Ikuya Nishimura

Reduction of polyethylene wear by concave dimples on the frictional surface in artificial hip joints

For the purpose of reduction of polyethylene wear generated in artificial hip joints, concave dimples were formed on the surface of the metal femoral head by electrical discharge etching with the constant diameter of 0.5 mm, pitch of 1.2 mm, and depth of 0.1 mm. Using a hip joint simulator, the total amount of polyethylene wear was 7.2 mg in the concave-patterned condition and 23.1 mg in the nonpatterned condition. The reasons for the reduction of polyethylene wear by the concave pattern may be i) a reduction of abrasive wear by providing escape dimples for wear particles and ii) an improvement in the lubricity on the frictional surface by the supply of lubricant that is stored in dimples.

A functionally graded titanium/hydroxyapatite film obtained by sputtering.

A functionally graded film of titanium/hydroxyapatite (HA) was prepared on a titanium substrate using a radio frequency magnetron sputtering. The ratio of titanium to HA was controlled by moving the target shutter. The film was composed of five layers, with overall film thickness of 1 μm. The HA was concentrated close to the surface, while the titanium concentration increased with proximity to the substrate. The bonding strength between the film and the substrate was 15.2 MPa in a pull-out test and the critical load from a scratch test was 58.85 mN. The corresponding values of a pure HA sputtered film were 8.0 MPa and 38.47 mN, respectively. The bonding strength of a pure HA plasma spray coating was 10.4 MPa in the pull-out test. The graded film and the pure HA film were sputter-coated to a thickness of 1 μm on titanium columns (10 mm in length and 4 mm in diameter). These columns were implanted in diaphyses of the femora of six adult dogs and a push-out test was carried out after 2, 4, and 12 weeks. After 12 weeks, the push-out strengths of the graded film, the pure HA film and the non-coated columns were 3.7, 3.5, and 1.0 MPa.

The outline sampling strategies for the femoral CT images

As the result of developments in computer technology in recent years, the calculation, simulation and analysis of the stress environment for the artificial hip prosthesis and the femur have been made possible. In order to perform an exact calculation, three-dimensional modeling with the hip prosthesis and femur is required. The modeling of a femur is done by reconstructing the femoral outline data from CT images using three-dimensional CAD. The outline extraction work is performed by the experience and subjectivity of the operator, and the reliability of the data and working efficiency is low. In this paper, algorithms that extract the femur outline from CT images automatically are proposed.

Bonding strength evaluation of Cementless Implant by grit blasting

As a method of porous coating for cementless implant, sintering and diffusion bonding are usually used. But the bonding techniques have trouble with decreasing fatigue strength and boundary separation. In this study, we applied grit blasting for porous coating. Polygonal iron particle was sprayed on the titanium base material by compressed-air power.

Shape Optimization of an Artificial Hip Prosthesis With 3D-FEM

A multiobjective optimization was used to solve several failure problems of cemented total hip arthroplasty. The objective functions were three; the principal stress in the bone cement, the shear stress of stem/cement interface and cement/bone interface. In the results, the cement stress was reduced by 49%, the stem-cement stress was reduced by 68%, and the cement-bone stress was reduced by 43%, compared with the basic model.© 2003 ASME

Shape Optimization of Femoral Components of an Artificial Hip Prosthesis Using the Three-Dimensional P-Version Finite Element Study and the In Vitro Measurement of Strain in the Bone Cement

Though Total Hip Arthroplasty (THA) is being performed with greater frequency every year for patients with endstage arthritis of hip, mechanical fatigue of bone cement leading to damage accumulation is implicated in the loosening of cemented hip components. This fatigue failure of bone cement has been reported to be the result of high tensile and shear stresses at the bone cement. The aim of this study is to design the optimum shape of femoral component of a THA that minimizes the peak stress value of maximum principal stress at the bone cement and to validate the FEM results by comparing numerical stress with experimental ones. The p-version three-dimensional Finite Element Method (FEM) combined with an optimization procedure was used to perform the shape optimization. Moreover the strain in the cement mantle surrounding the cemented femoral component of a THA was measured in vitro using strain gauges embedded within the cement mantle adjacent to the developed femoral stem to validate the optimization results of FEM.© 2002 ASME