DOI:10.2214/AJR.07.2716
AJR 2008; 190:27-31
© American Roentgen Ray Society
Does Extended-Field-of-View Sonography Improve Interrater Reliability for the Detection of Rotator Cuff Muscle Atrophy?
Eoin C. Kavanagh1,2,
George Koulouris1,
Laurence Parker1,
William B. Morrison1,
Diane Bergin1,
Adam C. Zoga1,
John A. Dlugosz1 and
Levon N. Nazarian1
1 Department of Radiology, Thomas Jefferson University Hospital, Philadelphia,
PA.
2 Present address: Division of Musculoskeletal Radiology, Department of
Radiology, University of Pittsburgh Medical Centre, 200 Lothrop St.,
Pittsburgh, PA 15213.
Received January 20, 2007;
accepted after revision July 16, 2007.
Address correspondence to E. C. Kavanagh
(kavanaghec{at}upmc.edu).
FOR YOUR INFORMATION
A data supplement for this article can be viewed in the online version of
the article at:
www.ajronline.org.
Abstract
OBJECTIVE. Assessment of rotator cuff muscle atrophy is an important
component of the shoulder sonogram. We hypothesized that
extended-field-of-view (EFOV) sonography would allow greater interrater
reliability than conventional sonography for the evaluation of rotator cuff
muscle atrophy.
MATERIALS AND METHODS. This retrospective study involved 50
consecutive patients who presented for shoulder sonography. All patients
underwent EFOV imaging of the supraspinatus and infraspinatus muscles in
addition to conventional imaging of each muscle. Five musculoskeletal
radiologists first assessed 50 EFOV images of the supraspinatus and
infraspinatus muscles and scored both muscles using a scale of 1-5. The
reliability of each method was determined by calculating intraclass
correlation coefficients (ICCs) according to a method developed by Shrout and
Fleiss. The significance of the difference between reliabilities for
conventional images and EFOV images was tested with a z-test.
RESULTS. For the EFOV images, the ICC for the supraspinatus muscle
was 0.77 and for the infraspinatus, 0.75. For the conventional images, the ICC
for the supraspinatus muscle was 0.52 and for the infraspinatus, 0.57. The
degree of interrater reliability for the five readers in our study was
significantly higher for the EFOV images than for the conventional images
(p < 0.0001).
CONCLUSION. EFOV sonography results in greater interrater
reliability than conventional sonography for the detection of rotator cuff
muscle atrophy. EFOV images of the rotator cuff muscles should be obtained as
part of routine shoulder sonography.
Keywords: muscle atrophy • rotator cuff surgery • rotator cuff tendons • shoulder • sonography • sports medicine • trauma
Introduction
Sonography is an established technique for imaging the shoulder and
is particularly useful for evaluation of the rotator cuff tendons
[1,
2]. Recognition of fatty
atrophy of the muscles of the rotator cuff is of clinical significance because
it has been shown that such patients may have poor outcomes after rotator cuff
surgery [3,
4]. Several reports addressing
the use of sonography for the detection of muscle atrophy of the rotator cuff
have been published in the medical literature
[5,
6]. Sonography has been shown
to be moderately useful for the detection of muscle atrophy when using MRI as
the gold standard [6].
Typically, sonographic images of the supraspinatus and infraspinatus
muscles are obtained as conventional sonography images that are limited in
their field of view by the size of the transducer footprint. The technology to
perform extended-field-of-view (EFOV) sonography has been available for
several years [7,
8]. This technique involves the
real-time generation of diagnostic-quality panoramic images. EFOV images can
show the supraspinatus and infraspinatus muscles side by side and provide an
internal reference for the detection of muscle atrophy. Consequently, we
hypothesized that EFOV sonography would allow greater interrater reliability
than conventional sonography for the detection of rotator cuff muscle
atrophy.
Materials and Methods
This study was approved by our institutional review board and involved a
waiver of consent because of its retrospective nature. A computer search of
our sonography reports database was performed, and 50 consecutive shoulder
sonographic studies were restored to our PACS system for review. Each of these
50 studies included conventional longitudinal views of the supraspinatus and
infraspinatus muscles individually and a longitudinal EFOV image of both
muscles side by side. EFOV imaging was performed using an image
registration-based position-sensing technique. Each examination was performed
by an experienced radiologist with more than 10 years of experience in
musculoskeletal sonography using a multifrequency linear probe with a peak
frequency of 12-13 MHz or in large patients using a 7.5-MHz probe with tissue
harmonic imaging on a commercially available sonography unit (HDI 5000,
Phillips Medical Systems; or a Sonoline Elegra, Siemens Medical Solutions).
