Indicators of superior glenoid labral detachment on magnetic resonance imaging and computed tomography arthrography

ORIGINAL

ARTICLES

Indicators of superior glenoid magnetic resonance imaging tomography arthrography Minoru Yoneda, Ken11 Hayashida,

Injuries of the superior glenoid labrum of the shoulder are often mistaken for the subacromial impingement syndrome or glenohumeral joint subluxation, because such injuries are not associated From the Shoulder and Sports Medicine Service, ment of Orthopaedic Surgery, Osaka Kosei-Nenkln pital, the Department of Orthopaedic Surgery, University MedIcal School, and Sekime Hosprtal Presented at the Sixty-first Annual Meeting Academy of Orthopaedic Surgeons, Louisiana, February 24-28, 1994. Reprint requests Mlnoru Yoneda, Orthopaedic Surgery, Osaka 4-2-78 Fukushima, Fukushima-ku, author or related benefit from research

Copyright Board

0 1998 of Trustees

1058-‘2746/98,‘$5

2

on

MD, Kazutaka Izawa, MD, Atsushl Hlrooka, MD, MD, and Shigeyuki Wakitani, MD, Osaka, Japan

The magnetic resonance imaging and computed tomography arthrographic findings of 36 shoulders with arthroscopically diagnosed detachment of the superior labrum were compared with those of 40 shoulders with a normal superior labrum to detect any findings specific to the injury. In this study we defined a specific magnetic resonance imaging finding as the presence of a linear, high-to-intermediate intensify area between the superior labrum and the glenoid rim on oblique coronal U-weighted images. We also defined a specific computed tomography arthrography finding as air entering between the superior labrum and the upper part of the glenoid surface. On the basis of these findings magnetic resonance imaging had a sensitivity of 4 I %, a specificity of 86%, and an accuracy of 63%, whereas computed tomography arthrography had a sensitivify of 45%, a specifici?/ of 93%, and an accuracy of 73%. Thus both of these procedures were specific for these parficulor findings, but they were neither sensitive nor accurate. (1 Shoulder Elbow Surg 1998;7:212.1

No

labral detachment and computed

00+0

of the Amencan New Orleans,

MD, PhD, Department of Kosei-Nenkin Hospital, Osaka 553 Japan.

lnstltutlon has In this study.

by Journal

DepartHosOsaka

of Shoulder 32/l/79886

received and

Elbow

financial Surgery

with any specific clinical symptoms, and there are no definitive provocative tests or imaging techniques for establishing the correct diagnosis. In fact, this condition was not recognized as a distinct clinical entity until arthroscopy became widely available as a diagnostic modality.16 This type of injury was first reported in 1985 by Andrews et al.’ as a tear of the anterosuperior glenoid labrum in a throwing athlete. In 1990 Snyder et al.19,*’ suggested that the various traumatic lesions of the whole superior glenoid labrum caused by superior compression-type injury could be considered as a single clinical entity and coined the term SLAP (superior labrum from anterior to posterior) lesion. The SLAP lesion is distinct from the lesion described by Andrews et al., which is believed to be caused by traction injury and is localized to the anterosuperior region. Snyder et al.19, *’ classified SLAP lesions into four morphologic types and subsequently into five types. However, the pathogenesis of these injuries is still somewhat controversial, and a number of diagnostic and therapeutic issues remain to be established. It is still unclear which glenoid labral injuries actually produce clinical symptoms. Superior glenoid labral injuries involving the biceps tendon/labrum complex (BLC) vary in severity from slight roughening of the surface to tearing or complete disruption. After the BLC completely detaches from the glenoid rim, it shows marked instability that easily causes downward displacement and interposition between the articular surfaces. This condition, the “detached and floating BLC,” often causes clinical symptoms and should be treated with surgery (Figure 1 ).‘, “, ** It is regarded as the most severe type of Snyder type II SLAP lesion for its complete detachment and instability. In 1988 we analyzed the clinical findings of athletes with various types of superior

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3

LHB

Humeral

Superior

. B

head

glenoid

Periosteai detachment of the BLC

LHB

1 Detached and floating biceps tendon/labrum complex (BLC) (A) k/B, Tendon of the long head of biceps, HH, humeral head, 9, superior labrum Diagram of normal BlC (B) Diagram of detached and floating BLC, detachment of BLC causes Instability and downward displacement of superior labrum (C) Figure

glenoid labral injury and also reported on arthroscopic treatment of the detached and floating BLC.*, 9, 23 From these therapeutic experiences and clinical analysis, we regard the detached and floating BLC as the most symptomatic lesion that requires surgical treatment. Unfortunately, such injuries are still difficult to detect before surgery and can generally be diagnosed only by arthroscopy. Because of its noninvasiveness, magnetic

resonance imaging (MRI) is a useful screening procedure for shoulder lesions, although no consensus has been reached as to whether MRI or double-contrast computed tomography arthrography (CTA) is more useful for clearly visualizing the intraarticular structures. “, ‘* The twin purposes of this study were to detect MRI and CTA findings specific for detachment of the superior glenoid labrum (detached and floating

