Non-specific inflammation and bone marrow depletion due to intramedullary porous hydroxyapatite application

Calcium hydroxyapatite (HA) ceramics are widely used in orthopaedic surgery and are known to be biocompatible, biodegradable, and osteoinductive. Recent studies of HA have identified early stage inflammatory reactions and third-body wear following hip replacement surgery. The aim of this study was to investigate the early stage inflammatory response toward HA by means of conventional radiography, histopathology, and scanning electron microscopy (SEM). HA was implanted into the medullary area of the tibiae of rabbits and followed from one week to six months. Radiography revealed local osteoporosis on Week 6 and Month 6 in some, but not, all rabbits. SEM presented favorable bonding between the implant and the cortical bone. Eosinophilic deposition, non-specific local inflammation, and bone marrow depletion were the histopathological findings. Multinuclear cells were identified in the inflammation area. Although bone ingrowth into the pores of the HA was demonstrated, there is no doubt that HA may cause an early inflammatory reaction in the bone marrow. This inflammatory reaction is followed by bone marrow depletion and may be the early sign and the cause of HA-coated implant failure.