The goal of the Shoulder iD™ Primary Reversed Glenoid Outcomes Clinical Study is to collect safety and performance data on the commercially available Shoulder iD™ Primary Reversed Glenoid device. The study will learn about standard device use in adult patients who have a functional deltoid muscle and massive and non-repairable rotator cuff tear. The main questions it aims to answer are: * What is the average improvement in patient-reported shoulder function after 2 years when compared to before the surgery, and * What is the rate of surgical revisions needed over a 10 year period Patients will be asked to will be asked to regularly attend their check-up visits with their surgeon (including having x-rays or CT images taken to check their shoulder and implant), to complete questionnaires to report how their shoulder is doing, and to tell their surgeon when they notice any changes.