Robert Georges
A. Ganneau, MD a Donald L. Renfrew, Y. El-Khoury, MD a James V. Nepola,
Glenoid
Labrum:
MD MD
M
Shoulder,
Shoulder, injuries,
studies,
414.1214
Radiology
1991;
dislocation,
414.436
a
Shoulder,
414.42
a
MR
resonance (MR) imaghas been proposed as a possible replacement for computed amthrotomogmaphy of the shoulder in the evaluation of the glenoid labmum (1-3). The purpose of our investigation was to determine how well abnommalities of the glenoid labmum can be evaluated with MR imaging.
SUBJECTS
AND
Nine patients
asymptomatic with shoulder
studied
with
MR
of
Radiology
(RAG., D.L.R., T.E.M., G.Y.E.K.), Orthopedic Surgery (J.V.N.), and Preventive Medicine (J.H.L.), College of Medicine, University of Iowa, Iowa City, IA 52242. From the 1990 27, sion ary C
scientific 1990; revision
assembly. requested
received January 29. Address reprint RSNA, 1991
22,
con-
institution
approved
the
study.
Imaging
was performed with a 1 .5-T superconducting magnet (Signa; GE Medical tems, Milwaukee), and we obtained ton-density
and
T2-weighted
axial
gap in a ma-
trix, and two signal averages were Three patients also underwent Tiweighted coronal oblique imaging.
The average men, 20-47
Syspro3-mm
sections with a 1-mm intersection all subjects. A 24-cm field of view, shoulder coil, a 192 X 256 acquisition
Received December 1991; requests
November 19; revi-
accepted Januto G.Y.E.K.
then brum
Imaging’
coached on MR
(five
was 29 years (range, of the volunteers com-
of these normal. The
in all
individuals
cases.
were
The
assumed
labra
to be
of the shown
la-
the junction of the fibrous labrum underlying cartilage. The anterior was considered blunt if it did not sharp
anterior
nor
margin
it was
case, out
margin,
was considered
the interpreting
ence,
location,
the
blunt
misshapen.
sheet,
have
whereas
significantly
a data
and the labrum
only For
and
filled
included
grade
the
of the
if
each
radiologists
which
a
poste-
pres-
labral
tear. The interpreters graded tears by means of Rowe and Zarin’s system (4): grade I = labrum separated from articular surface, grade II absent labrum, and grade III = absent labrum and deformity of the bony glenoid. Six months later, the same two interpreters
evaluated
the
aware of the overall al, they were blinded dividual
MR
images
for a second time using criteria. Even though
of
the
the same they were
results of the first tnto their previous in-
conclusions.
RESULTS The interpreters’ case-specific mesults, along with the standard of refemence, are shown in Table 1 The observer-specific MR imaging findings and the surgical findings are shown in Table 2. At the initial intempretation of the symptomatic patients, observer A achieved a sensitivity of 44.4% (exact 95% confidence interval [CI] = 13.7%, 78.8%) and a specificity of 66.7% (exact 95% CI 22.8%, 95.7%). Observer B had a sensitivity of 77.8% (exact 95% CI 40.0%, 97.2%) and a specificity of 66.7% (exact 95% CI = 22.8%, 95.7%). The specificities of the observers for the .
average
age
of the
consistent shoulder
with joint
patients
was
of arthroscopy Anthroscopy
28
by
subspecialist
with were
extensive available
by in all pawere per-
orthopedic experience. during
sunThe surgery.
and surgical findings standard of reference of glenoid abnormalities.
Two musculoskeletal interpreted
loskeletal
instability.
visualized
or surgery and surgery
formed
Anthroscopic sented the evaluation
shoulder
was
geons images
had
were
nal intensity within the labnum greater than that which is normally present at
plained of shoulder pain on had a history of shoulder problems. We imaged the arms
in interpretation images. They
examples of normal (Fig 1) and abnormal (Fig 2) labra. They then interpreted the MR images of the patients and volunteers without knowledge of the standard of reference. Decision criteria for evaluation of the labrum included a blunt margin of the labrum, absence of the labrum, or sig-
patients decision
used.
age of the volunteers
four women) years). None
means tients.
