Use of bioglass for orbital volume augmentation in enophthalmos: A rabbit model (Oryctolagus cuniculus)

Purpose: To investigate the clinical and histologic response of Novabone-C/M as an osteoproductive alloplastic implant for volume augmentation in the orbit in the treatment of enophthalmos and to compare its outcome alone versus its use in combination with autogenous bone or Medpor granules. Methods: Novabone-C/M, a bioactive silicone glass material, was implanted in the subperiosteal space of the left orbit of 12 New Zealand White rabbits. The animals were divided into 3 groups, each with 4 animals, based on the material implanted in the orbit: group 1, Novabone alone; group 2, Novabone plus Medpor granules; and group 3, Novabone plus autogenous bone fragments. All rabbits were studied clinically, radiographically, and histologically at 1-, 3-, and 6-month intervals. Animals underwent preoperative and postoperative computed tomography (CT) with 3-dimensional reconstruction, proptosis measurements, and volumetric analysis. Orbit specimens were studied histologically with mineralized bone stain (MIBS) to look for bone formation, reactivity, infection, implant resorption, and migration. Results: There were no signs of significant inflammation or infection. Subcutaneous migration of the implant was seen radiographically but not clinically in groups 1 and 3. Induced proptosis averaged 2.5 mm (at 1 month) and showed regression in all groups over a 6-month period but was not statistically significant. Implant volume was markedly reduced in all groups, averaging 69% in group 1, 37% in group 2, and 59% in group 3 at 6 months. New bone formation and bone remodeling was present in all 3 groups at 3 months and only in group 2 at 6 months. The rate and amount of implant remodeling and bone formation was greatest in the Novabone/ Medpor group (group 2). Conclusions: Bioglass particulate is biocompatible, easy to use in the orbit, and stimulates bone growth. Bioglass is associated with volume loss and migration over 6 months and may not provide adequate volume augmentation in the orbit when used alone for the treatment of enophthalmos. The duration and amount of bone formation may be enhanced when Novabone is used in conjunction with Medpor.