Distraction Osteogenesis and Its Challenges in Bone Regeneration

Introduction 1.1 Distraction osteogenesisBone is amongst the very few tissues in the human body that possess intrinsic capacity to heal spontaneously following injury.However, beyond a certain critical size defect, bone cannot heal by itself and outside intervention is required.Numerous techniques are available for the management of these defects, including the gold standard autogenous bone grafts, allografts, bone graft substitutes, vascularized fibular bone grafts and systemic administration of anabolic agents.All these techniques, however, do have limitations (Dimitriou et al., 2011;Nauth et al., 2011).Such instances of severe bone loss, whether due to congenital bony deficiencies or acquired causes, pose an immense challenge to the treating physicians, and it is in these cases that distraction osteogenesis could offer a viable and successful alternative to these techniques.Distraction osteogenesis (DO) is a surgical technique in which the intrinsic capacity of bone to regenerate is being harnessed to lengthen bones or to replace large segments of bone.It consists of the application of an external fixator to the affected bone (Figure 1), followed by an osteotomy of the bone and then gradual and controlled distraction is applied to the two bone segments.This controlled distraction, usually by an external fixator, generates new bone within the distracted gap.When the desired lengthening is obtained, distraction is stopped and the external fixator is kept on until the newly formed in the distracted gap is mechanically strong enough to allow removal of the fixator.DO is considered a type of in vivo bone tissue engineering and is superior to other methods of bone regeneration in the management of cases of bone loss, because this technique allows the spontaneous formation of de novo native bone without the need for bone grafts.DO also has the unique ability to regenerate bone and soft tissues simultaneously. Historical aspect of distraction osteogenesisCodivilla from Italy is credited for having performed the first lengthening procedure by applying skeletal traction through a calcaneal pin, following osteotomy of the femur (Codivilla, 1905 ).However, it was a Russian surgeon, Gavriil Ilizarov, who pioneered the biological principles of bone and soft tissue regeneration and popularized the technique of distraction osteogenesis, when he discovered that under slow and gradual distraction, new www.intechopen.comBone Regeneration 186 bone will regenerate in the distracted gap (Ilizarov, 1989a; Ilizarov, 1989b).Starting in the early 1950s, he worked in a village in Siberia, Kurgan, unknown to the rest of the world.Then, in 1982, he successfully treated a famous Italian explorer "Carlo Mauri" for a resistant non-union of his tibia and it was only then when his principles were made known to the Western World. Ilizarov principles or the law of tension stress (Green, 2011)Ilizarov developed the law of tension-stress, which describes the process of new bone and soft tissue regeneration under the effect of tension-stress caused by slow and gradual distraction.His biological principles can be summarized as follows: Minimal disturbance of bone and soft tissuesIlizarov showed that formation of new bone at the osteotomy site is definitely influenced by the amount of damage to the bone, medullary cavity, and periosteum.He described the new concept of corticotomy, where only the cortex of the bone is cut, preserving the periosteum and medullary cavity.The value of corticotomy has recently been questioned, because the medullary blood supply regenerates in 7 to 10 days following a complete osteotomy.The integrity of the periosteum is the only important factor for new bone formation at the site of the osteotomy. Delay before distraction(Latency phase) Duration of delay varies from 5 days in a child to about 10 days in a skeletally-mature patient.This allows the formation and organization of a hematoma. Rate and rhythm of distractionThe optimum rate was found by Ilizarov to be 1mm/day and the optimum rhythm of distraction was 0.25mm every 6 hours.Elongation of more than 2mm/day may lead to slowing of osteogenesis, while elongation of 0.5mm/day or less may lead to premature consolidation.An autodistractor causing a continuous gradual and slow distraction of 1.0 mm/day was found to be superior to a rhythm of four times a day. Site of lengtheningMetaphyseal lengthening leads to better osteogenesis than diaphyseal lengthening.The metaphyseal region contains much more cancellous bone than the diaphyseal region and this type of bone has a much higher potential for osteogenesis. Stable fixation of the external fixatorSimilar to fracture healing, this has been shown to be of paramount importance.Some axial micromotion is, however, beneficial to the consolidation of the regenerate bone. Functional use of the limb and intense physiotherapyDuring the whole lengthening procedure, this is of foremost importance in order to obtain a satisfactory outcome.www.intechopen.comDistraction Osteogenesis and Its Challenges in Bone Regeneration 187 4. Phases of distraction osteogenesis As shown in Figure 1, DO consists of the following phases: -Latency phase: This is the phase immediately following the osteotomy, where there is no distraction.It lasts 5 to 10 days -Distraction phase: the two bone segments are gradually distracted at a rate of 1.0 mm day in several increments, until the desired amount of lengthening is obtained.-Consolidation phase: distraction is ceased and the two bone segments are held in place until the newly formed bone in the distracted gap consolidates (about one month per cm lengthened) -Removal of the fixator. How to referenceIn order to correctly reference this scholarly work, feel free

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