is a Resident at the Department of Radiology at Wilford Hall
Medical Center in San Antonio, TX and
is an Assistant Professor at the Department of Radiology at the
Uniformed Services University in Bethesda, MD.
Rotator-cuff disease is a common cause of shoulder pain in both
young adults (athletes in particular) and the elderly. The cause
can be acute or repetitive chronic trauma to the rotator-cuff
tendons; in the older age group, degenerative changes are common
and can contribute to rotator-cuff injury. Conventional magnetic
resonance (MR) imaging and MR arthrography have become the standard
for the noninvasive imaging assessment of shoulder pain. A high
degree of sensitivity and specificity in the detection of
rotator-cuff tears is achievable with conventional MR imaging.
Moreover, MR arthrography can demonstrate an even higher degree of
accuracy in the assessment of the rotator injuries and is helpful
in the detection of partial-thickness tears, which become more
conspicuous following intra-articular contrast injection. If
rotator-cuff disease is not detected and treated early, significant
loss of shoulder function and range of motion can occur. Therefore,
recognizing cuff injury as well as its specific site of occurrence,
size, and extent, are a few of the important factors for
determining the best outcome for the patient. We present a review
of the MR findings of rotator-cuff pathology through a series of
images and illustrations.
The rotator cuff is comprised of four tendons, easily recalled
with the mnemonic "SITS," which stands for supraspinatus,
infraspinatus, teres minor, subscapularis. These four tendons
interdigitate distally to form a tendinous hood at their insertions
onto the tuberosities of the humerus. The supraspinatus tendon lies
between the acromial undersurface and the top of the humeral head.
The critical zone of avascularity is located 1 to 2 cm proximal to
the tendinous insertion at the superior impression of the humeral
head and is the most common site for tears. The supraspinatus,
infraspinatus, and teres minor tendons attach to the greater
tubercle from superiorly to inferiorly, respectively. The
subscapularis inserts onto the lesser tubercle. The coracoacromial
arch is bordered posteriorly by the humeral head, superiorly by the
acromion and coracoacromial ligament, and anteriorly by the
coracoid process and intervening coracoacromial ligament. Located
within the coracoacromial arch are the subacromial/subdeltoid
bursa, supraspinatus muscle and tendon, and the long head of the
The muscles of the rotator cuff each have well-defined
functions. The supraspinatus abducts the humerus. The infraspinatus
and teres minor collaborate to externally rotate the humerus. The
function of the subscapularis is to internally rotate the humerus.
Figure 1 demonstrates the important anatomic relationships of the
rotator-cuff tendons and muscles.
Surface coils are necessary for high-resolution images. There
are two basic types of shoulder surface coils: 1) coils that
conform to the shoulder; and 2) coils that are mounted on a
platform. A combination of coils may also be used. For example, a
flexible coil that conforms to the patient's shoulder may be used
when the patient is in the abducted and externally rotated (ABER)
position, and a platform coil may be used to perform the remainder
of the exam. One of the main disadvantages of the flexible or
curved coil is its susceptibility to artifact secondary to patient
motion. The platform coil, on the other hand, provides a high
signal-to-noise ratio but does not allow imaging in the ABER
position. The imaging protocol involves scanning a supine patient
with mild external rotation of the humerus or with the patient's
thumbs pointing toward the ceiling. Imaging is obtained with thin
3- to 4-mm slices in three planes: coronal oblique, sagittal
oblique, and axial. The actual imaging sequences can vary from
institution to institution, but the majority of shoulder MR imaging
usually invloves at least a fat-saturated fast-spin-echo (FSE)
sequence. The coronal oblique plane of imaging should be
perpendicular to the glenoid fossa or parallel to the supraspinatus
tendon. The sagittal oblique images should be parallel to the
glenoid fossa, from the scapular neck through the lateral aspect of
the rotator cuff. The axial images are performed from just above
the acromioclavicular joint through the inferior axillary
In 95% of cases of rotator-cuff pathology, injury is preceded by
subacromial impingement syndrome, which is a purely clinical