RSNA
Informed
years (range, 14-56 years). There were 11 male and five female subjects. All patients had a history of shoulder subluxation, and findings at a physical examination
179:519-522
Departments
imaging.
and 15 were
sent was obtained from all subjects foblowing explanation of the examination and the risks and benefits of the procedune. The Human Use Committee at our
The
the
METHODS volunteers instability
a
MR
ing
were
From
with
AGNETIC
nondominant terms:
E. Moore, FRACR H. Lemke, PhD
#{149} Jon
Evaluation
Fifteen patients with shoulder instability and nine asymptomatic volunteers were studied with magnetic resonance (MR) imaging. The shoulder joint was visualized by means of anthroscopy or surgery in all patients. Ten patients had abnonmalities of the glenoid labrum. Two musculoskeletal radiologists interpreted the MR images of the patients and volunteers without knowledge of the clinical history or surgical results. The surgical and anthroscopic results were used as the standard of reference in symptomatic patients. Observer A achieved a sensitivity of 44.4% and a specificity of 66.7%; observer B had a sensitivity of 77.8% and a specificity of 66.7%. In addition to the poor sensitivities and specificities, there was substantial intraand interobsenver variability. Assuming that the shoulders of the asymptomatic volunteers were normal, the specificities were 100.0% and 88.9% for observers A and B, respectively. In this small study, axial MR imaging was relatively insensitive and nonspecific in the evaluation of labral lesions. Further study will be necessary to determine the utility and limits of MR imaging in this regard. Index
#{149} Timothy
MR system
for
in
radiologists images at least
of the 2 years
MR
reprethe
who muscuwere
Abbreviation:
Cl
=
confidence
interval.
519
asymptomatic volunteers cannot be pooled with their specificities for the symptomatic patients. The specificities for the asymptomatic volunteers were 100% (exact 95% CI 66.4%, 100%) and 88.9% (exact 95% CI 51.8%, 99.7%) for observers A and B, respectively.
There was substantial interand intraobserver variability. At initial readings of the images of the symptomatic patients, the observers concummed on the true-positive findings in three of the nine subjects (33.3%) and on the true-negative findings in two of six subjects (33.3%). This result brings into question the interobserver variability. At the second evaluation, observer A concurred with himself in five of the nine patients (55.6%) with true-positive findings (three true-positive and two falsenegative findings) and in two of six patients (33.3%) with true-negative findings (two with false-positive findings). Observer B concurred with himself in seven of the nine patients (77.8%) with true-positive findings (six true-positive and one false-negative finding) and in four of six patients (66.6%) with true-negative findings (two true-negative and two false-positive findings). While the ability to correctly identify the presence of a tear was poor, grading of teams was even worse. Observer A correctly graded two of four tears (two of nine lesions) and observer B correctly graded four of seven (four of nine lesions). Figure 3 is an image of a grade I tear that neither observer correctly interpreted. Figure 4 is an image of a labrum that was incorrectly interpreted as a tear by observer B and correctly interpreted as normal by observer A.
Figure 1. MR image of normal shoulder of an asymptomatic volunteer. The anterior Iabrum (arrowhead) is pointed. There is signal intensity at the junction of the fibrous labrum and the anticulan cartilage of the glenoid, which is a normal finding. The postenor labrum (arrow) is rounded.
Figure 2. MR image of an abnormal shoulden. Surgical examination demonstrated an anterior labral tear. A segment of anterior labrum (large arrow) is separated from the remainder of the labrum by an area of intermediate signal intensity (small arrow).
Figure 3. MR image of a surgically proved grade I anterior labral tear. There is signal intensity within the anterior labrum (annow), but both observers decided that this signal intensity was within normal limits and read the study as negative.
Figure 4. MR image of a surgically proved normal anterior labrum. Observer A interpreted the signal intensity within the antenor labrum (arrow) as indicating a tear, while observer B interpreted the labrum as being normal.
specificity
cannot
performance
DISCUSSION In 1923
Bankant besion”-that is, the single abnormality responsible for recurrent subluxation and dislocation of the shoulder-is a lesion of the glenoid labrum. Subsequent investigators have proposed the anterior capsule (7,8), the subscapulanis muscle (9), or the anterior glenohumeral ligaments (10) as the essential structure of glenohumenal (5,6)
and
proposed
joint
that
stability.
denies labrum
again
Kohn
the importance in shoulder
symptoms.
