Chronic inflammation from polycarbonate motility peg inhibits osteogenesis in a human hydroxyapatite orbital implant

The histologic findings of a pegged hydroxyapatite orbital implant removed due to chronic inflammation and pain are described. A 44-year-old woman underwent explantation of a hydroxyapatite sphere and polycarbonate motility peg due to chronic redness, swelling, discharge, and pain. Histology revealed complete fibrovascularization of the implant, with approximately 90% ossification. No bone marrow was identified. Histologic sections revealed fibrous connective tissue at the periphery of a sclerotic bony mass with a granulomatous inflammatory infiltrate at the motility peg aperture. There were no bacterial, mycobacterial, or fungal organisms identified histologically or by culture. Consistent with previous reports, hydroxyapatite orbital implants are amenable to fibrovascular ingrowth and bony transformation. The presence of a granulomatous inflammatory reaction around the polycarbonate motility peg in this case may have prevented complete osseous transformation of the hydroxyapatite implant.