Tatsurou Inadome

Effect of surface roughness of hydroxyapatite—coated titanium on the bone-implant interface shear strength

We have investigated the bone-implant interface shear strength of hydroxyapatite (HA)-coated Ti-6Al-4V (HA-coating A) (roughness average, Ra = 3.4 +/- 0.5 microns) and HA-coated Ti-6Al-4V with a rougher surface (HA-coating B) (Ra = 8.4 +/- 1.8 microns). There was no significant difference between HA-coating A and HA-coating B implants with respect to the bone-implant interface shear strength as determined in push-out tests using the transcortical model in adult dogs. The bone-implant interface shear strength of bead-coated porous Ti-6Al-4V was significantly greater than that of both HA-coating A and HA-coating B implants. The failure site, as determined by scanning electron microscopy, was the coating-substrate interface, not the coating-bone interface. This indicates a need to protect the HA coating from the direct shear forces. HA coating enhances early bone growth into the porous surface of the implant. Long-term fixation should depend on bone anchoring to this porous surface. Hydroxyapatite coatings must be developed which do not obstruct the pores of the surface of the implant.

Hydroxyapatite‐coating on titanium arc sprayed titanium implants

We developed a new titanium spray technique using an inert gas shielded arc spray (titanium arc spray). Hydroxyapatite (HA)-coating can be applied to the implant without any surface pore obstruction after the rough surface is made by this technique. Scanning electron microscopy (SEM) of various porous implant surfaces after HA-coating revealed that the bead and fiber metal-coated implants had either a pore obstruction or an uneven HA-coating. On the other hand, the titanium arc sprayed implant demonstrated an even HA-coating all the way to the bottom of the surface pore. In the first set of animal experiments (Exp. 1), the interfacial shear strength to bone of four kinds of cylindrical Ti-6A1-4V (Ti) implants were compared using a canine transcortical push-out model 4 and 12 weeks after implantation. The implant surfaces were roughened by titanium arc spray (group A-C) and sand blasting (group D) to four different degrees (roughness average, Ra = group A: 56.1, B: 44.9, C: 28.3, D: 3.7 microns). The interfacial shear strength increased in a surface roughness-dependent manner at both time periods. However, the roughest implants (group A) showed some failed regions in the sprayed layers after pushout test. In the second set of animal experiments (Exp. 2), four kinds of Ti implants; HA-coated smooth Ti (sHA) with Ra of 3.4 microns, bead-coated Ti (Beads), titanium arc sprayed Ti (Ti-spray) with Ra of 38.1 microns and HA-coated Ti-spray (HA + Ti-spray) with Ra of 28.3 microns were compared using the same model as that in Exp. 1. The interfacial shear strength of HA + Ti-spray was significantly greater than that of sHA and Beads at both time periods, and that of Ti-spray at 4 weeks. Although a histological examination revealed that HA-coating enhanced bone ingrowth, sHA showed the lowest shear strength at both time periods. SEM after pushout test showed that sHA consistently demonstrated some regional failure at the HA-implant substrate interface. HA + Ti-spray had many failed regions either at the HA-bone interface or within the bone tissue rather than at the HA-implant substrate interface. These results suggested that the HA-coated smooth surfaced implants had a mechanical weakness at the HA-substrate interface. Therefore, HA should be coated on the rough surfaced implants to avoid a detachment of the HA-coating layer from the substrate and thus obtain a mechanical anchoring strength to bone. HA-coating on this new type of surface morphology may thus lead to a solution to the problems of conventional HA-coated and porous-coated implants.

Bone-implant interface mechanics of in vivo bio-inert ceramics

We have previously demonstrated that there was no significant difference between the affinity of bone to bio-inert ceramics and stainless steel in a histological study. In this study, the bone-implant interface shear strength of alumina ceramics (AI2O3), zirconia ceramics (ZrO2), stainless steel (SUS316L) and sintered hydroxyapatite (HA) were compared in 19 dogs using a transcortical push-out model of the femur 4 and 12 wk after implantation. The interface shear strength of HA was significantly greater than that of alumina ceramics, zirconia ceramics and stainless steel (P < 0.001). There was no significant difference between bio-inert ceramics and stainless steel.

