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Original Research

Evaluation of the Rotator Cuff and Glenoid Labrum

Using a 0.2-Tesla Extremity Magnetic Resonance

(MR) System: MR Results Compared to Surgical

Findings

Frank G. Shellock, PhD, FACSM,1* Jack M. Bert, MD,2 Hollis M. Fritts, MD,3

Cooper R. Gundry, MD,3 Ruth Easton, RT(R),2 and John V. Crues III, MD4

The purpose of this investigation was to evaluate the diag-nostic capabilities of magnetic resonance imaging (MRI)

performed using a dedicated-extremity MR system in de-tecting lesions of the rotator cuff and glenoid labrum. Thisretrospective study compared the MR results obtained in47 patients that underwent MRI using a 0.2-Tesla extrem-ity MR system (E-scan) to the surgical findings. MR imagesof the shoulder were obtained as follows: shoulder coil, T1-weighted, coronal-oblique and axial images; short Tauinversion recovery (STIR), coronal-oblique images; and T2-weighted, coronal-oblique, sagittal-oblique, and axial im-ages. The MR examinations were interpreted by threehighly experienced, musculoskeletal radiologists. Opensurgical (N 26) or arthroscopic (N 21) procedures wereperformed within a mean time of 33 days after MRI. Thesurgical findings revealed rotator cuff tears in 28 patientsand labral lesions in 9 patients. For the rotator cuff tears,

the sensitivity, specificity, positive predictive value, andnegative predictive value were 89%, 100%, 100%, and90%, respectively. For the labral lesions, the sensitivity,specificity, positive predictive value, and negative predic-tive value were 89%, 95%, 80%, and 97%, respectively. The findings indicated that there was good agreementcomparing the MR results obtained using the low-field ex-tremity MR system to the surgical findings for determina-tion of lesions of the rotator cuff and glenoid labrum. No-tably, the statistical values determined for the use of thisMR system were comparable to those reported in the peer-reviewed literature for the use of whole-body, mid- andhigh-field-strength MR systems. J. Magn. Reson. Imaging 2001;14:763770. 2001 Wiley-Liss, Inc.

Index terms: shoulder, MR; magnetic resonance (MR), com-parative studies; shoulder, surgery; lowfield MRI; extremity;rotator cuff

MAGNETIC RESONANCE IMAGING (MRI) is the nonin-

vasive procedure of choice for evaluation of diseases of

the shoulder, especially with regard to identifying le-

sions of the rotator cuff and glenoid labrum (114).

Shoulder MRI is typically performed with conventional,

whole-body MR systems.

The creation of new metal alloys has permitted the

development of smaller permanent magnets that, in

turn, have enabled the construction of MR systems that

are substantially smaller than whole-body scanners

(1524).

In 1993, the first extremity MR system became avail-

able on a commercial basis (Artoscan, Esaote, Genoa,

Italy; General Electric (GE) Medical Systems/Lunar

Corporation, Madison, WI). This scanner uses a low-

field-strength (0.2-Tesla) permanent magnet to image

feet, ankles, knees, hands, wrists, and elbows. Acquir-

ing MR examinations with this MR system offers several

distinct advantages over whole-body scanners, includ-

ing reduced overall costs, more convenient installation

and siting, and greater patient comfort and safety (15

26). Importantly, the diagnostic performance of the

present-day extremity MR system for evaluation of

musculoskeletal pathology has been reported to rival

that of mid- and high-field-strength MR scanners (15

18,2224). Disadvantages of the extremity MR system

are comparable to those of whole-body, low-field-

strength MR systems and include the inherent lower

signal-to-noise ratio (SNR) and longer overall examina-

tion times.

In 1999, another extremity MR system was developed

to image the shoulder in addition to the aforementioned

body part (E-scan, Esaote, Genoa, Italy; GE Medical

Systems/Lunar Corporation, Madison, WI). To our

knowledge, there has been no prior evaluation of the

diagnostic performance of this MR system for shoulder

MRI. Therefore, the goal of this investigation was to

determine the diagnostic capabilities of MRI performed

using this extremity MR system in detecting lesions of

the rotator cuff and glenoid labrum.

1University of Southern California, Los Angeles, California.2Summit Landmark Orthopedics, St. Paul, Minnesota.3Center for Diagnostic Imaging, Minneapolis, Minnesota.4Radnet, Los Angeles, California.

Contract grant sponsor: GE Medical Systems/Lunar Corporation.

