We developed LET (Lamellar Etched Titanium) porous structure as a new bone-prosthesis interface, which is made by piling up and fusing the etched titanium thin layers. This method can control pore size and porosity easily and obtain definite interconnective open pore structure (average porosity 65%, average pore size 500 micrometer)

Materials and method: The characteristics of bone ingrowth of LET coated with hydroxyapatite (HA) have been studied in a transcortical rabbit model.

We implanted two types of interface, one with LET and the other with a conventional rough surface structure, which is made with inert gas-shielded arc spraying (ISAS) technique (Ra 40 micrometer) Both materials have coated with HA using the flame spray method. Mechanical and histological studies were performed at 2, 4, 9 and 12 weeks.

Results: Previous scanning electron microscopy study of HA coated LET revealed an even HA layer consecutively distributed from its surface to the bottom without pore obstruction. Mechanical detaching tests showed that the interfacial tensile strength of LET increased with time and were significantly higher than that of ISAS at 4, 9 and 12 weeks (P< 0.05). Histological studies demonstrated that LET had induced deep and wide bone ingrowth into the pore structure. Even at 2 weeks, the immature bone trabeculae were observed stretching to the bottom of LET and, at 9 and 12 weeks, the new bones infiltrated into porous structure changed into maturing osseous tissue. Further, residual new bones of the detached side were observed in and on the pores of LET. It suggested that detaching occurred inside of new bones. In contrast, no residual bone was found onto ISAS implant at 4, 9 and 12 weeks.

Conclusion: The LET structure was proved to have desirable properties for bone ingrowth and, furthermore, the osteoinductivity of HA could enhance its character.