Stimulatory Effects of Ceramic Particles on the Production of Bone Resorbing Mediators

ABSTRACT We investigated the effects of size and dose of various ceramic particles on the release of bone-resorbing mediators from macrophages. Mouse macrophage cell line, J-774 was co-cultured with either alumina or hydroxyapatite particles. Uniform suspensions of alumina or hydroxyapatite particles, ranging in 1–1000 μm were prepared, and amount of 0.002 and 0.02gram of the particles were used in each group. After forty-eight hours of exposure, each medium was harvested and tumor necrosis factor-α (TNF-α), interleukin-6 (IL-6) and interleukin-1 α (IL-1α) levels were assayed by enzyme-linked immunosorbent assay kit. The release of TNF-α from macrophages was increased by smaller size of both particles in a dose-dependent fashion. IL-1α and IL-6 production were enhanced in a similar manner. Hydroxyapatite particles, especially in small size (1 μm), caused greater release of mediators than alumina particles. These results suggested that the particles small enough, even if it was biocompatible, had ability to stimulate bone resorption by increasing the production of bone-resorbing mediators.

Biomechanical Analysis of a New Type of Surface Total Hip Replacement

In this study we introduced a new type of surface replacement. The basic concept of the femoral component was to prevent stress shielding and avascular necrosis of the femoral head by minimizing the resurfaced area in comparison to the currently available surface replacement. A small peg was added to the center of the implant in order to provide the initial rigid fixation. In developing the new type of surface replacement, the fixation angle, covering angle, and effect of the femoral component peg on stress distribution, as well as the open angle of the acetabular component, were analyzed, using the rigid-body spring model and the finite element method. Two-dimensional finite element models and rigid-body spring models of the femoral head with the component were developed. The new and currently- used components were compared, and the effects of the fixation angle and the peg on stress distribution were analyzed. The optimal resurfaced area was also analyzed by changing the coverage angle from 120° to 180°, since an extremely small implant would lead to severely limited motion and failure of the fixation. For the acetabular component, the open angle should be decreased in order to prevent both socket-neck impingement and increase in the amount of resected bone in the acetabulum. However, the safety zone of the open angle must be also determined to avoid dislocation of the component. Rigid body spring models consisting of the acetabular and femoral components were developed with an anti-dislocation spring at the edge of the acetabular component. The direction of the resultant force that generates the force in the anti-dislocation spring was analyzed. Severe stress shielding was seen in the central portion of the femoral head with the current type of surface replacement, while the new type showed a similar pattern of stress distribution to that of the normal femoral head up to a coverage of 180°. Stress concentration was seen along the peg, while stress shielding occurred immediately below the implant with a long peg. Full coverage of the femoral head by the component and insertion of the implant parallel to the axis of the femoral neck could result in abnormal stress distribution, including stress shielding of the central portion of the femoral head and stress concentration at the medial side of the neck. A dislocation force was generated when the resultant force was applied within 30° of the edge of the acetabular component, which meant that there was a possibility of dislocation with an open angle of less than 120° under physiological loading conditions.

Stress X-ray Examination for Cruciate Ligament Deficient Knee

The accuracy of the stress X-ray examination for the cruciate ligament deficient knee was studied. A stress device with the knee in 90 degrees of flexion was used. The examination was useful for the complete deficiency of the posterior Cruciate ligament. While for deficiency of the anterior cruciate ligament or imcomplete posterior ligament injury, this method was not accurate. For getting higher accuracy, we must use MRI, tomography of the cruciate ligament after arthrography and stress X-ray with the knee in 30-degree flexion position.