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1 Department of Radiology, Technische Universität München, Klinikum
rechts der Isar, Ismaninger Strasse 22, Munich, D-81675 Germany.
2 Department of Sports Orthopedics, Technische Universität München,
Conollystrasse 32, Munich, D-80809 Germany.
Received April 3, 2003;
accepted after revision November 6, 2003.
Address correspondence to S. Waldt.
Abstract
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MATERIALS AND METHODS. Two hundred sixty-five MR arthrograms including 68 MR arthrograms of patients with arthroscopically proven SLAP lesions of the shoulder and 197 MR arthrograms of patients with an intact superior labrum and biceps anchor were retrospectively reviewed in random order. MR arthrography was performed using triplanar T1-weighted spin-echo sequences and a coronal oblique T2-weighted fast spin-echo sequence. MR arthrograms were evaluated by two radiologists with agreement by consensus, and the results were compared with arthroscopic findings.
RESULTS. Of 68 SLAP lesions, seven (10%) were arthroscopically classified as type I, 41 (60%) as type II (including 20 type II lesions with coexisting Bankart lesions [29%]), 14 (21%) as type III, and six (9%) as type IV. Compared with arthroscopy as the gold standard, MR arthrography showed a sensitivity of 82% and a specificity of 98% for the overall detection of SLAP lesions. MR arthrographic grading and arthroscopic grading were concurrent in 45 (66%) of 68 arthroscopic diagnoses. Of the surgically confirmed SLAP lesions, involvement of the biceps insertion and SLAP type II lesions with coexisting Bankart lesions were assessed correctly in 75% and 95% of cases, respectively.
CONCLUSION. MR arthrography is a highly effective method for the detection of SLAP lesions, but this technique is limited in the classification of different types of SLAP lesions. However, for preoperative planning MR arthrography provides accurate information about the stability of the biceps insertion and the presence of associated anteroinferior labral injuries.
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These arthroscopic grades do not correlate with the severity of clinical symptoms. The current concept is that lesions with an unstable biceps insertion provoke instability that often causes secondary problems, such as impingement or even rotator cuff tears. Lesions with unstable biceps insertion (types II and IV according to the classification system established by Snyder et al. [1]) require reattachment of the biceps tendon to reestablish the stabilizing effect of the biceps tendon, whereas débridement procedures are performed in cases of type III lesions. SLAP type I lesions usually do not require surgical treatment [2–4]. Thus, for the preoperative planning, discrimination of the types of SLAP lesions is of importance.
The purpose of this study was to evaluate the diagnostic performance of MR arthrography in the assessment of SLAP lesions of the shoulder with emphasis on the classification of SLAP lesions.
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Altogether, MR arthrograms of 265 patients (182 male and 83 female patients; age range, 15–64 years; mean age, 35 years; 170 right and 95 left shoulders) were evaluated retrospectively in this study. Arthroscopy was performed by two orthopedic surgeons experienced in shoulder surgery.
Clinical presentations comprised 110 patients with impingement syndrome, 134 patients with acute or chronic instability of the glenohumeral joint, and 21 patients with suspected SLAP lesions.
Twenty-six of the 68 patients with SLAP lesions had associated findings at arthroscopy: 20 SLAP type II lesions and one SLAP type III lesion had an additional Bankart lesion, three SLAP type I lesions were associated with tears of the supraspinatus tendon at the tendon insertion, and two SLAP type II lesions had an additional partial tear in the deep surface of the supraspinatus tendon. Fourteen patients with surgically confirmed SLAP lesions presented clinically with posterior glenoid impingement.
The average time interval between MR arthrography and shoulder arthroscopy of these 265 patients was 44 days (range, 1–145 days). None of the patients had previously undergone shoulder surgery.
Injection of contrast media for MR arthrography was performed under fluoroscopic guidance via an anterior approach. Intraarticular positioning of a 20- to 22-gauge needle (TSK-SUPRA, TSK) was confirmed by injection of a small amount of iodinated contrast medium (Ultravist [iopromide] 300, Schering). Subsequently, 12–20 mL of a 2.5-mmol/L solution (1:200) consisting of gadopentetate dimeglumine (Magnevist, Schering) and normal saline was injected. MRI was commenced immediately after contrast injection (within 15 min after intraarticular injection) on a 1.0-T system (Magnetom Expert, Siemens) using a dedicated shoulder coil. Coronal oblique, sagittal oblique, and axial T1-weighted spin-echo sequences (TR range/TE range, 500–700/14–16) and a coronal oblique T2-weighted fast spin-echo pulse sequence (3,000–4,200/90–115) were performed. Parameters for all sequences were a section thickness of 3 mm with a 0.1-mm intersection gap, a matrix size of 256 x 192, and a field of view of 14–16 cm.