*Address reprint requests to: F.G.S., 7511 McConnell Ave., LosAngeles,CA 90045. E-mail: Frank.Shellock@gte.net

Received June 15, 2001; Accepted August 21, 2001.

JOURNAL OF MAGNETIC RESONANCE IMAGING 14:763770 (2001)

2001 Wiley-Liss, Inc. 763DOI 10.1002/jmri.10014

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MATERIALS AND METHODS

The study population for this investigation was selectedfrom a consecutive group of patients with suspectedshoulder pathology who underwent MRI and surgery

between August 1999 and September 2000. Patients were not included if they had prior surgery or if thesurgical procedure was more than 180 days after MRI.

The study group consisted of 47 patients, 31 men and16 women, ranging in age from 1683 years old (meanage, 52 years old). Open surgical (N 26) or arthro-scopic (N 21) procedures were performed within amean time interval of 33 days (range, 8155 days) afterMRI by eight different surgeons specially trained in thediagnosis and treatment of shoulder disorders. The pa-tients rotator cuff and glenoid labrum were routinelyinspected by the surgeon in each case. MRI reports

were available to the surgeons at the time of surgery.

MRI

MRI was performed with a 0.2-Tesla extremity MR sys-tem (E-scan, Esaote, Genoa, Italy; GE Medical Sys-tems/Lunar Corporation, Madison, WI) and a dedi-cated, linear shoulder coil that has an integratedpreamplifier (Fig. 1). The gradient magnetic fields forthis MR system operate at 20 mT/m (slew rate, 25mT/m/msec).

The patients were imaged supine with the arm in aneutral position or mild external rotation. The followingprotocol was used: T1-weighted (TR/TE, 540/20 msec),coronal-oblique (i.e., oriented parallel to the longitudi-nal course of the supraspinatus tendon), and axialplanes; T2-weighted (TR/TE, 2,200/80 msec), coronal-oblique, sagittal-oblique (i.e., oriented orthogonal to

those of the coronal-oblique images), and axial planes;and short Tau inversion recovery (STIR) (TR/TI/TE,1,970/75/30 msec) coronal-oblique plane (40 of 47 pa-tients). The section thickness was 5 mm with an inter-section gap of 0.5 mm for all pulse sequences, with theexception of the STIR sequence, which used a 7-mmsection thickness and 1-mm inter-section gap. The fieldof view (FOV) was 1416 cm, the matrix size was 192128, and the number of excitations was 2. The imagingtime for this procedure ranged from 5070 minutes.Notably, the MR facility that conducted all of the MRI ofthe shoulder examinations is accredited for musculo-skeletal MRI by the Intersocietal Commission for the

Accreditation of Magnetic Resonance Laboratories(ICAMRL).

Interpretation of the MR Images

The MR images were interpreted by three board-certi-fied radiologists with extensive experience (two radiol-ogists were MR musculoskeletal fellowship trained with10 years of experience; one radiologist had 15 yearsof MR musculoskeletal reading experience) in muscu-loskeletal MRI. The radiologists interpreted the MR ex-aminations in an independent, prospective manner.

They had knowledge of the patients age, sex, and pre-sumptive diagnosis. The radiologists were not provided

instructions or guidance with regard to specific criteriato use to interpret the MR images, nor were concessions

made for the low-field-strength MR images. However,standard, previously described, well-accepted interpre-tation criteria were used (1 6,1013,2732).

Data Collection

The MRI and operative reports were reviewed to recordthe pertinent findings. Thus, data for the MR findings

were extracted directly from the original preoperativereports, while data for the surgical findings were ex-tracted from the original operative reports obtainedfrom the orthopedic surgeons. Notably, this basic studydesign (i.e., retrospective review of MR and surgicalreports) has been used in several prior evaluations per-formed to compare MRI to surgical findings (13,8,12).

Terms such as fibrillation, degeneration, tendonopa-thy, attenuation, fringe, and scuffing were categorizedas no tear in this study.

Statistical Analysis

The standard definitions for sensitivity, specificity, pos-itive predictive value, and negative predictive value

were applied to the results of this study with regard tothe use of MRI for diagnosis of a rotator cuff tear and/orlabral lesion, with the surgical findings used as the goldstandard. Sensitivity was defined as the quotient oftrue-positive diagnoses on MRI (numerator) and true-positive plus false-negative diagnoses (denominator).Specificitywas defined as the quotient of true-negativediagnoses on MRI (numerator) and true-negative plusfalse-positive diagnoses (denominator).

