Thigh pain appears often after THA used of the cement-less femoral components, but the appearance mechanism of thigh pain does not have been elucidated. As one factor of manifestation of thigh pain, it has been guessed that the pressure from the inside of medullary cavity of bone by the stem. The purpose of this study is confirming whether the flexor reflex is caused, by using the femur of a rabbit that applied the pressure from the inside of medullary cavity of bone.

Japanese white rabbits with weight of about 3kg were used. Evaluation of the appearance of the pain by the pressure was performed by measurement of the hind leg flexor activity produced by the flexor reflex. After confirming that appearance of the muscles activity by the pain reflex from adding the pain stimulus to the hind leg skin of rabbits, we loaded of the pressure into the inside of medullary cavity of bone and observed whether the muscles activity appears. As the laboratory animals model, we prepared two kinds of rabbits by the difference in the amount of reaming. And we tested how the differences show up between these two kinds of rabbits.

In the rabbits with few amounts of reaming, the flexor reflex appeared in low pressure. But, in the rabbits with many amounts of reaming, the flexor reflex did not appear in high pressure, either.

It is known that the somatic sensory nerves are distributed in the bone, and it is known that the sensory nerve ends exist in the medullary cavity of bone. It was suggested that the pain is induced, when the sensory nerve ends remained in the inside of medullary cavity of bone and the pressure in whicha reaction is possible was carried out there.

Prosthetic impingement after THA is to different for the angle and shape of the implant. Purpose of this study is examine the range of motion(ROM) on a computer when angle and shape of the implant are changed.

The 3D implant models were created on a computer. The angle was measured in the flexion, extension, adduction direction byevery 0.1 degrees. There are three kinds of acetabular abduction angle, two kinds of acetabular anteversion angle and two kinds of femoral anteversion angle. There are three kinds of the radius of neck and the neck shaft angle. All 324 patterns of the above model were measured.

When the radius of neck decreased, the ROM increased in all cases. When the neck shaft angle decreased, the ROM increased by almost all cases. When the acetabular anteversion angle increased, the ROM of flexion direction increased and adduction direction decreased, and as for the extension direction, all the factors had influenced the change in the ROM. When the acetabular angle increased, the ROM of the extension direction increased and the flexion directions decreased. As for adduction direction, femoral anteversion angle, acetabular anteversion angles, and the radius of neck had influenced the ROM. When the femoral anteversion angle increased, the ROM of flexion direction increased and extension, adduction direction decreased.

The clinical ROM is affected by the impingement of non-implant and the strain of the soft tissue. Therefore, It’ s considered that the clinical ROM is smaller than the ROM which was investigated in this study in many cases. When the radius of neck and the neck shaft angle decrease, the increase of the ROM expected. However the radius of the neck should not be decreased too much to avoid the decrease of the neck strength.

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.