DOI:10.2214/AJR.07.3962
AJR 2008; 191:1024-1030
© American Roentgen Ray Society
Usefulness of the Abduction and External Rotation Views in Shoulder MR Arthrography
Asgar M. Saleem1,
Joong K. Lee and
Leon M. Novak
1 All authors: Department of Radiology, Albany Medical Center, 43 New Scotland
Ave., Albany, NY 12208.
Received March 8, 2008;
accepted after revision April 19, 2008.
Address correspondence to A. M. Saleem
(saleea{at}hotmail.com).
Abstract
OBJECTIVE. The purpose of this article is to illustrate the
usefulness of the abduction and external rotation position in MR arthrography
of the shoulder.
CONCLUSION. The use of abduction and external rotation in shoulder
MR arthrography can be a helpful tool that complements sequences that use
conventional positions for characterizing a variety of abnormal conditions in
the shoulder.
Keywords: abduction view • external rotation view • MR arthrography • shoulder
Introduction
MR arthrography of the shoulder plays an important role in providing
additional information that is not found on standard MRI
[1]. Shoulder MR arthrography
has typically included a series of sequences with the arm positioned by the
patient's side. An additional sequence performed with the arm in abduction and
external rotation (ABER) has been shown to be useful in clarifying equivocal
findings or making diagnoses not detected on conventional positions in
shoulder MR arthrography [2,
3]. In this article, we review
the technique and normal anatomy of the ABER view and provide examples of
several abnormalities for which the ABER view is helpful in diagnosing.
Technique and Normal Anatomy
After conventional MR sequences are performed, the patient is repositioned
in ABER with the hand placed behind the head or neck and the elbow flexed
(Fig. 1A). With the
intraarticular administration of 1% lidocaine during direct arthrography to
improve patient comfort, and through proper patient education and preparation,
the ABER position is possible in most patients. In a review of 415 shoulder
arthrograms performed at our institution between January 2006 and December
2006, 95% of our patients were able to achieve the ABER position. In our
experience, the total additional time for ABER positioning and scanning is
only 5 minutes.
A coronal localizer sequence is acquired, with sections taken along the
axis of the humeral shaft (Fig.
1B). Transverse oblique T1-weighted images are then obtained (TR
range/TE range, 500–800/9–20; field of view, 12–15 cm;
section thickness, 3 mm; intersection gap, 0–0.5 mm; matrix,
256–192), ideally 45° off the vertical axis of the glenoid (Fig.
2A,
2B,
2C,
2D).
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Fig. 1B —Abduction and external rotation (ABER) view of the shoulder.
Imaging planes taken from coronal localizer sequence for ABER position. Planes
should be drawn in line with long axis of humeral shaft.
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Fig. 2A —Imaging planes for abduction and external rotation (ABER)
view of the shoulder. Diagram of oblique planes of ABER position. Sections are
ideally 45° off vertical axis of glenoid, which allows optimal
visualization of anteroinferior labroligamentous complex. This complex is
prone to effects of obliquity and volume averaging on conventional axial and
coronal sequences. Corresponding T1-weighted images are shown in
B–D.
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Fig. 2B —Imaging planes for abduction and external rotation (ABER)
view of the shoulder. 23-year-old man with normal anatomy. These images
correspond to planes shown in A and show locations of humeral head (H),
glenoid (G), acromion (A), supraspinatus (SS), subscapularis (SC), biceps
tendon (arrow, B), bicipital anchor (B), inferior glenohumeral
ligament (arrow, C), anteroinferior labrum
(arrowhead, C), and infraspinatus (IS).
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Fig. 2C —Imaging planes for abduction and external rotation (ABER)
view of the shoulder. 23-year-old man with normal anatomy. These images
correspond to planes shown in A and show locations of humeral head (H),
glenoid (G), acromion (A), supraspinatus (SS), subscapularis (SC), biceps
tendon (arrow, B), bicipital anchor (B), inferior glenohumeral
ligament (arrow, C), anteroinferior labrum
(arrowhead, C), and infraspinatus (IS).
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Fig. 2D —Imaging planes for abduction and external rotation (ABER)
view of the shoulder. 23-year-old man with normal anatomy. These images
correspond to planes shown in A and show locations of humeral head (H),
glenoid (G), acromion (A), supraspinatus (SS), subscapularis (SC), biceps
tendon (arrow, B), bicipital anchor (B), inferior glenohumeral
ligament (arrow, C), anteroinferior labrum
(arrowhead, C), and infraspinatus (IS).
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Rotator Cuff
The ABER position kinks the rotator cuff tendon, reducing the effacement of
its articular surface on the humeral head and improving its visualization.