All MR arthrograms were reviewed by two radiologists in consensus who had no knowledge of clinical histories and arthroscopic results. They reviewed these MR arthrograms for the first time during this study. At arthroscopy and MR arthrography, the SLAP lesions were classified as one of four types, according to the classification system established by Snyder et al. [1]. Further classification was performed in this study. SLAP type II lesions were subcategorized into two groups: type II lesions restricted to the superior glenoid labrum were demarcated form type II lesions with extension of the tear into the anteroinferior labrum. Type II lesions with coexisting Bankart lesions—type V lesions according the additional classification system by Maffet et al. [5]—were also evaluated in our study.
MRI criteria established in previous studies [6–8] were applied for detection and categorization of SLAP lesions: fraying of the free edge of the superior glenoid labrum evident on coronal oblique images characterized a SLAP type I lesion. A SLAP type II lesion was diagnosed if contrast media extended into the superior glenoid labrum and the biceps anchor, best visualized on coronal oblique MR images. Separation of the superior labrum from the glenoid rim on axial images was regarded as a corresponding finding but, as previously reported, was not reliable enough to be of high diagnostic value [8].
The following imaging features were used to differentiate between a SLAP type II lesion and a sublabral recess: lateral or superior extension of contrast media into the superior labrum and the biceps anchor indicated a SLAP type II lesion, whereas medial extension of the contrast media with a smooth linear appearance between the superior labrum and the glenoid rim was indicative of a sublabral recess. In the posterior third of the superior glenoid labrum, contrast media extension at the glenoid surface was a criterion for a labral tear.
An additional finding of a SLAP type II lesion with a coexisting Bankart lesion was a contrast media interface separating the avulsed anteroinferior labrum from the glenoid; this finding was best visualized on axial images. Extension of the labral tear was defined on sequential axial images and on sagittal oblique images.
Features of a SLAP type III lesion were an additional contrast media interface between the superior labrum and the preserved biceps anchor and a triangular segment or displacement of the superior glenoid labrum within the joint space evident on coronal oblique images. A type IV lesion was diagnosed if features of a type III lesion were present with additional evidence of an avulsion of the biceps anchor. Extension of contrast media into the biceps anchor on axial, coronal oblique, or sagittal oblique images with displacement of a bucket-handle fragment was considered indicative of a SLAP type IV lesion.
Imaging findings on MR arthrography were compared with arthroscopic findings in all patients. With arthroscopy as the gold standard, sensitivities, specificities, accuracies, negative and positive predictive values, and the corresponding 95% confidence intervals were calculated for the overall detection of SLAP types I–IV lesions. The same statistical values were calculated for SLAP types II–IV lesions. Because surgical treatment of SLAP type I lesions is not indicated, patients with evidence of SLAP type I lesions were regarded as cases that were negative for the presence of a SLAP lesion in one part of our analysis.
We assessed the degree of correlation between the MR arthrographic grading and the arthroscopic grading of SLAP lesions. For each subcategory of SLAP lesions (types I–IV lesions and type II lesions with coexisting Bankart lesions), the percentage of correctly classified lesions was calculated. Furthermore, we analyzed the mechanisms of injury in all patients with arthroscopically confirmed SLAP lesions and correlated this finding with the resulting type of SLAP lesion. Information about the mechanism of injury was taken from hospital records. SLAP lesions were attributed to four mechanisms of injury: external abduction, compression force on the biceps anchor, traction on the biceps anchor, and no specific mechanism of injury. The chi-square test was used to determine whether the correlation between the mechanism of injury and the resulting type of SLAP lesion was of statistical relevance.
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With MR arthrography, the correct diagnosis of a SLAP lesion was established in 56 of 68 patients, and an intact superior labral–bicipital complex was identified in 194 of 197 patients. Twelve lesions of the labral–bicipital complex were missed at MR arthrography (false-negative cases) (Fig. 3), and three lesions were not confirmed at surgery (false-positive cases) (Fig. 4).
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Regarding SLAP type I lesions as cases of negative findings, 61 SLAP lesions were encountered, of which 41 (67%) were classified at arthroscopy as type II (including 20 SLAP type II lesions with coexisting Bankart lesions [33%]), 14 (23%) as type III, and six (10%) as type IV lesions.
In detection of types II–IV lesions, MR arthrography had a sensitivity of 84% and a specificity of 99%. Exact agreement between MR arthrographic grading and arthroscopic grading was present in 45 (66%) of 68 arthroscopic diagnoses. Type I lesions were correctly categorized in 43% (3/7); type II lesions, in 73% (30/41); type III lesions, in 71% (10/14) (Fig. 5A, 5B); and type IV lesions, in 33% (2/6) (Fig. 6A, 6B, 6C, 6D).
