AJR 2003; 181:1449-1462
© American Roentgen Ray Society
Superior Labral Anteroposterior Tear: Classification and Diagnosis on MRI and MR Arthrography
Aurea V. R. Mohana-Borges1,
Christine B. Chung and
Donald Resnick
1 All authors: Department of Radiology, Veterans Affairs Medical Center and
University of California, San Diego, 3350 La Jolla Village Dr., San Diego, CA
92161.
Received March 13, 2003;
accepted after revision June 6, 2003.
Address correspondence to C. B. Chung
(cbchung{at}ucsd.edu).
Introduction
Lesions affecting the superior labrum were an almost unknown clinical
entity before the advent of arthroscopy. Since the description of superior
labral lesions in throwing athletes by Andrews et al.
[1] in 1985 and the
introduction of the acronym SLAP (superior labral anteroposterior) by Snyder
et al. [2] in 1990, increasing
attention to the diagnosis and treatment of these lesions has been noted in
both the orthopedic and radiology literature
[3–29].
Although the true prevalence of SLAP lesions in a population of patients with
shoulder problems is difficult to determine, arthroscopic studies report a
prevalence of SLAP lesions in the range of 3.9–6%
[2,
13,
23] in all patients undergoing
shoulder arthroscopy. Not only is the SLAP lesion encountered with relative
frequency, it is a lesion that has been associated with nonspecific shoulder
pain. A detailed understanding of the anatomy, anatomic variations, and
primary and associated problems of the SLAP lesion is necessary if the
radiologist is to provide the referring physician with adequate information
for diagnosis and treatment planning.
Although the four basic types of Snyder's classification are still widely
used, several authors have added descriptions of other SLAP lesions.
Currently, 10 types or patterns of SLAP lesions have been recognized, with a
further subdivision of the type II lesion into A, B, and C subtypes
(Table 1).
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TABLE 1 Current Superior Labral Anteroposterior (SLAP) Lesion Classification
with Associated Clinical Findings and Mechanisms of Injury
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The purpose of this article is to review this subject, to describe problems
related to normal anatomy and variants of the superior and anterosuperior
portions of the labrum, to perform a critical analysis of the current 10-grade
SLAP lesion classification and mechanisms of injury from the perspective of
MRI, and to describe an MRI approach to the diagnosis of such lesions. In
addition, a tailored algorithm for SLAP lesions based on MRI findings is
introduced.
Normal Anatomy
The glenoid labrum is a cuff of fibrocartilaginous tissue that surrounds
the glenoid cavity. It serves to deepen the glenoid fossa and to increase the
area of the articular surface that contacts the humeral head, both of which
increase joint stability. The labrum allows attachment of the tendon of the
long head of the biceps brachii muscle and glenohumeral ligaments
[30].
The normal labrum is approximately 3 mm high from base to apex and is 4 mm
wide at its base of insertion into the glenoid cartilage. It has low signal
intensity with all pulse sequences. However, its shape, size, and
configuration vary considerably
[31]. The superior part of the
labrum is normally more loosely attached and more mobile than the other parts.
This normal laxity leads to diagnostic difficulty in identifying SLAP lesions,
especially type II lesions
[30].
For purposes of localizing abnormalities, the labrum is usually divided
into four or six areas or in terms of time zones on the face of a clock. In
MRI reports, either of these labral divisions is acceptable, although the
description by time zones is preferable because it best characterizes the
extension of labral pathology (Fig.
1A,
1B). For the division into
clock zones, the labrum is likened to the face of a clock, with the superior
portion positioned at 12 o'clock and the inferior portion at 6 o'clock. By
convention, the anterior portion is positioned at 3 o'clock and the posterior
portion at 9 o'clock for both shoulders (Resnick D, unpublished data).
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Fig. 1A. —Labral division: two nomenclatures used for localization of
labral abnormalities. Diagram shows labrum viewed as "time zones"
on clock face. For both shoulders, 12- to 6-o'clock position faces anteriorly,
and 6- to 12-o'clock position faces posteriorly.
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Classically, SLAP lesions are centered at the attachment of the biceps
tendon, with variable extension to either the anterior or posterior portion of
the labrum. Determining the type of attachment of the biceps tendon to the
superior labrum and adjacent supraglenoid notch, as well as the presence of
anatomic variations, is the first step in accurate evaluation of this
region.
Normal Variants of the Superior and Anterosuperior Labrum:
Characteristics and Prevalence
Anatomic variations commonly occur in the 11- to 3-o'clock positions and
include sublabral recess, or sulcus; sublabral foramen, or hole; and Buford
complex.
The sublabral recess, or sulcus, is located at the 11- to 1-o'clock
position and represents a recess between the biceps-labral complex and the
superior portion of the glenoid cartilage (Fig.