Current
ion
consensus
varies;
cate that sponsible 520
a
in 1938,
the
“essential
(11)
orthopedic appears
there is no one for glenohumeral
Radiology
specifically
of the gienoid stability and opinto
mdi-
structure nestability.
Labral tears continue to be considered a source of pain by many orthopedic surgeons (12-14). Even if an isolated labral team is considered insignificant, labral tears are, in fact, seldom isolated. The presence of a labral lesion often indicates an underlying anterior capsule disruption. Double-contrast arthrography (15,16), arthrotomography (17-22), computed anthrotomography (20,2333), MR imaging (1-3), and MR anthrognaphy (34) have all been used to evaluate the glenoid labrum. Kieft et al (2) reported a sensitivity and specificity
of
100%
in
the
MR
evaluation of the glenoid Seeger et ab (1) reported of
100%;
erence
they
had
for negative
no
imaging
standard
have
of
at
tenpreting the
the
patients
so
we
investigators (c)
MR
differences
obogy
Other our
of
our
ex-
in in-
alone,
had
patients
to
interpret);
images
research
our
Ia-
possible
(b) variation
chance
in
in
glenoid
radiologists observers
images;
between
that
three
have
“easier”
achieved
of the
(by
in other
with and
method-
investigation
and
others. cannot
dismiss
However,
penienced nef-
than
in
numbers
groups.
least
(a)
better
MR
labrum
MR evaluation
were
The of
the
results
planations:
ity.
of
other
poor
brum
calculated.
glenoid
short by
The
We
labrum. a sensitivity
the
fell
achieved
imaging
examinations,
of
hands
the
be
characteristics
and
were
tab
radiologists,
the
our in
MR
observers image
subspecialist and
first
possibil-
were
ex-
interpretation
muscuboskeletheir
performance
May
1991
Table 1 Subject-Specific
Evaluations
of Labral
Tears
Observer
Standard of Reference
Patient
in Symptomatic
Observer
2nd Evaluation
1st Evaluation
+,II
TP
TP5
TPt
TP5
+,1I
TP
FN
TP
TP
3 4
+,II +,II
FN FN
TP TP
TP* TP*
TP TP
5
+,I
TP*
TP
TP
TP5
6
+,I
T
TP*
FN
TI’5
7
+,I
FN
TP5
TP
TP
8 9
+,I +,I
FN FN
FN FN
TI’ FN
FN FN
-
TN
FP
TN
TN
-
TN
FP
TN
TN
TN TN FP FP
FP FP FP FP
FP FP TN TN
FP Fl’ FP FP
-
= positive at surgery or arthroscopy for labral tear, tear or presumed normal. I grade I labral tear (labrum grade II labral tear (absent labrum). TP true-positive findings, false-positive findings, TN true-negative findings. a The observer also made a correct determination of grade.
Table Initial
2 MR Imaging
Findin
gs for All
Negativet
Volunteers
Subjects Finding
Patients
at MR Imaging Observer Positive
Positive5 A
Negative
Observer
4
2
0
5
4
9
7 2
2 4
1 8
B
Positive Negative
Positive Negative
at surgery at surgery
for labral tear. for labral tear.
