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Musculoskeletal Imaging |
1 Neuroskeletal Imaging, 255 N Sykes Creek Parkway, Merritt Island, FL
32953.
2 Department of Radiology, University of Miami School of Medicine, Miami, FL
33136.
Received December 24, 2003;
accepted after revision May 14, 2004.
Address correspondence to T. Magee
(tmageerad{at}cfl.rr.com).
Abstract
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MATERIALS AND METHODS. Conventional MRI and MR arthrographic examinations of the shoulder in 20 consecutive professional baseball players with shoulder pain were reviewed retrospectively by two musculoskeletal radiologists in consensus. These interpretations were compared with retrospective consensus interpretations of conventional MRI and MR arthrographic examinations of the shoulder obtained in a control group of 50 consecutive nonprofessional athletes with shoulder pain. MR images were assessed for full- or partial-thickness supraspinatus tendon tears, superior labral anteroposterior (SLAP) tears, and anterior or posterior labral tears.
RESULTS. In the 20 consecutive professional athlete patients, two full-thickness and six partial-thickness undersurface supraspinatus tendon tears were seen on MR arthrography but not seen on conventional MRI as well as six SLAP tears, two anterior labral tears, and one posterior labral tear. Three patients had both SLAP tears and full- or partial-thickness supraspinatus tendon tears. Of 14 patients with findings on MR arthrography that were not seen on MRI, 11 had arthroscopic correlation. In all 11, arthroscopic findings confirmed findings on MR arthrography. In the group of 50 nonprofessional athlete patients, five had additional findings on MR arthrography not seen on conventional MRI: two anterior labral tears, two partial-thickness supraspinatus tendon tears, and two SLAP tears. One patient had both a partial-thickness supraspinatus tendon tear and a SLAP tear seen on MR arthrography. The five patients with additional findings on MR arthrography had arthroscopy. In all five, arthroscopic findings confirmed the findings on MR arthrography.
CONCLUSION. MR arthrography is considerably more sensitive for detection of partial-thickness supraspinatus tears and labral tears than conventional MRI. MR arthrography showed injuries in addition to those seen on conventional MRI in 14 of 20 patients in the high-performance athlete group. These results suggest high-performance athletes may be a subgroup of patients for whom MR arthrography yields considerably more diagnostic information than conventional MRI.
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Identifying supraspinatus tendon tears on conventional MRI can be difficult in young throwing athletes because the tears are often small and may not appear as the large fluid-filled defects commonly seen in older patients [2, 3]. Also, supraspinatus tears can often occur in atypical locations [2]. In addition, labral tears are commonly present on MR images of the shoulder in high-performance athletes. These tears can be difficult to visualize on conventional MRI of the shoulder [2–5]. MR arthrography has been shown to be useful in revealing partial-thickness articular surface supraspinatus tendon tears and labral abnormalities [6–8]. For these reasons, we sought to retrospectively analyze our diagnostic accuracy on conventional MRI of the shoulder as opposed to MR arthrography of the shoulder in high-performance athletes (professional baseball players). We sought to compare that group with an age-matched group of nonprofessional athletes who also had undergone both conventional MRI and MR arthrography of the shoulder.
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All 20 patients also had MR arthrography performed immediately after conventional MRI. MR arthrography was performed with approximately 15 mL of a dilute mixture of Magnevist (gadopentetate dimeglumine, Berlex Laboratories) and saline (concentration, 0.15 mL of Magnevist per 20 mL of normal saline). A 22-gauge needle was placed in the glenohumeral joint via an anterior approach with the assistance of fluoroscopy. One of two musculoskeletal radiologists performed the injection. After injection of this mixture into the shoulder joint, the shoulder was exercised and oblique coronal, oblique sagittal, and axial fat-saturated T1-weighted images (677/12) were obtained. Oblique coronal fat-saturated T1-weighted images (677/12) obtained before MR arthrography for direct comparison with images obtained after MR arthrography. All MR arthrography was performed with a 12-cm field of view and a 4-mm slice thickness (with a 10% interslice gap). A shoulder array coil was used.