2A,
2B). Smith et al.
[17] reported an overall
prevalence of 73% (19/26 shoulders from donors with an age range at the time
of death of 26–79 years). More details were provided in the classic
cadaveric study of De Palma et al.
[32], in which the authors
further separated the specimens into groups according to their age at death.
No sublabral recess was observed in a group of fetuses and infants, although
it was identified in 17% of the specimens derived from persons in the second
decade of life, 50% of the specimens derived from persons older than 20 years,
and more than 95% of the specimens derived from persons in the seventh and
eighth decades of life. More recently, Fealy et al.
[33] reported a normal area of
separation of the anterosuperior labrum, located near the 1-o'clock position,
in specimens over 22 weeks of gestational age. Although the data are unclear
at which age normal labrum separation is found, they agree on the presence of
a focus of loose anterosuperior labral attachment. This area may progress to a
physiologic labral separation or be converted into pathologic detachments
(SLAP lesions) when subjected to excessive stress.
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Fig. 2A. —MRI features of sublabral recess in 40-year-old woman with MR
arthrogram of left shoulder. HH = humeral head, G = glenoid. Axial T1-weighted
fat-suppressed spin-echo image (TR/TE, 400/11) shows that sublabral recess
(arrowhead) has parallel orientation to glenoid cartilage in this
plane.
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Fig. 2B. —MRI features of sublabral recess in 40-year-old woman with MR
arthrogram of left shoulder. HH = humeral head, G = glenoid. Coronal
T1-weighted fat-suppressed spin-echo image (400/11) shows that recess outlined
by contrast material is linear and follows contour of glenoid cartilage
(arrow).
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The sublabral foramen, or hole, is located at the 1- to 3-o'clock
positions, anterior to the biceps-labral complex, and represents the space
between the anterosuperior labrum and the adjacent glenoid cartilage (Fig.
3A,
3B). Stoller
[34] reported its prevalence
as 11%, Williams et al. [35]
as 12%, and Ellman and Gartsman
[36] as 15%.
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Fig. 3A. —MRI features of sublabral foramen in 57-year-old man with
superior labral anteroposterior tear. HH = humeral head, G = glenoid. Axial
T1-weighted fat-suppressed spin-echo MR arthrogram (TR/TE, 500/15) shows
separation of anterosuperior labrum (arrowhead) from glenoid
cartilage.
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Fig. 3B. —MRI features of sublabral foramen in 57-year-old man with
superior labral anteroposterior tear. HH = humeral head, G = glenoid. Axial
T1-weighted fat-suppressed spin-echo MR arthrogram (500/15) at 3-o'clock
position shows that labrum (straight arrow) slips back and reattaches
to glenoid cartilage. Curved arrow indicates middle glenohumeral ligament.
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The Buford complex consists of an absence of the anterosuperior portion of
the labrum and is associated with a cordlike middle glenohumeral ligament
[35]
(Fig. 4). This complex was
first described by Williams et al.
[35] in 1994, with a
prevalence of 1.5%. They considered that the complex was "an
unusual-appearing anatomic variation that may lead the surgeon to confuse this
complex with a sublabral hole (foramen) or a pathologic labral
detachment." If the cordlike middle glenohumeral ligament is mistakenly
reattached to the neck of the glenoid cartilage at the time of surgery, severe
painful restriction of humeral rotation and elevation can occur.
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Fig. 4. —MRI features of Buford complex in 65-year-old man. Proton
density–weighted fat-suppressed image (TR/TE, 2,000/14) shows absence of
anterosuperior labrum associated with cordlike middle glenohumeral ligament
(arrow). HH = humeral head, G = glenoid.
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The reported frequency of these anatomic variations clearly differs because
of inconsistent use of the terms "sublabral recess" and
"sublabral foramen"; various methods of investigation that have
used cadaveric, surgical, or imaging data; and different patient populations.
Although the Buford complex is the easiest anatomic variation to differentiate
from a SLAP lesion, it is uncommon. Unfortunately, not only is the sublabral
recess the most difficult anatomic variation to differentiate from a SLAP
lesion, it is also the most frequently occurring. Indeed, some overlap of the
position of the sublabral recess and the sublabral foramen may exist,
depending on the type of attachment of the biceps tendon and the obliquity of
the glenoid bone. A sublabral recess and a sublabral foramen may coexist, and
when this configuration is present, the labral anatomic variation may extend
from the 11- to the 3-o'clock position. At times, this variation is impossible
to differentiate from a SLAP lesion by means of imaging methods. Furthermore,
a recent MRI study suggested that the inferiormost limit of the anterosuperior
labral variants may extend two sections below the midpoint of the glenoid
bone, which suggests that normal variants may extend below the 3-o'clock
position in a small number of people
[37].
