We have developed lameller etched titanium (L.E.T.) structure, as a new bone-prosthesis interface. L.E.T. has a laminating structure consisting of a thin board made of porous etched titanium layer. We call this structure, a space controlled interface, because its pore shape, pore size and porosity within the interface can be controlled easily.

Purpose: We compared the binding capacity of L.E.T. system with the conventional beads surface, by experimental study.

Materials and Methods: We implanted two types of interface in 30 canine femora, one with LET and, the other with a conventional beads surface structure as a control. Hydroxyapatite (HA) is coated on L.E.T. stem. The dogs were killed three, six, ten weeks later. The harvested femora were cut off seven sections follow by a push out strength test and calculate the rate of bone ingrowth by measuring images of backscattered electron imaging-scanning electron microscopy (BEI-SEM) of each cross section using the NIH Image. Thin-sectioned tissues were then stained with toluidine blue.

Results: The push-out strength of the L.E.T. stems were 146 to 384% greater and its rate of bone ingrowth were 193 to 226% greater than that of the conventional beads stems. HA coated L.E.T. implants had the new bone formation down to the bottom of the porous portion even after three weeks, the findings which was not seen in the conventional beads stems in microscopic and BEI-SEM finding.

Discussion and Conclusion: Space controlled interface (L.E.T.) was proven to keep an adequate pore within the interface and induce true bone ingrowth in the space. Using L.E.T. structure, faster bone ingrowth and stronger fixation of the stem to the bone can be obtained.

We developed LET (Lamellar Etched Titanium) porous structure as a new bone-prosthesis interface, which is made by piling up and fusing the etched titanium thin layers. This method can control pore size and porosity easily and obtain definite interconnective open pore structure (average porosity 65%, average pore size 500 micrometer)

Materials and method: The characteristics of bone ingrowth of LET coated with hydroxyapatite (HA) have been studied in a transcortical rabbit model.

We implanted two types of interface, one with LET and the other with a conventional rough surface structure, which is made with inert gas-shielded arc spraying (ISAS) technique (Ra 40 micrometer) Both materials have coated with HA using the flame spray method. Mechanical and histological studies were performed at 2, 4, 9 and 12 weeks.

Results: Previous scanning electron microscopy study of HA coated LET revealed an even HA layer consecutively distributed from its surface to the bottom without pore obstruction. Mechanical detaching tests showed that the interfacial tensile strength of LET increased with time and were significantly higher than that of ISAS at 4, 9 and 12 weeks (P< 0.05). Histological studies demonstrated that LET had induced deep and wide bone ingrowth into the pore structure. Even at 2 weeks, the immature bone trabeculae were observed stretching to the bottom of LET and, at 9 and 12 weeks, the new bones infiltrated into porous structure changed into maturing osseous tissue. Further, residual new bones of the detached side were observed in and on the pores of LET. It suggested that detaching occurred inside of new bones. In contrast, no residual bone was found onto ISAS implant at 4, 9 and 12 weeks.

Conclusion: The LET structure was proved to have desirable properties for bone ingrowth and, furthermore, the osteoinductivity of HA could enhance its character.

We developed K.K.S. (Keio-Kyocera Series) THA sytem. The aim is to develop original THA system suitable for Japanese patients. We produced MCF (means Medullary Canal Filling) stem, based on the anatomical anlysis of Japanese typical osteoarthritic patients (53 cases) by the measurements with CT scan. By the use of this stem, excellent canal fitting and initial rigid fixation can be obtained. We used this stem together with non-cement porous socket from 1992. At first the surface of this stem was smooth (S groupe), from 1994 the surface was altered to porous surface (P groupe), and then from 1995 HA coating to porous surface (H groupe) was added. The purpose of this study is to compare the biological fixation ability among stems with same shape and different surface.

Material and methods: Materials were patients for which Non-cement K.K.S. THA was done, 33 cases, 35 joints. Average age at operation was 55 (43-64) years old. Follow-up terms were 5-8 years. According to stem surface, all cases were divided to 3 groupes (S: 14 joints, P: 10 joints, H: 11 joints) and evaluated clinically and radiographically. The evaluation was done at the point of 5 years after operation for all cases. Clinically existence of thigh pain was evaluated. Radiographically sinking of the stem and osteolysis around femur were evaluated.

Results: Thigh pain was existed on S group: 6/14; 43%, P groupe: 0/10; 0%, H groupe: 2/11; 18%. Stem sinking was seen only on S groupe: 12/14; 84%. Osteolysis was seen only on 1 joint in S groupe. The result of S groupe was apparently poor clinically and radiographically.

Conclusion: To keep the early biological fixation of stem, not only anatomical shape for getting excellent canal fitting but also porous surface structure is needed.