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Musculoskeletal Imaging |
1 From the Departments of Radiology (C.W.A.P., M.Z., D.W., J.H.) and Orthopedic Surgery (C.G.), Orthopedic University Clinic, Balgrist Forchstrasse 340, CH-8008 Zurich, Switzerland. Received September 16, 1998; revision requested November 3; final revision received March 22, 1999; accepted July 1. Address reprint requests to C.W.A.P. (e-mail: pfirrm16@centralnet.ch).
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Abstract |
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MATERIALS AND METHODS: MR arthrograms in 50 consecutive patients (29 with normal subscapularis tendons, 11 with a lesion in the cranial quarter, seven with a major tear but not complete detachment, three with complete detachment) with arthroscopic or surgical confirmation were evaluated independently by two radiologists. Diagnosis was established on findings from transverse and/or parasagittal images.
RESULTS: With transverse images alone, sensitivity was 95%/100% (reader 1/reader 2); specificity was 55%/62%. With parasagittal images alone, sensitivity was 91%/91%; specificity was 76%/90%. With combined images, sensitivity was 91%/91%; specificity was 86%/79%. Interobserver agreement was substantial (
= 0.67). Forty-one of 50 (82%) grades for subscapularis abnormalities matched at MR imaging and surgery; nine mismatches differed by only one degree. Several signs were specific (90%–100%) but insensitive (29%–62%); these included leakage of contrast material onto the lesser tuberosity, fatty degeneration of the subscapularis muscle, and abnormality in the course of the long biceps tendon (luxation, subluxation).
CONCLUSION: MR arthrography is accurate in the detection and grading of subscapularis tendon lesions. Specificity of findings on transverse images for this diagnosis can be improved by including indirect signs and findings on parasagittal images.
Index terms: Magnetic resonance (MR), arthrography, 414.121411, 414.12143, 414.122 • Shoulder, arthrography, 414.122 • Tendons, injuries, 414.4199 • Tendons, MR, 414.121411, 414.12143, 414.122
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Introduction |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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Magnetic resonance (MR) imaging is accurate in the detection of abnormalities in the rotator cuff (8–13). However, most investigators have focused on supraspinatus tendon lesions. Little attention has been paid to disorders of the subscapularis tendon in the radiology literature (14,15). To our knowledge, no formal analysis of MR arthrography in the subscapularis tendon has been published. The purpose of this investigation was to assess the diagnostic accuracy of MR arthrography in the detection and grading of subscapularis tendon lesions.
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MATERIALS AND METHODS |
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Thirty-five patients were men, and 15 were women. Their ages were between 21 and 76 years (mean age, 50.6 years). Open surgery was performed in 29 patients, and arthroscopic surgery was performed in the remaining 21. The indications for surgery or arthroscopy were rotator cuff tear (n = 28), shoulder impingement syndrome (n = 7), instability (n = 6), or chronic shoulder pain with multiple clinical diagnoses (n = 9).
At surgery, the subscapularis tendon was normal (grade 0) in 29 patients. A lesion of the upper margin (tear or tendon degeneration of less than one-quarter of the craniocaudal diameter, grade 1) (16) was observed in 11, major tears (more than one-quarter of the craniocaudal diameter of the tendon, but no complete detachment; grade 2) was observed in seven, and complete detachment of the tendon from the lesser tuberosity (grade 3) was observed in three. Additional intraoperative findings were full-thickness (n = 23) or partial-thickness (n = 6) tears of the supraspinatus and infraspinatus tendons, lesions of the long biceps tendon (n = 24), and labral abnormalities (n = 11).
MR Imaging Protocol
MR imaging was performed with a 1.0-T system (Impact; Siemens Medical Systems, Erlangen, Germany). The shoulder was placed in a dedicated receive-only shoulder coil with the arm in a neutral position and the thumb pointing upward. All patients underwent MR arthrography after an injection of 10 mL of diluted gadopentetate dimeglumine (Magnevist; Schering, Berlin, Germany) with a concentration of 4 mmol/L. Informed consent was obtained from the patients before MR arthrography. This method was approved by the ethics committee of the hospital and by the responsible state agency.
The imaging protocol included the acquisition of parasagittal, transverse, and angled coronal images, which were not further used in this investigation. Parasagittal T1-weighted turbo spin-echo MR images (700/12 [repetition time msec/echo time msec]) were obtained in a plane tangent to the rim of the glenoid. Fifteen sections with a thickness of 5 mm and an intersection gap of 1.5 mm were acquired. The field of view was 16 or 18 cm. The image matrix was 192 x 256, and the echo train length was three. Four signals were acquired, which resulted in an imaging time of 3 minutes 20 seconds. To obtain the transverse images, a three-dimensional fast imaging sequence with steady-state precession (32/10), a flip angle of 40°, an 18-cm field of view, a 3.1-mm section thickness, and a 192 x 256 matrix with one signal acquired was used. Imaging time was 1 minute 40 seconds. An angled coronal T2-weighted turbo spin-echo sequence and an angled coronal three-dimensional fast imaging with steady-state precession (FISP; Siemens Medical Systems) sequence were also used, but images obtained with these sequences not evaluated in this investigation.
