MR Imaging of the Rotator Cuff and Rotator Interval

The rotator cuff is comprised of the supraspinatus, infraspinatus, subscapularis, and teres minor muscles and tendons. The four muscles of the rotator cuff act as stabilizers of the glenohumeral joint. The supraspinatus is primarily a shoulder abductor. The supraspinatus muscle originates along the dorsal surface of the scapula. The muscle fibers course in a lateral orientation and converge to form an anterior tendon although there is also a second smaller posterior tendon of the supraspinatus. The supraspinatus tendon is bordered superiorly by the subacromial-subdeltoid bursa and inferiorly by the joint capsule. Anteriorly, the more distal supraspinatus tendon converges with the coracohumeral ligament, and posteriorly it merges with the anterior fibers of the infraspinatus tendon. At the distal aspect of the rotator cuff, the supraspinatus and infraspinatus tendons splay out and interdigitate, forming a common continuous insertion on the middle facet of the humeral greater tuberosity. The supraspinatus tendon is best evaluated in the coronal oblique plane and the sagittal oblique plane, with the latter being helpful in evaluating the most anterior fibers of the supraspinatus. The region just medial to the convergence of the posterior fibers of the supraspinatus and the anterior fibers of the infraspinatus has been referred to as the posterior rotator interval [1]. The infraspinatus muscle externally rotates the shoulder, originating in the infraspinous fossa. The infraspinatus has a multipennate configuration, usually with three tendons, with the myotendinous junction having a somewhat fanlike configuration. The infraspinatus is best evaluated in the coronal oblique and sagittal oblique planes [1, 2]. The teres minor muscle originates along the upper two thirds of the lateral border of the scapula and blends into the posterior glenohumeral joint capsule more distally. The infraspinatus and teres minor externally rotate the shoulder, with the former also being an abductor and the latter being a weak adductor. The subscapularis muscle is a strong adductor and internal rotator. The subscapularis muscle originates from the subscapular fossa along the anterior aspect of the scapula. It inserts primarily on the lesser tuberosity, with superficial fibers extending to the greater tuberosity. Similar to the infraspinatus, the subscapularis has a multipennate configuration. The deep fibers of the subscapularis tendon blend with and reinforce the anterior capsule of the glenohumeral joint. The mid and distal portions of the middle glenohumeral ligament blend with the capsule and deep fibers of the subscapularis before inserting into the lesser tuberosity. The subscapularis is best evaluated in the axial and sagittal oblique planes.