The tendon of the long head of biceps is usually located inferiorly in the bicipital groove held there by the transverse humeral ligament. As it moves superiorly it arches through the rotator cuff interval where it is held by a sling formed by the superior glenohumeral ligament and the coracohumeral ligament (see diagram here)
When this ligament is deficient the tendon is free to dislocate medially. If the tendon of the subscapularis is intact then the tendon is seen lying anterior to it (as in this case). If, as is common, the subscapularis tendon is also deficient then the tendon of the long head of biceps can prolapse into the glenohumeral joint.
Diagnosis is best made on axial MRI images, where the bicipital groove is seen to be empty, and the tendon can be identified medially. If the tendon cannot be identified then a complete tear of the tendon should be sought.
For a non-annotated version of this image, please visit Radiopaedia.org here.
1. Musculoskeletal MRI - Kaplan
2. Krief OP “MRI of the Rotator Interval Capsule” AJR 2005; 184:1490-1494
Credit: Dr Frank Gaillard