• AC joint arthritis is caused by transmission of large loads through a small contact area
  • Epidemiology
    • demographics
      • more common with age but can occur by second decade of life
    • risk factors
      • prior AC separations
      • commonly associated with individuals who engage in constant heavy overhead activities
        • especially in weight-lifters and overhead throwing athletes 
  • Associated conditions
    • distal clavicle osteolysis 
  • Acromioclavicular Joint Anatomy 
  • Diarthrodial joint
    • articulates scapula to clavicle
    • contains a fibrocarilaginous disk
  • Ligaments
    • AC ligaments
      • provide anterior-posterior stability
        • posterior and superior AC ligaments most important for stability
    • Coracoclavicular ligaments
      • provide superior-inferior stability
  • Symptoms
    • activity related pain 
      • with overhead activity
      • with arm adduction
  • Physical exam 
    • palpation
      • pain with direct palpation of AC joint 
    • provocative tests
      • pain with cross body adduction test 
  • Radiographs 
    • recommended views
      • best evaluated using Zanca view (15 degree cephalic tilt) 
    • findings
      • can show osteophytes and joint space narrowing 
      • distal clavicle osteolysis
      • imaging findings do not always correlate with patient symptoms
  • MRI 
    • increased signal and edema in AC joint 
  • Nonoperative
    • activity modification and physical therapy
      • indications
        • indicated as a first line of treatment
      • technique
        • therapy should focus on strengthening and stretching of shoulder girdle
    • AC joint injection with corticosteroids 
      • can be both a diagnostic and therapeutic modality
      • access to the joint is challenging
        • 44% of AC joint injections miss the joint
  • 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 
          • open procedures require meticulous repair of deltoid-trapezial fascia
  • Arthroscopic distal clavicle resection 
    • should resect only 0.5-1cm of distal clavicle
  • AC joint instability
    • anterior-posterior instability
      • can be due to aggressive surgical distal clavicle resection (>1-1.5cm)
      • due to aggressive debridement sacrificing posterior and superior AC ligaments 
    • superior-posterior instability
      • usually iatrogenic due to aggressive surgical resection compromising coracoclavicular ligaments
  • Continued pain after surgery
    • most commonly due to failure of posterior-superior resection of distal clavicle 
  • Heterotopic ossification
  • Deltoid dehiscence
    • due to inadequate deltoid-trapezial  junction repair in open surgery

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