Analysis of MR Images
MR images were analyzed independently by two radiologists (M.Z., D.W.) who were specialized in musculoskeletal radiology. They were unaware of the surgical diagnosis. Three evaluations separated by 3-week intervals were performed. In the first session, only the parasagittal images were evaluated. In the second, only the transverse images were evaluated. In the third, one image from each imaging plane was made available. The radiologists were asked to classify the subscapularis tendon as normal or abnormal and to grade abnormal tendons according to the system used in the surgery reports (16) (Figs 1–4). Imaging criteria for the classification of the subscapularis tendon as normal or abnormal were the following: discontinuity of the tendon, contrast media entering into the tendon substance, circumscribed signal alteration of the tendon, and caliber changes.
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statistics (23). |
RESULTS |
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= 0.67). All signs were insensitive (29%–62%) but specific (90%–100%). Fatty atrophy of the upper half of the subscapularis muscle was observed in 10 (reader 1) or six (reader 2) of 21 subscapularis tendon lesions. Sensitivity for fatty infiltration of subscapularis tendon tears was 48%/29%, and specificity was 100%/100%. No correlation was found between subscapularis tendon abnormalities and fatty infiltration of the caudal part of the muscle (n = three for both readers). Abnormalities in the course of the long biceps tendon (luxation, subluxation) was observed in seven (reader 1) or eight (reader 2) cases; one case was false-positive for both readers (specificity, 97%/97%). Leakage of intraarticular contrast medium onto the lesser tuberosity was seen in nine (reader 1) or 10 (reader 2) patients on transverse images and in 15 patients (both readers) on parasagittal images. On transverse images, there were three (reader 1) or two (reader 2) false-positive cases (specificity, 90%/93%). On parasagittal images, there were three (reader 1) or two (reader 2) (specificity, 90%/93%).
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DISCUSSION |
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TOPAbstractIntroductionMATERIALS AND METHODSRESULTSDISCUSSIONReferences |
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The following three types of subscapularis tendon lesions can be discriminated: (a) the isolated subscapularis tendon tear (1,2), (b) the involvement of the subscapularis in large rotator cuff tears (4), and (c) the anterosuperior lesions of the rotator cuff (7,16). The isolated complete tear of the subscapularis tendon is rare. Its pathogenesis is usually traumatic and occurs after forceful external rotation of the adducted arm (1,2). Anterior shoulder dislocation and recurrent anterior instability have also been reported to be associated with isolated subscapularis tendon tears (25). The anterior extension of a large supraspinatus tear to the subscapularis tendon is far more frequent than are the isolated traumatic tears (4). The last type of tear that involves the subscapularis tendon is the anterosuperior lesion of the rotator cuff. It involves the interval structures of the rotator cuff such as the coracohumeral ligament, the superior glenohumeral ligament, and the adjacent borders of the supraspinatus and subscapularis tendons (7). Anterior extension of a large rotator cuff tear was observed in 16 of our patients. Four subscapularis tendon tears were limited to the anterosuperior complex. Only one patient had an isolated subscapularis tendon tear.
Lesions in the cranial part of the subscapularis tendon may be difficult to diagnose clinically and may even be missed during surgery if they are not specifically sought. Therefore, some authors suggest routine exploration of structures adjacent to the rotator interval in patients with supraspinatus tears during surgery because lesions can be missed without specific inspection (7). Even if a subscapularis tear is recognized, its extent may be difficult to assess during surgery because integrity may be mimicked by a scar that bridges the defect between the torn, medially retracted tendon and the lesser tuberosity. This scar can be mistaken for an intact tendon (1,4). Therefore, preoperative diagnosis of a subscapularis tendon lesion is important for the surgeon. During arthroscopy, the articular surface of the capsule may be visually intact in patients with complete subscapularis tendon tears. On probing, the finding of an unusually soft and elastic capsule may lead to the correct diagnosis (1).
Treatment for subscapularis tendon lesions is variable and depends mainly on the functional demand of the patient and the extent of the lesion. Conservative treatment with physiotherapy, corticosteroid injections, and pain medication is appropriate in patients with little functional demand. Arthroscopic débridement leads to pain relief and is indicated as a palliative treatment for small tears or tendon degeneration and for very large (inoperable) tears (16). Open surgery is performed mainly to restore function in younger patients or patients with high functional demand. Large irreparable tears are treated by transferring the pectoralis major tendon to the lesser tuberosity (5).
