Effects of interconnecting porous structure of hydroxyapatite ceramics on interface between grafted tendon and ceramics.

The purpose of this study was to evaluate histologically and biomechanically the interface between porous hydroxyapatite ceramics and a tendon grafted into ceramics, and to compare the interface in two ceramics with different porous structures: interconnected porous calcium hydroxyapatite ceramics (IP-CHA) with an effective porosity index (interpore diameter > 20 microm) of 63.6%, and porous calcium hydroxyapatite ceramics with less interconnection (HA-L) with an effective porosity index of 5.5%. The tendon-IP-CHA complex and the tendon-HA-L complex were implanted into the bone defects made in both knees of rabbits. With IP-CHA, abundant fibrous tissue, including vessels and collagen fiber continuity, was observed inside interface-region pores. The amount of osseous tissue in interface-region pores increased over time, and at 24 weeks after operation, the tendon was in direct contact with the osseous tissue in IP-CHA. With HA-L, the amount of fibrous tissue in interface-region pores was low and did not increase. The results of biomechanical analysis revealed that the maximum tendon pull-out load from IP-CHA was significantly higher than that from HA-L. With the porous hydroxyapatite ceramics having highly interconnecting porous structure, a bioactive interface was achieved between ceramics and grafted tendon. On the basis of these results, we conclude that bone defects, including tendon insertion, can be reconstructed using IP-CHA.