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Original Research |
1 Both authors: Department of Radiology, Neuroskeletal Imaging, 255 N Sykes Creek Pkwy., Merritt Island, FL 32953.
Received June 18, 2005;
accepted after revision August 17, 2005.
Address correspondence to T. Magee
(tmageerad{at}cfl.rr.com).
Abstract
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MATERIALS AND METHODS. Two experienced musculoskeletal radiologists retrospectively reviewed MR images of the shoulder in 150 consecutive patients who had subsequent arthroscopy. All patients had oblique coronal and sagittal T1-weighted and fat-saturated T2-weighted axial, oblique coronal, and sagittal imaging performed.
The radiologists interpreted the MR images by consensus without knowledge of the arthroscopy results. Scans were interpreted for full-thickness or partial-thickness supraspinatus tendon tears. If partial-thickness supraspinatus tendon tears were seen on MRI, the reviewers noted whether the partial-thickness tear was articular or bursal in location. The radiologists also separated the supraspinatus tendon tears into small (< 1 cm retraction from the humeral head) and large (> 1 cm retraction from the humeral head).
All 150 patients went on to arthroscopy. After consensus review of the MR images, arthroscopy results were compared with consensus MR interpretations.
RESULTS. Ninety-eight of the 150 patients had full-thickness supraspinatus tendon tears at arthroscopy. Twenty-six of the 150 patients had partial-thickness supraspinatus tendon tears. Seventeen of these 26 partial-thickness tears were along the articular surface and nine were along the bursal surface.
Ninety-six of 98 full-thickness tears seen at arthroscopy were seen on consensus MRI interpretation. All 26 partial-thickness tears seen at arthroscopy were seen at consensus MR interpretation; however, two of the partial-thickness articular surface tears seen at arthroscopy were interpreted as full-thickness tears on consensus MRI interpretation.
Twenty-eight of the 98 full-thickness supraspinatus tendon tears were small tears (< 1 cm retraction from the humeral head) on arthroscopy. Two of these 28 small tears seen on arthroscopy were not seen on consensus MRI interpretation. Twenty-six patients had intact supraspinatus tendons on both retrospective consensus MRI interpretation and at arthroscopy.
CONCLUSION. MRI of the shoulder at 3.0 T is highly sensitive and specific compared with arthroscopy in the detection of full-thickness and partial-thickness supraspinatus tendon tears.
Keywords: MRI • musculoskeletal imaging • shoulder • supraspinatus tendon
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To our knowledge, the sensitivity and specificity of 3.0-T MRI of the shoulder for detection of full- and partial-thickness supraspinatus tendon tears compared with arthroscopy have not been specifically assessed. We undertook a retrospective review of 150 shoulder MRI examinations to determine the level of sensitivity and specificity that MRI at 3.0 T provides for shoulder imaging of full- and partial-thickness supraspinatus tendon tears compared with arthroscopy. In addition, small tears (< 1 cm retraction from the humeral head) were specifically assessed.
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All patients underwent MRI of the shoulder in oblique coronal, oblique sagittal, and axial planes on a 3.0-T Signa scanner (GE Healthcare). Oblique coronal and sagittal fast spin-echo T1-weighted (TR/TE, 550/10; number of excitations [NEX], 2); oblique coronal and sagittal fast spin-echo T2-weighted (3,850/55; NEX, 4); and fast spin-echo proton-density axial (3,250/55; NEX, 3) sequences with a field of view of 14 cm on all images were used. Slice thickness was 4 mm with a 10% interslice gap on all sequences except for the fast spin-echo proton-density axial sequence, which had a 3-mm slice thickness. The echo-train length was 10 on all T2-weighted and proton-density sequences and 3 on the T1-weighted sequences. The bandwidth was 31.25 kHz on all sequences. The imaging time for the oblique coronal and sagittal T2-weighted sequences was 4 minutes 43 seconds. The imaging time for the proton-density axial sequences was 3 minutes 26 seconds, and the imaging time for the T1-weighted sequences was 2 minutes 28 seconds. The matrix for all T2-weighted sequences was 320 x 320, and the matrix for all T1-weighted sequences was 320 x 256. A prototype USA Instruments three-channel phased-array shoulder coil was used.
