β-Tricalcium phosphate for bone replacement: stability and integration in sheep.

Implants of microporous β-tricalcium phosphate (β-TCP) were developed for primarily stable supply of bone defects. A consistent stability over the healing period should be retained in sheep. β-TCP cylindrical shaped implants, with 7 mm diameter, 25 mm length, medium pore diameter 5 μm and 40% porosity were developed. Fresh bone defects of 21 sheep in the medial femur condyle were filled with the implants. At time zero, after 6, 12 and 24 weeks the knees of each 7 animals were studied. Specimens were investigated radiologically, followed by biomechanical and histological analysis. Radiological analysis showed progressive resorption. 6 weeks after surgery results of the indentation test were slightly lower, after 12 and 24 weeks higher than on the healthy opposite knee. At 6 weeks a phagocyte reaction overbalanced. After 12 weeks bone regeneration around the implant was seen. After 24 weeks a highly advanced resorption of TCP implant was realized. The trabecular structure of the new bone increased after 24 weeks. Using microporous β-TCP implants continuous stable filling of bone defects can be reached in sheep. Microporous β-TCP implants are resorbed and replaced by bone.