summary An Os Acromiale is an unfused secondary ossification center of the acromion that can be associated with shoulder impingement and rotator cuff tendonitis. Diagnosis is made with axillary lateral radiographs of the shoulder. Treatment is observation in the majority of cases with operative management reserved for patients who have persistent shoulder impingement or rotator cuff disease that have failed nonoperative management. Epidemiology Incidence common 8% bilateral in 60% Demographics more common in males more common in African American Anatomic location most common location is the junction of meso- and meta-acromion Etiology Associated conditions shoulder impingement rotator cuff disease meso-acromion is associated with rotator cuff tendonitis and full thickness tears (in 50%) Anatomy 3 ossification centers meta-acromion (base) origin of posterior portion of deltoid meso-acromion (mid) origin of middle deltoid pre-acromion (tip) origin of anterior deltoid fibers and coracoacromial ligament Results from failure of fusion between ossification centers Blood supply acromiale branch of thoracoacromial artery Presentation History pain from impingement login to view 1 more bullet from motion at the nonunion site (painful synchondrosis) incidental finding on radiographs trauma can trigger onset of symptoms from previously asymptomatic os acromiale Imaging Radiographs recommended views best seen on an axillary lateral of the shoulder CT indications to better visualize the nonunion site to detect degenerative changes (cysts, sclerosis, hypertrophy) Treatment Nonoperative observation, NSAIDS, therapy, subacromial corticosteroid injections indications login to view 1 more bullet Operative two-stage fusion indications login to view 1 more bullet technique login to view 6 more bullets arthroscopic subacromial decompression and acromioplasty indications login to view 1 more bullet open or arthroscopic fragment excision indications login to view 2 more bullets results login to view 2 more bullets Complications Deltoid weakness from fragment excision Persistent pain/weakness Prognosis Poorer outcomes after rotator cuff repairs in patients with meso-os acromiale