SLAP Lesion Classification and Mechanisms of Injury
Classification
Snyder et al. [2] classified
SLAP lesions into four types on the basis of arthroscopic evaluation
(Table 1 and Fig.
5A,
5B,
5C,
5D). The type I lesion is
characterized by fraying but with no frank tear of the articulating surface of
the superior portion of the glenoid labrum and with an intact biceps tendon
(Fig. 6). The type II lesion
consists of superior labral fraying with stripping of the superior part of the
labrum and attached biceps tendon from the underlying glenoid cartilage
(Fig. 7). The type III lesion
is a bucket-handle tear of the superior portion of the labrum with the central
portion of the tear often displaced into the joint and the peripheral portion
firmly attached to the glenoid cartilage (Fig.
8A,
8B). The biceps tendon and
labral-biceps anchor extension were not involved. The type IV lesion consists
of a bucket-handle tear of the superior portion of the labrum similar to the
type III lesion, but with the tear extending into the biceps tendon
(Fig. 9). The reported
frequency of types I–IV SLAP lesions has varied in the literature (type
I, 9.5–21%; type II, 41–55%; type III, 6–33%; type IV,
3–15%). Type II SLAP lesions are by far the most frequent type
identified on arthroscopy, and a similar predominance is expected on MRI
[2,
13,
23].
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Fig. 5A. —Schematic representations of superior labral anteroposterior
(SLAP) lesions I–IV in sagittal plane. In these diagrams, for better
visualization, SLAP lesions II–IV are represented as displaced tears.
Arrow = superior labrum tear, A = acromion, Cl = clavicle, C = coracoid
process, S = supraspinatus myotendinous junction, I = infraspinatus
myotendinous junction, T = teres minor myotendinous junction, Sub =
subscapularis myotendinous junction, B = biceps tendon, SGHL = superior
glenohumeral ligament, MGHL = middle glenohumeral ligament, IGHLC = inferior
glenohumeral ligament complex. SLAP I lesion corresponds to fraying of
superior labrum (arrow).
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Fig. 5B. —Schematic representations of superior labral anteroposterior
(SLAP) lesions I–IV in sagittal plane. In these diagrams, for better
visualization, SLAP lesions II–IV are represented as displaced tears.
Arrow = superior labrum tear, A = acromion, Cl = clavicle, C = coracoid
process, S = supraspinatus myotendinous junction, I = infraspinatus
myotendinous junction, T = teres minor myotendinous junction, Sub =
subscapularis myotendinous junction, B = biceps tendon, SGHL = superior
glenohumeral ligament, MGHL = middle glenohumeral ligament, IGHLC = inferior
glenohumeral ligament complex. SLAP II lesion corresponds to stripping of
superior labrum and attached biceps tendon from glenoid (arrow).
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Fig. 5C. —Schematic representations of superior labral anteroposterior
(SLAP) lesions I–IV in sagittal plane. In these diagrams, for better
visualization, SLAP lesions II–IV are represented as displaced tears.
Arrow = superior labrum tear, A = acromion, Cl = clavicle, C = coracoid
process, S = supraspinatus myotendinous junction, I = infraspinatus
myotendinous junction, T = teres minor myotendinous junction, Sub =
subscapularis myotendinous junction, B = biceps tendon, SGHL = superior
glenohumeral ligament, MGHL = middle glenohumeral ligament, IGHLC = inferior
glenohumeral ligament complex. Lesions correspond to bucket-handle tear of
labrum (arrow) with intact biceps tendon (SLAP III, C) and
with tear extending into biceps tendon (SLAP IV, D).
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Fig. 5D. —Schematic representations of superior labral anteroposterior
(SLAP) lesions I–IV in sagittal plane. In these diagrams, for better
visualization, SLAP lesions II–IV are represented as displaced tears.
Arrow = superior labrum tear, A = acromion, Cl = clavicle, C = coracoid
process, S = supraspinatus myotendinous junction, I = infraspinatus
myotendinous junction, T = teres minor myotendinous junction, Sub =
subscapularis myotendinous junction, B = biceps tendon, SGHL = superior
glenohumeral ligament, MGHL = middle glenohumeral ligament, IGHLC = inferior
glenohumeral ligament complex. Lesions correspond to bucket-handle tear of
labrum (arrow) with intact biceps tendon (SLAP III, C) and
with tear extending into biceps tendon (SLAP IV, D).
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Fig. 6. —Type I superior labral anteroposterior lesion: proton
density–weighted fat-suppressed coronal image shows fraying of superior
labrum (arrow). Note full-thickness tear of supraspinatus tendon
(arrowhead). HH = humeral head, G = glenoid.
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Fig. 7. —Proton density–weighted fat-suppressed coronal image
(TR/TE, 3,000/20) shows type II superior labral anteroposterior lesion in
52-year-old man. Note globular area of increased signal intensity at base of
superior labrum compatible with labral tear (arrow). HH = humeral
head, G = glenoid.
