Acromio-clavicular separation masked by muscle spasm.

Weight-bearing views in suspected acromio-clavicular separation may be misleading if there is extensive spasm of the deltoid and trapezius muscles. The effect of this spasm may be lessened by strapping the weights to the wrist rather than having them hand-held. However, if there is strong clinical suspicion of an acromio-clavicular separation and the stress films, however taken, fail to reveal an upward displacement of the clavicle or widening of the joint space, the study should be repeated after infiltration of the acromio-clavicular joint with local anesthetic.