This reduced tension allows intraarticular contrast material to more easily
flow into any defect, increasing the sensitivity of detecting
partial-thickness tears, which may be missed on conventional sequences (Fig.
3A,
3B). The ABER view also helps
in grading the severity of partial tears by allowing measurement of the
horizontal component of the tear and detecting the presence of delamination
[4] (Fig.
4A,
4B). Familiarity with the
effects of the decreased tension on the rotator cuff in the ABER position is
also important because several variable appearances may be mistaken for
rotator cuff abnormalities (Fig.
5A,
5B).
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Fig. 5A —Variable appearances may be mistaken for rotator cuff
abnormality. 58-year-old man with normal variant of beaklike projection off
articular surface of rotator cuff tendon (arrow). Cause is unknown
but may be tendon folding.
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Fig. 5B —Variable appearances may be mistaken for rotator cuff
abnormality. 59-year-old woman with pseudotear. Intraarticular contrast
between folds can mimic a tear (arrow), typically near level of
scapular spine (asterisk). Awareness of this variant avoids
false-positive diagnoses.
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Anteroinferior Labroligamentous Complex
The ABER position puts tension on the inferior glenohumeral ligament, which
allows improved sensitivity in detecting abnormalities of the joint capsule
and the anteroinferior labroligamentous complex
[5] (Fig.
6A,
6B).
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Fig. 6B —33-year-old man with partially detached tear of
anteroinferior labrum. T1-weighted image with arm in abduction and external
rotation shows partially detached tear of anteroinferior labrum
(arrowhead) and normal intact periosteum (arrow). Note
paralabral cyst in spinoglenoid notch (asterisk).
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The ABER view also helps in evaluating Bankart tears and their variants
(Fig. 7A,
7B,
7C). In the Perthes lesion,
the labral complex is detached from the glenoid, but the stripped peri osteum
remains intact. The labral complex can often be in a normal position on
conventional sequences. The ABER position can separate the base of the labrum
and therefore help visualize Perthes lesions
[6] (Fig.
8A,
8B). Conversely, some Perthes
lesions can in fact be realigned with the glenoid on ABER positioning after
displacement is shown on conventional sequences
[7]. Preoperative detection is
important because Perthes lesions may appear similar to normal labrum without
probing at arthroscopy, and their presence may alter surgical planning.
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Fig. 7A —Bankart tears and variants. 58-year-old man with osseous
Bankart lesion. T1-weighted image with arm in abduction and external rotation
(ABER) shows tear and displacement of anteroinferior labrum (white
arrow) and bone loss of anterior glenoid (black arrow).
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Fig. 7B —Bankart tears and variants. 25-year-old man with anterior
labroligamentous periosteal sleeve avulsion lesion. T1-weighted ABER image
shows avulsed and inferomedially displaced anteroinferior labrum
(arrow).
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Fig. 7C —Bankart tears and variants. 22-year-old man with glenolabral
articular cartilage disruption lesion. T1-weighted ABER image shows
anteroinferior labral tear with contiguous chondral defect (white
arrow) in contrast to normal posterior articular cartilage (black
arrow)
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Fig. 8B —17-year-old boy with Perthes lesion. T1-weighted image with
arm in abduction and external rotation. With tension on inferior glenohumeral
ligament, anteroinferior labroligamentous complex becomes displaced
(arrowhead), and intact periosteum, stripped from glenoid, is now
visible (arrow).
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The ABER view is also useful in postoperative patients, especially when
artifacts or irregularities on conventional sequences make it difficult to
determine whether a recurrent labral tear is present
[8]
(Fig. 9).
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Fig. 9 —30-year-old man with recurrent pain after repair of Bankart
lesion. T1-weighted image with arm in abduction and external rotation shows
intact scar complex without recurrent detached tear. Conventional sequences
had shown equivocal irregularity of anteroinferior labrum. Note tear of
posterosuperior labrum (arrow).
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Microinstability
Microinstability patterns in the shoulder result from abnormal translation
of the humeral head. In these patterns, the humeral head does not dislocate
but rather shifts abnormally, resulting in a spectrum of lesions that affect
the superior half of the shoulder, including the rotator cuff interval, biceps
pulley, the bicipital–labral complex, and the rotator cuff.
The most common lesions seen in microinstability patterns are the superior
labral anteroposterior (SLAP) tears and their variants. The ABER position can
effectively visualize the proximal long-head biceps tendon and
bicipital–labral anchor and aid in evaluating SLAP tears and
abnormalities of the bicipital–labral complex
(Fig. 10).