diagnosis defined as a painful compression, in an awake patient, of
the supraspinatus tendon, subacromial/subdeltoid bursa, and long
head of the biceps tendon between the coracoacromial arch and the
humeral head. Pain is usually progressive and aggravated by raising
the arm in a position of abduction and external or internal
Impingement syndrome commonly occurs in patients under the age of
40 and is usually secondary to repetitive elevation and abduction
of the arm during occupational or athletic activities; it also
commonly occurs in the elderly as a result of subacromial
osteophyte formation and other degenerative changes around the
acromial-clavicular joint and coracoacromial arch. Predisposing
factors include certain acromial shapes, slopes, and positions
(Figures 2A through 2E, Table 1); presence of an os acromiale
(Figure 2F); acromioclavicular joint degenerative and hypertrophic
changes (Figure 2G); chronic glenohumeral joint instability
resulting in degenerative changes (Figure 3A); a thickened
coracoacromial ligament (Figure 3B); supraspinatus muscle
hypertrophy (Figure 3C); posttraumatic deformities; calcific
tendonitis (Figure 3D); a prominent greater tuberosity; and
posterior superior glenoid impingement. The supraspinatus tendon is
by far the most frequently injured rotator-cuff tendon, largely
because of its more superior location relative to the other
rotator-cuff tendons, resulting in its closer proximity to the
acromion and distal clavicle, two common offending agents. The
severity of impingement is directly related to rotator-cuff
degeneration or tears. The diagnosis of "impingement syndrome"
cannot be made with MR imaging, but is inferred from narrowing of
the acromiohumeral distance or stenosis of the supraspinatous
MR imaging characteristics of rotator-cuff
MR imaging, with its excellent soft-tissue contrast and
multiplanar capability, is the imaging study of choice for the
evaluation of the painful shoulder. Normally, the uninjured
rotator-cuff tendon shows uniform low signal intensity. Any
deviation from this MR appearance is suspicious for pathology.
There are four major types of tendon pathology: 1) tendonapathy or
tendinosis; 2) surface degeneration or fraying; 3)
partial-thickness tear; and 4) full-thickness tear. Early collagen
fiber breakdown within a tendon is termed tendonapathy or
tendinosis and is an early sign of impingement. Use of the term
tendonitis should be avoided, as there is no histologic evidence of
significant inflammation. MR imaging characteristics of
tendonapathy include intermediate signal intensity (higher signal
than normal tendon, but lower than joint fluid) on T1-weighted
(T1W) imaging, proton-densityweighted (PDW) imaging, and
T2-weighted (T2W) imaging, without focal tendon disruption (Figures
4A and B). The signal intensity on T2W images is equal to or higher
than that on T1W images, but should be less than joint fluid
signal. Tendon enlargement is often an associated finding in
Histological examination of tendinopathy shows mucoid and
fibrillary degeneration, with evidence of scarring.
Tendon surface degeneration or fraying is an irregularity of the
tendon surface that is more common on the bursal side (Figure 4C)
and is often associated with increased signal in the subacromial/
subdeltoid bursa. It is important, especially in athletes, to be
able to distinguish these injuries from partial tears, as the
latter can be surgically repaired for restoration of function.
However, making this distinction can often be difficult on
conventional MR imaging due to the magic-angle effect, focal fat,
muscle fibers, or subclinical degeneration.
The addition of frequency selective fat-suppression technique
improves the detection of rotator-cuff tears. The use of
gadolinium-DPTA in MR arthrography to distend the joint is useful
in revealing small undersurface or articular surface abnormalities
of the supraspinatus tendon.
To further improve detection of undersurface abnormalities, the
ABER position can be used to increase the separation of the
supraspinatus tendon from the humeral head and encourage spreading
of any torn and frayed edges, thereby increasing the visibility of
The characteristics of partial-thickness tears on MR imaging are
focally increased signal on T1W and T2W images (signal intensity
similar to that of joint fluid on T2W images), with involvement of
either the articular (Figure 5A) or bursal tendon surface or
intrasubstance of the supraspinatus tendon (Figure 5B).
