POROUS CERAMICS AS BONE-GRAFT SUBSTITUTES IN LONG-BONE DEFECTS - A BIOMECHANICAL, HISTOLOGICAL, AND RADIOGRAPHIC ANALYSIS

Three porous ceramic bone graft materials were compared with regard to their ability to heal a 2.5 cm defect created surgically in a bilater al canine radius model. The ceramic materials were analyzed at 12 and 24 weeks after surgery and included tricalcium phosphate, hydroxyapati te, and collagen hydroxyapatite, which contained a mixture of 35% tric alcium phosphate and 65% hydroxyapatite with added collagen. Each mate rial was evaluated alone and with added bone marrow aspirate. All the implants were compared with a graft of autogenous cancellous bone in t he contralateral radius. Biomechanical testing and radiographic evauat ion revealed that the addition of bone marrow aspirate was essential f or tricalcium phosphate and hydroxyapatite to achieve results comparab le with those of cancellous bone. Collagen hydroxyapatite performed we ll without the addition of bone marrow although the addition of marrow did have a positive effect. Further qualitative radiographic and hist ological analysis demonstrated that tricalcium phosphate was the only ceramic that showed any sign of degradation at 24 weeks. This observed degradation proved to be an important factor in evaluating radiograph s because the radiodensity of collagen hydroxyapatite and hydroxyapati te interfered with the determination of radiographic union. At 24 week s, tricalcium phosphate with bone marrow was the material that perform ed most like cancellous bone. In this study, the biomechanical and rad iographic parameters of tricalcium phosphate with bone marrow were rou ghly comparable with those of cancellous bone at 12 and 24 weeks. Tric alcium phosphate was the only implant that showed significant evidence of degradation at 24 weeks by both histological and radiographic eval uations, and this degradation took place only after a degree of mechan ical competence necessary for weight-bearing was achieved.