Definition: Sprain or tear of the acromioclavicular (AC) and coracoclavicular (CC) ligaments.

Mechanism: Typically a fall on or direct blow to the acromion with the humerus adducted, forcing the acromion inferiorly and medially relative to the clavicle.


  • True incidence unknown because many with mild injuries do not seek medical attention.
  • Most common type of shoulder injury amongst young athletes.
  • Male predominance 5:1 due to increased participation in contact sports. (Rockwood 1996)

Physical Exam

AC Joint Injury (

AC Joint Injury (

  • Point tenderness to palpation over the AC joint and, depending on degree of injury, the CC joint.
  • Prominence of the clavicle and associated swelling in more severe injuries.
  • Arm typically held in adduction against the body with poor range of motion of the shoulder secondary to pain.
  • Scarf test – patient elevates arm to 90 degrees and adducts across the front of the body, elicited pain in the AC joint is a positive test.
  • Review of the complete shoulder exam


Injury Classification System 

Rockwood Classification System (

Rockwood Classification System (

  • Rockwood Classification
  • Type I: AC sprain, unaffected CC ligament; normal x-ray or slight AC widening.
  • Type II: AC tear/CC sprain, inferior border of clavicle elevated but not displaced beyond superior aspect of acromion; normal CC space.
  • Type III: AC tear/CC tear, inferior border of clavicle beyond superior aspect of acromion, CC displacement but less than twice normal joint distance.
  • Type IV: AC tear/CC tear, lateral clavicle posteriorly displaced into trapezius (see on axillary view).
  • Type V: AC tear/CC tear, CC displacement greater than twice normal joint distance, may cause tenting or ischemia of overlying skin.
  • Type VI: AC tear/CC tear, clavicle located beneath acromion or coracoid; very rare.

X-Ray Findings

  • Normal AC joint distance <5mm. Variation exists but with clinical suspicion any measurement >8mm is concerning for injury, comparison to normal contralateral side also useful.
  • Normal CC joint distance 10-13mm. Displacement measured from superior border of the coracoid process to the inferior border of the clavicle.
  • A Zanca view, an AP with 10-15 degrees cephalic tilt, may help better visualize the AC joint by eliminating overlying bony images when evaluating for type II injury.

    AP View of Shoulder (

    AP View of Shoulder (

G – glenoid fossa

H – humeral head

A – acromion

C – coracoid process

S – scapula

Cl – clavicle

Emergency Department Management

  • Grade I and II injuries: sling for 3-7 days, taking into account severity of pain and patient age. Encourage early range of motion, especially in elderly patients. (Montellese 2004)
  • Type III injuries: Ensure orthopedic follow up for possible operative management.
  • Type IV-VI injuries: Uncommon and are frequently in the setting of polytrauma. They require careful examination to evaluate for signs of vascular injury. Orthopedic consultation recommended for evaluation and operative planning.



  • Most Type I-II injuries regain full range of motion by 6 weeks and can return to normal activity by 12 weeks. Mild type I injuries may require only a few days away from usual activities.
  • Type III management often dictated by patient age and lifestyle with majority being non-operative Spencer 2007. If operative management deferred patient will usually remain in a sling for 2-3 weeks.
  • Return to full activity following surgery for more severe injuries is usually 6 months.

Take Home Points

  • Diagnosis of AC injuries is frequently made on physical exam; lack of x-ray findings does not rule out a type I injury.
  • Recommend early range of motion in commonly seen mild AC joint injuries.
  • Recognize severe injury patterns and carefully evaluate for vascular compromise.


Baxter A. Emergency Imaging: A Practical Guide. Stuttgart, Germany: Thieme; 2016: 412-413.

Montellese P, Dancy T. The acromioclavicular joint. Prim Care. 2004; 31:857.

Quillen D et al. Acute Shoulder Injuries. Am Fam Physician. 2004; 70(10): 1947-1954. PMID: 15571061.

Raby N, Berman L, de Lacy G. Accident and Emergency Radiology: A Survival Guide. Philadelphia, PA: Elsevier Saunders; 2005: 68-89.

Rockwood CA Jr et al. Fractures in Adults. 4th ed. Philadelphia, Pa: Lippincott-Raven; 1996.

Spencer EE Jr. Treatment of grade III acrimioclavicular joint injuries: a systematic review. Clin Orthop Relat Res 2007; 455:38. PMID: 17179783.