骨接合プレートにおけるタッピング固定を利用したポリアキシャルロッキング機構の設計指針の提案

抄録

An osteosynthesis plate consists of a plate and screws. It is a medical instrument for repositioning the broken parts of bones to their appropriate positions. There are two types of screws used with the osteosynthesis plates. The one is a monoaxial screw and the other is a polyaxial one. The latter can be fixed at within a certain angle with the plate. By these screws, one can reposition the pieces of a broken bone to a mechanically and anatomically right position. However, the polyaxial screws usually have problems of reduced fixing force when used with thin plates. Thus, we devised a plate with small fins inside of the holes so that the screws cut into the inner surface of the hole easily and fixed strongly by thread tapping. First, we found the optimum combination of plate and screw materials. Next, we investigated the effect of the widths of fins and inner diameters for the purpose of optimizing the tightening torque. In addition, we clarified the process of plastic deformation during destructive fixation test. As a result, we could propose a new polyaxial locking system with performance equivalent to existing products. Furthermore, we considered an optimum screw shape that can disperse stress using FEM analysis..