Vacuum phenomenon in the shoulder of a child.

A 10-year-old boy struck a car bonnet following which his left shoulder got pinned under the wheel. No life-threatening injuries were identified. However, the patient sustained extensive abrasions to the back and the left shoulder, a closed deformity of the left clavicle and a swollen, but stable right knee. The patient was neurovascularly intact globally and all joints had a full range of motion. Plain radiographs suggested a possible greenstick fracture of the left clavicle, but also free gas within the left glenohumeral joint. Concern was raised of an unidentified open injury to the joint. CT was supportive of the finding of gas within the left glenohumeral joint, but ruled out the possible greenstick fracture as a spurious finding. There were no other injuries. The gas was within the left glenohumeral joint and was consistent with vacuum phenomenon. The injury was treated expectantly and the child made a full recovery.