Osseous tissue reaction around hydroxyapatite block implanted into proximal metaphysis of tibia of rat with collagen-induced arthritis

This study was conducted to investigate the influence of osteoporosis on new bone formation around a hydroxyapatite (HA) block implanted into the proximal metaphysis of the tibia of rats with collagen-induced arthritis (CIA). Ten rats were immunized with an emulsion of bovine type II collagen and Freund's complete adjuvant (arthritis group). Another 10 rats, which were not immunized were used as the control group. Seventeen days after immunization, HA block was implanted into the proximal metaphysis of the tibia. Four weeks after implantation, all rats were killed. The serum level of tetrate-resistant acid phosphatase (TRAP), bone mineral density (BMD) in the proximal metaphysis of the tibia and the affinity index in the arthritis group were 28.0+/-3.5 IU/ml, 130.3+/-28.7 mg/cm2 and 77.6+/-10.8%, respectively, and those in the control group were 24.6+/-5.5 IU/ml, 175.9+/-30.5 mg/cm2 and 56.3+/-14.8%. The serum level of TRAP was higher (P < 0.05) and BMD was lower (P < 0.005) in the arthritis group. The amount of new bone formation around the HA block was larger (affinity index, P < 0.05) in the arthritis group than in the control group. These findings suggest that bone formation around HA block might be enhanced even in conditions associated with highly activated bone resorption and bone formation, such as arthritis.