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Twenty-two of the surgically confirmed SLAP lesions were overlooked or classified into wrong subcategories at MR arthrography. Eight lesions classified as type II injuries at arthroscopy showed findings consistent with a sublabral recess at MR arthrography. Three lesions classified as type I injuries at arthroscopy were overlooked at MR arthrography. Eleven of the surgically confirmed SLAP lesions were classified into wrong subcategories (Table 2).
Involvement of the biceps anchor was assessed correctly in 75% (51/68) of arthroscopically proven SLAP lesions. Twenty SLAP type II lesions with extension of the labral tear into the anteroinferior labrum were diagnosed at arthroscopy. Nineteen (95%) of these lesions were detected and graded correctly at MR arthrography (Fig. 7A, 7B, 7C). One arthroscopically confirmed SLAP type II lesion with a coexisting Bankart lesion was classified as a SLAP type I lesion at MR arthrography. One lesion classified as a type II lesion with a coexisting Bankart lesion at MR arthrography was identified as a type III lesion at arthroscopy with extension of the labral tear into the anteroinferior labrum. The chi-square test (p < 0.0001, contingency coefficient = 0.726) showed a statistically significant correlation between the mechanism of injury and the resulting type of SLAP lesion. Table 3 shows our results with regard to the correlation of the mechanism of injury with the resulting type of SLAP lesion.
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The superior portion of the glenoid labrum is functionally important because it serves as an anchor for the biceps tendon, which provides stability to the glenohumeral joint. Impingement or even rotator cuff tears can be caused secondary to superior shoulder instability originating from an unstable biceps insertion, which is present in SLAP types II and IV lesions [10, 11]. In our study, 14 patients with SLAP lesions presented clinically with posterior glenoid impingement; tears in the deep surface of the supraspinatus tendon were found in only three cases. Therefore, the clinical presentation of patients is often complex and is not necessarily indicative of a SLAP lesion [2]. Thus, a reliable and accurate imaging diagnosis of this type of injury is important.
With a sensitivity of 84% and a specificity of 99% for the detection of SLAP types II–IV lesions, our results are comparable with the results of studies on the diagnostic accuracy of MR arthrography observed in smaller series [6, 7]. Compared with MR arthrography, unenhanced MRI has been shown to have lower sensitivities for the detection of SLAP lesions in all studies [12, 13] with the exception of a study by Connell et al. [14]. The inclusion of type I lesions slightly modifies our results with sensitivity and specificity decreasing to 82% and 98%, respectively.
Because surgical treatment is based on the integrity of the biceps anchor, preoperative discrimination of the types of SLAP lesions is important. Types II and IV lesions require refixation of the biceps tendon to reestablish the stabilizing effect of the biceps tendon, whereas débridement procedures are performed in cases of type III lesions. SLAP type I lesions usually do not require surgical treatment [2–4]. Because the Bankart lesion is the most important cause of anterior shoulder instability, discrimination of SLAP type II lesions with extension of the labral tear into the anteroinferior labrum is of clinical and therapeutic relevance [2, 15]. Reconstruction of the anteroinferior labral capsular complex is of particular importance in the treatment of SLAP type II lesions with a coexisting Bankart lesion.
Arthroscopy revealed seven SLAP type I lesions, of which only three (43%) were detected and graded correctly on MR arthrography. Furthermore, three false-positive type I lesions were diagnosed on MR arthrography; all of these lesions occurred in elderly patients with rotator cuff lesions. Regarding SLAP type I lesions, our results are consistent with those of Hodler et al. [16]. Those researchers deduced that fraying of the superior labrum cannot be accurately detected on MRI. Because SLAP type I lesions represent degenerative changes of the superior labrum, which do not require surgical treatment [17], the performance of MR arthrography for the diagnosis of SLAP lesions is, in our opinion, not influenced by this detriment.
Thirty (73%) of 41 arthroscopically proven SLAP type II lesions were graded correctly on MR arthrography. Only three lesions were classified into the wrong subcategory. In eight cases, sublabral accumulations of contrast media were interpreted as sublabral recesses rather than type II lesions at MR arthrography. Our results are consistent with results from previous cadaveric and clinical studies that indicate an overlap between type II injuries and sublabral recesses at MR arthrography [5, 18–20]. However, in view of the absence of false-positive findings with interpretation of sublabral recesses as SLAP type II lesions and the fact that the lesions misinterpreted at MR arthrography were diagnosed at early stages of SLAP surgery, sublabral recesses might have been misdiagnosed as SLAP lesions at surgery.