All 150 patients had their MRI examinations retrospectively reviewed by consensus of two reviewers. The reviewers were blinded to the results of arthroscopy at the time of consensus review. Consensus was achieved when both reviewers agreed that a full- or partial-thickness supraspinatus tendon tear was present or not on an MRI examination. Intrasubstance partial-thickness supraspinatus tendon tears were not assessed because they could not be correlated with arthroscopy. Other findings, such as labral tears, were not assessed at the time of retrospective review. Retrospective MRI interpretations were then correlated with the results of arthroscopy. The MRI criterion used for diagnosis of full-thickness supraspinatus tendon tears was the visualization of a complete defect in the supraspinatus tendon extending from the articular to the bursal surface of the tendon. The MRI criterion used for diagnosis of partial-thickness supraspinatus tendon tears was the visualization of a partial defect in the supraspinatus tendon extending along either the articular or bursal surface of the tendon. On all partial-thickness tears, an MRI estimation of the percentage of fibers disrupted was made as was a determination of whether the partial-thickness tear was along the articular or bursal surface. Supraspinatus tendon tears were also divided into small (< 1 cm retraction from the humeral head attachment site) and large (> 1 cm retraction from the humeral head attachment site).
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On arthroscopy, 98 patients had full-thickness supraspinatus tendon tears. Ninety-six of these full-thickness supraspinatus tendon tears were seen on consensus MRI review. Two of the full-thickness supraspinatus tendon tears seen on arthroscopy were not seen on consensus MRI review.
Twenty-six patients had partial-thickness supraspinatus tendon tears on arthroscopy with 17 of these tears along the articular surface and nine along the bursal surface. All nine bursal surface tears were seen on consensus MRI review. Fifteen of the 17 articular surface tears were seen on consensus MRI review. Two of the 17 articular surface tears were described as full-thickness tears on consensus MRI review. Both of these were considered small tears (< 1 cm retraction from the humeral head attachment site).
Twenty-six patients had intact supraspinatus tendons on arthroscopy. All 26 had their supraspinatus tendons described as intact on consensus MRI review.
Tendon tears other than the supraspinatus tendon were not analyzed in this study because our orthopedic surgeons operate primarily on the basis of whether the supraspinatus tendon is torn. In this series, there were no isolated tendon tears other than the supraspinatus tendon.
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MRI at 1.5 T or lower has been less sensitive and specific for the detection of partial-thickness supraspinatus tendon tears than it has for the detection of full-thickness tears. A partial tear is diagnosed when there is a tendon defect that is intrasubstance or that extends to either the articular or bursal surface only. In previous studies, MRI sensitivity for detection of partial-thickness tears of the supraspinatus tendon ranged between 35-87% [5]. The sensitivity for the diagnosis of partial tears has been described as poor [5].
In our study, MRI detection and characterization of partial-thickness tears was sensitive (88%) and specific (100%). This difference may be attributable to the fact that with a better signal-to-noise ratio (SNR) on 3.0-T imaging, the contrast of the torn as opposed to the intact portion of the tendon may be better delineated compared with 1.5-T or lower scanners.
On retrospective MRI review, attempts were made to estimate the percentage of fibers disrupted. This was also done by the orthopedic surgeons during arthroscopy. The MRI estimates of the percentage of torn fibers correlated well with the estimates given by the orthopedic surgeons on arthroscopy reports except for two cases in which full-thickness tears were described on MRI, whereas partial-thickness tears were seen at arthroscopy. Fifteen tears were characterized as articular surface and nine as bursal surface on MRI. These findings correlated with findings on arthroscopy.
Two articular surface partial-thickness supraspinatus tendon tears seen on arthroscopy were described as full-thickness tears on MRI. Those articular surface partial-thickness tears were each described as approximately 70% of the expected thickness of the supraspinatus tendon on arthroscopy. Each of these two supraspinatus tendon tears extended from the humeral head attachment site by less than 1 cm.
