Distraction rate and latency: factors in the outcome of pediatric mandibular distraction

Distraction osteogenesis was initially devised as a way to lengthen the lower extremity. All the basic tenets of the technique were developed based on this use. This includes both the supposed need for a latency period before distraction begins (3 to 5 days) and the ideal rate of distraction (1 mm/day). There is no evidence that these values apply to craniofacial distraction osteogenesis, particularly in children. Indeed, with the markedly improved blood supply in the face when compared with the lower extremity and the use of the technique in children versus adults, one might assume that a shorter latency period and a more rapid rate of distraction are possible.

This study is a retrospective review of 22 pediatric patients with mandibular hypoplasia undergoing mandibular distraction osteogenesis. All patients were operated on by a team consisting of an oral surgeon and a plastic surgeon. All the distraction devices used were external. All patients had a latency period, before activation, of less than 24 hours and a distraction rate of 2 mm/day.

Two patients developed cellulitis at the pin sites, one patient developed premature healing, one patient developed a nonunion that required further surgery. This was the only patient in the series who had distraction of a previous bone graft. No patient undergoing distraction of native mandible developed a nonunion.

Eliminating the latency period and rapidly distracting the mandible in pediatric cases has an acceptably low complication rate. This benefits the patient in terms of an overall reduction in the amount of time that the child needs to remain in the distraction device. The patient spends less time with the distraction device, thus reducing the potential morbidity and increased cost of the treatment. Potential explanations for why this variation in distraction technique is successful include the improved blood supply in the face of children and the failure of external devices to translate all the distracted movements to the bone interface. Some of this force is translated into both bending of the pins and migration of the pins through bone. Although a latency period might be necessary in the distraction of the lower extremities, the application of this concept to the craniofacial skeleton in children is erroneous.