Unusual variation of the rotator interval: insertional abnormality of the pectoralis minor tendon and absence of the coracohumeral ligament.

Abstract

To evaluate the anomalous insertion of the pectoralis minor tendon with absence of the coracohumeral ligament on MR arthrography and to demonstrate the associated findings seen with this anatomical variation. We retrospectively reviewed the 335 MR arthrograms of the shoulder joint (mean age 37.8 years) performed from March 2000 to February 2008. Images were evaluated with attention to anomalous insertion of the pectoralis minor tendon and the coracohumeral ligament. Anomalous insertion of the pectoralis minor tendon was demonstrated in 5 out of 335 shoulders (1.5%). The pectoralis minor tendons crossed over the coracoid process and attached directly to a glenohumeral joint capsule, and the coracohumeral ligament was absent in these 5 patients. In these patients, injected contrast material was noted to extend over the coracoid process along the course of the pectoralis minor tendon. Among 5 patients, 3 patients (60%) were diagnosed with SLAP (superior labrum anterior to posterior) lesions. Anomalous insertion of the pectoralis minor tendon to the glenohumeral joint capsule and associated absence of the coracohumeral ligament is well demonstrated on MR arthrography. It is an unusual variant of the pectoralis minor muscle insertion, and may be a possible contributing factor in the development of a SLAP lesion.