Partial-thickness tears can be graded according to the depth of the
On MR imaging, a full-thickness tear of a tendon has the
appearance of high signal involvement of the tendon, usually
extending vertically or obliquely from the articular to the bursal
surface (Figure 6A). Conventional MR imaging has a sensitivity of
92% to 96% for the detection of full-thickness tears.
A complete tear or rupture is complete disruption of the entire
tendon, leaving a fluid-filled gap separating the torn tendinous
ends, usually with medial retraction of the torn tendon as a
secondary sign (Figure 6B). The Patte classification is frequently
used to describe and communicate the degree of tendon retraction in
complete tears (Figure 7, Table 2).
Over time, atrophy and fatty infiltration of the associated muscle
develop and can be a useful secondary sign of chronic rotator-cuff
tears (Figure 8). Subacromial/subdeltoid bursal fluid is a
sensitive but relatively nonspecific finding in rotator-cuff tears.
Unlike injuries of the supraspinatus tendon, subscapularis tendon
tears (Figure 9) are relatively uncommon and typically present in
elderly patients with recurrent anterior shoulder dislocation. They
often occur in conjunction with other rotator-cuff injuries.
Isolated subscapularis tendon tears are less common but can result
from trauma, eccentric overload, or rotator-cuff degenerative
disease. Primary signs of a tear may be limited to the upper third
of the tendon.
Other reported causes of subscapularis injury include long head of
the biceps tendon dislocation, massive rotator-cuff tears, and
subcoracoid impingement (congenital or posttraumatic/postsurgical).
Tears of the infraspinatus tendon (Figure 10) are relatively
common; only tears of the supraspinatus tendon are more common. The
pathogenesis and mechanism of tendon injury is similar to that of
the supraspinatus tendon, and concomitant tears of these two
tendons form the most common combination when tears of more than
one tendon are present. Tears of the teres minor tendon are rare,
particularly in isolation.
It is important to be cognizant of an artificial high signal
appearance within the supraspinatus tendon known as the magic-angle
phenomenon, which usually occurs at the critical zone of the
supraspinatus tendon and can mimic tendon pathology. A useful
discriminator between the magic-angle phenomenon and a true tendon
tear is the appearance of high signal intensity on T2W imaging,
indicative of a true tear. In contrast, the increased signal of the
magic-angle phenomenon seen on T1W images remains isointense to the
adjacent muscle or does not increase in signal intensity on T2W
Asymptomatic shoulder MR imaging
Surprising findings have occurred in asymptomatic patients who
undergo shoulder MR imaging. Rotator-cuff tears have been reported
in 34% of asymptomatic patients.
It has been noted that the frequency of tears increases with age,
with partial-thickness tears being more common than full-thickness
tears. It is important to be aware that MR imaging findings may not
correlate with the patient's symptoms.
The long head of the biceps tendon
The long head of the biceps tendon stabilizes the anterosuperior
portion of the rotator cuff by its position in the bicipital groove
anteriorly and its attachment to the glenoid labrum superiorly.
Tears of the subscapularis tendon in particular have been
associated with medial subluxation or dislocation of the biceps
tendon or tendonopathy.
The biceps tendon is also frequently injured (Figure 11) in
association with the tears of the superior and anterior portions of
the rotator cuff. When tears of the supraspinatus and subscapularis
tendons are detected, specific attention should be directed to the
condition of the long head of the biceps tendon.
Rotator-cuff injuries are a common cause of shoulder pain.
Conventional MR imaging provides high accuracy in the detection of
rotator-cuff tears. MR arthrography demonstrates even higher
accuracy, but is invasive to some degree and is used more often
when there is evidence of glenohumeral instability. This pictorial
review should help to familiarize radiologists and clinicians with
characteristic MR findings of rotator-cuff pathology.