Hiroshi Tsumura

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.

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.

Three-dimensional MRI reconstructions of musculoskeletal tumors. A preliminary evaluation of 2 cases.

We have developed a new method for three-dimensional (3D) reconstruction of malignant bone and soft-tissue tumors from MRI. Data from transverse images of T2-weighted images were transferred into a personal computer. The contours of tumors, major vessels, major nerves and bones were outlined, whereupon the 3D data were processed into a 3D display, using a solid model. The determination of tumor volume both before and after preoperative adjuvant therapy was quantified. The 3D images allowed a better understanding of the relationship between the tumor and the major vessels and nerves, thereby aiding in preoperative planning. The images also provided a quantitative, reproducible measurement of the effect of adjuvant therapy.

Biomechanical Analysis of Three-Dimensional Osteotomy at the Distal End of the Radius for Kienböck’s Disease with Flexion Deformity of the Lunate

Failure of radial closing wedge osteotomy for advanced Kienbock’s disease frequently reveals a flexion deformity of the lunate and the collapse and fragmentation of its volar half. We performed biomechanical analyses including a rigid-body spring model and the finite-element method and demonstrated that the flexion deformity of the lunate increases contact pressure at the volar half of the radiolunate and capitolunate joints. The increased contact pressure could therefore lead to collapse and fragmentation of the volar half of the lunate. A new three-dimensional osteotomy, consisting of a radial closing wedge osteotomy and an extension osteotomy, was developed to achieve better alignment of the capitolunate joints. The three-dimensional osteotomy may therefore be an effective procedure for Kienbock’s disease having a flexion deformity of the lunate.