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Musculoskeletal Imaging |
1 From the Departments of Diagnostic Radiology (W.H.J., T.R.M., L.D.K.) and Orthopedic Surgery (L.D.K., J.M.M., P.A.R., J.P.D.), Yale University School of Medicine, 333 Cedar St, Rm MRC 147, New Haven, CT 06520. Received February 23, 2000; revision requested April 8; revision received May 17; accepted June 28. Address correspondence to T.R.M. (e-mail: mccauley@biomed.med.yale.edu).
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ABSTRACT |
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 TOP ABSTRACT INTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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MATERIALS AND METHODS: The MR arthrograms in 80 patients who underwent arthroscopy and MR arthrography during a 54-month period were retrospectively reviewed. MR arthrograms were independently scored by three observers for the presence and type of SLAP lesion. Type I SLAP lesions were regarded as negative as they most often are not clinically relevant. Interobserver agreement for detection of SLAP lesions was calculated by using 
coefficients. The differences in areas under the receiver operating characteristic (ROC) curves were assessed with a univariate z score test.
RESULTS: At arthroscopy, there were 25 SLAP tears: type II (n = 22), type III (n = 2), and type IV (n = 1). Sensitivity, specificity, and accuracy of each reader were 92%, 84%, and 86%; 92%, 82%, and 85%; and 84%, 69%, and 74%, respectively. Interobserver agreement for SLAP tears was substantial ( = 0.77) to moderate ( = 0.52, = 0.44). The areas under the ROC curves for each reader were 0.94, 0.93, and 0.83, which were not significantly different.
CONCLUSION: MR arthrography of the shoulder is reliable and accurate for detection of SLAP tears.
Index terms: Magnetic resonance (MR), arthrography, 414.121415, 414.12143 • Shoulder, arthrography, 414.121415, 414.12143 • Shoulder, injuries, 414.4819 • Shoulder, MR, 414.121415, 414.12143
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INTRODUCTION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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The purpose of our study was to determine the reliability and accuracy of MR arthrography in the diagnosis of SLAP lesions of the glenoid labrum.
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MATERIALS AND METHODS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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Injection of the joint was performed with fluoroscopic guidance and an anterior approach. A 20-gauge spinal needle (Becton Dickinson, Franklin Lakes, NJ) was placed in the glenohumeral joint. One to 5 mL of iohexol (Omnipaque 300 mg/mL; Nycomed Amersham, Princeton, NJ) was used to verify intraarticular injection. Gadoteridol 0.5 mmol/mL (ProHance; Bracco Diagnostics, Princeton, NJ) diluted 1 to 250 in normal saline solution was injected along with approximately 0.2 mL of 1:1,000 epinephrine (American Regent Laboratories, Shirley, NY). MR arthrography of the shoulder was initiated 10–60 minutes after intraarticular injection and was performed with a 1.5-T imager (Signa; GE Medical Systems, Milwaukee, Wis) with a dedicated phased-array shoulder coil. Patients underwent imaging with the humerus in neutral position. Fat-suppressed T1-weighted (600–800/13–16 [repetition time msec/echo time msec]) sequences were used in transverse, coronal oblique (parallel to the long axis of the supraspinatus tendon), and sagittal oblique (perpendicular to the long axis of the supraspinatus tendon) planes. Double-echo fast spin-echo pulse sequences were used to obtain coronal oblique intermediate-weighted MR images (2,000–4,500/14–21) and T2-weighted MR images (2,000–4,500/76–112) with an echo train length of 12. The sagittal oblique fat-suppressed T1-weighted images were acquired in 45 of the 80 patients. The coronal oblique double-echo fast spin-echo pulse sequence was omitted in one patient. The other sequences were used in all patients. MR imaging parameters for all sequences were: field of view, 15–16 cm; two signals acquired; matrix size, 256 x 192 or 160; section thickness, 3 mm; intersection gap, 0.3 mm.
MR arthrograms were retrospectively reviewed and scored independently by three musculoskeletal radiologists (W.H.J., T.R.M., L.D.K.) for the presence or absence of SLAP lesions. The presence of SLAP lesions was evaluated with a five-level confidence score: 0, definitely absent; 1, probably absent; 2, equivocal; 3, probably present; 4, definitely present. The confidence score for the presence of SLAP lesion with each imaging series (fat-suppressed T1-weighted transverse, coronal oblique, and sagittal oblique series and intermediate- and T2-weighted coronal oblique series) was determined separately, and then an overall confidence score based on all imaging series was determined by each reader.
