Histologically demonstrated skull bone integration in a hydroxyapatite prosthesis in a human

Abstract

Dear Editor,Surgical treatment for skull bone defects consists ofcranioplasty using different materials including polyme-thylmethacrylate, titanium, resin prostheses, polyesther andceramics [1–4]. The increasing tendency to employ decom-pressive craniectomy for the treatment of cerebral traumahas led to the need for high-quality materials that canpossibly be both resistant and biocompatible. An additionaladvantage could be osteoinductivity, with promotion ofosteoblastic migration across the prosthesis. This propertycan be found in porous custom-made hydroxyapatite (HA)prostheses, which have been shown to induce osteogenesisin experimental animal models [4]. We had the opportunityto demonstrate that osteogenesis induced by bioceramicprotheses occurs also in humans.A 69-year-old woman had been operated on for leftatypical parasagittal meningioma in 2006 at the Departmentof Neurosurgery of the Istituto Neurologico “Carlo Besta”in Milan. The need to remove the bone flap developedduring surgery as the bone was infiltrated by the lesion.One year after her first surgery, the patient underwentcranioplasty with a previously manufactured custom-madehydroxyapatite ceramic new flap. The prosthetic bone flapwas obtained by three-dimensional stereolithography basedon a computerized tomography 3D model of the patient’sskull and bone defect. The material consists of poroushydroxyapatite (including both macropores and micro-pores). Because of recurrence of the meningioma, sheunderwent Cyberknife therapy and, subsequently, furthersurgery 2 years after the first operation. The size of thelesion and the tight adherence of the ceramic material to theskull forced us to remove the prosthesis together with aportion of the surrounding skull, thus resulting intoenlargement of the craniotomy. The removed flap was thensent for histological examination, which revealed thepresence of fresh bone tissue along the superior margin ofthe prosthesis and of bone formation along the interface(Fig. 1).The thickness (in frontal sections) of both the syntheticand the newly developed bone was 4.38 mm; the thicknessof the autologous bone layer was 0.13 mm.The search for perfect or nearly perfect bone integrationin bone prostheses implanted as cranioplasty has led to thedevelopment of new materials that could help the fusionwith the bone edges. In our patient porous hydroxyapatiteshowed these characteristics. The mainstay is obviously thebone integration at the interface with the used material, butin our case new bone formation occurred also along thesuperior surface of the prosthesis. Although several reportsof radiologically demonstrated successful bone-prosthesisfusion exist [5], this is the first report in the literature ofeffective bone-HA integration in humans as demonstratedin the postoperative histological examination.