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

Conventional distraction osteogenesis has been performed by using either pe rcutaneous pins attached to a thread and screw mechanism, or a thread and s crew mechanism that is implanted but still requires turning by a percutaneo us instrument or device. In these situations there is always the risk of in fection passing to the bone via the percutaneous connection. We have develo ped a totally implantable hydraulic mechanism, which is activated in much t he same way as injection into the port of a tissue expander. Preliminary in vitro testing has suggested that our mechanism can produce sufficient forc e at appropriate rates of distraction to have a promising role in distracti on osteogenesis. We examined the effect of osseous distraction on the crani al 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 anima l model was used in a pilot study to test the plausibility and examine the physiology of cranial-vault distraction osteogenesis using a totally implan table hydraulic device. Two sheep had a device implanted in the temporal fo ssa so as to push the craniotomised cranial cap upwards. Distraction was pe rformed for 13 days beginning 1 week after craniotomy. After 9 weeks of con solidation, 5.5 mm and 7.4 mm of new woven bone of normal cranial thickness were demonstrated. (C) 2001 The British Association of Plastic Surgeons.