Positive predictive value was defined as the quotientof true-positive diagnoses (numerator) and all positivediagnoses (true-positive plus false-positive diagnoses

(denominator)). Negative predictive value was definedas the quotient of true-negative diagnoses (numerator)and all negative diagnoses (true- plus false-negativediagnoses (denominator)).

RESULTS

Using the surgical findings as the gold standard, therewere 28 rotator cuff tears (i.e., 21 full-thickness tears; 2small tears, 8 10 mm; and 5 partial tears) and 9 labrallesions (anatomic distribution: 2 superior-labrum an-terior-posterior (SLAP); 3 superior; 1 anterior and su-perior; 2 anterior, superior, and posterior; and 1 re-

ported massive tear) found in the patients. Ten patientshad neither a rotator cuff tear nor a labral lesion, whileone patient had both. The sensitivity, specificity, andpositive and negative predictive values for the MR read-ings for the rotator cuff and glenoid labrum are pre-sented in Table 1. Figures 24 show examples of shoul-der MR images selected to illustrate the results of thisstudy. Notably, MR images are representative examplesof the images that were acquired and that formed the

basis for the accuracy rates presented in our paper.

Rotator Cuff

For the rotator cuff, MRI correctly identified 25 of the 28

tears (89%). There were no false positives. For the threefalse negatives, partial-thickness tears of the rotator

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cuff were missed by MRI that were seen on arthroscopicprocedures. Thus, none of the full-thickness tears weremissed by MRI. The positive predictive value, the per-centage of all (i.e., both full-thickness and partial-thick-ness) rotator cuff tears diagnosed on MRI that were

subsequently diagnosed at surgery was 100%. The neg-ative predictive value was 90%.

Glenoid Labrum

For the glenoid labrum, MRI correctly identified eight of

nine lesions (89%). For the two false positives, MRI

reported small tears seen on the superior aspect of the

labrum that were found to be normal on open surgicalprocedures. For the one false negative, a SLAP lesion

Figure 1. a: The 0.2-Tesla extremity MR system (E-Scan) used to perform shoulder MRI in this study. Note the linear shouldercoil positioned in the center of the scanner. b: Example of patient positioned in the extremity MR system for MRI of the shoulder.

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may be indistinguishable from that which occurs withdegeneration, tendinitis, or tendonopathy (2,30 32).

The similarity and overlap of signal patterns for theselesions generally creates interpretation problems re-

gardless of the field strength of the MR system, theshoulder coils, or the pulse sequences used for imaging

(17,30).In a recent study that involved an analysis of inter-

pretive errors related to the use of high-field MRI todiagnose rotator cuff tears, Balich et al (30) reported

that detection of partial tears was much less sensitiveand this low sensitivity could not be improved withcurrent imaging techniques or increased reader experi-

ence. While the use of intra-articular gadolinium orsaline (i.e., MR arthrography) may improve the sensi-tivity and specificity of MRI for partial tears (30), it is

unlikely to influence the ability of MRI to detect intra-subtance or bursal-sided partial-thickness tears, and

this invasive procedure increases the time and expenseof the examination. Additionally, the overall impact on

patient care is debatable.It is crucial to differentiate between full-thickness

and partial-thickness tears because the treatments forthese rotator cuff lesions differ. A full-thickness tear

typically requires surgery. Typical clinical managementof a partial-thickness tear initially involves conservative

treatment, with surgical intervention utilized if symp-toms persist for more than 6 months. Thus, from apatient management consideration, there may be no

major implications for missing partial tears on MRI,especially since therapeutic decisions for these rotator

cuff disorders are predominantly guided by clinicalfindings. However, some surgeons may elect to treat a

partial-thickness tear in the dominant arm of an activeindividual with debridement and, when appropriate,

acromioplasty or excision of acromioclavicular (AC)joint spurs.

Shoulder MRI is generally considered useful for de-tection of labral pathology (813,33,34). Studies usingconventional MRI (i.e., without the use of intra-articu-lar contrast) performed with mid- and high-field-strength MR systems have reported sensitivities rang-

ing from 44%95% and specificities ranging from 63%91% for the glenoid labrum (including identification ofSLAP lesions) (811,15,33,34). Differences in imagingprotocols and techniques probably contribute to these

variances in sensitivity and specificity. Additionally, anumber of interpretation pitfalls exist that may be re-sponsible for the wide differences in diagnostic capabil-ities reported for the use of MRI in diagnosing labrallesions (12).

