Clinical History: A 52 year old man presents with chronic shoulder pain. Oblique coronal fat-suppressed T2-weighted (1a) and axial fat-suppressed proton density-weighted (1b) images are provided. What are the findings? What is your diagnosis?
Full thickness tear of the subscapularis tendon with medial dislocation of the long tendon of the biceps brachii.
Isolated tears of the subscapularis tendon are far less common than tears associated with other tendons of the rotator cuff. Combined supraspinatus, infraspinatus and subscapularis tendon tears, described as “anterosuperior rotator cuff tears,” are important to recognize, since involvement of the subscapularis tendon may necessitate a different surgical approach for repair. Subscapularis tears can be difficult to diagnose both clinically and arthroscopically, so preoperative recognition with MRI is essential for a complete and timely repair.1,2 Failure to diagnose associated subscapularis tendon tears preoperatively has been implicated in failed rotator cuff repair.3 Furthermore, timely – diagnosis of such tears is essential, since repair before six months of symptoms results in a more favorable outcome.1
The subscapularis tendon originates at the anterior surface of the scapula and inserts onto the lesser tuberosity of the humerus. Fibers also extend laterally and superiorly to insert into the transverse humeral ligament, thus contributing to the stability of the biceps tendon within the intertubercular sulcus, along with the coracohumeral ligament, and fibers of the supraspinatus tendon.4 With a full thickness tear of the superior fibers of the subscapularis tendon, the medial wall of the intertubercular groove is disrupted, and the biceps tendon is free to dislocate medially, either into the anteromedial soft tissues, or juxtaposed between the humeral head and glenoid. The patient in this case also had a full thickness tear of the supraspinatus tendon, with medial retraction of the tendon edge, (fig 4a), but the coracohumeral ligament remained intact (fig 5a).
In patients with suspected subscapularis tendon abnormalities, MRI allows assessment of the coracoid index (CI) and the coracohumeral distance. Abnormalities of these indices have been shown to result in an increased risk of subscapularis disruption. The coracohumeral distance assesses the space between the tip of the coracoid process and the lesser tuberosity (Figure 6a), and ideally is measured with the humerus in maximal internal rotation, which may not be possible in the presence of a subscapularis tendon tear. The CI is independent of humeral head rotation, since it measures extension of the coracoid process beyond a line drawn in tangent to the articular surface of the glenoid (Figure 7a). A normal CI has been reported as 8.2mm.5 The patient in this case had a CI of 16 and a coracohumeral distance of 3mm (average normal = 11mm; average symptomatic =5.5).4 An elevated CI and a reduced coracohumeral distance suggest the diagnosis of subcoracoid impingement.
Although there had been some debate as to whether subcoracoid impingement exists, it is now more widely recognized as a factor, along with subacromial impingement, in the etiology of rotator cuff tears. Combined coracoplasty, acromioplasty, and resection of the coracoacromial ligament have been advocated in such cases.3
This month’s case of subscapularis tendon tear with medial dislocation of the biceps tendon demonstrates the importance of preoperative MRI in diagnosing the extent of large rotator cuff tears. Subscapularis tendon tears may be difficult to diagnose clinically and arthroscopically, but both full thickness and partial thickness tears are clearly demonstrated on MRI. Evaluation for subcoracoid impingement is also facilitated by MRI.
1 Warner, Jon JP, Higgins, Laurence, et al: Diagnosis and Treatment of Anterosuperior Rotator Cuff Tears. J Shoulder Elbow Surg 2001;10:37-46.
2 Pfirrmann, Christial WA, Zanetti, Marco, et al: Subscapularis Tendon Tears: Detection and Grading at MR Arthography. Radiology, 1999; 213: 709-714.
3 Lo, Ian KY, Burkhart, Stephen S: Current Concepts in Arthroscopic Rotator Cuff Repair (Spotlight on Surgical Techniques). Am J Sports Med, March-April 2003
4 Clark JM, Harryman DT. Tendons, ligaments, and capsule of the rotator cuff: gross and microscopic anatomy. J Bone Joint Surg [Am] 1992; 74:713-725.
5 Ferrick, Michael R: Coracoid Impingement. Am J Sports Med, Jan 2000.
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