Rockwood Adults CH34

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SECTION TWO • Upper Extremity

Magnetic Resonance Imaging and Arthrography Traditional magnetic resonance imaging (MRI) is a diagnostic tool to complement both physical examination and standard radiographs in the management of patients with anterior shoul- der instability. It is utilized for evaluation of soft tissues, which can be performed with high contrast and spatial resolution. Mag- netic resonance (MR) accuracy in identifying labral and rotator cuff tears in the literature ranges from 70% to 100%. 198,241,266 The acquired multi-planar imaging allows for the detailed evaluation of the glenoid, labrum, joint capsule, and rotator cuff in differ- ent planes. MR arthrography or arthrogram (MRA) refers to MRI of a joint that has been injected with an intra-articular contrast agent such as diluted gadolinium or saline solution. The contrast material is injected prior to MRI by fluoroscopic or ultrasound guidance under strict aseptic technique. By distending the joint capsule, the cartilage, ligaments, and labrum are outlined with contrast, increasing the sensitivity for detecting tears and other lesions. It should be noted that in the acute dislocation setting, a joint effusion with distension of the joint may outline these structures similarly, making the arthrogram unnecessary. 266 This form of MRI has proven utility by increasing both sensitivity and specificity in detecting injuries to the capsulolabral–ligamentous complex as compared to traditional MRI. 8 In a meta-analysis of the diagnostic test accuracy of MRA compared to MRI for the detection of glenoid labral injuries, Smith et al. 218 evaluated 6 studies including 4,667 shoulders. They found greater diagnos- tic test accuracy for MRA over MRI in the detection of glenoid labral lesions (MRA sensitivity 88% and specificity 93% vs. MRI sensitivity 76% and specificity 87%). With standard MRI or MRA, the shoulder is routinely posi- tioned in neutral or partial external rotation but other alterna- tive positions can be used to increase the sensitivity for detecting labroligamentous injuries. Abduction and external rotation (ABER) of the arm is an alternative position that is utilized to increase the sensitivity and specificity for detecting anteroin- ferior labroligamentous injury. 230 However, limited ROM or

pain may prohibit patients from performing this provocative maneuver. Schreinemachers et al. 206 retrospectively compared the accuracy of MRA and MRA in the ABER position for the detection and characterization of anteroinferior labroligamen- tous lesions with arthroscopic evaluation as the standard. The authors found that full routine MRI or MRA examination had similar accuracy as the ABER sequence in evaluating the antero- inferior labral–ligamentous complex. Conversely, Tian et al. 230 performed a similar study evaluating the added value of the ABER position and found that the sensitivity of MRA with the ABER position for detecting anteroinferior labral lesions was significantly higher than that of the MRA in neutral position and more effective in identifying Perthes lesions. MRAs can also demonstrate a patulous capsule on the coro- nal, sagittal, and axial imaging in patients with MDI (Fig. 34-22). MRAs can be helpful in evaluating lesions of the rotator interval and other associated findings as well that may ultimately affect the eventual surgical plan. 183 The presence of glenoid dysplasia, increased capsular cross-sectional area, and increased glenoid retroversion have all been found to be associated with increased posterior labral tears and symptomatic instability. 68,69 Parada et al. also demonstrated that glenoid retroversion was signifi- cantly increased in patients with symptomatic posterior labral tears but there was no significant association between instabil- ity and increased humeral head subluxation. 181 Often, patients with MDI will present to the orthopedic surgeon already having had an MRI or MRA and so these studies should be reviewed. Clinicians should keep in mind, however, that the diagnosis of MDI is a clinical one, and as such, the need for expensive and/ or invasive imaging should be weighed against the information that will be gained from these studies. Computerized Tomography Scan Computerized tomography (CT) has traditionally been the main diagnostic imaging modality for evaluating bone loss related to anterior shoulder instability. 226 CT scans are readily available,

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Figure 34-22.  A: Coronal T2-weighted MRA image shows patulous inferior capsule ( arrow ) in a patient with MDI. B: Sagittal oblique T2 MRA also confirms the enlarged capsule ( arrow ). C: Axial T2 MRA image demonstrates increased posterior capsule volume ( arrow ) without any evidence of posterior labral tear in this patient with MDI.