One-step transport-disk distraction osteogenesis (TDDO) is effective for repairing segmental mandibular defects. The authors studied whether it was effective for reconstructing angled large mandibular defects using a two-step TDDO procedure in seven patients suffering from neoplasm. In the two-step TDDO procedure, the first distraction (horizontal distraction) was initiated immediately after mandibulectomy, aimed at restoring the mandibular body. It was followed by the second distraction, which was obliquely vertical and aimed at restoring the height of the ramus. The distraction rate was set at twice 0.4 mm/day. The treatment lasted for 14–18 months. The horizontal distraction length ranged from 48 to 55 mm, and the vertical one from 33 to 43 mm, with full ossification in the distraction area. No obvious shift of mandible, malocclusion or mouth opening limitation was observed. Patients had a regular diet and spoke clearly. In conclusion, the two-step TDDO is still an option for the reconstruction of large angled mandibular defects when patients are prudently selected, despite the long treatment period required.
Large mandibular defects resulting from tumor resection lead to severe aesthetic and functional sequelae. The patient’s postoperative quality of life largely depends on the quality of the mandibular reconstruction. Vascularized or non-vascularized bone grafting has been the mainstay of mandibular reconstruction treatment because of its predictable effect, but its use of autogenous bone and the donor site morbidities caused by its harvesting encouraged the authors to seek an alternative .
Distraction osteogenesis is often used to correct craniomaxillofacial bone malformations . Transport-disk distraction osteogenesis (TDDO) has been applied clinically to reconstruct craniomaxillofacial bone defects resulting from tumor resection . In this method, a bone segment is osteotomized adjacent to the defect and then distracted slowly across the defect so that new bone forms in the continuously widening gap, eventually leading to reconstruction of the bone defect. The distracted bone segment is referred to as the transport disk . Constantino et al. carried out a series of studies in dogs on the biomechanical properties of reconstruction of mandibular defect with TDDO and concluded that the bone regenerated by TDDO is strong enough to resist the forces of mastication . Since then, clinical cases of mandublar reconstruction with TDDO have been reported .
Despite its success in reparing segmental bone defects, it is impossible for a single TDDO procedure to reconstruct a mandibular defect that involves the body, angle and the whole ramus. There are two difficulties: the defect size is beyond the maximal limitation of most internal distraction systems; and the angled shape can not be formed with a single TDDO.
In the present study, this type of mandibular defect was reconstructed successfully with a double-step TDDO procedure, in which the first TDDO was horizontal distraction and aimed at restoring the mandibular body, and the second was vertical distraction and aimed at reconstructing the height of the ramus. The indications, limitations and noteworthy aspects of this method are described.
Patients and methods
Patients with a unilateral mandibular defect involving the posterior part of the body, the angle and the whole ramus were candidates for this study. They were informed about the options for mandibular reconstruction, including traditional vascularized or non-vascularized bone grafting and the double-step TDDO. Those preferring the double-step TDDO method were involved in the present study. The double-step TDDO method was applied in 7 consecutive patients suffering from benign neoplasm of the mandible. The patients’ clinical data are given in Table 1 .
|Case||Sex/Age (ys)||Diagnosis||Distraction length (mm)||Bone quality||Max. insical opening (mm)||Midline shift||Occlusion||Treatment duration (month)||Follow-up (month) *|
|4||M/25||Odontogenic keratocyst||53||42||Excellent||35||No||Mild anterior open bite||16||11|
|6||F/33||Ameloblastoma||47||36||Excellent||37||No||Mild anterior open bite||14||5|
Ablative surgery and horizontal distraction procedure
All patients underwent CT scanning preoperatively. The scanning data were used to manufacture a solid model using rapid prototyping techniques. Mandibulectomy was simulated and the horizontal distraction procedure (including size of the transport disk, the distraction orientation and length; Figs. 1 and 2 ) was planned with the solid model.
A sub- and retro-mandibular incision was made combined with an intra-oral incision under general anesthesia. The soft tissues around the lesional mandible were elevated. The elevation was performed in the subperiosteal plane in an area where the periosteum was beyond a safe surgical margin. Otherwise, the periosteum had to be sacrificed. Extensive elevation of the healthy mandible should be avoided. Especially for the bone that was to be made into the transport disk, elevation of the tissues on the medial side of the healthy mandible had to be strictly prevented. Mandibulectomy was performed beyond the safe surgical margin (0.5 cm from the lesion) and the lesional mandibular block was removed, including the whole ramus, the angle and the posterior part of the body ( Fig. 3 ).
The intra-oral incision was sutured in two layers; the oral mucosa and the sub-mucosal layer. A transport disk of about 14×18 mm was osteotomized on the mandibular stump. Special attention was paid to avoid lacerating the soft tissues attaching to the medial side of the transport disk. The internal distraction device (Cibei Med, Cixi, China) was fixed to the transport disk and the remaining mandible (remaining basal bone), with the transport segment in close contact with the basal bone ( Fig. 4 ). The activation arm was submandibularly placed and the extra-oral incision was sutured in layers. The distraction was started at the rate of twice 0.4 mm per day after a latency period of 7 days and ended when the expected distraction length was reached. The consolidation period was continued for at least 16 weeks, decided by the degree of calcification in the distraction gap on the panoramic radiograph.