Musculoskeletal ImagingRotator cuff
1. Anatomya cuff that reinforces the fibrous capsule of the glenohumeral joint, formed by the tendons of the supraspinatus, infraspinatus, teres minor and subscapularis muscles (Fig.1).
2. Pathology
Abnormalities of this structure are common, especially in elderly persons.
Degeneration of the rotator cuff leads to characteristic radiographic abnormalities, including elevation of the humeral head with respect to the glenoid cavity, joint space narrowing (to less than 6 mm), eburnation and cysts of humeral head and acromion, and cystic and notchlike defects in the humeral surface near the bicipital groove. Degeneration of the rotator cuff appears to have a significant association with osteoarthritis of the glenohumeral joint. Progressive superior migration of the humeral head causes an instability, increasing wear of cartilaginous surfaces and leading to cuff tear arthropathy. Alternatively, abnormal accumulation of calcium hydroxyapatite crystals may induce an enzymatic attack on the periarticular tissues, which eventually may be manifested as an arthropathy designated the Milwaukee shoulder syndrome.
Tears of the rotator cuff may be complete (full thickness) or incomplete (partial thickness) (Fig.2). In complete tears an abnormal communication between the glenohumeral joint and bursa allows contrast material to collect within the subacromial bursa. Precipitating factors include trauma, attrition, ischaemia, and impingement. Most cases of rupture of the cuff occur during movements and activities that would not usually damage the involved musculotendinous units, but possibly the rupture results from weakening of tendons by some combination of age, repetitive stress, corticosteroid injection, hypovascularity or damage produced by impingement.
Arthrography, MR imaging and ultrasonography of the glenohumeral joint can be used to evaluate the rotator cuff. Chronic tears may produce characteristic findings on routine radiography:
narrowing of the acromiohumeral space;
reversal of the normal inferior acromial convexity; and
cystic lesions and sclerosis of the acromion and humeral head.
Small cystic lesions can be noted along the inferior aspect of the acromion and appear within the greater tuberosity.
Standard arthrography remains a popular diagnostic method for some rotator cuff tears (see arthrography (III:1), Fig. 1). MR imaging is also useful, owing to the high signal intensity of tendons on some sequences, which is indicative of tears. Full-thickness tears of the rotator cuff are characterized by presence of a tendinous defect that is filled with fluid or granulation tissue and retraction of the musculotendinous junction.
High-resolution linear array real-time ultrasonography may be successful in revealing abnormalities of the rotator cuff, but examination of the tendons in two orthogonal planes is recommended whenever possible. Diagnostic criteria include nonvisualization of all or part of the cuff, discontinuity, and focal abnormal echogenicity. Articular and bursal effusions commonly accompany large tears.
Tendinitis from overuse has been well known to occur in some patients with rotator cuff abnormality; however, a more appropriate term for this process is tendinosis or tendinopathy rather than tendinitis. On MR images increased signal intensity may be observed in a tendon with normal or abnormal morphology and an intact peribursal fat plane on T1-weighted and proton density spin-echo MR images and less evidently on T2-weighted spin-echo MR images.
DR/RB