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Figure 2 Arthroscoprc classtficatron of downward drsplacement of detached superior glenord labrum Severe displacement. free central border of labrum was located near center of glenoid fossa and noticeably interposed between humeral head and fossa (A). Detachment of biceps tendon/labrum complex was shown by probing (B) Slight displacement no interposition of labrum was observed (C). Detachment of biceps tendon/labrum complex was shown by probing (D) D-/B, Tendon of long head of biceps, HH, humeral head, SI, superior labrum.

BLC) and to assess the diagnostic value imaging modalities for this type of injury.

of both

MATERIAL AND METHODS Thirty-six patients (33 male patients and 3 female patients, 36 shoulders) had arthroscopically diagnosed detached and floating BLC among 341 patients who underwent arthroscopy at our department or related hospitals from February 1986 to

February 1993. The age at the time of arthroscopy ranged from 14 to 48 years (mean 24 years). MRI was used to examine 22 affected shoulders in 22 patients, whereas CTA was performed to assess bilateral shoulders in 29 patients. MRI was performed with a permanent magnet system (0.2 Tesla Hitachi MRP 20) with a dedicated loop coil. The slice thickness was 7 mm without interslice gap in the oblique coronal (per-

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A : 22 pauents

B 2 patients

c

et al.

5

12 patients

Figure 3 Schematic representation of extent of glenold labral damage In patients with detached superior glenold labrum Localized to superior region. 10 o’clock to 2 o’clock position (A). Posterior to superior. 9 o’clock to 2 o’clock positlon (B) Superior to anterior 10 o’clock to 3 o’clock position (C)

pendicular to glenoid surface), oblique sagittal (parallel to glenoid surface), and axial planes. Eight slices of images were obtained in the oblique coronal and axial planes, and 1 1 slices of images were obtained in the oblique sagittal plane. Tlweighted images were obtained by the spin-echo method (TR 4005OO/TE 25), and T2-weighted images were acquired by the Field-echo method (TR 500-700/TE 35/FA30”). The field of view was 30 cm, two signals were averaged, and the matrix was 256 x 256 in all planes. Double-contrast CTA was performed by injecting 2 ml 76% diatrizoate (Urografin, Nihon-Schering, Japan) and 15 ml of room air. Images were acquired immediately after intraarticular injection with a Yokogawa 8600 or Shimazu SCT4500TE scanner under the following conditions: a slice thickness of 5 mm (12 slices per case), an interslice gap of -2 mm, a window level of 140 to 200, and a window width of 1000 to 2000. During all radiographic procedures the patient’s arm was placed in the palm-up position. In the patients with detached and floating BLC, downward displacement was classified with arthroscopy as severe when the free central border of the labrum was located near the center of the glenoid fossa and noticeably interposed between the humeral head and the fossa. In such cases obvious instability of the BLC resulting from its complete detachment and relatively broad width of the superior labrum, which may be a cause of interposition, were observed. Displacement was classified as slight when the BLC detached and floated completely but was not so displaced as to cause the interposition of the labrum. According

to these criteria 16 patients had severe displacement, and 20 had slight displacement (Figure 2). The lesions were also classified into three types according to the range of injury (Figure 3). The injury was localized to the superior glenoid labrum (10 o’clock to 2 o’clock position) in 22 patients, extended from the posterior to the superior region (9 o’clock to 2 o’clock position) in 2 patients, and extended from the superior to the anterior region (10 o’clock to 3 o’clock position) in 12 patients. Concomitant intraarticular injuries were present in 10 patients in the form of an incomplete tear of the articular surface of the rotator cuff. As a control group 40 patients (33 male patients and 7 female patients, 40 shoulders) with no arthroscopic abnormalities of the superior glenoid labrum were studied. The age of these patients at arthroscopy ranged from 13 to 43 years (mean 22 years). Sixteen of them had subacromial bursitis, 14 had injuries of the anterior glenoid labrum, 5 had injuries of the posterior glenoid labrum, 3 had incomplete tears of the articular surface of the rotator cuff, and 2 had other shoulder joint disorders. MRI was performed in 21 patients (21 shoulders), whereas CTA was performed on both shoulders in all 40 patients. Arthroscopic surgery was subsequently performed by orthopaedic surgeons (M. Y., assisted by K. H.) who specialize in the diagnosis and treatment of shoulder disorders. All surgical reports and procedural videotapes were reviewed by them to confirm the types of the injuries. The MRI images and CTA images were reviewed retrospectively. Blinded to the clinical information and re-

