Aim of this study was to investigate the potential influence of Critical Shoulder Angle (CSA) as a predisposing factor for the development of degenerative full-thickness rotator cuff tears (DRCT) or primary glenohumeral osteoarthritis (PGOA). A systematic review of the Pubmed, Scopus, Mendeley, ScienceDirect and the Cochrane Central Register of Controlled Trials online databases was performed for literature regarding CSA and its association with DRCT and PGOA. In order to evaluate solely the relationship between CSA as a predisposing factor for the development of the aforementioned degenerative shoulder diseases (DSDs), we precluded any study in which traumatic cases were not clearly excluded. Our search strategy identified 289 studies in total, nine of which were eligible for inclusion based on our pre-established criteria. Quality assessment contacted using the Newcastle Ottawa Scale for case-control studies. There were a total of 998 patients with DRCT and 285 patients with PGOA. The control groups consisted of a total of 538 patients. The mean CSA ranged from 33.9° to 41.01° for the DRCT group, from 27.3° to 29.8° for the PGOA group and from 30.2° to 37.28° for the control group. All studies reported statistically significant differences between the DRCT and PGOA groups and the respective control groups. Our study results showed that there is moderate evidence in the literature supporting an intrinsic role of CSA in the development of DSDs. Level of evidence: IV. Systematic review of diagnostic studies, Level II-IV.