Images obtained in an age-matched control group of 50 nonprofessional athletes with shoulder pain who underwent conventional MRI and then immediately underwent MR arthrography were also analyzed and compared with the findings in the professional athlete group. These 50 patients were not specifically a group of throwing athletes but rather a cross section of the general population. MRI shoulder examinations of this group of 50 patients were performed between July 2003 and August 2003. The examinations were interpreted in consensus retrospectively by two musculoskeletal radiologists. The age range of the 50 patients was 18–45 years (mean, 26 years). All 50 patients were examined using the same imaging parameters as those used to examine the professional athletes.
All 20 conventional MRI and MR arthrographic examinations obtained in the professional baseball players and all 50 conventional MRI and MR arthrography examinations obtained in the nonprofessional athletes were retrospectively reviewed in consensus by two musculoskeletal radiologists, each with more than 10 years of experience interpreting musculoskeletal MRI examinations. The conventional MR images and MR arthrograms were reviewed in a random order, with studies of both professional athletes and nonprofessional athletes mixed together so as not to bias the reviewers. The reviewers were blinded to names of patients, prospective MRI reports, and arthroscopic results if any.
A superior labral anteroposterior tear (SLAP) was defined as a superior labral irregularity and high signal on T2-weighted images in the superior labrum or as fluid extending into the superior labrum on postarthrographic images. An anterior or posterior labral tear was defined as an area of abnormally increased signal in a labrum or as an irregular or detached labrum. A full-thickness supraspinatus tendon tear was defined as a tear or gap in the supraspinatus tendon extending through the entire expected thickness of the tendon. A partial-thickness supraspinatus tendon tear was defined as an incomplete gap or tear in the supraspinatus tendon with high signal on T2-weighted images extending into the tendon or as fluid extending into the tendon on postarthrographic images.
The observers assessed the images for the presence of anterior or posterior labral tears, SLAP tears, and full- or partial-thickness supraspinatus tendon tears. The observers did not grade the findings on the images (i.e., for high- or low-grade SLAP tears, large or small supraspinatus tendon tears, or detached or nondetached labral tears) but rather simply assessed whether such lesions were present or not. On retrospective review, positive findings were described only when both observers could definitively diagnose a labral tear or supraspinatus tendon tear on the basis of the images provided.
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Of the remaining six patients, two had SLAP tears; one had an anterior labral tear; and one had a posterior labral tear. These tears were seen on both conventional MRI and MR arthrography. All four of these tears were confirmed at subsequent arthroscopy. Two patients had no abnormality revealed on conventional MRI or MR arthrography. As of this date, neither of the two patient has had arthroscopic correlation.
In the control group of 50 nonprofessional athlete patients, five had findings on MR arthrography in additional to those seen on conventional MRI. Two partial-thickness supraspinatus tendon tears, two SLAP tears, and two anterior labral tears were seen on MR arthrography that were not seen on conventional MRI (one patient had both a SLAP tear and a partial-thickness supraspinatus tendon tear) (Figs. 6A, 6B, 7A, 7B, 8A, 8B).
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In the remaining 45 patients of the group, the following findings were seen on both conventional MRI and MR arthrography: eight SLAP tears, three anterior labral tears, two posterior labral tears, and three full-thickness and four partial-thickness supraspinatus tendon tears (Figs. 9A, 9B and 10A, 10B). Twenty-five patients had no abnormality revealed on conventional MRI or MR arthrography.
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A high prevalence of positive findings on conventional shoulder MRI and MR arthrography was also seen in the nonprofessional athlete patients. This prevalence was not as high as in the professional athlete group. Twenty of the 50 patients had findings on both conventional MRI and MR arthrography. Five of these patients had additional findings on MR arthrography that were not seen on conventional MRI examination.
