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Journal of Postgraduate Medicine, Vol. 48, Issue 4, 2002 pp. 270-274 Magnetic Resonance Arthrography in Recurrent Anterior Shoulder Instability as Compared to Arthroscopy: A Prospective Comparative Study Parmar H, Jhankaria B**, Maheshwari M, Singrakhia M*, Shanbag S**, Chawla A, Deshpande S* Departments of Radiology and Orthopaedics*, Seth G. S. Medical College and
K. E. M. Hospital, and Jhankaria Imaging Center**, Mumbai, India. Code Number: jp02092 Abstract: AIM: To evaluate the accuracy of magnetic resonance (MR) arthrographic imaging in the diagnosis of glenoid labral and ligament tears in recurrent shoulder instability. SETTINGS AND DESIGN: Prospective, comparative study at a tertiary care centre. PATIENTS AND METHODS: Patients with three or more episodes of anterior shoulder dislocation were enrolled in the study. They were subjected to magnetic resonance arthrography (MRA) for delineation of abnormalities. The findings obtained at MRA were compared with those found at arthroscopy and surgical exploration. RESULTS: MRA detected glenoid tears in all 22 patients with 20 (90%) patients having antero-inferior tears, 3 (14%) patients had superior labral involvement and 2 (10%) patients had posterior labral abnormality. On arthroscopy, antero-inferior, superior and posterior labral tear were found in 21 (95%), 5 (22%) and 7 (32%) patients respectively. MRA showed a sensitivity of 95%, and a specificity of 100% for the detection of the antero-inferior labral tears. The sensitivity of MRA for the detection of superior, middle and inferior glenohumeral ligament tear was 83%, 80% and 86% with a specificity of 100%, 71% and 93% respectively. MRA was 100% sensitive for the detection of rotator cuff injuries and detection of bony lesions like Hill-Sach's and bony Bankart's lesion. CONCLUSIONS: MRA is a sensitive and specific modality for evaluation of anterior shoulder instability. (J Postgrad Med 2002;48:270-274) Key Words: MR arthrography, Glenoid labral tear, Shoulder instability Shoulder is one of the most unstable and frequently dislocated joints in the body and accounts for nearly 50% of all the dislocations.1 Prior to the advent of magnetic resonance imaging (MRI), plain radiography and cumbersome arthrography were the only tools for evaluation of the shoulder joint. MRI has changed the whole perspective of shoulder imaging. MR imaging allows visualisation of soft tissues and as well as osseous pathology in exquisite details that was not possible by conventional radiographs and arthrogram or even computerised tomographic (CT) scan. Although MR has been shown to be superior in imaging rotator cuff tears, there is some discrepancy in the role of conventional MR in detection of labral lesions.2 The sensitivity of this new modality is sought to be improved by passive distension of the joint by positive MR contrast. This allows visualisation of the glenoid labrum, glenohumeral ligament, rotator cuff and other intracapsular structure in great details.2 We conducted a study to evaluate the accuracy of MRA imaging in the diagnosis of glenoid labral and ligament tears in patients with recurrent shoulder instability.
Patients and Methods This prospective study was conducted over a 7-month period after obtaining clearance from the institution's Ethics committee. Patients with recurrent anterior dislocation of the shoulder, defined as three or more episodes of anterior dislocations were enrolled. Patients with congenital habitual dislocation and those without any history of trauma were excluded from the study. Plain radiographs of shoulder joint in antero-posterior view (in neutral and internal position) were obtained and evaluated for the presence of any bony lesions. The procedure of shoulder arthrogram was performed using standard fluoroscopy guided anterior approach. 0.1 cc of gadopentate dimeglumine (Magnevist, Schering, Germany) and 2 cc of ioxaglate sodium meglumine (Hexabrix 320 Mallinckrodt, Guerbet, S.A.) mixed in 20 cc of normal saline was used as a contrast medium. The volume required ranged from 12-25 cc with average of 18 cc. Optimal images were obtained within 45 minutes of injection. MR imaging was later on performed on a 0.2 Tesla open MR system (Magnetom Open Viva, Siemens Medical Systems, Erlangen, Germany). Axial, oblique coronal and oblique sagittal images were obtained in all cases. Spin echo (SE) axial images were obtained with TR/TE/NA of 528/26/2 for T1 weighted images (WI) and 2840/102/3 for T2W images with 4 mm slice thickness and 1 mm intersection gap. Oblique coronal sections were obtained with SE 528/26/1 (TR/TE/NA) with 4 mm slice thickness and 1 mm intersection gap. Oblique sagittal images were also obtained with 528/26/2 (TR/TE/NA) with 4 mm slice thickness and 1 mm intersection gap. Dual echo in steady state (DESS) images were obtained with a TR/TE/NA of 41/12/1 in axial and sagittal planes. A 180-200 mm field of view and 256 X 256 acquisition and 512 X 512 display matrix were used in all our cases. The position of the patient was supine and the affected arm was in neutral position. Two qualified radiologists, who were given only the clinical details of the patients, interpreted all images independently. Damage of the labrum was diagnosed when a normal low signal intensity, cross sectional appearance was disrupted or when abnormal signal intensity was noted. Tears were considered to involve the anterior or posterior part of the labrum if tears were seen on axial images. Tears were classified as superior or inferior labrum if they were visualised on coronal images. The signal intensity was compared with that of the nearby muscles and posterior labrum for comparison. Arthroscopy was performed by different surgeons in all the patients within 10 days of patients having undergone MRA. Findings obtained on arthroscopy were considered as the gold standard for the diagnosis of the labral and gleno-humeral ligament pathology. Based on their appearances at arthroscopy labral tears were defined as frank tears, absence of labrum or marked fraying or degeneration.
