Osteopontin and bone repair in rabbit tibial defect

Human osteopontin (OPN) was produced by a recombinant technique. A circular defect was created in each tibia of 30 adult rabbits. The animals were divided in six equal groups. Four animals of each group were randomly chosen as experimental group in which OPN coated hydroxyapatite granules (OPN-HA) and non-coated hydroxyapatite (HA) granules were inserted alternatively in created defects. One animal of each group was used as control animal to observe the spontaneous healing process of the defects. The created defects in these animals did not receive any implants. The animals were sacrificed after 1, 2, 6, 12, 18 and 30 weeks. The histological sections were magnified and scanned digitally. In the first measurement, the total amount of bone formation in the entire defect was calculated. In a second measurement, new bone formation was quantified at the edges and at the centre of the defects. The total amount of bone formation in OPN treated defects was significantly higher, whereas no significant difference of bone formation was observed at the edges or at the centre of the defects. A careful interpretation of these results suggests that human OPN might stimulate bone formation in the rabbit tibia.