A Case of Aseptic Cyst Originating from Hydroxyapatite Granules and Tricalcium Phosphate Composite Implants Uused for Orbital Fracture Repair

Abstract

　　Mixed implants comprising hydroxyapatite granules and tricalcium phosphate composite（HAP/TCP）are expected to be histotropic and result in a lower frequency of foreign body reaction. We report a case of postoperative aseptic cyst after reconstruction of the orbital medial wall and floor using two HAP/TCP plates. The patient visited our hospital 3 years after reconstruction because of diplopia. Magnetic resonance imaging revealed a cyst on the artificial bone implant compressing the eyeball. The cyst and HAP/TCP were removed under general anesthesia. Although histological examination demonstrated surface ossification around the HAP/TCP, no bone fusion with surrounding bone was noted. Bacterial examination revealed the cyst to be aseptic. This supports the theory that repeated irritation due to two HAP/TCP plates causes inflammatory responses involved in cyst formation. This case suggested that long-term follow-up is necessary after reconstruction using HAP/TCP.