Recent clinical reports documenting passive intracranial translocation of microplates and microscrews have prompted concerns regarding brain biocompatibility and neurotoxicity of fixation hardware used in craniofacial surgery. Although the effects of commercially pure
titanium.
Vitallium (
cobalt-
chromium-
molybdenum),
stainless steel, and various
alloys have been well assessed in bone and soft tissues, there are no comprehensive studies of these materials in the brain. To investigate this, the biocompatibility of
titanium,
vitallium, and 316L
stainless steel was evaluated in the rabbit brain and compared with
silicone elastomer shunt tubing, a material that is used commonly as a neurosurgical implant material with well-established brain biocompatibility. Forty-eight juvenile New Zealand White rabbits were randomly assigned to one of three groups and underwent placement of either commercially pure
titanium microscrews,
vitallium microscrews, or 316L monofilament
stainless steel wire into the parietal region.
Silicone elastomer strips of similar size were implanted in the contralateral hemisphere of each rabbit. Animals were assessed daily for signs of neurotoxicity. Rabbits in each group were sacrificed at 2, 4, 8, and 26 weeks following implantation. Brains were sectioned at the implantation site and were examined by means of standard
hematoxylin and
eosin stains and with immunohistochemical markers sensitive to inflammatory changes in the brain. None of the animals showed any behavioral changes or
neurologic deficits suggestive of either systemic or localized toxicity from the implant materials.
Silicone clastomer was found to cause the least amount of
inflammation relative to other materials tested at all sacrifice points, suggesting that as a standard neurosurgical implant material, it is an appropriate control for studies of brain biocompatibility. At 2 weeks,
titanium was found to cause the largest inflammatory response in surrounding brain parenchyma based on analysis of markers for microglial proliferation,
gliosis, and leukocyte infiltration. At the 26-week endpoint of our study, the biocompatibility of
titanium was nearly equal to the biocompatibility of
vitallium based on all studied markers of
inflammation. A progressive increase in the inflammatory response surrounding
stainless steel implants was noted at 8 and 26 weeks. Relative to all materials studied, at 26 weeks the greatest leukocyte response was found with
stainless steel implants. Our results indicate that at the 26-week end-point of our study,
titanium and
vitallium incited a similar inflammatory response in the rabbit brain that was greater than the response found with
silicone elastomer, a standard neurosurgical implant material, but less than that found with
stainless steel wire, which is commonly recommended as an alternative fixation material.