• A progressive degenerative disease of the acromioclavicular (AC) joint
    • most common condition of the AC joint
  • Etiology
    • transmission of large loads through a small contact area resulting in repetitive microtrauma
      • axial loading 
      • same mechanism as distal clavicle osteolysis
  • Epidemiology
    • demographics
      • more common with age but can occur by second decade of life
    • risk factors
      • trauma
        • clavicle fractures
        • AC joint stability (prior AC separation)
      • distal clavicle osteolysis 
        • associated condition
      • inflammatory arthropathy
        • rheumatoid arthritis
      • prior septic AC joint
      • athletics with frequent and/or heavy overhead activities
        • weight-lifters
        • overhead throwing athletes
  • Osteology
    • diarthrodial joint
      • articulation of the scapula (medial acromion) and the lateral clavicle
      • oblique orientation of joint surface
    • contains a fibrocartilaginous intraarticular disc between the osseous elements
      • analogous to the meniscus of the knee
      • involutes with age, disintegrates by age 40
  • Motion
    • primarily gliding motion
    • rotational motion is minimal
      • clavicle rotates 40-50° posteriorly with shoulder elevation
      • only ~8° rotation through the AC joint, due to synchronous scapuloclavicular motion
  • Stability
    • static
      • joint capsule
      • acromioclavicular (AC) ligaments
        • control horizontal motion and anterior-posterior stability
        • posterior and superior AC ligaments are most important for stability
      • coracoclavicular (CC) ligaments
        • two ligaments
          • conoid
            • medial
            • inserts on clavicle 4.5cm medial to lateral edge
            • most important for vertical stability
          • trapezoid
            • lateral
            • inserts on clavicle 3cm medial to lateral edge
        • control vertical motion and superior-inferior stability
    • dynamic
      • anterior deltoid
      • trapezius
  • High contact forces across AC joint
    • result from
      • small articular surface area
      • oblique joint surface orientation
      • articular disc degeneration wirth age
      • high axial and rotational loads
  • History
    • activity related superior shoulder pain 
      • exacerbated by
        • overhead activity
        • arm adduction (reaching across chest)
        • pressing motion (ex. bench press, push up)
        • laying on affected side (ex. while sleeping)
  • Physical examination 
    • palpation
      • AC joint tenderness with direct palpation 
      • prominence of the distal clavicle (osteophytes)
    • provocative tests
      • cross body adduction test 
        • patient forward elevates arm to 90° and maximally adducts arm across chest
        • positive result is pain localized to the AC joint
  • Radiographs 
    • recommended views
      • true AP and axillary lateral views
      • Zanca view 
        • 15° cephalic tilt with patient in upright position
        • best evaluates the AC joint
    • findings
      • osteophytes and joint space narrowing 
      • distal clavicle osteolysis
      • imaging findings do not always correlate with patient symptoms
        • often will have degenerative findings of the AC joint on radiographs without clinical signs or symptoms
  • MRI 
    • may see T2 signal hypertensity consistent with edema in AC joint 
    • useful for visualizing associated pathology
      • rotator cuff tendons
      • long head of biceps tendon
  • Nonoperative
    • activity modification and physical therapy
      • indications
        • first line of treatment
      • technique
        • avoid aggravating manuevers such as pushing or pressing activities
        • physical therapy should focus on strengthening and stretching of shoulder girdle
    • corticosteriod injection 
      • indications
        • can be both diagnostic and therapeutic modality
      • technique
        • access to the AC joint is challenging
          • injections often miss the joint (~44%)
          • ultrasound improves accuracy of injection
      • outcomes
        • 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 associated injuries 
            • associated pathology is common, involving the 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
  • Arthroscopic distal clavicle resection
    • should only resect 0.5-1cm of distal clavicle
  • AC joint instability
    • anterior-posterior instability
      • aggressive distal clavicle resection (> 1-1.5cm)
      • aggressive debridement sacrificing posterior and superior AC ligaments 
    • superior-posterior instability
      • aggressive surgical resection compromising coracoclavicular ligaments
  • Persistent pain
    • most commonly due to incomplete resection
      • posterior-superior area of the distal clavicle 
  • Heterotopic ossification
  • Deltoid dehiscence
    • inadequate deltotrapezial fascia repair after open distal clavicle resection

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