivity of 84-100% and a specificity of 77-97% for full-thickness tears^{18, 19, 20, 21}; however, the accuracy for partial-thickness tears is lower. MR arthrography may be helpful for better demonstrating articular-surface partial-thickness tears. Angling the oblique coronal or oblique sagittal images to the rotator cuff surface at the suspected tear site can improve the accuracy of conventional MRI.

False Positives/Negatives

There are 3 other abnormalities of the rotator cuff that can mimic an RCT: degeneration, tendinopathy, and cuff strain. Rotator cuff degeneration is common in older individuals and appears as an ill-defined area of increased signal on T2-weighted MRIs within the substance of the cuff. All rotator cuffs undergo age-related degeneration in which the normally compact and well-organized collagen fibers are replaced by intermediate-signal myxoid and eosinophilic material.

As aging progresses and the rotator cuff is put under repeated stress, small fissures can develop within the cuff substance and appear as thin areas of fluid on MRI. If the MRI contrast and brightness are set too high (ie, windowed too tightly), these fissures can occasionally bloom and appear as a tear that extends to the surface of the cuff (see Image 9).

MULTIMEDIA

Section 5 of 6  

• Authors and Editors
• Introduction
• Differentials
• MRI
• Multimedia
• References

Media file 1:  Shoulder. Hooked anterior acromion. Reprinted with permission from Tuite et al.
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Media file 2:  Supraspinatus tendon. Reprinted with permission from Michael Tuite, MD.
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Media file 3:  Normal intratendinous signal.
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Media file 4:  Partial-thickness tear seen better on angled oblique sagittal views.
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Media file 5:  Full-thickness tear.
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Media file 6:  Rim-rent or partial-thickness articular-surface tendon avulsion (PASTA) tear.
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Media file 7:  Chronic full-thickness tear.
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Media file 8:  Bursal surface partial-thickness tear.
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Media file 9:  Articular- and bursal-surface partial-thickness tears.
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Media file 10:  Tendinopathy.
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Media file 11:  Intramuscular cyst and partial-thickness tear.
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Media type:  MRI

REFERENCES

Section 6 of 6

• Authors and Editors
• Introduction
• Differentials
• MRI
• Multimedia
• References

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Article Last Updated: May 22, 2007