Acromioclavicular joint injury

Last updated: September 14, 2023

Summarytoggle arrow icon

Acromioclavicular joint injury is usually caused by direct injury to the acromion during a fall on an adducted arm. It is classified according to the Rockwood classification, which considers the extent of injury to the acromioclavicular (AC) ligament and the coracoclavicular (CC) ligament, as well as the displacement of the clavicle and type of dislocation in the AC joint. Patients present with local tenderness, swelling, limited range of motion, and/or deformity of the joint. X-ray is used to diagnose joint subluxation and clavicular displacement. Treatment is usually conservative and may include rest and analgesia for a few weeks. Surgery is recommended for more severe injuries when ligament repair is required.

Etiologytoggle arrow icon

  • Most common: direct force injury to the superior aspect of the acromion while the arm is adducted (e.g., a fall while cycling or riding a horse)
  • Less common: indirect injury via falling on an outstretched hand, which transmits force up the arm through the humerus to the acromion, causing displacement that distresses the AC ligaments

Clinical featurestoggle arrow icon


Diagnosticstoggle arrow icon

Rockwood classification of AC joint injury
Injury type AC ligament Joint capsule CC ligament Distal clavicle Deltoid and trapezius muscles
Type I
  • Sprained
  • Intact
  • Intact
  • Intact
  • Intact
Type II
  • Ruptured
  • Sprained
  • AC joint widening and minimal elevation
  • Possibly partial detachment from clavicle
Type III
  • Ruptured
  • Moderately elevated and unstable to stress
  • Reducible (“piano key” sign)
Type IV
  • Ruptured
  • Posteriorly displaced through the trapezius
  • Not reducible
Type V
  • Ruptured
  • Severely elevated
  • Not reducible
Type VI (rare)
  • Ruptured
  • Inferiorly displaced in subcoracoid position


Treatmenttoggle arrow icon

Acute management

Conservative treatment

Surgical treatment

Long-term management

References: [1][2]

Complicationstoggle arrow icon

We list the most important complications. The selection is not exhaustive.

Referencestoggle arrow icon

  1. Acromioclavicular (AC) Joint Injuries. Updated: January 20, 2017. Accessed: November 18, 2017.
  2. Quillen DM, Wuchner M, Hatch RL. Acute shoulder injuries. Am Fam Physician. 2004; 70 (10): p.1947-54.
  3. Gorbaty JD, Hsu JE, Gee AO. Classifications in Brief: Rockwood Classification of Acromioclavicular Joint Separations. Clinical Orthopaedics and Related Research®. 2016; 475 (1): p.283-287.doi: 10.1007/s11999-016-5079-6 . | Open in Read by QxMD
  4. Owens BD. Acromioclavicular Joint Injury. In: Young CC, Acromioclavicular Joint Injury. New York, NY: WebMD. Updated: October 22, 2018. Accessed: January 13, 2019.
  5. Rockwood Classification of Acromioclavicular Joint Injury. Updated: January 1, 2019. Accessed: January 13, 2019.

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