The success of surgical treatment is jeopardized by delayed diagnosis. In two series published in the orthopedics literature (1,3), the mean delay to surgery was 9 or 15 months. In one of these series (3), a subscapularis tendon tear was not diagnosed in the shoulders of 12 of 14 patients until MR imaging was performed. Therefore, imaging can reduce the delay in surgical intervention.
MR arthrography is superior to standard MR imaging in the depiction of partial tears in the supraspinatus and infraspinatus tendons (11). For this reason, we routinely use MR arthrography in our institution when the differentiation among degeneration, partial tears, and small full-thickness tears in the rotator cuff is of clinical importance. The sensitivity is between 71% and 100%, and specificity is between 84% and 100% (11,12). In our study, sensitivity was 91% and specificity was 86% for the detection of subscapularis tendon lesions; thus, these findings lie within the range of findings for other rotator cuff abnormalities. Because diagnostic accuracy of fat-saturated MR imaging is known to be superior to conventional MR imaging for the diagnosis of rotator cuff lesions (12), the acquisition of coronal oblique fat-saturated images has been introduced into the standard protocol at our institution. We still prefer parasagittal nonsaturated T1-weighted images for the depiction of subtle changes in signal intensity in the tendon and of fatty atrophy in the muscle.
There are some possible study limitations to mention. Although open surgery and arthroscopy were the best standards of reference achievable in this study setting, both were imperfect because of their potential to cause underestimation of subscapularis tendon lesions (1,4,7). When using these data, readers must be aware of the small number of patients (n = 21) with subscapularis tendon tears. The grading system used in this study reflected the development of subscapularis tendon tears, usually in a craniocaudal direction at the site of the insertion at the lesser tuberosity. It may not be suitable for all subscapularis tendon lesions, such as tears medial to the insertion, at the lesser tuberosity, or tears in the muscular part.
In previous investigations, the transverse images have usually been preferred for the depiction of subscapularis tendon abnormalities (3,14). However, at MR imaging in other tendons and ligaments (in the ankle or occasionally in the knee), images that are oriented perpendicularly to the structure under investigation have been advocated (26,27). Our results indicate that such an imaging strategy may also be useful for depicting the subscapularis tendon. Specificity for subscapularis tendon abnormalities with parasagittal images was higher than that obtained with transverse images (76%/90% vs 55%/62%), although comparable sensitivities were found. With regard to grading, parasagittal images were superior to transverse images ( = 0.59/0.73 vs = 0.33/0.38).
The leakage of contrast material from the joint space onto the lesser tuberosity has been described as a sign for subscapularis tendon tear at standard or computed tomographic arthrography (1,28,29). In our investigation, this sign was specific (90%/93%). However, its sensitivity was poor and varied for observers and imaging planes (29%–62%) (Fig 5). Scar tissue that prevents the leakage of contrast media into defects in the subscapularis tendon could be a cause of false-negative diagnoses at MR arthrography.
Muscle atrophy and fatty degeneration develop after rotator cuff tears occur and are an important (negative) predictor for the success of surgical interventions (4,16,18). There is a delay of at least 6 weeks for fatty infiltration to develop (18). Fatty infiltration that involves more than half of the cross-sectional area of the muscle has been considered to be a relative contraindication for surgical reconstruction. Therefore, preoperative assessment with imaging studies is important (16). Besides the therapeutic impact, atrophy and fatty infiltration may be helpful for correct diagnosis during MR imaging (Fig 6). Atrophy of the supraspinatus muscle and fatty infiltration has been shown to be specific (97%) for a rotator cuff tear (17). On the basis of our results, the presence of fatty degeneration as diagnosed on MR images is also a specific sign for subscapularis tendon lesions. Fatty atrophy must be evaluated in the cranial part of the subscapularis muscle because the inferior part is rarely involved.
Biceps tendon abnormalities are associated with subscapularis tendon abnormalities because of a close anatomic relationship (14,20,21). Some authors (4,16) consider medial dislocation of the long biceps tendon to be diagnostic for a subscapularis tendon tear. Our results support the importance of this association. In the presence of a biceps tendon subluxation or dislocation, a subscapularis tendon lesion must be suspected (Figs 2b, 4b). Tendinopathy or partial volume effects in the long biceps tendon might influence the assessment of the subscapularis tendon at its cranial border and could be a potential cause of diagnostic error.
In conclusion, MR arthrography is accurate in the detection and grading of lesions in the subscapularis tendon. The specificity of findings on transverse images for this diagnosis can be improved by including ancillary signs and findings from parasagittal images.
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Footnotes |
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References |
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