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A 30 year old man was referred by the accident and emergency (A&E) department to the oral and maxillofacial surgery unit with small puncture lacerations on his left cheek and lower neck. The patient, a metal fitter, had been hammering on a piece of metal that shattered on impact. Local examination revealed two small lacerations (approximately 2 cm each) sited in the left cheek and left inferior neck region. Two discrete metal foreign bodies (approximately 1 cm in diameter) were detected by plain radiography (true lateral skull) (fig 1). The foreign body in the left cheek region was readily palpated through the skin and was retrieved via a small skin incision under local anaesthesia. The fragment in the neck was located in deeper subcutaneous tissues and was not readily palpable. Initial attempts to retrieve the object using surgical exploration with the aid of an image intensifier failed. The main reason for leaving metal fragments is that the removal procedure is laborious, destructive of surrounding tissues and may leave scars on the surrounding skin. The orthodontic consultant was subsequently consulted by the maxillofacial surgeons to explore the possibility of using a rare earth magnet for the retrieval of the metallic object. A neodymium iron boron magnet was held over the laceration and the metal fragment was instantaneously attracted onto the surface of the magnet (fig 2). The lacerated sites were closed with Ethilon sutures and healing was uneventful.
Penetrating injuries caused by sharp metallic objects constitute a major proportion of all lacerations observed in emergency departments.1 Once embedded in soft tissues, metallic fragments, particularly when small and multiple, are difficult to detect and retrieve. Detection in vivo may be facilitated by various investigative techniques including plain radiography, xerography, computed tomography, ultrasonography and metal detectors.2, 3 Retrieval conventionally follows meticulous surgical exploration of the lacerated site. The metallic fragment in this report possessed sufficient iron content to permit its retrieval by a magnet held at the wound opening. Neodymium iron boron is the most powerful rare earth magnet used in dentistry, particularly in the orthodontic movement of impacted teeth.4 Developments in magnet technology have resulted in marked improvements in the flux density that, in turn, has led to greater attraction forces and concomitant reductions in size. The energy density stored per unit volume is about eight times that of traditional AlNiCo horseshoe magnets and nearly 40 times that of the “fridge decoration” type magnet. Because magnetic force obeys the inverse square law, a sufficient number of magnets must be held in close proximity to the wound opening to exert adequate retraction of the foreign body. In addition, the magnet should be carefully positioned to ensure that the “trough” of maximum attraction (immediately below the magnets) runs over or close to the buried fragments. This method should ensure the safe removal of all reasonably superficial (5–10 mm) metal fragments that are magnetic. Accidental removal of other metallic objects such as aneurysm clips, while a theoretical possibility, is not a real risk as with magnetic resonance imaging magnets, as the “throw” of stray magnetic field is very much less. In other words the field is much more concentrated (that is, focused flashlight beam compared with the array of fluorescent tube lights). Cost of magnets obviously depends on size, coatings applied and quantity purchased but for those used in this report a price of a few pounds per magnet would be charged for small quantities. The magnets can be chemically sterilised and reused but not autoclaved as the high temperatures would destroy the magnetism.
Special training should not be needed by the A&E doctors provided they understand the anatomy of the area in which they are working and simple precautions are used for handling and storing the magnets. This technique of relatively atraumatic, reliable and rapid magnetic removal of metallic foreign bodies is recommended and the low cost of the magnets should ensure every A&E department adds them to the armamentarium.
Conflicts of interest: none.
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