The patient was examined while sitting in a chair, with the sonographer
standing behind the patient (Figs.
1 and S1). (Figure S1, video
clips, can be viewed in the AJR electronic supplement to this
article, available at
www.ajronline.org.)
The written reports for each of these 50 sonographic studies were also
evaluated for the reported integrity of the rotator cuff and the presence or
absence of rotator cuff muscle atrophy. All study readers were blinded to
these reports.
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Fig. 1 —Extended-field-of-view (EFOV) sonographic technique for evaluation
of supraspinatus and infraspinatus muscles in 36-year-old male volunteer.
Static EFOV sonographic image created from Figure S1, video clips available as
supplemental data at
www.ajronline.org,
shows supraspinatus (S), infraspinatus (I), and trapezius (T) muscles. There
is acoustic shadowing from scapular spine (asterisk).
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Fig. 2A —42-year-old man with shoulder pain. Conventional longitudinal image
of supraspinatus muscle (S), which was graded as normal, shows pinnate pattern
of hypoechoic muscle fibers separated by hyperechoic fibroadipose septa
(arrowhead). Supraspinatus muscle is comparable in echogenicity to
overlying trapezius muscle (T).
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The EFOV images from each case were then saved in a research database, and
their order was randomized. The conventional longitudinal images of the
supraspinatus and infraspinatus muscles from each case were then saved on a
separate research database and were also randomized. The patient information
and imaging parameters were masked from all images. All images were labeled to
indicate the location of the supraspinatus and infraspinatus muscles.
This study involved five readers who are fellowship-trained musculoskeletal
radiologists different from the radiologist who performed the sonography
examinations. All of the readers first attended a 15-minute educational
presentation given by the lead author showing examples of the normal
sonographic appearance of the rotator cuff muscles and examples of fatty
atrophy on both conventional and EFOV images. Normal muscle was defined as
muscle with normal echogenicity, a normal pennate pattern (hypoechoic with
hyperechoic fibroadipose septations arranged in a pennate pattern converging
to a hyperechoic tendon), and normal muscle volume and contours as compared
with accompanying rotator cuff muscles (Figs.
2A,
2B and
3). Fatty muscle atrophy was
defined as muscle with increased echogenicity, loss of the normal pennate
pattern, and decreased muscle volume and indistinct muscle contours as
compared with accompanying rotator cuff muscles (Figs.
4,
5,
7). These evaluations were all
performed subjectively, not quantitatively.
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Fig. 3 —37-year-old woman with shoulder pain. Extended-field-of-view
sonogram shows supraspinatus (S) and infraspinatus (I) muscles, which were
graded as normal. Note acoustic shadowing from scapular spine
(asterisk). Muscle echogenicity is compared with overlying trapezius
muscle (T).
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Fig. 4 —54-year-old man with shoulder pain. Conventional longitudinal image
of supraspinatus muscle (S) shows increased echogenicity and poor definition
of normal pennate pattern of muscle fibers compared with overlying trapezius
muscle (T). These findings are consistent with fatty muscle atrophy of
supraspinatus muscle.
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Fig. 5 —67-year-old woman with shoulder pain. Conventional longitudinal
image of infraspinatus muscle (I) shows increased echogenicity, decreased
muscle volume, and loss of normal pennate pattern of muscle fibers. These
findings are consistent with fatty muscle atrophy of infraspinatus muscle.
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Fig. 7 —57-year-old woman with shoulder pain. Extended-field-of-view (EFOV)
sonogram shows supraspinatus (S) and infraspinatus (I) muscles, which were
graded as atrophy. Note acoustic shadowing from scapular spine
(asterisk). Also shown is a stairstep artifact (arrows) from
EFOV technique.
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Each reader first assessed the 50 randomized EFOV images of the
supraspinatus and infraspinatus muscles and scored both muscles using a scale
of 1-5 as follows: 1, normal muscle; 2, probably normal muscle; 3, unsure; 4,
probably fatty atrophy; and 5, definitely fatty atrophy. Each reader then
assessed the 50 pairs of conventional images of the supraspinatus and
infraspinatus muscles and recorded a score for each muscle using the same
scale as for the EFOV images. All results were collected in a computer
database for statistical analysis. The reliability of each method was
determined by calculating the intraclass correlation coefficient (ICC)
according to a method developed by Shrout and Fleiss
[9]. The significance of the
difference between reliabilities for conventional images and EFOV images was
tested with a z-test. Significance was defined as a p value
of < 0.05.