Results Twenty two patients (all males, age ranging from 16 to 50 years) were enrolled in the study. The mean duration of shoulder instability prior to evaluation was 28 months (range 6- 96 months). MR arthrogram detected glenoid tears in all the 22 (100%) patients of which 20 (91%) had antero-inferior tears, 3 (14%) had superior labral involvement and 2 (9%) had posterior labral abnormality. The antero-inferior labrum showed Bankart's lesion (Figure 1) in 12 (55%) patients, ALPSA (Anterior labrum periosteal sleeve avulsion) lesion (Figure 2) in 5 (23%) and GLOM (Glenoid labrum ovoid mass) lesion in 1 patient (5%). Two patients (9%) had absent or completely denuded labrum. Other abnormalities associated with anterior labral tears were severely truncated labrum (15%) and absent labrum (15%). Three patient with superior labral involvement had SLAP (Superior labrum anterior posterior) lesion. MRA further detected superior, middle and inferior GHL tears in 5 (23%), 14 (64%) and 7 (32%) patients, respectively. Arthroscopy detected the antero-inferior labral tear in 21 (95%) patients, superior and posterior labral involvement in 5 (23%) and 4 (18%), respectively (Table 1). It also revealed superior, middle and inferior GHL tears in 6 (27%), 15 (68%) and 7 (32%) patients, respectively. MRA showed a sensitivity of 95% and a specificity of 100% for the detection of the antero-inferior labral tears. Sensitivity was less for superior and posterior labral tears being 60% and 50% respectively. The sensitivity of MRA for the detection of superior, middle and inferior glenohumeral ligament tear was 83%, 80% and 86% with a specificity of 100%, 71% and 93%, respectively. MRA was 100 % sensitive for the detection of the rotator cuff injuries and detection of bony lesions like Hill-Sach's (Figure 3) and bony Bankart's lesions. MRA, however, missed loose bodies in the joint space in three patients, which were subsequently found on arthroscopy. Although we reported capsular abnormalities in 12 (55%) patients, there was no information contained about the capsule in the arthroscopy report and hence their sensitivity could not be evaluated. The procedure of MRA was not associated with any morbidity. None of our patients complained of excessive pain, fever or restricted movement of the joint after the arthrogram. Mild pain was noticed for a maximum of 24 hours and could be managed with analgesics. Discussion Disability due to recurrent subluxation of the humerus is a common clinical problem. It is due to a glenoid labrum injury or a lax capsular mechanism. Although the most important structures within the capsular mechanism have yet to be determined, arthroscopic surgical repair of the anterior labrum is providing clinical improvement.3 Therefore, accurate identification of the labral and glenohumeral ligament tears has become a significant diagnostic goal. Before the introduction of MR imaging, only invasive tests like arthrography, CT arthrography (CTA) or arthroscopy were available for successful evaluation of the labrum. Though CTA offers excellent sensitivity and specificity4 in identifying labral tears, it involves ionising radiation and is limited only to axial imaging. Also few portions of the superior labrum and the glenohumeral ligaments cannot be visualised opitmally.5 The non-ionising, multi-planar imaging by MR makes it an attractive imaging modality. Addition of contrast into the joint followed by MRA further enhances the sensitivity offered by plain MR imaging.6 In fact, MRA using dilute gadolinium is becoming the imaging gold standard for the evaluation of glenoid labrum.7,8 The pathological results of recurrent instability have been well documented.9-12 The most common abnormality is the detachment of the antero-inferior labrum, the Bankart's lesion.9 Other pathological findings in chronic shoulder instability include joint capsule stripping from the scapula, rotator cuff tears and disease of the biceps tendon along with the bony Bankart's lesion and Hill-Sach's defect.13 We could successfully diagnose anterior and anteroinfeior labral tears with a sensitivity of 95% and a specificity of 100%. This sensitivity compares favourably with the studies done by others.7,14 The most common appearance of a torn anterior labrum was visible as a linear signal intensity cutting through the substance of the labrum as seen in 60% of the cases. An additional interesting appearance of the torn labrum was the GLOM lesion. This represented a dark rounded mass of tissue and proton density on T2 W images, which was best seen at the base of the coracoid. GLOM is felt to represent the torn anterior labrum that had retracted superiorly. Other interesting injuries