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B

Figure 4 Magnetic resonance imaging appearance Linear high-intensity area between superior labrum IntermedIate Intensity area In superior labral region

sults of arthroscopy, two orthopaedic surgeons (K. I., assisted by A. H.) who specialize in diagnostic imaging of shoulder disorders reviewed the images and recorded diagnostic conclusions. RESULTS MRI findings. MRI was performed in 22 of the 36 patients with detached and floating BLC. T2weighted oblique coronal images that passed through the center of the glenoid fossa revealed a linear, high-intensity area between the superior labrum and the glenoid rim (Figure 4, A) in three (14%) patients and a linear or globular intermediate intensity area (Figure 4, 6) in six (27%) pa-

of detached superior and glenoid rim

glenoid labrum Linear or

(A).

/arrow). globular

(B).

tients. A linear high-intensity or intermediate intensity area observed only between the glenoid labrum and the upper part of glenoid surface was regarded as a normal finding. Only the lesion continuing over the glenoid rim was regarded as an abnormal finding. This abnormality of the superior labrum was observed in nine (41%) patients. MRI showed a similar linear intermediate intensity area in 3 (14%) of the 2 1 patients in the control group with an arthroscopically normal superior labrum (a 14% false-positive rate) (Table I). No abnormality of the superior labral region was detected in the oblique sagittal and axial planes.

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Table

I Diagnostic

value

of magnetic

resonance Specific

Detached

and

computed

tomography

findings

Positive

Present Absent Total

tendon/abrum

Negative

9 3 12

Diagnostic value of MRI: Sensitivity: 75%; Negative predictive value: Diagnostic value of CTA: Sensitivity: 81%; Negative predictive value: Biceps

MRI

and

7

arthrography Specific

CTA

findings

floating

BLC

SK,

Imaging

et al.

complex;

9/22 18/3 1 13/29 37/53 MRI,

13 18 31

= 44%; = 58%; = 45%; = 70%; magnetic

Total

22 21 43

Positive

13 3 16

Negative

Total

16 37 53

29 40 69

Specificity: 18/2 1 = 86%; Positive predictive value: 9/l 2 = Accuracy: 27/43 = 63%. Specificity: 37/40 = 93%; Positive predictive value: 13/l 6 = Accuracy: 50/69 = 73%. resonance imaging; CTA, computed tomography arthrography.

CTA findings. CTA was performed in 29 of the 36 patients with a detached and floating BLC. It revealed well-circumscribed air between the superior labrum and the upper part of the glenoid surface (Figure 5, A) in nine (3 1%) patients and air partially occupying this region (Figure 5, 8) in four (14%) patients. This abnormal CTA finding was observed in 13 (45%) patients. We termed this CTA finding the trapped-air sign. A similar CTA appearance of the superior labrum was also observed in 3 of the 40 patients in the control group who had normal arthroscopic findings (a 7% falsepositive rate) (Table I). Correlation between the degree of displacement and positive findings. The correlation between the degree of displacement of the superior labrum observed by arthroscopy and the presence of positive MRI or CTA findings was also studied. CTA findings were positive in 5 (31%) of the 16 patients with mild labral displacement and in 8 (6 1%) of the 13 patients with severe displacement. These findings indicate that CTA is more likely to give a false-negative result when there is slight displacement of the labrum. MRI was positive in 4 (36%) of the 1 1 patients with slight labral displacement and in 5 (45%) of the 1 1 patients with severe displacement. No significant correlation was found between the presence of positive MRI findings in patients with detached and floating BLC and the extent of labral displacement (Table II). Diagnostic benefit. When a linear area of highto-intermediate intensity located between the superior labrum and glenoid rim was regarded as MRI evidence of a detached and floating BLC, the predictive value of MRI was 75% with a sensitivity of 41%, specificity of 86%, and accuracy of 63%. When the trapped-air sign was regarded as CTA

