Two patients present to your emergency department: Patient 1 is a 17 year-old soccer player who fell during a game onto their right side and is now complaining of mild right shoulder pain. You obtain x-rays (Figure 1). Patient 2 is a 21 year-old motorist who lost control and went over the handlebars. They heard a pop and are complaining of left shoulder pain. You obtain shoulder x-rays (Figure 2). For these cases, what are your diagnoses, expected physical examination findings, and emergency department management?

grade II AC separation

Figure 1: Image courtesy of Dr Benoudina Samir,

Grade IV AC separation

Figure 2: Image courtesy of Dr Craig Hacking,

  • Acromioclavicular (AC) Joint Separation:
    • Case 1 (Figure 1): Type II AC joint separation
    • Case 2 (Figure 2): Type IV AC joint separation.
      • Pearl: Because this dislocation is primarily posterior, it can be easily missed on an AP film. An axillary view (Figure 3) is typically required to make the diagnosis.
Grade IV AC separation

Figure 3: Axillary view showing clavicle (dashed line) displaced posteriorly in comparison to the acromion (solid line) in a Type IV. Image courtesy of Dr Bijoor,, edits by Dr Luz Silverio

  • AC joint separations can occur from blunt trauma to the shoulder, most commonly from falling onto a shoulder with an adducted arm [1]. This forces the acromion inferomedially and the clavicle superiorly.
  • AC joint separations are classified using the Rockwood Classification System [2]. It grades the degree of separation of both the AC ligament and the coracoclavicular (CC) ligament. See Table 1 and Figure 4.
IAC sprain, normal radiograph
IIAC torn, CC sprained, clavicle does not elevate above the superior border of the acromion
IIIAC and CC torn; clavicle is above the superior border of the acromion and <25mm of displacement measured at the CC space.
IVAC and CC torn; posterior displacement of the clavicle.
VAC and CC torn; >25mm of superior displacement of the clavicle at the CC space.
VIAC and CC torn; distal clavicle is displaced inferiorly and underneath the coracobrachialis/biceps tendon. Very rare.

Table 1: Rockwood Classification for AC joint separation

shoulder separation

Figure 4: Normal Acromioclavicular (AC) and Coracoclavicular (CC) Spaces. AC Space should be 5-8 mm (red). CC Space (green) should be 10-13 mm. Image courtesy of Dr Jeffrey Hocking,

  • A patient with an AC dislocation will have tenderness at the distal clavicle and AC joint and an abnormal contour of the affected shoulder when compared contralaterally. There may be referred pain to the trapezius.
  • Pearl: Consider other etiologies that may mimic an AC separation – clavicle fracture, shoulder dislocation, rotator cuff tear, pneumothorax, superior labral antero-posterior (SLAP) lesion of the shoulder, or cervical radiculopathy.
  • Plain films of the shoulder and clavicle. Ensure an axillary view is performed to evaluate for a type IV.
    • Pearl: Contralateral films may be helpful to improve classification [3].
  • Type I to II are managed conservatively with rest, ice, and analgesics.
    • Pearl: Sling and encourage early mobilization as tolerated to avoid adhesive capsulitis.
  • Type III injuries may require operative intervention for overhead laborers, elite athletes, or patients with greater than 20mm of CC space.
  • Types IV to VI injuries are managed operatively with AC joint fixation or ligament reconstruction [4, 5].
  • Case 1 (Type II AC): Type I to III AC separations can be discharged with close sports medicine/orthopedic follow-up. Encourage early range of motion. Counsel that it can take approximately 6 weeks to regain functional motion and approximately 12 weeks to regain normal activity. Physical therapy may be required.
  • Case 2 (type IV AC): Type IV to VI AC joint injuries require operative repair. Orthopedic consultation is recommended to facilitate operative planning.

For more information about acromioclavicular separations, University of Washington has a great AC joint reference and Orthobullet’s review of acromioclavicular separations is also worth checking out. Want more SplintER

For more cases like these, you can subscribe to the Ortho EM Pearls email series hosted by Drs. Will Denq, Tabitha Ford, and Megan French, who have kindly shared some of their content with ALiEM.


  1. Vanhoenacker F, Maas M, Gielen JL. Imaging of Orthopedic Sports Injuries. Springer Verlag. (2006) ISBN:3540260145
  2. Kiel J, Kaiser K. Acromioclavicular Joint Injury. In: StatPearls. Treasure Island (FL): StatPearls Publishing; 2019 jan. PMID: 29630240
  3. Ibrahim ef, Forrest NP, Forester A. Bilateral weighted radiographs are required for accurate classification of acromioclavicular separation: An observational study of 59 cases. Injury Int J Care Injured 46(2015)1900-1905. PMID: 26194267
  4. Stapczynski, J S, and Judith E. Tintinalli. Tintinalli’s Emergency Medicine: A Comprehensive Study Guide, 8th Edition. New York: McGraw-Hill Education, 2016. ISBN: 9780071794763
  5. Favorito, PJ., Herbst., KA., Acromioclavicular joint injuries, Shoulder and Elbow Trauma and its Complications., Woodhead Publishing Series in Biomaterials., Volume 1., Pages 215-231., 2015. ISBN: 9781782424727
Sergio Alvarez, MD

Sergio Alvarez, MD

Senior Resident, Class of 2020
UCSF-ZSFGH Emergency Medicine Residency
Department of Emergency Medicine
University of California, San Francisco
Sergio Alvarez, MD

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Megan French, MD, FACEP

Megan French, MD, FACEP

Emergency physician
Utah Emergency Physicians
Megan French, MD, FACEP

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William Denq, MD CAQ-SM

William Denq, MD CAQ-SM

Assistant Professor
Department of Emergency Medicine
University of Arizona
William Denq, MD CAQ-SM


Clinical Assistant Professor Emergency Medicine and Sports Medicine University of Arizona George Washington University '18 University of Pittsburgh '14 and '10