To overcome the controversial points of present porous surfaces structure for cementless artificial hip joint, the new porous surface structure was developed. This new porous surface structure is made on base metal directly, therefore it has no interface between base metal and porous seen in the usual porous structure. The new porous surface structure was manufactured by making holes in base metal using laser beam machining. Diameter, pitch and depth of holes were 0.3mm, 1mm and 1mm, respectively. These values were decided referring to other porous structures like bead porous or fiber mesh porous. The aim of this study is to make an investigation into effectiveness of new porous surface structure by animal experiments.

In order to evaluate the bone in growth ability of the new porous surface structure, experiments on animals were carried out. The cylindrical samples those had new porous surface structure were implanted into lateral femora of dogs. At the same time, samples those had usual porous surface structure (bead porous) were implanted into opposite femora as control. The diameter of samples were 4.5mm, and length of samples were 15mm. The implants were retrieved at either 6 or 12 weeks after operations and push out tests were carried out immediately.

New porous surface structure showed high bonding strengths (13–15MPa) equal to the bead porous, and the bone ingrowth ability higher than the usual porous surface structure.

New porous surface structure has bone-in growth ability on an equlity with usual porous surface structure. The structural merits of the direct porous is it has no boundary surface between base metal and porous structure. The unification of the materials which has different function will solve the issue of the stability between porous structure and base metal interface.