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Fig. 8A. —Proton density–weighted coronal images (TR/TE,
2,500/15) of type III superior labrum anterior and posterior lesion. HH =
humeral head, G = glenoid. Abnormal signal intensity is visible between
superior labrum and glenoid cartilage (arrow) and between biceps
tendon and superior labrum (arrowhead).
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Fig. 8B. —Proton density–weighted coronal images (TR/TE,
2,500/15) of type III superior labrum anterior and posterior lesion. HH =
humeral head, G = glenoid. Note that labral abnormality extends posteriorly
and biceps insertion (arrow) appears preserved.
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Fig. 9. —Type IV superior labral anteroposterior (SLAP) lesion in
52-year-old man after fall from ladder with progressive shoulder pain and
weakness 1 month before MRI evaluation. Coronal proton density–weighted
fat-suppressed image (TR/TE, 3,000/13) shows enlargement and abnormal signal
intensity of biceps anchor (arrow) and adjacent superior labrum. SLAP
IV lesion and dislocated torn biceps tendon were identified at surgery. HH =
humeral head, G = glenoid.
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The first revised classification of SLAP lesions was reported by Maffet et
al. [15] in 1995
(Table 1 and Fig.
10A,
10B,
10C). Three new categories of
lesions were described as follows: type V, Bankart lesion with superior
extension to include the biceps tendon and superior labrum (Fig.
11A,
11B); type VI, anterior or
posterior flap tear in conjunction with separation of the biceps tendon
superiorly (Fig. 12A,
12B); and type VII, biceps
tendon–superior labrum separation extending anteriorly to include the
middle glenohumeral ligament (Fig.
13A,
13B).
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Fig. 10A. —Schematic representations of superior labral anteroposterior
lesions V–VII in sagittal plane. A = acromion, Cl = clavicle, C =
coracoid process, S = supraspinatus myotendinous junction, I = infraspinatus
myotendinous junction, T = teres minor myotendinous junction, Sub =
subscapularis myotendinous junction, B = biceps tendon, SGHL = superior
glenohumeral ligament, IGHL = inferior glenohumeral ligament complex, MGHL =
middle glenohumeral ligament. Type V lesion corresponds to Bankart lesion with
superior extension (arrows) to include biceps tendon and superior
labrum.
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Fig. 10B. —Schematic representations of superior labral anteroposterior
lesions V–VII in sagittal plane. A = acromion, Cl = clavicle, C =
coracoid process, S = supraspinatus myotendinous junction, I = infraspinatus
myotendinous junction, T = teres minor myotendinous junction, Sub =
subscapularis myotendinous junction, B = biceps tendon, SGHL = superior
glenohumeral ligament, IGHL = inferior glenohumeral ligament complex, MGHL =
middle glenohumeral ligament. Type VI lesion corresponds to anterior or
posterior flap tear (arrow) in conjunction with separation of biceps
tendon superiorly.
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Fig. 10C. —Schematic representations of superior labral anteroposterior
lesions V–VII in sagittal plane. A = acromion, Cl = clavicle, C =
coracoid process, S = supraspinatus myotendinous junction, I = infraspinatus
myotendinous junction, T = teres minor myotendinous junction, Sub =
subscapularis myotendinous junction, B = biceps tendon, SGHL = superior
glenohumeral ligament, IGHL = inferior glenohumeral ligament complex, MGHL =
middle glenohumeral ligament. Type VII lesion corresponds to biceps-labral
complex tear (arrow) with extension to MGHL (arrowhead).
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Fig. 11A. —MR arthrography in 31-year-old man with history of shoulder
dislocation shows type V superior labral anteroposterior lesion. HH = humeral
head, G = glenoid. Coronal T1-weighted fat-suppressed image (TR/TE, 500/13)
shows superior labral tear (curved arrow) and large Hill-Sachs lesion
(straight arrow).
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Fig. 11B. —MR arthrography in 31-year-old man with history of shoulder
dislocation shows type V superior labral anteroposterior lesion. HH = humeral
head, G = glenoid. Axial T1-weighted fat-suppressed image (500/13) shows
Bankart lesion (arrow). Sequential images in axial plane (not shown)
depicted extension of Bankart lesion to superior labrum.
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Fig. 12A. —Type VI superior labral anteroposterior lesion in 40-year-old
man with shoulder pain and superior labral tear. HH = humeral head, G =
glenoid. Fat-suppressed T1-weighted MR arthrograms were obtained before
(A) and after (B) arm traction. Note that morphology of abnormal
superior labrum is best shown with arm traction (B) and displays small
fragment of labrum partially attached to anchor (arrows). Pattern of
superior labral tear was believed to be complex and most likely represented
small flap tear.
