Acromioclavicular joints  
 

The patient stands in the anatomical position and an AP film is taken that includes both acromioclavicular joints in the same image. This allows comparison of the two joints. Occasionally, a second film is taken while the patient holds weights in both arms. This is the "stress view" that helps elucidate acromioclavicular joint separation by increasing the load that the joint has to bear. If there is ligamentous injury, the joint space will widen.

 
The two spaces requiring careful evaluation are the acromioclavicular joint space and the coracoclavicular space. These should be symmetric on the right and left and should not be abnormally widened. Increased distances across the spaces indicate a degree of joint separation or sprain. The film here was taken of a college football player who suffered an AC separation on the right side. Note the widening compared to the left side.