The primary objective of this study is to examine the optimization of Reverse Shouder Arthroplasty implant position between GPS and conventional techniques. The secondary objective is to assess the effect of implant position using GPS vs. conventional techniques on ROM and patient reported outcomes. Long-term follow-up to 10 years with minimum 2 year follow-up for patients.

Inclusion Criteria:

• Patient is at least 21 years of age at the time of surgery
• Patient is indicated for reverse shoulder arthroplasty
• Patient is willing to participate by complying with pre- and postoperative visit requirements
• Patient is willing to participate for the entire length of the prescribed follow-up (minimum 2 years)
• Patient is willing and able to review and sign a study informed consent form
• Preop CT scan is within 3 months of the date of surgery

Exclusion Criteria:

• Revision shoulder arthroplasty
• Reverse shoulder arthroplasty for fracture
• Need for structural glenoid bone graft
• Osteomyelitis of the proximal humerus or scapula; if a systemic infection or a secondary remote infection is suspected or confirmed, implantation should be delayed until infection is resolved
• Inadequate or malformed bone that precludes adequate support or fixation of the prosthesis
• Neuromuscular disorders that do not allow control of the joint
• Significant injury to the brachial plexus
• Non-functional deltoid muscles
• The patient is unwilling or unable to comply with the post-operative care instructions
• Patients who are a known drug or alcohol abuser, or have a psychological disorder (e.g. schizophrenia major depression, bipolar disorder, etc.) as defined by the DSM4 that affect follow-up care or treatment outcomes.
• Alcohol, drug, or other subtance abuse
• Any disease state that could adversaly affect the function or longevity of the implant
• Patient is pregnant
• Patient is a prisoner
• Patient who are currently involved in any personal injury litigation, medical-legal or worker's compensation claims

Patients who meet eligibility criteria - Patients who consent to participate to return for follow-up visits out to 10 years