SLAP lesions with extension of the labral tear into the anteroinferior labrum were classified correctly in 95% of surgically proven cases. In those lesions, the large extent of labral injury probably caused the avulsed fragment to be easily elevated by the contrast media, demarcating the exact course of tearing. Furthermore, those lesions could not be misinterpreted as sublabral recesses because of the large extent of labral lesions.
Types III and IV lesions were graded correctly in 71% and 33% of cases, respectively. The course of labral tears in SLAP types III and IV lesions is complex, diagnosed when contrast media is seen extending into the superior labrum and between the superior labrum and the biceps anchor with or without extension to the biceps tendon. Correct classification of these lesions was, at times, difficult because not all components of the labral tear were delineated by contrast media.
Involvement of the biceps anchor was assessed correctly in 75% (51/68) of arthroscopically proven SLAP lesions. Extension of the labral tear into the biceps anchor was overlooked in two type IV lesions and in 11 type II lesions. In both cases of type IV lesions and in one type II lesion, capsular distention was inadequate and may have contributed to the extension to the biceps anchor being missed. Intraarticular application of sufficient contrast media with adequate capsular distention appears to be a prerequisite for correct categorization of SLAP lesions. However, healing changes and resynovialization may also prevent contrast media extension in preexisting tears.
Different mechanisms of injury have been proposed as causes of SLAP lesions [1, 5, 21]. SLAP injuries may result from compression forces to the shoulder, usually after a fall onto an outstretched arm or from traction on the biceps anchor, often secondary to repetitive overhead use. SLAP lesions also may occur as a result of external abduction forces, frequently in association with lesions of the anterior labrum–ligament complex in patients with anterior instability. Handelberg et al. [21] assumed that different mechanisms of injury result in different types of SLAP lesions. Fifteen (75%) of 20 patients with type II lesions without extension to the anteroinferior labrum in our study were athletes with overhead sports activity. In eight (57%) of 14 patients with type III and three (50%) of six patients with type IV lesions, SLAP lesions occurred after a fall onto the outstretched arm, whereas 19 (95%) of 20 of patients with SLAP type II lesion with a coexisting Bankart lesion presented with acute or chronic instability. Type I lesions were present in athletes with overhead sports activity (four of seven type I lesions) and in elderly patients with impingement pain (three of seven type I lesions). We deduce from our results that athletes with overhead sports activity are prone to develop SLAP type I or II lesions. SLAP type I lesions are also a typical finding in elderly patients, resulting from physiologic degenerative changes rather than from a specific pattern of injury. Patients who present after a fall onto an outstretched arm are more likely to have SLAP type III or IV lesions. Type II lesions with extension of the labral tear into the anteroinferior labrum are strongly associated with acute or chronic instability. In those lesions, the anteroinferior labral lesion can be considered as the main injury with the SLAP lesion being an associated injury [2].
Our study has several limitations. Although arthroscopy was the best standard available for this study, it is an operator-dependent method. In our opinion, misinterpretation of sublabral recesses and SLAP type II lesions at arthroscopy was a probable source of error. Because of the developing understanding of the functional importance of SLAP lesions, there was a learning curve of the arthroscopic shoulder evaluation from 1996–2002, which led to a more precise arthroscopic categorization of SLAP lesions and associated injuries. The fact that the decision to perform arthroscopy was based not only on clinical findings but also on imaging findings introduced a verification bias. We did not assess interobserver variation because all MR arthrograms were analyzed by two radiologists in consensus. Although the total number of SLAP lesions was higher in our study than in previous studies [6, 7], the number of SLAP types I and IV lesions was relatively small in our patient population.
The performance of MR arthrography in the evaluation of SLAP lesions could be improved by taking advantage of new hardware. Higher spatial resolution allows more accurate visualization of the labral–bicipital complex. Using one sequence in the abduction–external rotation position would probably improve diagnosis of associated injuries, especially partial tears of the rotator cuff and injuries of the anteroinferior labrum–ligament complex [22].
In conclusion, MR arthrography is a highly effective method for the detection of SLAP lesions. The remaining difficulty in the detection of SLAP lesion seems to be the high prevalence of sublabral recesses, with similar MR arthrography findings as type II lesions. However, the distinction of sublabral recesses and SLAP type II lesions may be difficult even at arthroscopy.
Our results suggest that MR arthrography is limited regarding the classification of SLAP lesions. However, for preoperative planning MR arthrography provides accurate information about the stability of the biceps insertion and the presence of associated anteroinferior labral injuries.
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TopAbstractIntroductionMaterials and MethodsResultsDiscussionReferences |
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