Cranial distraction osteogenesis in sheep using a totally implantable hydraulic mechanism: early results

Conventional distraction osteogenesis has been performed by using either percutaneous pins attached to a thread and screw mechanism, or a thread and screw mechanism that is implanted but still requires turning by a percutaneous instrument or device. In these situations there is always the risk of infection passing to the bone via the percutaneous connection. We have developed a totally implantable hydraulic mechanism, which is activated in much the same way as injection into the port of a tissue expander. Preliminary in vitro testing has suggested that our mechanism can produce sufficient force at appropriate rates of distraction to have a promising role in distraction osteogenesis. We examined the effect of osseous distraction on the cranial vault. Expansion of the cranial vault by distraction osteogenesis is not widespread in clinical practice, in part because of the risk of infective complications of the extra-dural space. We were, therefore, presented with an ideal opportunity both to test the new distraction device and to examine the effect of distraction osteogenesis on the cranial vault. A sheep animal model was used in a pilot study to test the plausibility and examine the physiology of cranial-vault distraction osteogenesis using a totally implantable hydraulic device. Two sheep had a device implanted in the temporal fossa so as to push the craniotomised cranial cap upwards. Distraction was performed for 13 days beginning 1 week after craniotomy. After 9 weeks of consolidation, 5.5 mm and 7.4 mm of new woven bone of normal cranial thickness were demonstrated.