DO POROUS CALCIUM HYDROXYAPATITE CERAMICS CAUSE POROSIS IN BONE - A BONE DENSITOMETRY AND BIOMECHANICAL STUDY ON CORTICAL BONES OF RABBITS

Porous calcium hydroxyapatite (CHA) ceramics are biocompatible and pre sent osteoconductive properties. These ceramics are widely used in ort hopaedic surgery; however, it is not yet known whether they have some adverse effects on bone and bone marrow healing. Our previous radiolog ical study revealed possible local porosis at the adjacent sites of th e CHA ceramic. Histological findings of the same study revealed bone m arrow swelling and depletion at the implantation site. Osteoclasts rem oved particles of the implant that may be the cause of local porosis. In the present study, possible local osteoporosis was evaluated by bon e densitometry analyses, and compression and three-point bending tests . CHA particles were implanted into the left limbs and a sham operatio n was utilized on the right limbs of 75 white rabbits. The animals wer e followed up for 23 weeks for bone mineral density and for 6 months f or biomechanical analyses. The CHA implanted area and its distal or pr oximal adjacent areas were evaluated with a Hologic QDR-2000 bone dens itometer. Three-point bending and compression tests were performed wit h an M-30 K material testing device. The results revealed a time-depen dent bone density increase at the CHA implantation site and no signifi cant porosis at adjacent areas of the implant. The stiffness of CHA-im planted bones in three-point bending is larger than that of the contro l group. CHA-implanted rabbit bones presented a different fracture pat tern from the control group. The stiffness of the control and CHA-impl anted bones generally increased with time indicating no adverse effect s of porous CHA ceramics in bone and bone marrow healing. The clinical relevance of this work is that porous CHA ceramics do not cause local porosis at adjacent areas when implanted into osseous sites. Bone den sity increased at the implantation site indicating new bone formation. These ceramics are biomechanically stable and they increase the stiff ness of implanted bone. CHA is a safe material with minimal adverse ef fects and can be used as a bone substitute.