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Fig. 12B. —Type VI superior labral anteroposterior lesion in 40-year-old
man with shoulder pain and superior labral tear. HH = humeral head, G =
glenoid. Fat-suppressed T1-weighted MR arthrograms were obtained before
(A) and after (B) arm traction. Note that morphology of abnormal
superior labrum is best shown with arm traction (B) and displays small
fragment of labrum partially attached to anchor (arrows). Pattern of
superior labral tear was believed to be complex and most likely represented
small flap tear.
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Fig. 13A. —66-year-old man with type VII superior labral anteroposterior
lesion showing extension to middle glenohumeral ligament. HH = humeral head, G
= glenoid. Coronal T2-weighted fat-suppressed image (TR/TE, 2,000/80) obtained
in oblique coronal plane shows superior labrum tear (arrow).
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Fig. 13B. —66-year-old man with type VII superior labral anteroposterior
lesion showing extension to middle glenohumeral ligament. HH = humeral head, G
= glenoid. Axial T2-weighted fat-suppressed image (2,600/63) shows thickening
of middle glenohumeral ligament (arrow) associated with high
signal.
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With the work of Morgan et al.
[21] in 1998, the first
variation related to the initial SLAP lesions described by Snyder et al.
[2] was introduced
(Table 1). Three distinct type
II SLAP lesions were described on the basis of anatomic location. A type IIA
abnormality represents an anterosuperior labral lesion, a type IIB abnormality
represents a posterosuperior lesion, and a type IIC abnormality represents a
superior lesion with both anterior and posterior components.
Between 1997 and 2000, three additional types of SLAP lesion (VIII, IX, X)
were introduced in informal talks, small meetings, and conferences (Fig.
14A,
14B,
14C and
Table 1). The type VIII lesion
is described as a superior labral tear with posterior extension that is
similar to Morgan's IIB lesion but more extensive (Resnick D, unpublished
data) (Fig. 15A,
15B). The type IX lesion was
described as a complete or almost complete detachment of the entire labrum
related to extensive anterior and posterior components of the superior labral
tear (Fig. 16A,
16B). The type X lesion was
described as a tear of the superior labrum with extension to the rotator cuff
interval (Beltran J, presented at the annual meeting of the Radiological
Society of North America, Chicago, IL, December 2000) (Fig.
17A,
17B).
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Fig. 14A. —Schematic representations of superior labral anteroposterior
(SLAP) lesions VIII–X in sagittal plane. A = acromion, C l =clavicle, C
= coracoid process, S = supraspinatus myotendinous junction, I = infraspinatus
myotendinous junction, T = teres minor myotendinous junction, Sub =
subscapularis myotendinous junction, B = biceps tendon, SGHL = superior
glenohumeral ligament, MGHL = middle glenohumeral ligament, IGHLC = inferior
glenohumeral ligament complex. Type VIII lesion corresponds to superior labral
lesion with posterior extension (arrow) that is similar to type IIA
lesion, although more extensive.
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Fig. 14B. —Schematic representations of superior labral anteroposterior
(SLAP) lesions VIII–X in sagittal plane. A = acromion, C l =clavicle, C
= coracoid process, S = supraspinatus myotendinous junction, I = infraspinatus
myotendinous junction, T = teres minor myotendinous junction, Sub =
subscapularis myotendinous junction, B = biceps tendon, SGHL = superior
glenohumeral ligament, MGHL = middle glenohumeral ligament, IGHLC = inferior
glenohumeral ligament complex. Type IX lesion corresponds to complete or
almost complete detachment of labrum involving extensive anterior and
posterior components (arrows).
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Fig. 14C. —Schematic representations of superior labral anteroposterior
(SLAP) lesions VIII–X in sagittal plane. A = acromion, C l =clavicle, C
= coracoid process, S = supraspinatus myotendinous junction, I = infraspinatus
myotendinous junction, T = teres minor myotendinous junction, Sub =
subscapularis myotendinous junction, B = biceps tendon, SGHL = superior
glenohumeral ligament, MGHL = middle glenohumeral ligament, IGHLC = inferior
glenohumeral ligament complex. Type X lesion corresponds to SLAP lesion with
extension of labral tear (arrow) to rotator interval or structures
that cross it.
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Fig. 15A. —Type VIII superior labral anteroposterior lesion in
31-year-old man with shoulder pain. HH = humeral head, G = glenoid. Coronal
T1-weighted fat-suppressed image (TR/TE, 400/12) shows superior labral tear
(arrow).
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Fig. 15B. —Type VIII superior labral anteroposterior lesion in
31-year-old man with shoulder pain. HH = humeral head, G = glenoid. Axial
T1-weighted fat-suppressed image (400/12) shows tear extending to posterior
labrum (arrowhead). Anterior labrum (arrow) is normal.
