Bone Distraction                                                                                  

Bone Distraction            

External skeletal fixation is a common method of repair of mandibular fractures in small animals. The kirschnner-Ehmer external skeletal fixator (ESF) is widely used for extremities; however, the bulk and weight of the bar and clamps make it less amenable for all types of mandibular fractures. Functional and aesthetic reconstruction of the mandible after bone loss continues to be affordable in head surgery.

Grafts, flap and synthetic material have been used to reconstruct the mandible; unfortunately, grafts and flaps results in added donor site morbidity beside long operative time and may be of limited availability. Synthetic materials generally retain the characteristics of a foreign bodily and fail to full replace the missing tissue in appearance or function. As a result no uniformly successful methods of reconstructing mandibular defects exists.  An alternative method which was recently developed for mandibular reconstruction is mandibular bone lengthening by the technique of distraction osteogenesis. This technique has gained wide spread orthopedic acceptance but has recently been applied to craniofacial skeletal defects.

The concept of distraction reconstruction follows a biological principal that gradual traction applied to living tissue create stress that stimulate growth and regeneration.This concept was used for bone regeneration and lengthening and the technique was known as distraction ontogenesis. This form of distraction utilize a transport disc of bone that cut from one end of the mandible. When compared with other method; the magnitude of the required surgery is relatively minor; it supplies bone of the same quality and characters of the original mandibular bones; it can replace traumatic mandibular loss and perhaps most important of all is the gradual lengthening of the surround soft tissue.

Figure 1: After insertion of the 4 pin in the proximal and distal mandibular stump. B. After ceation of the segmental mandibular defect.

Figure 2: The osteotomy site (arrow) and creation of the transport disk and the distractor is attached to the mandible.

Figure 3: Dorsoventral postoperative radiograph showing proper insertion of the distractor. The segmental defect (arrow) appears as a radiolucent area. A transmandibulae K-wire attach the distractor to the mandible.

Figure 4: An oblique radiograph of the reconstructed mandible one week after initiation of distraction. The segmental mandibular defect and the regenerate bone shown to have the same density of the surrounding soft tissue.

Figure 5: An oblique radiograph of the reconstructed mandible at 15 days after complete distraction. A central vertically oriented radiolucent zone existed at this time.

Figure 6: Dorsoventral radiograph of figure 5.

Figure 7: An oblique radiograph of the reconstructed mandible at 7 weeks after complete distraction; the entire regenerate shoed progressive calcification but not to the same degree as normal mandibular bone.

Figure 8: Dorsoventral radiograph of figure 8.

Figure 9: C, probably positioned distractor in its place just before its removal; D, just after removal of the distractor.

Figure 10: An oblique radiograph of the reconstructed mandible at 10 days after removal of the distractor , the regenerate segment remains less radiodense than the preexisting mandible.

Figure 11: Dorsoventral radiograph of the reconstructed mandible at 4 weeks after distractor removal, the regenerate segment (2 arrows) calcify to the same degree as normal mandibular bone with compression osteosynthesis (arrow) between the transport disk and distal mandibular stamp. Below, gross appearance of the reconstructed mandible.