The most common cause of shoulder pain is rotator cuff disease
secondary to impingement syndrome. With its great sensitivity to
soft-tissue abnormalities, MRI is ideally suited for the evaluation
of impingement syndrome. It can detect the full gamut of rotator
cuff disease easilyfrom bursitis through tendonitis to frank
tears of the rotator cuff tendons. This issue of Applied Imaging
will discuss these findings, as well as the diagnosis of shoulder
dislocation.William G. Bradley, Jr., MD, PhD, FACR
MRI of the Shoulder
The traditional imaging evaluation of the shoulder has been
performed with plain films. While plain films can demonstrate
fractures, advanced osteoarthritis, and radiodense or radiolucent
bone-marrow abnormalities, they are insensitive to soft-tissue
abnormalities involving the rotator cuff tendons, the biceps
tendon, or the fibrocartilaginous glenoid labrum. For evaluation of
these structures, magnetic resonance imaging (MRI) is required.
This issue of
describes the major indications for MRI in the evaluation of the
Rotator Cuff Disease
The rotator cuff is composed of the supraspinatus,
infraspinatus, teres minor, and subscapularis tendons that attach
on the humeral head. MR imaging of the shoulder for suspected
rotator cuff disease is best performed in the coronal oblique plane
(parallel to the supraspinatus muscle), in the sagittal oblique
plane (perpendicular to the angled coronal), and in the axial
Typically, 3- to 4-mm thick proton-density and T
-weighted (T2WI) conventional or fast spin echo images are acquired
with an additional fat-saturated T2WI fast spin echo or short TI-
inversion recovery (STIR) sequence (both of which null fat signal
and bring out subtle fluid collections) in the angled coronal
Neither intravenous nor intra-articular contrast are generally used
for shoulder pain without a history of dislocation.
The concept of rotator cuff impingement dates back to Neer,
who first called attention to an abnormally shaped acromion as the
initial cause of impingement (Figure 1). An abnormally hooked (Type
III) or laterally down-sloping acromion impinges upon the
supraspinatus tendon during shoulder elevation, leading initially
to bursitis, then to tendonitis, and finally to frank tearing and
disruption. The primary treatment for impingement syndrome,
therefore, is an anterior acromioplasty.
The earliest MR finding in impingement syndrome is thickening of
the fat pad of the subacromial-subdeltoid bursa
(Figure 2). While the normal bursal fat pad is 1-mm thick, it
becomes thicker with bursitis. On fat suppressed T2WI (either fat
-weighted fast spin-echo at high field or STIR at any field
strength), fluid may be seen in the bursa. With isolated bursitis,
the supraspinatus tendon is of normal thickness and intensity.
The normal supraspinatus muscle is recognized as a horizontal,
cigar-shaped structure on the coronal oblique view (Figure 3). The
supraspinatus tendon normally appears as a dark structure (Figure
4) passing under the acromion, inserting on the greater tuberosity
of the humerus.
The musculotendinous junction (Figure 3), i.e., the junction
between the supraspinatus muscle and the darker tendon, should be
at approximately 12 o'clock on the humeral head "clock" in the
angled coronal plane. With the shoulder in a neutral position,
i.e., neither internally nor externally rotated, the supraspinatus
tendon curves anteriorly to attach on the greater tuberosity of the
humerus; therefore, it is best visualized on more anterior sections
than its muscle belly in the angled coronal plane. The actual
attachment of the supraspinatus tendon on the humeral head is the
least well vascularized portion of the tendon ("critical zone") and
is generally the earliest site of tearing (Figure 3).
The diagnosis of tendonitis is made on the basis of tendon
thickening and increased signal on T2WI (Figure 5).
Increased signal without tendon thickening is indicative of myxoid
degeneration or "tendinosis" (Figure 6).
Signal as bright as fluid on a T2WI is diagnostic of a tear (Figure
7). These can be partial thickness tears in either a
superior-inferior (SI) direction or an anterior-posterior (AP)
direction. Partial thickness tears in the SI direction are
subcategorized according to involvement of the bursal surface or
the articular surface. Partial thickness tears in the AP direction
are categorized as to whether they are anterior or posterior. In
general, partial thickness tears do not result in retraction of the
Complete tears of the supraspinatus tendon are recognized on the
basis of fluid-intensity signal in the expected position of the
normally dark tendon (Figures 3 and 7). Complete tears lead to
retraction of the muscle belly and the medial displacement of the
musculotendinous junction (Figure 3). The length of retraction
should be the same length as the fluid collection along the former
course of the supraspinatus tendon. MR is also excellent at
diagnosing supraspinatus muscle atrophy (Figure 3), which, if
sufficiently severe, may be a contraindication to rotator cuff
Larger tears of the supraspinatus tendon are generally
associated with tears (or at least tendonitis) of the infraspinatus
tendon as well. Since both tendons angle anteriorly toward their
attachments on the humeral head, the tendon identified on the most
posterior coronal oblique sections through the supraspinatus muscle
belly is actually the infraspinatus. Further posteriorly, the
muscle fibers of the infraspinatus run obliquely rather than
horizontally (like the supraspinatus). The teres minor has the same
oblique course as the infraspinatus only more inferiorly, i.e.,
below the coracoid process.
