DISCUSIÓN

Discussion of the article "Complications of self-tapping bone screws for maxillomandibular fixation in the treatment of jaw fracture"

Discusión del artículo "Complicaciones de los tornillos de bloqueo intermaxilar en el tratamiento de las fracturas mandibulares"

Rafael Martín-Granizo López

Servicio de Cirugía Oral y Maxilofacial. Hospital Clínico San Carlos, Madrid, España

Maxillomandibular fixation (MMF) screws are one of those empirical discoveries that are made in surgery sometimes, whose importance in daily practice is only recognized years later. Something apparently as simple as screws was not described in the scientific literature until 1989.¹ Since then, the use of MMF became generalized and, naturally, the medical industry began to come up with more specific screw designs. It should be remembered that there were no special screws for MMF then and we used the standard 1.5- mm or 2-mm diameter titanium miniplate screws (Fig. 1). Of course, these screws required first drilling in the bed and the oral mucosa was opened before they were placed. Inserting the screws through the mucosa seemed «heretical.» Later, MMF screws of more advanced design began to appear: they had a wider and rounder head than a normal screw to prevent pressure sores and the encroachment of the oral mucosa, a small hole in the head to allow a wire to be threaded in the case of rigid MMF, a small canal between the head and shaft to comfortably lodge elastic bands in the case of elastic MMF, as well as a cross-marked tab to easily position and remove the screw without having to use special screwdrivers (Fig. 2A). The industry also tried to reduce costs by manufacturing the screws in steel instead of titanium since, after all, the material was going to be removed later. However, the lower resistance of the steel screws at first led to fractures at the junction between the head and the shaft with some frequency.² A major advance in the design of these screws was the addition of a very sharp tip to facilitate transmucosal placement and of a self-tapping system that made it unnecessary to drill before insertion, even in hard bones like the jaw and bone with a thick cortical. This innovation also protects dental roots from damage during screw insertion because when the screw encounters increased resistance, it turns aside and around the dental root. An advance in these screws is now extremely popular: microscrews or microimplants for orthodontic traction. This technique now is perfectly integrated into practice and produces excellent results.

The authors of the present article meticulously review their experience with the use of these screws for the treatment of mandibular fractures. Although this is the main indication of these screws, it is not the only indication. They are routinely used in orthognathic surgery,⁴ in oncologic surgery to maintain dental occlusion before implanting a bone graft, and in other types of fracture, such as maxillary or tooth socket fractures. In fact, only two specific articles have been published on the complications of these screws, although other clinical reviews describe the incidence of complications with this technique.

The advantages of these screws are explained perfectly by the authors. The fundamental advantage is that they save surgical time and can be inserted under local anesthesia in simple fractures. Of course, they also prevent the risk of accidental pricks that existed when MMF was done with the tedious Ehrlich splints and wires (Fig. 2B). It should be remembered that one of the first uses of these screws was for to manage fractures in patients with HIV or HBV infection. In contrast, one of their main problems, as indicated in the present article, is in the reduction of highly comminuted fractures or in toothless patients. In addition, it is a technique that, while simple for an oral and maxillofacial surgeon, is still a "blind" technique. In inexperienced hands, they can tremendously increase the rate of complications.⁵

I recall a case that occurred in a regional hospital in which facial fractures were operated on by a traumatologist, who was very satisfied because he or she «had found a very useful hole for introducing a Kirschner needle into the mandibular body for the treatment of mandibular fractures» (sic). Evidently, this is the mental foramen, out of which the inferior dental nerve emerges. I trust that this is an isolated occurrence and that nowadays, with the excellent training of our specialists and the implantation of our specialty in hospitals, it is merely anecdotal. The complication rate that the authors cite coincides with other reviews, about 4%.^6,7 A more recent review (2007) by Coletti et al. mentions 39%, with 8% of patients who accumulate more than one complication;⁸ the rate of root damage was 4%, whereas in the present article it is 4.4%.⁹ Some authors have suggested an association between the complication rate with these screws and the surgeon’s experience, because these self-tapping bone screws on many occasions are placed by medical residents or surgical assistants. ^5,9

I would only like to make a few simple observations on the splendid article discussed here. Recently, in some cases, we have placed three screws in each dental arcade, one midline, because this gives us better control over the vector of forces applied to the screws (Fig. 3). In addition, the elastic bands usually used are for orthodontics and they are sometimes too short to join screws that are very separated. Also, we usually choose the shortest screws (normally 8 or 11 mm long), because this allows us to avoid some complications of perforating two cortical layers, particularly in the mandible. On the other hand, as the authors suggest, we usually insert the screws in the junction between the adhered and free gum to avoid pressure ulcers (Fig. 4). When we use MMF screws in orthognathic surgery (in subcondylar mandibular osteotomy) or panfacial fractures, on some occasions we insert 4 screws or more into each dental arcade (Fig. 5), two in the molar zone, applying force on the bone, and not the usual elastic fixation on orthodontic brackets, which can cause dental movement (Fig. 6).¹⁰

References

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