Distraction osteogenesis presents a unique form of clinical tissue engineering.
Using easily controlled mechanical conditions (ie, slow gradual distraction of the corticotomized or osteotomized bone fragments), a clinical is able to guide the formation of new bone and its spatial orientation to form a structural part of the distracted bone. This happens without application of any growth factor or other controlling agents. There is no question about the biological feasibility of the distraction method in promotion of human bone regeneration. The technique also works during gradual transportation of a bone segment.
The critical factors of the process appear to be the stability of fixation, the rate of daily distraction, and the preservation of the local soft-tissue envelope and vascular supply. The mechanical window for distraction osteogenesis seems to be fairly wide. In fact, the primary target of the applied tensile stress may be not only the osteoblasts but also the endothelial cells in the induction of angiogenesis. The angiogenic mechanism of action would explain the reported efficiency of the distraction treatment both in infected and irradiated bones.
The distraction techniques are demanding and time consuming but relatively reliable in achieving the original goals of surgery. Bone healing problems are not infrequent, but they usually respond to modification of the treatment strategy. Biomechanical and surgical principles are important since delayed consolidation not uncommonly reflects technical errors such as an overly traumatic corticotomy, an initial diastasis, instability (lack of fixation), or overly rapid distraction.
The distraction technique was originally applied in limb-lengthening procedures and in salvage of congenital, posttraumatic, or other acquired limb deformities.
In these procedures, the muscle has proved to be the single largest limiting factor. For anamatical reasons, selected craniofacial reconstruction may be the most amenable to application of the distraction techniques. The main disadvantages of gradual mechanical distraction in corrective procedures are those related to external fixation. With careful technique, the risk of external fixation problems can be reduced, but not eliminated.
There remain many unanswered biomechanical questions in distraction osteogenesis. They range from the molecular mechanisms of distraction osteogenesis to computer-assisted surgery planning, and to better design of distraction devices capable of multiplanar correction of complex deformities.
The cranio facial skeleton can be distracted, with new bone formation.
The structures that can be distracted are:
- mandible,
- alveolar processes,
- maxilla,
- orbits.
After the application of the distraction device, patients are able to continue distraction (usually 1mm/day for 25-30 days) with special instruments.