S.A. Schendel, B. Safa and D. Kahn

Division of Plastic and Reconstructive Surgery Stanford University School of Medicine, Stanford, CA, U.S.A.

Background

Distraction osteogenesis is becoming an accepted modality for mandibular bone-lengthening. Furthermore, the osteodistractor has undergone significant evolution since the application of the technique to craniofacial skeleton.

Recent years have marked a proliferation of internal distractors which are smaller in size, are not readily visible, and do not necessitate percutaneous pinning as with external devices. These internal devices, however, have been predominantly uni-planar, therefore distracting along a single vector.

Multiplanar distractors currently exist but remain primarily external in design and distract via complex, imprecise movements.

Human mandibular growth has been shown to occur by a unitary logarithmic spiral by Rickets and Moss. This study evaluates a semi-buried distractor whose design mimics this pattern of spiral growth.

Design

The device used in this study is curvilinear in shape and is composed of a titanium body. Three titanium footplates anchor the device to the mandible. The activation mechanism is composed of nitinol thereby allowing the mechanism to flex with the curve of distractor (Figure 1).

Figure 1: The device is composed of a curved titanium body with three titanium footplates which anchor the device to the mandible. The activating mechanism is composed of the nitinol.

Methods

The distractor was placed unilaterally on 5 beagles ranging from 3-6 months old (Figure 2). After three days of latency, each mandible was distracted at 2mm/day (0.5mm every 6 hours) for 5 days (10mm). After three days of consolidation, the mandibles were harvested and examined grossly and histologically (H&ampE and Trichrome).

Figure 2: This is an intra-operative picture showing the position of the osteotomy, device placement, and activating mechanism.

Results

The hemimandibles underwent an average distraction of 9.6mm. No cases of non-union or premature consolidation were seen. The distracted segments were histologically indistinguishable from samples from linear external distractions at the same rate as evaluated by a blinded pathologist. The animals tolerated the distraction procedure well.

Conclusion

We have shown that curvilinear distraction replicating the natural logarithmic growth curve of the mandible is possible. Furthermore, the new bone formed is histologically indistinguishable from bone formed with external linear distraction. Finally, the device is well-tolerated during the procedure.

References

1. Ilizarov, G.: The Principles of the Ilizarov Method, Bull Hospital of Joint Diseases Orthopedic Institute, 1988, 1-48
2. Ilizarov, G - Transosseous osteosynthesis theoretical and clinical aspects of the regeneration and growth of tissue, New York: Springer Verlag, 1992.
3. Karp, W.S., Thorne, C.H., McCarthy J.G., Sissores, H.A.: Bone Lengthening in the craniofacial skeleton, Annals of Plastic Surgery, 1990, 24, 231-237
4. Moss, M., Salentjin, L.: The logarithmic growth of the human mandible, Acta Anatomica, 1970, Vol 77, 341-360
5. Ricketts, R.M., DDS: A principle of archial growth of the mandible, Angle Orthodontist, Vol 42, 4, 368-386

©2001 by Monduzzi Editore S.p.A - MEDIMOND Inc.