Two articles in the orthopedics literature indicate that partial-thickness supraspinatus tendon tears of greater than 50% thickness should be surgically repaired. In the two patients in whom full-thickness tears were described on MRI but 70% partial-thickness tears were seen on arthroscopy, the surgeons involved indicated that the MRI overestimations did not affect surgical management because the tears would be treated surgically in either case [6, 7].
The subset of supraspinatus tendon tears retracted from the humeral head attachment site by less than 1 cm accounted for the two false-negative interpretations of supraspinatus tendon tears on MRI. Both of these tears were described as retracted by less than 1 cm on arthroscopy.
Twenty-six patients had intact supraspinatus tendons on arthroscopy. All 26 of these patients had the supraspinatus tendon described as intact on MRI.
The high accuracy of 3.0-T MRI scanners for the detection of full-thickness supraspinatus tendon tears was also found to be true for 1.5-T or lower MRI scanners. In the two cases in which a full-thickness tear was not seen on MRI, a tear could not be seen retrospectively even when arthroscopic results were known. Presumptively, there was fibrosis in the area of the supraspinatus tendon tear simulating an intact tendon in these cases.
MRI at 3.0 T allows for a higher SNR compared with MRI at 1.5 T. The spin-spin relaxation time, T2, remains fairly constant at different field strengths. However the spin-lattice relaxation time, T1, increases as the field strength increases. Therefore, on 3.0-T scanners, the TR must be longer than on 1.5-T scanners to maximize the SNR gain. At 3.0 T, the TR must be longer to attain the same type of contrast on T1-weighted images as seen at 1.5 T. Also on 3.0-T scanners, the TE must be slightly shorter than on 1.5-T scanners to account for decreased T2 relaxation time [8, 9].
The parameters used for our shoulder imaging study have an increased TR and a decreased TE on all sequences compared with the parameters previously used on our 1.5-T MRI scanner. We made this change to optimize the SNR on the 3.0-T MRI scanner.
The higher SNR of 3.0-T MRI can also be used to improve imaging speed or resolution. However, there is increased T1 relaxation time and decreased T2 relaxation time at 3.0 T compared with 1.5 T. Also, at 3.0 T, there is increased sensitivity to magnetic susceptibility artifact and chemical shift artifact compared with 1.5 T. To reduce the chemical shift artifact, we have doubled our bandwidth on 3.0 T compared with the bandwidth used at 1.5 T. Doubling the bandwidth results in a reduction of SNR by the square root of 2. The increase in SNR has allowed for faster imaging at 3.0 T with improved resolution and thinner slice thickness compared with 1.5 T [9]. In our practice, we have experienced faster throughput and higher-resolution imaging and are more confident in making a diagnosis of a full- or partial-thickness supraspinatus tendon tear after changing to 3.0-T imaging from 1.5-T imaging.
MRI at 3.0 T appears particularly useful in the delineation of small full-thickness and partial-thickness supraspinatus tendon tears. Our accuracy in the diagnosis of partial-thickness supraspinatus tendon tears is significantly better than those previously reported at 1.5 T [1-5]. In the two patients in whom full-thickness supraspinatus tendon tears were described on MRI and high-grade partial-thickness tears were found at arthroscopy, there was no practical effect on surgical management because these patients would have been treated surgically in either case. The accuracy of MRI at 3.0 T in the diagnosis of partial-thickness supraspinatus tendon tears is particularly important in that most surgeons operate on partial-thickness supraspinatus tendon tears when they reach 50% or greater [6, 7].
There are limitations to this study. The MR images were analyzed retrospectively after arthroscopy rather than prospectively. MR images were reviewed by consensus so intraobserver or interobserver variability could not be assessed. The surgeons were not blinded to the MRI results before arthroscopy.
In conclusion, 3.0-T MRI of the shoulder in detection of full- and partial-thickness supraspinatus tendon tears compares highly favorably in sensitivity and specificity with previous studies performed on 1.5-T field strength or lower scanners. On occasion, small (< 1 cm) full-thickness tears may be difficult to visualize on MRI. This may be due to fibrosis at the site of the tear simulating an intact tendon on MRI.
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