evidence of a detached superior glenoid labrum, this modality had a predictive value of 8 1% with a sensitivity of 45%, specificity of 93%, and accuracy of 73%. Although CTA had a slightly greater predictive value than MRI, both procedures had a low sensitivity and a high specificity. These results indicate that “specific” imaging findings were not so common in detached and floating BLC but that a diagnosis of this condition was likely to be correct if such findings were present. MRI positivity was not influenced by the degree of downward displacement of the labrum, and this modality simply detects detachment of the labrum from the glenoid rim. Compared with MRI, CTA seemed to be more useful for preoperative assessment of the degree of displacement, A typical case with positive MRI and CTA findings (case 1) is presented in Figure 6. DISCUSSION Literature survey. Only a few reports have been done on imaging diagnosis of the detached superior glenoid labrum. Legan et al.‘* assessed the diagnostic benefit of MRI for anterior, superior, posterior, and inferior detachment of the labrum and reported a 99% specificity, 75% sensitivity, and 95% accuracy for the superior labrum based on a comparison of 12 patients with unspecified detached superior labral injuries and 74 members of a control group. They referred to a defect of the superior labrum and presence of a linear, highintensity area that completely divided the labrum in the oblique coronal view. Cartland et al.2 studied MRI findings in 10 patients with injuries of the superior labrum and in 7 members of a control group. They reported that abnormal findings were observed in all of the patients with labral injury and none of the members of the control group. Labral detachment was present in 2 of the 10 patients

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Figure

[arrow) partially

of detached superior 5 Computed tomography arthrography ap earance Well-circumscribed air between superior la If rum and u per parf of glenold Plgament * Superior glenohumeral occupying this region (B)

with labral injuries and was specifically indicated by the presence of a round, high-intensity area between the superior labrum and the glenoid rim or a high-intensity area at the site of labral attachment in oblique coronal images. Both of these reports indicated a higher specificity and sensitivity of MRI than was obtained in our study. This discrepancy may be primarily attributed to thinner slice thickness (3 to 4 mm) used in the other studies. Another possibility is that the results were biased by the small number of patients with a detached

glenold surface

Surg

7998

labrum Atr

(A)

superior glenoid labrum in both studies. On the other hand, Hodlet et al.‘O reviewed nine cases of the magnetic resonance arthrography findings of the superior labral lesion and concluded only the complete detachments were able to be detected even with MRI arthrography. They emphasized consideration of a normal variation and normal separation in the aging process. With regard to diagnostic CTA, Hunter et al.” reported abnormal findings in 15 of 17 patients with superior labral injuries (no control study) and

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Figure 6 Case 1 positive by both MRI and CTA Twentyyear-old man who was plicher In unlverslty baseball team had right shoulder paln on throwing. Both MRI (A) and CTA (B) showed abnormalities of superior labrum /arrow], whereas arthroscopy (C) detected detached and floating biceps tendon/labrum complex with severe displacement Detachment of biceps tendon/labrum complex was shown by probing (D)

et al.

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II Relatlonshlp of drsplacement

between

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lmaglng

findlngs

Positive

Severity Slight Severe Slight Severe

of displacement (n = 16) (n = 13 (n = I J) (n = 1 1)

computed tomography netic resonance imaging.

CTA,

CTA (II = 13)

(%)

and

the

findings MRI (n = 9) (%)

5 (31)

8 (61) -

4 (36)

-

5 (45)

arthrography;

MRI,

mag-

stated that all four patients with a detached superior labrum showed abnormalities including elevation of the labral-capsular transition site above the coracoid process and separation of the labrum from the capsule. They suggested that CTA is more clinically useful, because MRI and magnetic resonance arthrography are somewhat unsuitable for routine examination as a result of the long image acquisition time. Thus the diagnostic benefits of MRI and CTA for the detached superior labrum have not previously been assessed in a study based on direct intraindividual comparison. This study detected MRI and CTA findings specific to a detached superior labrum and demonstrated the superiority of CTA in assessing the severity of displacement when compared with MRI. The reasons for the false-negative and false-positive results in our series are discussed in the following text. False-negative results. False-negative results may have been related to slight displacement of the superior labrum. Possible procedural causes may include selection of an inappropriate slice thickness, slice angle, slice location and arm position, and loss of the injected air during CTA. In this study MRI was performed with a 7 mm slice thickness, and CTA was performed with a 5 mm slice thickness, so only one or two slices were useful for the diagnosis of a detached and floating BLC. Thus these examinations should ideally be performed with a thinner slice thickness and interval. However, for the routine screening procedure it is difficult to perform these examinations with such a thin slice because of the long acquisition time, greater exposure to radiation, and cost. Although we used a permanent magnet MRI with a low magnetic field (0.2 T) in this study, we do not