The type of SLAP lesion was categorized according to Snyder et al (1). For type I, the superior labrum has marked fraying with a degenerative appearance. For type II, the superior labrum and attached biceps tendon are stripped off the underlying glenoid. For type III, a bucket-handle tear is present in the superior labrum. For type IV, a bucket-handle tear of the superior labrum is present in the superior labrum and the tear extends into the biceps tendon. These criteria were used for categorization at both MR arthrography and arthroscopy. At MR arthrographic review, an additional category of "indeterminate for sublabral recess versus type II SLAP tear" was used when a linear collection of contrast material extended beneath the labrum. Thus, for MR arthrography, any labrum interpreted as having a confidence score greater than 0 for the presence of a SLAP lesion was also categorized for morphology as type I, II, III, or IV SLAP or as "indeterminate for sublabral recess versus type II SLAP tear." The readers also recorded the presence and location of other labral tears and rotator cuff tears. Each reader was blinded to the clinical information and results of arthroscopy. MR arthrography was considered negative for SLAP lesion if the overall confidence score was 0–2 and positive if the score was 3–4.
MR arthrographic and surgical findings as determined from surgical reports were compared in all patients. Sensitivity, specificity, accuracy, and positive and negative predictive values for each reader were calculated for the detection of SLAP tears. For these calculations, type I SLAP lesions were regarded as negative, because type I SLAP lesions are considered a degenerative process and most often are not clinically relevant (3,11). At our institution, an isolated type I SLAP lesion identified at MR arthrography is not an indication for surgery, whereas surgery is performed for type II, III, or IV SLAP lesions.
Interobserver agreement for detection of SLAP lesions was calculated by using coefficients. The value can be interpreted as poor, = 0; slight, = 0–0.20; fair, = 0.21–0.40; moderate, = 0.41–0.60; substantial, = 0.61–0.80; or almost perfect, = 0.81–1.00 (12). To evaluate overall performance of the readers, receiver operating characteristic (ROC) curves for each reader were calculated by using an ROC analysis program with differences in areas under the ROC curves assessed by using a univariate z score test (CORROC2; Charles Metz, University of Chicago, Ill. Available at www-radiology .uchicago.edu/krl/toppage11.htm). To determine whether any of the imaging series provided more accurate identification of SLAP tears, the results for identification of SLAP tears for each reader were calculated on the basis of interpretation of each imaging series alone, as well as for the overall interpretation. Differences in sensitivity and specificity for interpretations based on different imaging series were tested for significance by using the McNemar statistic.
After correlation with arthroscopic reports, MR arthrograms of patients with SLAP lesions and false-positive cases were reviewed again by one reader to determine whether individual imaging features could be identified to decrease the number of false-positive tear interpretations. Imaging features examined on fat-suppressed coronal oblique T1-weighted images included the number of images behind the biceps anchor that showed contrast material extending beneath the labrum, irregularity of the margins of the contrast material extending beneath or into the labrum, extension of contrast material into the labral substance, and the presence of linear contrast material pointing laterally toward the biceps anchor. On coronal oblique T2-weighted images, the presence of sublabral or intralabral increased signal intensity on the second-echo image was assessed. Statistical analysis was performed with the Student t test for the number of images behind the biceps anchor that showed contrast material extending beneath the labrum. For all other comparisons, the 
2 test was used to determine whether any of these findings was useful for discriminating false-positive cases from cases of SLAP tears. For all statistical comparisons, significance was defined as P less than .05.
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RESULTS |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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With MR arthrography, the sensitivity and specificity for the first reader were 92% (23 of 25) and 84% (46 of 55), for the second reader were 92% (23 of 25) and 82% (45 of 55), and for the third reader were 84% (21 of 25) and 69% (38 of 55), respectively (Table 1). For detection of SLAP tears, interobserver agreement was substantial ( = 0.77) between the first and second readers, and moderate ( = 0.52 and 0.44, respectively) between the first and third readers and the second and third readers. For detection of SLAP tears, the areas under the ROC curves for each reader were 0.94, 0.93, and 0.83, respectively (Fig 1). These areas were not significantly different.
