Acromioclavicular joint injury - Rockwood type III

Case contributed by Leonardo Lustosa
Diagnosis certain


Motor vehicle accident. Patient fell from his motorcycle onto his left shoulder. Piano key sign upon physical examination.

Patient Data

Age: 20 years
Gender: Male

Shoulder radiograph revealed a raised clavicle. The coracoclavicular and acromioclavicular distances are widened (see annotated images below).

This indicates an acromioclavicular joint injury.

There are no associated fractures.

Annotated images of the coracoclavicular (CC) distance and acromioclavicular (AC) distance. Both distances are widened.

  • CC distance: 17.01 mm
  • AC distance: 10.30 mm

An acromioclavicular joint injury with a CC distance of <25 mm is classified as a Rockwood type III.

Case Discussion

Acromioclavicular joint injuries are usually the result of a direct hit to the shoulder which can rupture ligaments such as the coracoclavicular and acromioclavicular ligaments.

In the present case, the positive piano key sign upon physical examination raised suspicion of an acromioclavicular dislocation. The coracoclavicular and acromioclavicular distances are important measurements in the evaluation of their respective ligaments which may be injured when an acromioclavicular joint injury is suspected.

Normal range of the CC distance is 11-13 mm.

Normal range of the AC distance is 1-3 mm.

Widened distances indicate an acromioclavicular joint injury.

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