骨接合プレートにおけるタッピングを用いた新しいポリアクシャルロッキング機構の提案

抄録

An osteosynthesis fixing system 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 locking type and the other is a polyaxial one. The latter can be fixed at any angle within a certain range. 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 reduced fixing force on thin plates. Thus, we aimed at the development of new mechanism of polyaxial locking system which fixes screws and plate with plastic deformation by self-tapping. We devised the polyaxial locking system with small fins inside of the hole. The screws can be screwed into the inner surface of the hole easily and fixed strongly by thread tapping. First, we considered the optimum combination of plate and screw materials. As a result, it was found that a combination of Ti-6V-4Al plate and Co-Cr alloy screw that has a large hardness difference is good. After the optimum combination of the plate and screw materials were determined, we investigated width of fin and inner diameter for the purpose of reducing the tightening torque. Experimental results showed that the fixing strength and tightening torque are equivalent to those of existing products.