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regard the weakness of the magnetic field as the main cause of the low sensitivity.14 The scanner we used has the vertical field system with solenoidal surface coil that provides a higher S/N ratio. It also has a gantry that has a large opening (1 m) and short depth (0.47 m), which enables one to easily position the shoulder of the patient in the center of the magnet field. Such a gantry decreases motion artifacts caused by the patient’s stress resulting from unnatural positions and a narow space. In addition, the permanent magnet MRI with a low magnetic field generally has higher contrast resolution, because the low magnetic field makes the longitudinal relaxation time shorter. It has also been reported that loss of the air injected during CTA may result in insufficient air entering the space between the detached labrum and the glenoid rim. ” We always perform the CTA immediately after the intraarticular injection, and no such cases were observed in our series. It may also be necessary to devise an arm position that is more suitable than the palm-up position used in this study to obtain images better emphasizing downward displacement of the detached and floating BLC. In the future a higher sensitivity may be obtained by MRI arthrography with Gd-DTPA or other contrast agents, although this procedure is invasive and thus eliminates one of the main advantages of conventional MRl.13, 15, l8 False-positive results. The primary cause of false-positive MRI may be the presence of normal anatomic variations that are easily confused with pathologic changes. These variations can be distinguished from the pathologic lesion only by arthroscopy. In this respect the imaging of the normal variations is not exactly a “real” false-positive. Typical normal variations are a relatively wide superior labrum that resembles a triangle in crossslice and overlaps the glenoid rim3, 5, 6 (Detrisac type I, a meniscoid pattern, Figure 7), a labrum with a very proximal attachment to the glenoid rim that produces a deep sulcus between labrum and rim (a normal SUICUS),~ a glenoid labrum with no attachment to the rim (a sublabral hole, Buford complex),5, 6, 2o and the presence of artitular cartilage near the labral attachment.24 In addition, MRI has a higher contrast resolution and higher sensitivity to qualitative changes than CTA, and this might have led to the detection of degenerative changes or horizontal tears within

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Wide superior

: Normal

11

labr urn

: sulcus

Atiicular

cartilage

Figure 7 lllustratlon showing normal anatomic varlatlons of superior glenold labrum, which are easily confused with pathologic condition on radiographlc examination Superior glenold labrum may have wide and free central border overlapping glenold rim (Detrlsac Type I)( It may have normal sulcus caused by proximal attachment to glenoid rim, and artlcular cartilage may be present near srte of labral attachment Those vanatlons are easily dIstinguIshed on arthroscopy from detached and floating biceps tendon/labrum complex, because they do not show any dynamic lnstabllitles on probing

the labrum that could not be seen at arthroscopy? CTA has a higher spatial resolution and a greater sensitivity to intraarticular changes than MRI, and it was able to detect air between the displaced labrum and the glenoid rim. Thus the most likely cause of false-positive CTA studies seems to be normal anatomic variations (Figure 7). Although none of the three patients in the control group with false-positive CTA findings was definitely considered to have an anatomic variation at arthroscopy, pannus formation with marked intraarticular inflammation was noted in all three cases, and this may have influenced the radiographic findings. Further investigation is required to clarify this point. One of the three patients who had a false-positive result by MRI showed a normal variation or anatomy (Figure 8). Therefore accurate information on normal anatomic variations is required before images of the shoulder joint are interpreted. CONCLUSIONS The MRI finding specific to a detached and floating BLC was the presence of a linear, high-tointermediate intensity area between the superior labrum and the glenoid rim on T2-weighted oblique coronal images, whereas the specific CTA finding was an entering of air (“the trapped-air

Figure 8 Case 2 false- osltlve by magnetic resonance Imaging Fifteen-year-old t: oy who was baseball outfielder for hlah school team had rlaht shoulder Daln while throwlng i\j\agnetlc resonance lmiglng suggested abnormalities of superior labrum, however, arthroscopy showed that labrum was not detached but Instead had deep sulcus where it was attached to glenold rim. This normal anatomlc variation led to false-positive magnetic resonance Imaging d;agnosls

sign”) between the superior labrum and the upper part of the glenoid surface. Both MRI and CTA had a high specificity and a low sensitivity for diagnosing the detached and

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floating BLC on the basis of these specific findings. Thus detached and floating BLC is very likely to be present if either of these findings is observed. The more marked the labral displacement became, the more likely it was that CTA could detect detached and floating BLC. In contrast, there was no significant correlation between MRI findings and the severity of displacement. Therefore CTA is more useful for the preoperative assessment of the extent of labral detachment and displacement.

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17

Resch H, Golser K, Thoenr H, Sperner G. Arthroscoprc repair of superior glenoid labral detachment (the SLAP lesson) J Shoulder Elbow Surg 1993;2: 147-55

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The authors thank Kiyofumi lida, RT, and Kenii Yoshino, RT, for their assistance with this study.

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