How is acromioclavicular separation graded radiographically?

Grade I: Not detectable by routine plain film. The acromioclavicular joint space is 0.8 to 1.0 cm and the coracoclavicular distance is normal. May see widening of the acromioclavicular joint with stress.

Grade II: The acromioclavicular joint space is widened to 1.0 to 1.5 cm and the coracoclavicular distance may widen with stress.

Grade III: The acromioclavicular joint space is greater than 1.5 cm and the coracoclavicular distance is increased by 50% or more.