did not improve with experience or time (indeed, their performance deteriorated at the second reading). may well be that others are more skilled at interpretation of MR images of the glenoid and are able to obtain better results. An important issue,
cate
however,
the
ogists
is whether
technique (or
even
for general all
It
to advo-
radiol-
muscuboskeletal
ra-
diobogists), and our results indicate that at least some subspecialists will have significant difficulties with interpretation of MR images of the labrum. It is of note that by obtaining MR images of the babrum before administration tmast material,
of intracapsular conFlannigan et al (34)
achieved a sensitivity much more comparable
33%, our mesults than those of Kieft et al (2) and Seeger et al (1). It is also of note that our interpreters could differentiate images from patients from those of asymptomatic volunteers quite well, an
observation
Volume
2nd
Evaluation
1
Note.-+ for labral
a
1st Evaluation
B
2
10 ii 12 13 14 15
t
Patients
A
179
that
a
Number
of only with
suggests
2
some
-
negative
at surgery
or arthroscopy
separated from articular surface), FN false-negative findings,
II FP
-
skill in the interpretation of images. Simply because a test may help distinguish healthy volunteers from patients, however, does not mean that the test will help distinguish patients with a particular disease from patients without a particular disease (35). Small sample sizes result in large CIs, and whereas the sensitivity on initial reading of observer A, for example, was 44.4%, the 95% CI was 13.7%, 78.8%. It may be that the labra of our patients were, by chance alone, more difficult to evaluate with use of MR imaging, and that MR imaging is a better test than is suggested by our results. It is also possible that other investigators have results similar to ours, but have not published their data because of the tendency to submit positive results. This would lead to a bias in the literature, with publication of those studies that, by chance alone, showed MR imaging of the glenoid to be efficacious. There are important differences in research methodology between our study and those of Kieft et ab (2) and Seeger et al (1). Kieft et al used a lowem field strength magnet (0.5 T vs 1.5 T) and thicker sections (5 mm vs 3 mm), but our studies were comparable with respect to imaging sequences, number of signal acquisitions, and matrix size. The images from the studies of Kieft et al and Seeger et al were interpreted by two radiologists in conference; our interpretems performed independently. Since (at least at the initial interpretation) one of our readers consistent-
ly undercabbed lesions while the othen consistently ovemcalied them, confemence interpretation may have improved our results. On only one case were both interpreters incorrect: both reported the images of one patient as negative (Fig 3), and at sumgery the patient was found to have a labmal tear. Assuming that the correct interpreter would have been able to convince the incorrect interpreter to change his mind (which may not have been the case), conference reading would have significantly improved sensitivity and specificity. In practice, most radiology intempretations are performed by a single radiobogist rather than by a team. Seeger et al (1) also report much better results of evaluation of the glenoid labrum with MR imaging. Their technique was very similar to ours with respect to section thickness and imaging plane; they used a lower field strength magnet (0.3 T vs 1.5 T) and a somewhat smaller field of view (17-19.2 cm vs 24 cm). However, the MR examination was used to determine whether the patients needed surgery; all 27 patients who underwent surgery in this retrospective study had positive MR imaging examinations. Limiting results to those with positive tests could significantly adversely affect the calculated sensitivity and specificity. Kieft et al (2) and Zlatkin et al (36) have observed that MR imaging cannot demonstrate the capsule insertion site in the absence of an effusion or arthmogram. Although we agree with Kieft et al that capsular stripping (or normal variation with the anterior
capsule
insertion
at
a point
other than on the labmum) will not require an arthrotomy in the absence of labmal abnormality, the converse is not true. Thus, if a patient has an abnormal labrum and a tight anterior capsule that inserts at the labrum, amthroscopic surgery is an option, whereas insertion of the capsule on the neck of the scapula (type II or III capsular insertion) precludes simple anthroscopic repair. Regarding technique, we used a 24-cm field of view for the following reasons: (a) Early in the study, use of a smaller field of view and thin sections damaged the gradient coils of our machine; (b) other investigators used a 24-cm field of view for study of the shoulder; and (c) a smaller field of view increases resolution but decreases signal-to-noise ratio (37). It is possible that a smaller field of view would result in increased image quality. Radiology
a
521
In conclusion, in our small series we found MR imaging to be insensitive and nonspecific in the evaluation of labral abnormalities. Since theme is presently a minimally invasive alternative that evaluates both the labmum and the capsule insertion site-CT arthmography-we do not believe that MR imaging should be the procedure of choice to evaluate the glenoid labrum. MR arthmography represents an alternative, but since it is as invasive and more costly than CT arthrography, while probably being no more sensitive or specific for glenoid labrum abnormalities, we advocate CT amthmogmaphy as the examination of choice for labral abnommalities. Further studies with more patients and, possibly, use of different imaging parameters (eg, a smaller field of view) will be helpful in determining the true utility of MR imaging in the evaluation of the glenoid labrum. U
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