Summary AC arthritis is the most common cause of AC joint pain with repetitive microtrauma leading to the development of osteoarthritis in the AC joint. Diagnosis is made with dedicated shoulder radiographs that reveal osteophytes and joint space narrowing in the AC joint. Treatment is a trial of NSAIDs, activity modifications, and corticosteroid injections. Arthroscopic versus open distal clavicle excision is indicated for patients with persistent symptoms that have failed nonoperative treatment. Epidemiology Demographics more common with age but can occur by second decade of life more common in weight-lifters and other sports Risk factors trauma post-traumatic (i.e. clavicle fractures, AC instability) distal clavicle osteolysis inflammatory arthropathy (i.e. RA) post-infectious arthropathy (i.e. septic arthritis) Commonly associated with individuals who engage in constant heavy overhead activities especially in weight-lifters and overhead throwing athletes Etiology Pathophysiology AC joint arthritis is caused by transmission of axial large loads through a small contact area resulting in repetitive microtrauma (same mechanism as distal clavicle osteolysis) Anatomy Acromioclavicular Joint Anatomy diarthrodial joint articulation scapula to clavicle contains a fibrocartilaginous intraarticular disc analogous to the meniscus of the knee Small articular surface area with relatively high axial and rotational loads leads to high contact forces across AC joint Exacerbated by articular disk degeneration and oblique joint surface orientation Ligaments acromioclavicular (AC) ligaments provide anterior-posterior stability posterior and superior AC ligaments are most important for stability coracoclavicular (CC) ligaments provide superior-inferior stability Presentation Symptoms activity related superior shoulder pain with overhead activity with cross body arm adduction with O'Brien's active compression test (at 90 degrees forward flexion) exacerbated with pressing motion (i.e. bench press, push-up) and leaning on affected side (i.e. while sleeping) Physical examination palpation pain with direct palpation of AC joint prominence of the distal clavicle (osteophytes) provocative tests pain with cross body adduction test Imaging Radiographs recommended views best evaluated using Zanca view (15° cephalic tilt) Findings osteophytes and joint space narrowing distal clavicle osteolysis imaging findings do not always correlate with patient symptoms (often present on radiographs without clinical signs or symptoms) MRI increased signal and edema in AC joint visualize associated pathology (i.e. rotator cuff, long head of biceps tendon) Treatment Nonoperative activity modification and physical therapy first line of treatment avoid aggravating activity such as pushing/pressing activities physical therapy should focus on strengthening and stretching of shoulder girdle AC joint injection with corticosteriods can be both diagnostic and therapeutic modality access to the AC joint is challenging AC joint injections often miss the joint ultrasound improves accuracy of injection most patients do not experience long term relief after injections Operative arthroscopic vs. open distal clavicle resection (Mumford procedure) indications severe symptoms that have failed nonoperative treatment outcomes open vs. arthroscopic based on surgeon preference and comfort arthroscopic resection has the advantage of allowing evaluation of the glenohumeral joint and treatment of any associated injuries (rotator cuff, long head of biceps and glenoid labrum) can combine diagnostic arthroscopy with open distal clavicle resection open procedures require meticulous repair of deltotrapezial fascia Techniques Arthroscopic distal clavicle resection should only resect 0.5-1cm of distal clavicle Complications AC joint instability anterior-posterior instability can be due to aggressive surgical distal clavicle resection ( >1-1.5cm) aggressive debridement sacrificing posterior and superior AC ligaments superior-inferior instability usually iatrogenic due to aggressive surgical resection compromising coracoclavicular ligaments Persistent pain most commonly due to incomplete resection of distal clavicle posterior-superior area of the distal clavicle Heterotopic ossification Deltoid dehiscence inadequate deltotrapezial fascia repair after open distal clavicle resection