This chapter is an outline of the basic principles of magnetic resonance imaging (MRI) of the shoulder with an emphasis on the clinical issues related to the imaging findings of shoulder pathology. The radiologic technique for shoulder imaging and basic shoulder anatomy are first discussed. An outline of common pathologic processes of impingement and instability follows. Next, there is a delineation of the disease processes of “dead arm,” acromioclavicular separation, and pectoralis major rupture. Then there is a discussion of tenosynovitis, arthritis, neoplasia, and avascular necrosis. Lastly, there is a synoptic discussion of common surgical procedures for impingement and instability along with common operative and postoperative complications of these techniques.
Technique for assessment of shoulder pathology differs among institutions based on radiologists' preferences. A few general comments about conventional and arthrographic MRI protocols will be made.
The shoulder in a conventional MRI exam is acquired in partial external rotation in the axial, coronal and sagittal planes. Confirmation of pathology in different planes and sequences increases diagnostic accuracy. The coronal plane is acquired along the long axis of the supraspinatus tendon. The sagittal plane is acquired parallel to the glenoid articular surface and perpendicular to the long axis of the supraspinatus. Other views such as abduction and external rotation (ABER) in the coronal plane may be obtained as part of a conventional or arthrographic exam.1 The anterior band of inferior glenohumeral ligament is optimally depicted on the abduction external rotation view, as it is under tension. The abduction external rotation view of the shoulder is helpful in demonstrating subtle anterior inferior labral tears, partial articular surface rotator cuff tears, and instability of the shoulder in ABER.
Sequences may be tailored according to clinical indication. MRI shoulder protocols typically involve fat-saturated proton density images that are sensitive to internal derangement. T2 star gradient recall echo images are employed in the assessment of the labrum and for detection of substances that produce susceptibility effects such as calcium hydroxyapatite or loose surgical hardware. T1-weighted images are useful for the assessment of bone marrow derangement or rotator cuff atrophy (Figure 12-1). Non-fat-saturated T2-weighted images are useful in characterizing tendon pathology, particularly discerning tendinosis from tear (Figure 12-2).
Chronic muscle atrophy. T1-weighted sagittal image optimally depicts advanced muscle atrophy and fatty degeneration around the shoulder including the supraspinatus (black arrow).
Tendinosis of the supraspinatus tendon. Coronal oblique T2-weighted image shows intermediate signal in the tendon indicating tendinosis.
MR arthrography is employed for the detection of subtle rotator cuff tears or labral pathology in patients with a negative conventional MRI, the assessment of the postoperative shoulder, and the demonstration of communication between the joint ...