Use of a custom designed external fixator system to treat ballistic injuries to the mandible

Abstract

The authors describe a custom designed mandibular external fixator II system that can be used to treat complex, comminuted fractures. The system is adjustable and lightweight, quick, robust, simple to apply, and allows mouth opening during healing, It is well suited to use in the modern war surgery environment. The authors present a case of successful treatment of a ballistic fracture of the mandible using this device.

In 21st century conflicts, the use of body armour and improvised explosive devices have changed injury patterns. The incidence of maxillofacial injuries has risen to 21% to 30% of combat casualties. Fractures of the mandible are seen frequently as the lower face is often unprotected. Ballistic high-energy exchange trauma to the mandible results in complex and comminuted mandibular fractures with penetrating, perforating, or avulsive hard and soft tissue injuries .

External fixators have proved a popular method of treating ballistic injuries to the mandible , but traditional external fixators have significant disadvantages. Systems incorporating an acrylic bar with metal pins require extra materials and equipment, and are not quickly applied; once in place, they cannot be adjusted . The use of fixators designed to treat wrist fractures, although quick and simple to apply, are bulky to wear and the bar shapes and pins are not customised for the mandible. In contrast, the mandibular external fixator II (MEF II) system (Synthes Medical Ltd, Welwyn Garden City, AL7 1LG, UK) has titanium bars that are shaped to conform to the contours of the mandible. This allows the main bar to stand just 1 cm from the skin surface over the mandible so the whole system is less obtrusive. As the bar is closer to the bone than in other systems, it gives more stability at the fracture sites. Unlike conventional external fixators , special titanium pins have the correct length of screw head for the parasymphyseal, body and ramus regions of the mandible. The novel combination clamps to connect the fixator bar, pins and any additional connecting titanium rods are of a snap-on design. They can connect two rods in any orientation and are easier to use than previous mandibular external fixator clamp designs. The system is adjustable and lightweight. The authors present a case of a gunshot wound of the mandible treated successfully using the MEF II system.

Case report

A 25-year-old soldier was shot in the face, at distance, by a high velocity round. The bullet entered his left cheek and lodged beneath the skin of his neck in the left occipital area. Computed tomography (CT) scans showed the position of the bullet, and fractures of his mandible at the left parasymphysis and complex comminuted fractures at the left angle and ramus ( Fig. 1 ). He had a stable fracture of the lateral mass of his first cervical vertebra and mild weakness of the mandibular division of his facial nerve from the gunshot injury. Contrast CT showed no vascular damage. There was palpable mobility of the fractured ramus parts and the patient could not occlude his teeth together fully. He was placed on intravenous antibiotics and analgesics.

Fig. 1
Three dimensional CT scan showing fractures at the left parasymphysis, complex comminuted fractures at the left angle and ramus and a bullet beneath the left occiput.

The following morning he underwent reduction and stabilization of his manbibular fractures using the MEF II system under general anaesthetic. A small skin incision was made over the bullet and it was removed. The missile tract was thoroughly debrided but care was taken not to open the intact soft tissues over the shattered mandibular ramus. Four bone screws were placed in the alveolus between the roots of the premolar teeth in each quadrant and the correct occlusion established, using wires wrapped around the bone screws. The customised external fixator bar was cut and adapted to lie in position, 1 cm from the mandible skin surface. One parasymphysis pin was placed anterior to the canine region fracture, one body pin behind the mental nerve, and two ramus pins in the proximal condylar fragment. A closed approach using a stab skin incision and trochar was used. Three of the pin holes were drilled and the mandibular thickness measured to place a pin with adequate thread length to engage both mandibular cortices. A self-drilling hand-pressure technique was used to place the more anterior of the condylar fragment pins to help avoid placing the pin in a fracture site. The fracture reduction and occlusion were checked constantly during the procedure to ensure that they were not displaced by the manipulation of the mandible. The intermaxillary wires were released but the bone screws were left in place. The occlusion was noted as correct and the fracture fixation firm. The soft tissue cheek wound was packed with idodoform paste and ribbon gauze.

Postoperatively, the patient made a good recovery. Radiographs showed good fracture reduction and placement of the MEF II system screws ( Fig. 2 ). Although he could achieve maximal intercuspation of his teeth the patient tended to posture his mandible to the right. Light training elastics were placed between the bone screws on each side to guide him into the correct occlusion. He was discharged 2 days postoperatively with a 5-day course of oral antibiotics.

Feb 7, 2018 | Posted by in Oral and Maxillofacial Surgery | Comments Off on Use of a custom designed external fixator system to treat ballistic injuries to the mandible
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