Supraspinatus tendon tears have previously been described as being difficult to see on conventional MRI in young athletic individuals [2]. In our professional athlete group, two patients had full-thickness and six patients had partial-thickness supraspinatus tendon tears seen on MR arthrography that were not seen on conventional MRI. Six of these eight patients had tears requiring surgical intervention. In the nonprofessional athlete group, two patients had partial-thickness supraspinatus tendon tears seen well on MR arthrography but not seen on conventional MRI. Neither of these tears required surgical intervention, but one was confirmed arthroscopically at the repair of a SLAP tear. The reason that these tears were not seen on conventional MRI is open to speculation. One reason may be that the tears were secondary to repetitive microtrauma (of throwing) with resultant healing and fibrosis. Therefore, the typical appearance of a fluid signal in the area of tearing may not be present but rather be replaced by fibrosis with signal characteristics similar to those of the native supraspinatus tendon. An alternative explanation is that the portions of supraspinatus tendon adjacent to these tears may coapt, making tears difficult to see without fluid being injected into the joint.
Labral tears are common in athletes. Labral tears can be difficult to visualize on conventional MRI, especially when such tears are not displaced [2–4]. In the professional athlete group, nine additional labral tears were seen on MR arthrography that were not seen on conventional MRI. Eight of these tears required surgical intervention. Three patients had both SLAP tears and supraspinatus tendon tears repaired during the same surgery. In the group of nonprofessional athletes, two anterior labral tears and two SLAP tears were seen on MR arthrography that were not seen on conventional MRI. These four tears were confirmed arthroscopically.
The professional athlete population had a high rate of positive findings on MRI and MR arthrography. Eighteen of the 20 patients had abnormalities on conventional MRI or MR arthrography or both. If MR arthrography had not been performed in this population, 17 abnormalities in 14 patients (six SLAP tears, two anterior labral tears, one posterior labral tear, and two full-thickness and six partial-thickness supraspinatus tears) would not have been identified. Eleven of these patients had surgical intervention as a result of the additional findings on MR arthrography.
The nonprofessional athlete population also had a high prevalence of positive findings on MRI and MR arthrography. Twenty of the 50 patients had abnormalities on conventional MRI or MR arthrography or both. If MR arthrography had not been performed in this population, six abnormalities in five patients (two anterior labral tears, two partial-thickness supraspinatus tendon tears, and two SLAP tears) would not have been identified.
Overall, MR arthrography altered treatment in 11 of the professional athletes. Findings on MR arthrography that were additional to those on conventional MRI and that required surgical intervention included two full-thickness and three partial-thickness supraspinatus tendon tears, six SLAP tears, two anterior labral tears, and one posterior labral tear. Three patients had both SLAP tears and supraspinatus tendon tears repaired during the same surgery. MR arthrography altered treatment in four of the nonprofessional athletes. Findings on MR arthrography that were additional to those on conventional MRI and that required surgical intervention included two anterior labral tears and two SLAP tears.
The reason MR arthrography yielded additional information more often in the professional athlete population than in the nonprofessional athlete population is open to speculation. In the professional athlete, supraspinatus tendon injuries and labral tears may be due to chronic microtrauma that results in subtle injuries with some degree of fibrosis, making the injuries difficult to visualize without contrast material being injected into the joint. In the nonprofessional athlete, supraspinatus tendon injuries and labral tears may be more commonly due to a specific injury that results in larger and more readily visible tears. Therefore, in most cases, contrast material in the joint may not be necessary to visualize the tears.
The population that we studied was a group of elite athletes (professional baseball players) and, therefore, extrapolating our findings to the general population may be difficult. Because of the results we described, we perform shoulder MR arthrography in our practice on all throwing athletes and no longer perform conventional MRI in this population. We supplement the contrast-enhanced fat-saturated T1-weighted images with fat-saturated T2-weighted images obtained in the coronal and sagittal planes.
Shoulder MR arthrography is more sensitive than conventional shoulder MRI for lesion detection in the general population also. However, whether this modest added benefit warrants the performance of arthrography on all patients remains to be determined.
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