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Fig. 16A. —Type IX superior labral anteroposterior lesion in 34-year-old
man with history of shoulder trauma. HH = humeral head, G = glenoid. Coronal
proton density–weighted image (TR/TE, 2,600/15) reveals superior labral
tear (arrow).
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Fig. 16B. —Type IX superior labral anteroposterior lesion in 34-year-old
man with history of shoulder trauma. HH = humeral head, G = glenoid. Axial
gradient-echo image (450/15; flip angle, 30°) shows superior labral tear
that extends anteriorly (arrow) and posteriorly (arrowhead)
below 3- and 9-o'clock positions.
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Fig. 17A. —Type X superior labral anteroposterior lesion in man with
history of labral tear. HH = humeral head, G = glenoid. Coronal fat-suppressed
T1-weighted arthrogram of right shoulder shows superior labral tear
(arrow).
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Fig. 17B. —Type X superior labral anteroposterior lesion in man with
history of labral tear. HH = humeral head, G = glenoid. Axial fat-suppressed
T1-weighted arthrogram shows tear extending to area of rotator interval
(arrow).
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Although they are controversial, the introduction of different types of
SLAP lesions represents an attempt to emphasize associated abnormalities and
the variable extension of these lesions that may prove important for
treatment. Extension to some structures such as the anteroinferior labrum and
the middle glenohumeral ligament implies some sort of glenohumeral
instability, and the definition of the precise labrum abnormality may affect
presurgical decision making. For example, type I lesions are usually treated
with conservative maneuvers or simple surgical débridement, type II
lesions are usually treated with biceps anchor stabilization, types III and IV
are usually treated with excision of the bucket-handle tear and eventual
biceps tenodesis or labral repair, types V and VI are usually treated with
labral repair or débridement and biceps anchor stabilization, and type
VII is usually treated with biceps anchor stabilization and repair of the
middle glenohumeral ligament
[38]. From the imaging point
of view, however, the current SLAP lesion classification is extensive and not
easily applied to MRI. Presently, the literature does not support the position
that MRI can accurately differentiate all 10 SLAP lesion types. Furthermore,
no agreement has been reached as to whether extensive labral lesions such as
types VIII and IX should be classified as SLAP varieties or as extensive
labral abnormalities.
Mechanisms of Injury
Although several distinct mechanisms of injury have emerged, some
controversy exists as to which is the most common cause of a SLAP lesion
[2,
15]. One mechanism (the most
common in the Snyder et al. [2]
series) is a compression force applied to the shoulder, usually occurring as
the result of a fall onto an outstretched arm, with the shoulder positioned in
abduction and slight forward flexion at the time of impact
[2]. Marrow edema resulting
from the impact may be identified on MRI; if it is associated with an
anteroinferior dislocation, a Hill-Sachs deformity as well as a Bankart lesion
may be present. A second mechanism (the most common in the Maffet et al.
[15] series) is related to
traction on the arm as a result of either a sudden pull, throwing, or other
overhead sports-related motion
[15]. Once again, associated
findings that may be visualized on MRI are undersurface tears of the rotator
cuff, cystic lesions in the humeral head (posterosuperior internal
impingement), and capsular laxity. In several studies, however, correlation of
the mechanism of injury with the type of SLAP lesion has not been
provided.
It has been postulated that different mechanisms of injury result in
different types of SLAP lesions. Athletes who use repetitive overhead arm
motions are prone to develop a type I or type II lesion (fraying or detachment
of the labrum), whereas patients who present after a fall onto an outstretched
arm are more likely to have a type III, IV, or VI lesion (bucket-handle tear
or flap tear) [2,
15,
21,
30]. Type I lesions have also
been associated with labral degeneration in older persons. Types V and VII
lesions appear to be more frequent in patients with glenohumeral joint
instability resulting from an acute injury: a Bankart lesion is associated
with anteroinferior instability, and middle glenohumeral ligament tear is
associated with straight anterior dislocation.
MRI Techniques
Standard MRI
MRI has proved to be a sensitive, specific, and accurate modality for
evaluating the glenoid labrum. It has also proven to be valuable as a
noninvasive technique for evaluating patients with possible SLAP lesions. The
glenoid labrum is routinely evaluated in all three imaging planes. Although
the axial plane is usually emphasized as best for labral evaluation, several
authors have found the coronal plane most sensitive in the diagnosis of SLAP
lesions [12]. The superior
labrum is situated in a more curved area of the glenoid bone and therefore is
more subject to partial volume artifacts with the biceps tendon and adjacent
glenoid margin in the axial plane as opposed to the coronal plane. The
sagittal plane often displays part of the labrum superimposed on the adjacent
glenoid margin and is thought to be less useful for the diagnosis of SLAP
lesions. However, the sagittal plane is suitable for evaluating displaced
fragments (bucket-handle and flap tears) and the extension of lesions in terms
of time zones [12].
