A novel unidirectional porous hydroxyapatite in canines

A novel, unidirectional porous hydroxyapatite with a unidirectional and interconnected pore structure and an average pore size and porosity of 100–300 µm and 75%, respectively, was fabricated using a freeze-casting technique. The authors estimated the osteoconductive capacity and bioresorbable property of unidirectional porous hydroxyapatite following its long-term implantation in four dogs. A cortical bone defect at the proximal tibia and an osteochondral defect through the femur condyle were created. Unidirectional, porous hydroxyapatite was implanted into the each cavity. In the bone-defect model, bone ingrowth in one of the two samples at 1 year postimplantation was observed. In each sample at 2 and 3 years postimplantation, bone ingrowth as well as gradual resorption of unidirectional porous hydroxyapatite and the replacement by the trabecular bone was observed. The bone ingrowth area ratio (per cent of total newly formed bone area/unidirectional porous hydroxyapatite area of each region) was 0 and 36% after 1 year, 28% after 2 years and 49% after 3 years in each dog. In the osteochondral defect model, the resorption of unidirectional porous hydroxyapatite and bone remodeling were noted in all samples. Thus, unidirectional porous hydroxyapatite is bioresorbable and facilitates bone regeneration for several years after intraosseous implantation.