An experimental study of the effects of craniofacial growth on the long-term positional stability of microfixation

Recent clinical reports have documented a potential problem associated with the use of microfixation in the growing craniofacial skeleton, i.e., the finding of microplates and microscrews within the endocranial cavity during repeat surgery. This animal experiment using Yorkshire pigs was designed to determine if this type of passive internal displacement could be demonstrated in an animal model, the frequency of internal displacement, and the potential consequence of such events from a neurohistological standpoint. Ten female Yorkshire piglets underwent left unilateral fronto-orbital advancement at age 3 weeks, fixation being achieved with microplates and screws. The position of the hardware was determined by direct inspection, after they were killed at 6 months of age (skeletal maturity). Ten microplates (28%) showed complete intracranial translocation, whereas nine (27%) remained on the ectocranial surface. The majority, 16 (44%), were between the outer and inner cortices of the calvaria. Gross examination of the brain tissue underlying the translocated hardware showed indentation "pits" forming as a result of such translocation. Histological examination of the cerebrum and meninges of these pits revealed loss of the most superficial connecting cell layer, with focal neuronal distortion. The leptomeninges were intact and there was no cerebritis, gliosis, or hypoxic change. These findings confirm that in this pig model microfixation hardware will undergo passive intracranial ranial translocation and that there are demonstrable histological alterations in the underlying brain and meninges. The long-term effects of these observed anatomical changes are unknown.