The improved detection of partial rotator cuff tears in the ABER position
allows better characterization of other microinstability lesions such as the
superior labrum anterior cuff (SLAC) lesion. In the superior labrum anterior
cuff lesion, a tear of the anterosuperior labrum with additional involvement
of the rotator interval results in anterosuperior instability. This
instability results in abnormal contact between the rotator cuff and the
glenoid, causing partial tears of the articular surface of the anterior
supraspinatus. It is therefore important to identify surface tears of the
rotator cuff in the presence of a superior labral tear because doing so may
alert the clinician to more complex microinstability patterns that may not
have otherwise been suspected.
Microinstability lesions also include laxity or tears of the superior
glenohumeral and middle glenohumeral ligaments. The ABER position complements
conventional sequences by enabling further assessment of the middle
glenohumeral ligament, which may be lax and difficult to fully evaluate on
conventional sequences (Fig.
11).
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Fig. 11 —28-year-old man with superior labral tear involving bicipital
anchor (white arrow). Biceps tendon is diffusely thickened
(asterisk); longitudinal split tear was seen on other views. Middle
glenohumeral ligament (black arrow) is not involved.
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The Throwing Athlete
The posterior "peel-back" SLAP tear is another microinstability
lesion that is unique to high-level throwing athletes with glenohumeral
internal rotation deficit and contracture of the posterior joint capsule.
These patients develop an abnormal posterosuperior shift of the glenohumeral
contact point in abduction and external rotation during the late cocking phase
of throwing [9]. The abnormal
forces generated cause a peeling back and torsion of the bicipital anchor,
transmitting increased force to the posterior bicipital–labral complex
and posterosuperior labrum, resulting in a posterior SLAP-2 tear
(Fig. 12).
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Fig. 12 —Diagram of torsion of bicipital anchor in abduction and
external rotation (arrow), transmitting abnormal forces on
posterosuperior labrum, which causes posterior "peel-back"
superior labral anteroposterior tear.
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The ABER view recreates this decentering of the humeral head that occurs in
the cocking phase in these patients. When SLAP tears are discovered in a
high-level throwing athlete, the finding of posterosuperior shift of the
glenohumeral contact point on the ABER view can help suggest the diagnosis of
the peel-back lesion secondary to altered biomechanics
(Fig. 13).
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Fig. 13 —Diagram of effect of glenohumeral internal rotation deficit
and posterior capsular contracture during cocking phase of throwing, which is
reproduced in abduction and external rotation (ABER) position. Glenohumeral
contact point is normal in neutral position but migrates posterosuperiorly in
ABER position. Observing this shift of contact point (red
arrows) on ABER view can help suggest posterior
"peel-back" superior labral anteroposterior tear. White arrow
indicates normal contact point. SGHL = superior glenohumeral ligament, MGHL =
middle glenohumeral ligament, AIGHL = anterior band of inferior glenohumeral
ligament, PIGHL = posterior band of inferior glenohumeral ligament, which is
contracted.
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Although it is a separate entity, internal impingement is now hypothesized
to be due to the same altered biomechanics secondary to glenohumeral internal
rotation deficit and posterior capsular contracture. Contact between the
rotator cuff and the posterosuperior glenoid alone has been shown to be a
normal physiologic finding in asymptomatic individuals in abduction and
external rotation [10,
11]. However, when this
contact is seen with cystic changes in the humeral head and corresponding
"kissing" tears in the articular surface of the rotator cuff and
posterosuperior labrum on the ABER view, the diagnosis of internal impingement
can be suggested [12]
(Fig. 14).
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Fig. 14 —41-year-old woman with internal impingement. T1-weighted
image with arm in abduction and external rotation shows corresponding tears of
posterosuperior labrum (arrowhead) and articular surface of
supraspinatus tendon (arrow), as well as contact between rotator cuff
and labrum. Contact alone without additional lesions can be a normal
physiologic finding.
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Miscellaneous Conditions
In providing a different view and orientation of the shoulder, the ABER
view can help in detecting or further characterizing paralabral cysts,
chondral lesions, and loose bodies (Fig.
15).
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Fig. 15 —50-year-old man with chondral defect of humeral head.
T1-weighted image with arm in abduction and external rotation shows focal
defect of articular cartilage on humeral head (arrow) that was not
seen on conventional sequences.
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Conclusion
With proper patient education and optimal technique, the ABER view can be
done efficiently and effectively in all routine MR arthrograms of the
shoulder. When performed correctly, it serves as a useful tool in the
evaluation of many shoulder abnormalities.
Acknowledgments
We thank Michael Ciarmiello for his help in preparing illustrations for
this article.
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Abstract
Introduction