Results
Of the 50 patients, 27 were men and 23 were women, with a mean age of 62
years (range, 37-92 years). By report, 27 patients had sonographically normal
supraspinatus and infraspinatus muscles, 12 had fatty atrophy of both muscles,
seven had isolated fatty atrophy of the supraspinatus muscle, and four had
isolated fatty atrophy of the infraspinatus muscle. All but two cases with
fatty atrophy of both muscles had massive rotator cuff tears noted in their
reports, with involvement of both the supraspinatus and infraspinatus tendons.
All seven cases of isolated fatty atrophy of the supraspinatus tendon had an
accompanying full-thickness supraspinatus tear. All four cases with isolated
infraspinatus fatty atrophy had full-thickness tears of the supraspinatus and
infraspinatus tendons. Of the 27 patients without fatty atrophy, eight had
full-thickness supraspinatus tears and four had partial-thickness
supraspinatus or infraspinatus tendon tears.
The results of the scoring for the supraspinatus and infraspinatus muscles
for all readers using conventional and EFOV images are given in Tables
1 and
2.
The results of the Shrout-Fleiss
[9] reliability test for
interrater reliability are shown in Table
3. For the EFOV images, the interrater reliability was good, but
for the conventional images, the interrater reliability was only moderate.
When comparing EFOV images with conventional images for the evaluation of the
supraspinatus and infraspinatus muscles by the five readers, the ICC was
significantly higher for the EFOV technique (p < 0.0001).
Discussion
Atrophy of the rotator cuff muscles is an important clinical finding in
patients who are potential surgical candidates for rotator cuff repair because
patients with muscle atrophy have poorer postoperative outcomes overall than
those who do not [3,
4]. Atrophy of the rotator cuff
muscles can occur for a variety of reasons, the most common being chronic
tears of the rotator cuff muscles. Rotator cuff muscle atrophy can also occur
as a result of neural compression from lesions, such as paralabral cysts, and
can occur secondary to denervation from inflammatory causes, such as
Parsonage-Turner syndrome.
Both CT and MRI are reliable methods for assessing fatty atrophy of the
rotator cuff muscles
[10-12].
Sonography is an excellent alternative to MRI of the rotator cuff, but wide
acceptance of sonography is slowed by its operator dependence. Physicians may
be especially hesitant to adopt sonography in practices where they routinely
perform off-line interpretation of images obtained by sonographers. The use of
standardized protocols and objective diagnostic criteria for rotator cuff
tears helps improve the accuracy and reproducibility of sonography. However,
sonographic assessment of muscle atrophy may be more subjective; therefore, a
method to improve interrater reliability is desirable. Sonographic evaluation
of fatty muscle atrophy has been previously described, and imaging findings
include loss of visibility of the central tendon and loss of the normal
pennate pattern [6]. Increased
muscle echogenicity and decreased muscle bulk have also been used as
sonographic indicators for the presence of muscle atrophy
[5]. These previous studies
used conventional images of the rotator cuff muscles for the detection of
muscle atrophy.
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Fig. 6 —54-year-old man with shoulder pain. Extended-field-of-view sonogram
shows supraspinatus muscle (S) graded as normal and fatty atrophy of
infraspinatus muscle (I). Note acoustic shadowing from scapular spine
(asterisk). T = trapezius muscle.
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EFOV sonography has been shown to be useful in musculoskeletal examinations
because it allows a greater area to be shown on a single image
[13]. Technically, these scans
are relatively simple to obtain, requiring a steady hand and knowledge of the
potential artifacts that can occur (Fig.
5B). An EFOV image of the supraspinatus and infraspinatus tendons
allows the muscles to be compared directly with each other. As an internal
control, these muscles can also be compared with the overlying trapezius
muscle, which tends not to undergo fatty atrophy in isolated rotator cuff
disease.
Our study had several limitations. We did not have a gold standard for
muscle atrophy. Therefore, we can evaluate only the interrater reliability of
EFOV, not its accuracy. Nevertheless, other authors have already evaluated the
accuracy of sonography for the detection of muscle atrophy
[6] and that was not the
objective of our study. We also were limited by reading images retrospectively
on a PACS system without real-time patient interaction. One advantage of
real-time imaging is immediate contralateral comparison, which may be helpful
in diagnosing subtle cases of atrophy. There is also an element of bias in our
study because the readers were aware that they were reviewing either EFOV or
conventional images at the time of image interpretation.
In conclusion, the results of our study show a significantly higher
interrater reliability for the sonographic assessment of atrophy of the
rotator cuff muscles using EFOV technology than using conventional images of
the rotator cuff muscles. We therefore suggest that EFOV images of the rotator
cuff muscles be obtained routinely, especially in patients who are being
evaluated as candidates for rotator cuff repair.
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Abstract
Introduction