The subscapularis tendon and muscle are best evaluated in the
axial plane. The subscapularis tendon attaches near the bicipital
groove. Fibers of the subscapularis tendon may blend with the
fibers of the transverse ligament, which covers the bicipital
groove. Thus, tears of the subscapularis tendon (Figure 8) are
often associated with dislocation of the biceps tendon (Figure 9)
medial to the bicipital groove.
Rotator cuff degeneration is often associated with bicipital
tendonitis (Figure 10). This appears as increased size of the
bicipital tendon with or without increased signal intensity. Fluid
around the bicipital tendon without enlargement is inconsequential,
i.e., it does not constitute tenosynovitis (as the bicipital tendon
sheath communicates freely with the glenohumeral joint). Since the
biceps tendon must pass through the rotator cuff "interval" to get
to the superior glenoid labrum, fluid surrounding the tendon could
potentially be mistaken as a tear of either the supraspinatus or
the subscapularis tendons, particularly on sagittal views (Figure
Occasionally synovial cysts or masses in the suprascapular
(spinoglenoid) notch can lead to pain, simulating a rotator cuff
tear (Figure 12). The suprascapular nerve supplies sensory to the
supraspinatus tendon and motor to the infraspinatus muscle.
Therefore, compression of this nerve by a cyst or mass can lead to
fatty atrophy of the infraspinatus muscle, as well as symptoms of a
rotator cuff tear.
While most cases of supraspinatus impingement are thought to be
due to an abnormal shape of the acromion or an under-surface spur,
degenerative changes in the acromioclavicular joint can also cause
impingement (best visualized in the oblique coronal plane).
The shoulder is a ball-and-socket joint; however, the bony
glenoid "socket" per se is very shallow. The fibrocartilage of the
glenoid labrum (Figure 8) increases its surface area by 60%,
increasing the stability of the joint; however, it is still the
joint most prone to dislocation. Shoulder dislocation can be
classified as "anterior," "posterior," or "bidirectional,"
referring to the position of humeral head relative to the glenoid.
Anterior shoulder dislocations are most common with the humeral
head dislocating anterior and inferior to the coracoid process.
With sufficient force, the bony labrum may be fractured (Bankart
lesion) and the posterolateral superior aspect of the humeral head
may be impacted (Hill-Sachs fracture) (Figure 2).
Frank fractures are generally evident on plain films, however,
they can be equally well visualized by MRI. MRI also has the
advantage that it can diagnose milder forms of trauma where the
humeral head is bruised but its cortex is not frankly disrupted.
Such "bone bruises" are well seen on MR techniques, which tend to
highlight fluid while suppressing the normal fatty signal in the
humeral epiphysis, e.g., fat-saturated T2WI fast spin echo
techniques at high field
or STIR techniques at any field.
Milder trauma sufficient to cause shoulder dislocation without
fracture of the bony glenoid may strip the cartilaginous glenoid
labrum (Figure 13). On axial images, the low-intensity triangle of
the glenoid labral fibrocartilage is absent or displaced. It should
be noted that the middle glenohumeral ligament runs adjacent to the
anterior glenoid labrum in a superior to inferior course and can
easily be mistaken for a labral tear.
When in doubt, injection of a dilute solution of gadolinium (1:100
in normal saline) into the shoulder joint under fluoroscopy is an
extremely sensitiveif somewhat more invasive technique to
demonstrate labral tears.
With intra-articular gadolinium, imaging is generally performed
with thin (i.e., 3 mm) T1WI in the axial, angled coronal, and
angled sagittal planes (with fat saturation at high field).
Posterior shoulder dislocations are much less common than
anterior dislocations and, generally, are seen in the setting of
seizures. In this situation, the geometry is reversed: the
posterior glenoid labrum is torn or fractured and the
superior/anterior humeral head is bruised or fractured. These are
called "reverse Bankart" and "reverse Hill-Sachs" lesions.
Over the past decade, MRI has evolved into the imaging modality
of choice for the evaluation of the painful or unstable shoulder.
MRI can demonstrate the full spectrum of rotator cuff disease
easily, as well as evaluating the bony abnormalities leading to
impingement syndrome in the first place. MRI with intra-articular
gadolinium is useful for demonstrating tears of the glenoid labrum.
Finally, as in other parts of the body, MRI is significantly more
sensitive and specific for the detection of bony abnormalities
(infarcts or metastatic disease) than plain films.
Clinical Quiz: True or False
1. MRI is the procedure of choice to evaluate any patient with
2. MRI is the procedure of choice to diagnose rotator cuff
3. MRI frequently affects management of rotator cuff tears.
4. MRI can diagnose glenoid labral tears.
5. CT is better than MRI to detect subtle fractures of the
1. False. Certain patients (e.g., those with pacemakers or
ferromagnetic intracranial aneurysm clips) can't have MRI. Also,
for fractures, plain films are often sufficientand less
2. True. MRI can diagnose bursitis, tendonitis, and frank tears
with disruption of one or more rotator cuff tendons.
3. True. The amount of retraction may determine whether a
surgeon approaches a shoulder arthroscopically or through an
arthrotomy. Also, patients with marked atrophy of the supraspinatus
muscle may not be candidates for surgery.
4. True. Large tears can be diagnosed on a routine MRI study,
however, smaller, nondisplaced tears require the injection of a
dilute solution of gadolinium into the joint space for optimal
5. False. Even without frank cortical disruption, MRI can
diagnose the bone marrow edema associated with trabecular fractures
or bone bruises much more readily than CT.