Using the extremity MR system, the sensitivity andspecificity for assessment of the glenoid labrum were89% and 95%, respectively. Again, this diagnostic per-formance was comparable to that reported for mid- andhigh-field MR systems. For the two false positives, the

MR reports indicated the presence of ill-defined (i.e.,the specific term used by the interpreting radiologist inthe MRI report) tears that were found to be normal onopen surgical procedures. For the one false negative,the MR report indicated that the glenoid labrum ap-pears intact without visualization of a discrete labraltear, while a type I SLAP lesion was seen on arthros-copy.

The difficulty of using conventional MRI to diagnoseand characterize SLAP lesions is well known

Figure 4. Axial, T1-weighted MR image of the shoulder show-

ing a tear of the anterior glenoid labrum, confirmed by surgicalfindings.

Figure 3. Coronal-oblique, T1-weighted MR image of theshoulder showing a SLAP tear, confirmed by surgical findings.

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(8,9,11,12). In general, the use of intra-articular con-trast improves the diagnostic capabilities of MRI for thisapplication (14). Therefore, in our opinion, it may beadvisable to use this technique for patients who present

with physical findings suggestive of superior labral le-sions.

In general, the findings of this investigation showed

the ability of a low-field extremity MR system to accu-rately identify lesions of the rotator cuff and glenoidlabrum. Studies comparing the performance of conven-tional MRI using high-field vs. low-field MR systems forassessment of labral lesions have been conducted by anumber of research groups (8,3335). Allmann et al (33)reported that shoulder MRI at 0.2- and 1.0-Tesla wascomparable. In their study group of 35 patients, thesensitivity and specificity were 91% and 91%, respec-tively, for labral pathology for both the 0.2- and 1.0-

Tesla MR systems (33).Shih et al (34) studied patients that underwent MRI

performed with 0.3- and 1.5-Tesla MR systems. Withregard to labral lesions, the performance of the high-

field and low-field MR systems was almost equal (34).However, for the rotator cuff, Shih et al (34) reportedthat the high-field MR system was better in the differ-entiation of tendinitis from tears, in the confirmation of

bursitis, and in the detection of subscapularis lesions.Notably, Shih et al (34) did not use fat suppression orSTIR techniques for the shoulder imaging protocols,

which may explain these findings (to be discussedlater).

Tung et al (8) determined the performance character-istics of high-field (1.5-Tesla) and low-field (0.2-Tesla)MRI for diagnosis of SLAP tears. The sensitivity/speci-ficity of high-field vs. low-field MRI was 95%/63% and

64%/79%, respectively (8). Thus, the performancecharacteristics of high-field MRI were reported to besuperior to those of low-field MRI. However, Tung et al(8) obtained MR images in oblique sagittal and obliquecoronal planes using a frequency-selected fat-saturatedpulse sequence, without acquiring MR images with acomparable technique (e.g., STIR) for the low-field MRexaminations. Additionally, they used smaller sectionthicknesses (as Tung et al (8) indicated, thinner slicesshould also increase the sensitivity of MRI for detectingtears of the glenoid labrum) and smaller FOVs for thehigh-field MR studies. These major protocol differencesdetract from the relative significance of their finding forhigh- vs. low-field MR systems.

The relationship between image quality and magneticfield strength has created a strong bias in favor of theuse of high-field MR systems. However, advances inlow-field MR technology, including new magnet de-signs, improved RF coils, faster gradient systems, andmore sophisticated pulse sequences, have helped tocounter the previous limitations of low-field-strengthMR systems (16). Even though the SNR is directly pro-portional to field strength, the inherent lower SNR may

be addressed on low-field MR systems by using addi-tional signal averages or excitations, narrower band-

widths, better RF coil designs, and optimized pulse se-quences (16). The protocol that was used for shoulder

MRI was devised to accomplish this important aspect oflow-field MRI. Furthermore, for musculoskeletal MRI,

the contrast-to-noise ratio (CNR) is a more clinically

relevant parameter because it determines the extent to

which adjacent structures can be distinguished from

one another and the general conspicuity of pathologic

findings (16). Unlike SNR, the CNR for MRI does not

increase substantially with the strength of the static

magnetic field (16). The CNR is primarily dependent on

imaging parameters.Of further note regarding the issue of SNR for low-

field MR systems, we would like to emphasize that,

despite obtaining MR images of the shoulder that may

be less aesthetically pleasing compared to what is rou-

tinely acquired using a high-field MR system, the diag-

nostic accuracy of the dedicated-extremity MR system

was comparable to that reported for high-field MR sys-

tems.