noted were ALPSA lesion seen in 5 (22%) patients. It is very similar to the classic Bankart's lesion but here the labral ligament is complex, is displaced medially with an intact scapular periosteum. Sensitivity of MRA diminished when it came to the diagnosis of the posterior and superior labral tears. The inferior labrum is not well visualised due to the redundant capsule overlying this region. Capsular stripping is well seen because of good distension of joint space by the contrast. Capsular stripping can be missed in a routine MR imaging unless the dislocation is acute or there is joint effusion.15 Capsular stripping without coexistent labral abnormalities is rare and will not require an arthrotomy. Therefore, the limitations of MRI in depicting this abnormality are not clinically significant. Although our study shows MRA to be very sensitive to the anteroinferior labral tears, sensitivity for glenohumeral ligament tears was much less. This was especially true for MGL and MGL tears were missed in 20% (3/15) and were falsely detected in 29% (2/7) of cases. This is because of a number of anatomical variations of MGL that may mimic a ligament tear. Loose body and joint space can occur in a chronic dislocation. These were most likely missed due the error at the reading by the radiologists. The error in missing them was human and not technical. They were detected in retrospect on MRA after knowing the arthroscopy findings. The high prevalence of labral abnormalities in predominantly young and athletic patients included in the study introduces an inherent bias. These results cannot be extrapolated to the elderly individuals in whom degenerative changes of the labrum may lead to false positive results. While this selection bias for our studies may slightly influence our results, we believe that the sensitivity and specificity of the study is fairly accurate. The procedure of MRA was well tolerated by patients without any significant morbidity. Pain, if present lasted for a maximum duration of 24 hours and could be managed with analgesics. In conclusion, it can be said that MRA is a valuable tool for the detection of tears in patients with recurrent shoulder instability. It is highly sensitive and specific in detecting antero-inferior labral tears (the commonest injury causing recurrent anterior shoulder instability).
Acknowledgements We acknowledge the help of Dr. G. R. Jhankaria for allowing the use of fluoroscopic equipment and Drs. A. Narvekar and V. Prabhu for referring the patients.
References
Expert's Comments The authors of this paper provide additional evidence that MR arthrography is very accurate for diagnosing anteroinferior labral tears, and is the best imaging examination for detecting Bankart tears and the Bankart variants. Although conventional MR is accurate for imaging rotator cuff tears, most authors are now reporting that conventional MR will only demonstrate about two-thirds of chronic labral tears. Some authors have shown a higher accuracy for conventional MR in selected populations with a high prevalence of patients with a known anterior dislocation, and conventional MR is probably adequate for imaging patients with acute injuries where the effusion and bone marrow edema can greatly assist in making the diagnosis. MR arthrography of the shoulder provides even more information if the arm is scanned in the abduction-external rotation (ABER) position. Although the patient has to be removed from the center of the MRI scanner and the arm repositioned into abduction and external rotation, this has been shown to further increase the already high sensitivity of MR arthrography for labral tears.1 The ABER position can also demonstrate small tears of the anterior band of the inferior glenohumeral ligament, as this ligament is pulled taut by the overhead positioning of the arm. The ABER position is also ideal for showing the small articular surface partial thickness tears at the supraspinatus-infraspinatus interval that are seen in athletes who use an overhead motion. By including at least an oblique coronal T2-weighted sequence so as not to miss bursal surface partial thickness cuff tears or spinoglenoid notch ganglion cysts, MR arthrography is now the gold standard for imaging the shoulder prior to surgery. Michael J Tuite, M.D. Department of Radiology, University of Wisconsin Medical School, U.S.A
References
This article is also available in full-text from http://www.jpgmonline.com/ © Copyright 2002 - Journal of Postgraduate Medicine The following images related to this document are available:Photo images[jp02092f2.jpg] [jp02092f1.jpg] [jp02092t1.jpg] [jp02092f3.jpg] |
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