Variations in the anatomy of the anterior-inferior rotator cuff: the "infraglenoid muscle".

During the dissection course, 67 shoulders from 35 cadavers were investigated for an "infraglenoid muscle" (IGM). Of the 67 shoulders, 43 cases showed an IGM. When present, the IGM originated at the so-called "marginal axillary groove" of the Scapula. Of these, 86% of the muscles inserted at the crest of the lesser tubercle, 12% at the lesser tubercle itself and 2% at both anatomical structures. During its twisted course it was observed near the capsule of the shoulder joint. All detected IGMs were separated from the subscapular muscle (SM) by a distinct fascia. Due to its anatomical position and its innervation by the axillary nerve, demonstrated in 19 of 43 shoulders, the IGM should be considered to be independent of the SM. The accessory subscapular muscle, previously described by other authors, must be distinguished from our IGM, mainly due to its origin on the surface of the SM. Considering our mere descriptive findings the biomechanical implications of the IGM concerning the rotator cuff will have to be investigated in future studies.