Focal and/or diffuse increases in signal intensity on

T2-weighted images are associated with rotator cuff

and labral pathology (112,2734). For shoulder MR

examinations, it is important to perform fat-sup-

pressed, T2-weighted imaging for optimal diagnostic

performance because this technique appears to be

more sensitive to increases in signal intensity as a re-

sult of the extended gray scale (5,7,28,29,36). For ex-

ample, Reinus et al (5) reported that use of the fat

suppression technique improved the detection of both

full-thickness and partial-thickness tears of the rotator

cuff, compared with standard spin-echo pulse se-

quences.

Using a low-field MR system, it is difficult to acquire

fat-suppressed MR images using frequency-selective

techniques because the difference between the fat and

water spectral peaks is field-strength dependent (16).

Therefore, in this study, the MR protocol involved ac-

quisition of fat-suppressed images using a STIR pulsesequence (i.e., for 40 of the 47 patients imaged using

this pulse sequence). Notably, the use of the STIR se-

quence has been reported to be more sensitive than

fat-suppressed, T2-weighted techniques for detection of

musculoskeletal lesions (3739). Thus, it is possible

that the use of the STIR sequence contributed to the

overall positive findings of this investigation.

Our investigation had a number of possible limita-

tions. First, it was a retrospective study that included a

large number of symptomatic patients (based on a thor-

ough examination by the referring orthopedic surgeon).

Therefore, bias was introduced in favor of diagnosing

rotator cuff and labral lesions on MRI, even though thereviewing radiologists were unaware of the final surgi-

cal findings.

Second, this investigation was subject to verification

or work-up bias (8). That is, it is well-known that when

a study is restricted to patients who require an invasive

test to verify disease, then the study population may be

biased toward patients with more severe disease. In this

study, the reference standard was the surgical findings

for the patients. Obviously, patients with negative find-

ings on MRI are unlikely to undergo surgical proce-

dures, and this tendency may result in a report of rel-

atively higher sensitivity for MRI than is true because

the number of negative tests (both false negative andtrue negative) is decreased. The lack of an adequate

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control group is understandable and unavoidable con-sidering the invasive aspects of the gold standard test.

Third, the radiologists who interpreted the MR im-ages were experienced, musculoskeletal MR specialists.In general, more knowledgeable readers have a greaterability to identify shoulder pathology on MR images(28,29,31). A considerable degree of experience is re-

quired before one becomes adept at interpreting MRimages, particularly with regard to shoulder MR, due tothe various interpretive pitfalls present for this joint(1,12,29).

Fourth, the use of arthroscopic procedures (arthro-scopic procedures were used for 21 of 47 patients, 45%of the patients in this study, as opposed to open surgi-cal procedures) as a gold standard of reference may bea weakness because there may be surgeon-dependent

variations, and more importantly, subtle findings mayescape arthroscopic visualization (29,40). Further-more, some arthroscopists routinely explore the sub-acromial space, while others do not. Such problems of

visualization may be compounded by the presence of

synovitis and marked degeneration of the glenohumeraljoint, as well as bursitis and marked degeneration af-fecting the subacromial space (29).

Finally, there was no attempt to assess inter- or in-traobserver variability for the results of this study. This

was not a primary goal of this investigation (i.e., similarto other previously published, peer-reviewed articlesthat evaluated the diagnostic performance of shoulderMRI that, likewise, did not evaluate these factors) (13).

Additionally, it was deemed unnecessary to determineinter- and intraobserver variability because of the ex-tensive experience of the reading radiologists. Previousstudies performed to assess intra- and interobserver

variability for MRI of the shoulder indicated that high values are directly related to the level of training andexperience of the radiologist (29,30).

In conclusion, the findings of this study indicatedthat shoulder MRI performed with a low-field extremityMR system exhibited acceptable diagnostic accuracy indepicting lesions of the rotator cuff and labrum basedon a comparison between the MR results and surgicalfindings. The overall diagnostic capabilities were com-parable to those reported in the peer-reviewed literaturefor the use of whole-body and mid- and high-field MRsystems.

ACKNOWLEDGMENT

An unrestricted research grant was provided by GEMedical Systems/Lunar Corporation, Madison, WI, toF.G. Shellock to support this investigation.

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