Reverse total shoulder arthroplasty (RTSA) is a useful treatment option for patients with irreparable massive rotator cuff tears and cuff tear arthropathy (CTA). The goal of this CEU course is to appraise the correlation between preoperative deltoid muscle volume and postoperative practical consequences subsequent to RTSA by panoptically analyzing the demographic, clinical, and radiological factors involving known prognostic factors and preoperative deltoid volume.