Case: We report a patient with osteoarthritis of the shoulder joint who underwent reverse shoulder arthroplasty and showed anatomical variation in the subscapularis muscle (SM). A variation of the rotator cuff originating from the anteroinferior aspect of the glenoid was separated from the SM by a septum and was named infraglenoid muscle (IGM).
Conclusion: We suggest that the IGM may serve as an additional dynamic stabilizer for external rotation. Studying this particular muscular variation would lead to better understanding of the anatomical structures around the glenoid cavity.