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2 test for all other comparisons). |
DISCUSSION |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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We found that the coronal oblique imaging plane was the most sensitive and the sagittal oblique plane was not sensitive for detection of SLAP tears, which is similar to the findings in a study (9) of nonenhanced MR imaging. The overall interpretation with all imaging sequences and interpretation with the fat-suppressed coronal oblique T1-weighted sequence provided the highest sensitivity for detection of tears. Interpretation based on the other individual sequences improved specificity, but with associated decreased sensitivity. On the basis of the higher specificity, the diagnosis of tear can be made with greater confidence when it is visible on the coronal oblique intermediate- and T2-weighted images. However, we interpret for SLAP tears with use of all imaging sequences because the higher sensitivity will result in fewer missed SLAP tears. High sensitivity is more important than high specificity because SLAP tears can be difficult to identify on the basis of clinical examination, often leading to delayed diagnosis (1).
We reexamined the presence of individual imaging findings with retrospective review to determine whether any one of these findings could be used to decrease the number of false-positive cases. It has been suggested that the presence of contrast material pointing medially rather than laterally toward the long head of the biceps tendon can be used to identify false-positive cases (10). We did not perceive this finding, or the other findings we examined, helpful in discriminating SLAP tears from false-positive interpretations. In our study, 60% of false-positive cases were due to sublabral contrast material interpreted as indicative of tear. The difficulty in discriminating sublabral recess versus tear is consistent with results from cadaveric studies (13,14), which indicates that overlap exists between type II SLAP tear and sublabral recess at MR imaging. False-positive interpretation also could be related to the loose attachment of the superior labrum to the glenoid and to the extension of hyaline cartilage over the edge of the glenoid rim at the 12-o’clock position (15). Meniscoid-type superior labrum has been described as a source of false-positive interpretation (8), but in our study there was only one patient in whom a meniscoid-type superior labrum was described at surgery, and this was associated with a type II SLAP tear. It is possible that a recently described technique with MR imaging during the application of traction to the arm may improve the ability of MR arthrography to discriminate between a sublabral recess and SLAP tear (16).
Although the number of type I, type III, and type IV tears was small, our results suggest that discrimination of these tears at MR imaging could be difficult. Our readers would have had higher overall accuracy categorizing tears if they had assumed all tears were type II rather than attempting to classify them on the basis of MR arthrographic appearance because of the high prevalence of type II tears in our population (88%). According to a report (17) in 10 patients in which nonenhanced MR imaging (n = 7) and MR arthrography with normal saline solution (n = 3) were used, MR examination was useful in establishing the type of SLAP lesion. In this prior study (17), the radiologists were aware of the surgical findings, which may have improved their performance. Our results are similar to those found in the recent MR arthrographic study by Bencardino et al (10) in which 76% (13 of 17) of SLAP tears were correctly classified. Larger studies will be needed to determine the accuracy for discriminating different types of SLAP tear.
This study had several limitations. The findings at arthroscopy could have been biased by the availability of the clinical MR reports. This was unavoidable because virtually all patients undergoing shoulder arthroscopy at out institution have been examined with MR arthrography to determine the need for surgery. Although the interpretation of the presence of SLAP tear by the orthopedist could have been biased, the type of tear was probably not biased, as the classification of tear type was not included in the clinical MR arthrography reports. Bias could have also been introduced for comparison of the individual imaging sequences because interpretation of the individual sequences was performed with the other imaging sequences available. This bias would likely lead to decreased discrepancy between interpretation of the different imaging sequences, and thus the differences found between imaging sequences in this study likely are valid. Another limitation is the small number of type III and IV tears present in the patient population. Finally, this study included only patients who underwent arthroscopic evaluation. Thus, the accuracy for diagnosis in patients not undergoing arthroscopy could not be assessed.
In conclusion, MR arthrography of the shoulder is a reliable and accurate diagnostic study for the detection of SLAP tears.
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FOOTNOTES |
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Abbreviations: ROC = receiver operating characteristic, SLAP = superior labral anterior posterior
Author contributions: Guarantors of integrity of entire study, W.H.J., T.R.M.; study concepts, all authors; study design, T.R.M.; definition of intellectual content, W.H.J., T.R.M.; literature research, W.H.J.; clinical studies, all authors; data acquisition, all authors; data analysis, W.H.J., T.R.M.; statistical analysis, W.H.J., T.R.M.; manuscript preparation, W.H.J., T.R.M.; manuscript editing, review, and final version approval, all authors.
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REFERENCES |
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TOPABSTRACTINTRODUCTIONMATERIALS AND METHODSRESULTSDISCUSSIONREFERENCES |
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