Introduction: The purpose of this study was to determine if glenosphere tilt relative to the scapular spine in the coronal plane would predispose fixation to mechanical failure. We reviewed the radiographs of 262 patients treated with a Reverse Shoulder Prosthesis (RSP) for rotator cuff insufficiency in the setting of glenohumeral arthritis. The spinospheric angle, the arc subtended by the baseplate and scapular spine in the coronal plane, was measured for each patient. ASES scores, range of motion and catastrophic failures of baseplate loosening were also recorded. Methods: Post-operative radiographs of 262 patients treated with an RSP were retrospectively identified and their spinospheric angles measured and recorded. Measurements were made on digital, Grashey view radiographs using a computer guided goniometer (Medview 5.1; StorComm Inc, Jacksonville, FL). Average time to follow up was 27 months (range 6-84 months). Three blinded observers, none of whom were the primary surgeon, were utilized. Inter-observer scores of reliability and variation coefficients were also calculated. Results: Coronal plane tilt measured 71.8° (range 50°-96°, SD 8.2°) for the 262 patients. In the ten failures mean tilt was 77° (range 71°-84°, SD 5°). This difference was significant (p=0.0099). The time from implantation to failure ranged from 15 to 55 months (mean 32 months). There were 66 patients whose spinospheric angle was 78° or greater. The mean ASES score of 64.6 for this group did not differ significantly from the mean of 64.5 (p=0.95) calculated for the 196 patients with a tilt angle of 77° or less. Range of motion values were also not significantly different between the two groups. Interobserver reliability between the three observers was strong with an average coefficient of variation of 3.1%. Conclusion: Patients who have their glenosphere tilted superiorly have an increased risk of catastrophic mechanical failure. Patients at risk for early failure appear clinically no different from patients not predisposed to catastrophic loosening. If noted, the author indicates something of value received. The codes are identified as follows: a, research or institutional support; b, miscellaneous funding; c, royalties; d, stock options; e, consultant or employee. *The Food and Drug Administration has not cleared the drug and/or medical device for the use described in this presentation (ie, the drug or medical device is being discussed for an “off-label” use). If noted, the author indicates something of value received. The codes are identified as follows: a, research or institutional support; b, miscellaneous funding; c, royalties; d, stock options; e, consultant or employee. *The Food and Drug Administration has not cleared the drug and/or medical device for the use described in this presentation (ie, the drug or medical device is being discussed for an “off-label” use). If noted, the author indicates something of value received. The codes are identified as follows: a, research or institutional support; b, miscellaneous funding; c, royalties; d, stock options; e, consultant or employee. *The Food and Drug Administration has not cleared the drug and/or medical device for the use described in this presentation (ie, the drug or medical device is being discussed for an “off-label” use).