ZILRETTA in Subjects With Shoulder Osteoarthritis

Primary Objective: To assess the efficacy of ZILRETTA on pain following an intra-articular (IA) injection in subjects with glenohumeral osteoarthritis (OA) relative to normal saline placebo Secondary Objective: * To assess the efficacy of ZILRETTA on pain following an IA injection in subjects with glenohumeral OA relative to triamcinolone acetonide injectable suspension, and normal saline placebo * To assess the safety of ZILRETTA in subjects with glenohumeral OA relative to normal saline placebo

This is a multi-center, randomized, double-blind, parallel-group study to evaluate the efficacy and safety of ZILRETTA in subjects with glenohumeral OA. This study will be conducted at approximately 25 study sites in the United States. Subjects will be screened to confirm the diagnosis of OA and eligibility based on the Inclusion and Exclusion Criteria. Approximately 150 male or female subjects, 50 to 80 years of age inclusive, will be enrolled, randomized to 1 of 2 treatment groups (2:1), and treated with a single IA injection of either: * Treatment Arm: 32 mg ZILRETTA, * Treatment Arm: placebo (normal saline). ZILRETTA, or normal saline placebo will be administered as a single IA injection with a 24-week follow-up period with a primary endpoint at Week 12. The study will involve a Screening period (a minimum of 10 days, up to a maximum of 35 days), pre-treatment phase, dosing at Baseline/Day 1, and 8 additional outpatient visits at Weeks 2, 4, 8, 12, 16, 20, and 24/End of Study (EOS) during the study. At specified times throughout the study, subjects will undergo physical examinations, index shoulder assessments, and index shoulder X-rays; blood will be collected for laboratory safety tests; and vital signs will be collected. Information regarding adverse events (AEs) and prior and concomitant medications and treatments will be collected from the time of signing the Informed Consent Form (ICF) through the Week 24/EOS visit. Information regarding rescue medication usage, Average and Worst daily Pain score (0-10 Numeric Rating Scale (NRS); 0 = no pain, 10 = worst possible pain) in the index shoulder, and Sleep Interference (SI) will be completed daily via an electronic diary (eDiary) and reviewed for compliance by site staff at each study visit. At the Screening Visit, subjects will be registered in the eDiary and receive instructions on its use. Subjects will complete accurate pain reporting (APR) and placebo response reduction (PRR) training prior to completing all questionnaires.