The diagnosis of SLAP tears is based on abnormalities in signal intensity
and morphology (Figs. 18 and
19). MRI findings reported to
be characteristic of SLAP lesions include increased signal in the labrum, with
or without extension to the biceps anchor, and cleavage of the superior labrum
[12]. This cleavage may also
communicate with a superior paraglenoid cyst.
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Fig. 18. —36-year-old man with shoulder pain and clinical findings
suggestive of impingement. Unstable superior labral anteroposterior II lesion
was surgically confirmed. Coronal proton density–weighted fat-suppressed
image (TR/TE, 2816/13) shows abnormal signal intensity at base of superior
labrum with Y-shaped appearance.
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Fig. 19. —Coronal proton density–weighted fat-suppressed image
(TR/TE, 3,000/30) obtained in 61-year-old man with superior labral
anteroposterior lesion surgically confirmed. Note abnormal morphology of
superior labrum. Sequential image (not shown) showed adjacent paraglenoid
cyst.
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Pitfalls in standard MRIs are related to the presence of transitional
zones, intralabral signal without surface irregularity or definite labral
tear, and partial volume with the glenohumeral ligaments. The transitional
zone is the area located between the fibrocartilage of the labrum and the
hyaline cartilage of the glenoid (Fig.
20). In standard images, higher signal intensity is present
between the labrum and glenoid cartilage in short-TE sequences, occurring in
the transition zone between two histologic structures. Areas of the
transitional zone do not fill with contrast material in arthrographic images
[12]. Intralabral signal is a
common finding and may be associated with magic angle phenomena or
intrasubstance labral degeneration. Partial volume averaging with the
glenohumeral ligaments is also a common finding, and careful evaluation of the
whole extension of structures usually allows differentiation of a normal
structure from a tear (Fig.
21A,
21B).
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Fig. 20. —MR arthrogram in 38-year-old man shows transitional zone.
Axial T2-weighted fat-suppressed image (TR/TE, 3,000/60) shows no fluid
between anterosuperior labrum and adjacent glenoid cartilage. Area of
intermediate signal intensity (arrow) represents transitional zone
between fibrocartilage of labrum and hyaline cartilage of glenoid. HH =
humeral head, G = glenoid.
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Fig. 21A. —MR arthrograms of right shoulder in man with shoulder pain
and superior labral anteroposterior (SLAP) lesion. HH = humeral head, G =
glenoid. Coronal T1-weighted fat-suppressed image (TR/TE, 600/15) shows
abnormal morphology at insertion site of biceps tendon (arrow). This
finding was initially interpreted as double Oreo cookie sign. Sequential
images (not shown) revealed partial volume with superior glenohumeral
ligament.
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Fig. 21B. —MR arthrograms of right shoulder in man with shoulder pain
and superior labral anteroposterior (SLAP) lesion. HH = humeral head, G =
glenoid. Coronal T1-weighted fat-suppressed image (600/15) obtained posterior
to level of A reveals labral tear (arrow) characterized as
SLAP II tear.
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MR Arthrography
The need for MR arthrography as a supplement to standard MRI has not been
established. Controversies are related to the cost, invasiveness, and marginal
improvement in the diagnostic accuracy of MR arthrography when compared with
standard MRI in the evaluation of SLAP lesions
(Table 2). Contrast material in
the joint often leads to a more optimal visualization of a variety of
intraarticular structures and increases the confidence level for the diagnosis
of SLAP lesions [30].
MR arthrographic findings of SLAP tears are associated with the insinuation
of the contrast material into the labral tear. Fluid interposed between the
glenoid cartilage and the superior labrum in the coronal plane (two bands of
low signal intensity surrounding a band of high signal intensity) has the
appearance of a single Oreo cookie (Fig.
22A,
22B). This configuration is
observed with either a sublabral recess or a type II SLAP lesion. An
interesting analogy was made regarding the appearance of a sublabral recess in
conjunction with a SLAP III lesion, which was designated the double
"Oreo cookie" configuration (Fig.
22A,
22B).
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Fig. 22A. —Schematic representations in coronal plane of single and
double "Oreo cookie" configurations. Single Oreo cookie
configuration is characterized by fluid between labrum and glenoid cartilage.
This finding could be observed with either sublabral recess (arrow)
or type II superior labral anteroposterior lesion.
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Fig. 22B. —Schematic representations in coronal plane of single and
double "Oreo cookie" configurations. Double Oreo cookie
configuration is characterized by fluid between labrum and glenoid cartilage
and between two pieces of labrum. Arrow indicates sublabral recess and
arrowhead indicates labral tear.
