Acromioclavicular joint injury


Right shoulder anatomy with AC Ligaments.
  • Occurs via direct trauma to the adducted shoulder
  • Accounts for 40% of all shoulder injuries and 10% of all injuries in collision sports (football, hockey, etc.)[1]
  • Acromioclavicular (AC) and coracoclavicular (CC) ligaments may be affected
  • Routine use of stress radiographs is controversial (low yield)

Clinical Features

Acromion-clavicle injury. Note that the left shoulder is lower and the "piano key"; Screws on the radiography are a former trauma repair and unrelated to present trauma.
  • Tenderness directly over AC joint (with possible deformity)
  • AC compression test
    • Passively flex arm so It is parallel with ground; then passively adduct across body
      • Pain suggests AC joint injury
  • Ability to touch contralateral shoulder with injured arm suggests lack of shoulder dislocation

Differential Diagnosis

Shoulder and Upper Arm Diagnoses



Refered pain & non-orthopedic causes:



AC Separation XRAY (enhanced).png
  • AP shoulder (highly consider comparison view)
    • AC joint
      • Normal width of AC joint in adults is 1-3mm
      • By age 60 width is often less than 1mm
      • Children and adolescents have a slightly wider joint space
    • CC joint
      • Normal distance is 11-13mm
      • Comparison to opposite CC joint space is more important
        • Increase in CC distance of 25-50% indicates complete CC ligament disruption
    • Zanca view (AP with 10-15 degree cephalic tilt)
      • Consider if AP view is ambiguous, concern for type II injury or distal clavicle injury
    • Axillary view
      • Obtain if coracoid tenderness is present to rule-out associated coracoid fracture
      • Helps to confirm ant-post position of clavicle in injury types III-IV


AC joint separation
Classification Anatomic Injury Exam X-ray Image
Type I
  • AC ligament sprain
  • AC joint intact
  • Mild swelling, no deformity
  • CC ligaments are nontender
  • Only distal-most 1-2cm of clavicle is tender
  • Active overhead and cross-body ROM are limited by pain
  • Often no abnormality is seen on xray
  • Slight widening of the AC joint may occur

Classification type 1 of AC separation.png

Type II
  • AC ligament torn
  • Coracoclavicular (CC) ligament may be partially torn but is intact
  • Prominent and tender AC joint with significant swelling
  • Minimal tenderness of CC ligaments reflecting lack of significant injury
  • May be instability of the distal clavicle in the horizontal plane
  • Partial elevation of the distal clavicle with no or minimal widening of CC distance

Classification type 2 of AC separation.png

Type III
  • AC and CC ligaments torn
  • Complete dislocation of the joint
  • Deformity of the AC joint is clearly visible
  • Marked tenderness of CC ligaments (helps distinguish Type 3 from type 2)
  • Palpable posterior fullness or deformity despite significant swelling
  • Elevated distal clavicle and increased CC distance
  • Distal clavicle is positioned above the plane of the top of the acromion

Classification type 2 of AC separation.png

Type IV
  • Complete dislocation with posterior displacement of distal clavicle in/through trapezius
  • SC dislocation may be appreciated
  • Axillary view required to visualize the posterior dislocation

Classification type 4 of AC separation.png

Type V
  • More severe form of type III injury
  • Superior dislocation of the joint of 1-3x the normal spacing
  • CC ligament distance is increased 2-3x normal *Disruption of the deltotrapezial fascia
  • Shoulder appears to droop
  • Severe superior displacement of clavicle (may cause tenting, ischemia of skin)
  • Clavicle is perhced above the muscle and does not reduce when patient shrugs shoulder
  • Clavicle is elevated above acromion approximately 1-3x width of the clavicle
  • CC distance is increased 2-3x normal range

Classification type 5 of AC separation.png

Type VI
  • Complete dislocation with clavicle displaced inferiorly
  • Complete disruption of the AC and CC ligaments

Classification type 6 of AC separation.png


Type I

  • Rest, ice, sling
  • ROM and strengthening exercises as soon as tolerated
  • Return to sport or work is limited only by pain

Type II

  • Rest, ice, sling x 3-7 days
  • ROM and strenghtnening exercises as soon as tolerated
  • Return to sport or work once full ROM and strength are regained

Type III

  • Rest, ice, sling x2-3 weeks
  • ROM and strengthening exercises as soon as tolerated
  • Return to sport or work 6-12 weeks following injury
  • Ortho consultation within 1 week

Types IV-VI

  • Require orthopedic evaluation; emergent if neurovascular compromise exists
  • Generally operative


  • Admission Criteria
    • Neurovascular compromise
    • Open or unstable fractures
    • Admission for operative repair may be needed for Types IV, V, and VI
  • Discharge Criteria
    • Type I/Type II may be discharged with orthopedic follow-up
    • Type III may be discharged with urgent orthopedic follow-up

See Also


  1. Sirin E, Aydin N, Mert Topkar O. Acromioclavicular joint injuries: diagnosis, classification and ligamentoplasty procedures. EFORT Open Rev. 2018;3(7):426-433. Published 2018 Jul 17. doi:10.1302/2058-5241.3.170027