Vacuum phenomenon in the shoulder of a child

Correspondence to Partha Ray, [email protected]

Background

Gas collection within a closed joint space is known as the vacuum phenomenon.^1–3 The vacuum phenomenon is usually observed in intervertebral discs on routine spinal CT. Case reports exist reporting vacuum phenomenon in association with fractures of the mandibular condyle,⁴ the knee⁵ and the pubic bone⁶, it has been described as a sign of delayed or non-united fractures.^{6 7} The phenomenon has also been reported in association with infections,⁸ dislocated joints,⁹ in the ankle¹⁰ and in spinal discs and intervertebral spaces.^{5 6 8 11} A number of reports exist of vacuum phenomenon in the shoulder,^12–14 but none within the English language literature. Furthermore, vacuum phenomenon in children is extremely rare; indeed, to our knowledge it has only been discussed in two papers, neither of which are readily available in English.^{15 16} The finding of vacuum phenomenon on its own, without any other clinical pathology may not lead to any complications. However, it is an important clue for occult penetrating injuries, subtle fractures, recent dislocation/relocation injuries and trauma to the joint which may otherwise go unnoticed. Additionally, awareness of such a phenomenon can prevent clinicians from misdiagnosing chondrocalcinosis or intra-articular loose bodies.^{7 9 17} We report the unusual case of vacuum phenomenon in the shoulder of a child following trauma.

Case presentation

A 10-year-old boy struck a car bonnet before being pinned under a wheel by his left shoulder. In the Accident and Emergency Department, full Advanced Trauma Life Support (ATLS) protocols were followed. The patient remained stable and conscious throughout the primary survey and no life-threatening injuries were identified. Secondary survey identified pain and extensive abrasions to the back and the left shoulder, a closed deformity of the left clavicle and a swollen, but stable right knee.

Investigations

Plain radiography suggested superior migration of the humeral head, a possible greenstick fracture or plastic deformity of the left clavicle and also free gas within the left glenohumeral joint (figure 1). Repeated examination revealed superficial abrasions to the back and the left shoulder with no conclusive penetrating injury. The left arm was neurovascularly intact and movements of the shoulder, although laboured and tender, had a full range of...