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In 1997, Beltran et al.
[18], in a review of MR
arthrography of the shoulder, indicated that the sublabral recess is oriented
medially, whereas labral tears in this location are oriented laterally in
coronal oblique images. These criteria are based on the anatomic observation
that the normal contour of the glenoid cartilage follows the contour of the
underlying bone [17]. The
normal recess is located between the biceps tendon attachment and the glenoid
cartilage, and it has a parallel orientation to the glenoid cartilage, best
shown in the coronal and axial planes. SLAP lesions usually extend posteriorly
to the biceps anchor in the coronal plane and have a parallel or more oblique
orientation with an anterior opening, best shown in the coronal and axial
planes, respectively (Fig.
23A,
23B). Although not an absolute
criterion, this observation helps to differentiate these conditions.
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Fig. 23A. —42-year-old man with posterior extension of superior labral
anteroposterior tear on MR arthrograms. HH = humeral head, G = glenoid. Axial
T1-weighted fat-suppressed image (TR/TE, 600/13) shows irregular margin of
superior labral tear (arrow), oriented parallel to glenoid
surface.
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Fig. 23B. —42-year-old man with posterior extension of superior labral
anteroposterior tear on MR arthrograms. HH = humeral head, G = glenoid.
Oblique coronal T1-weighted fat-suppressed image (600/13) shows tear extending
posteriorly to biceps tendon origin (arrowhead).
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Practical MRI Approach to the Diagnosis
We propose an MRI approach for evaluating suspected SLAP lesions based on
specific abnormalities of the biceps-labral complex, presence or absence of
extension of the lesion, and presence or absence of abnormalities of a number
of additional structures (ligaments, adjacent cartilage, and tendons)
(Fig. 24).
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Fig. 24. —Diagram shows MRI algorithm for superior labral
anteroposterior (SLAP) lesions based on specific abnormalities of
biceps-labral complex, presence or absence of extension of tear, and presence
or absence of abnormalities of additional structures.
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The first step of this approach is related to the evaluation of the
characteristics of the biceps-labral complex. Snyder's
[2] classification is used as
the basis for this description because of its simplicity and its widespread
use in the literature. The labral tear is further characterized as
nondisplaced or displaced. The criteria used are similar to those used for the
description of torn menisci in the knee. A nondisplaced tear shows on short-TE
sequences as a region of intermediate to high signal intensity that extends to
the articular surface of the labrum. In arthrograms, the gadolinium is
expected to extend through this defect. A displaced tear is one that has a
bucket-handle or flap component (Fig.
24). A displaced tear can also be characterized as a free fragment
that has lost its connection with the parent labrum.
The second step describes the extension of the superior labral lesion to
other areas of the labrum. To be considered an extended lesion, the labral
abnormality must be in anatomic continuation with the lesion that involves the
biceps-labral complex. This step includes the current types V, VIII, and IX
SLAP lesions, as well as the three subdivisions of SLAP II lesions.
The third step is related to the description of the associated
abnormalities of the glenohumeral ligaments, joint capsule, articular
cartilage, and tendons. Examples are extension of the lesion through the
middle glenohumeral ligament (type VII SLAP lesion); superior glenohumeral
ligament, coracohumeral ligament, rotator interval capsule (type X SLAP
lesion); and inferior glenohumeral ligament (not described in the current SLAP
lesion classifications). Abnormality of the adjacent cartilage such as a
chondral flap, chondral defect, or chondral irregularity should also be
considered. Associated abnormalities of the cuff tendons include undersurface
tears of the supraspinatus and infraspinatus tendons attributed to
posterosuperior and anterosuperior internal impingement and tears of the
superior part of the subscapularis tendon and the most anterior part of the
supraspinatus tendon that are associated with rotator interval lesions.
Conclusion
In summary, we suggest a tailored approach to MRI diagnosis of SLAP tears
based on analysis of the biceps-labral complex, the extension of tears, and
the associated lesions in other structures. MRI analysis in multiple planes
and close attention to clinical history and mechanisms of injury are strongly
recommended. When appropriate, radiologists should describe the lesion as
indeterminate for sublabral recess versus SLAP lesion and suggest clinical
correlation or MR arthrography for better delineation of the labral
abnormality. In tailored examinations, stress maneuvers such as arm traction
[39] or additional planes such
as the one parallel to the biceps tendon
[40] may be implemented.
Radiologists should perform a dedicated approach to these lesions with the
description of the biceps-labral complex abnormality; extension of lesions in
terms of time zones; and associated lesions in ligaments, adjacent cartilage,
and tendons.
References
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- Cartland JP, Crues JV III, Stauffer A, et al. MR imaging in the
evaluation of SLAP injuries of the shoulder: findings in 10 patients.
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Introduction
Normal Anatomy
