人工股関節スパイラルステムのデザイン(4部 生体への負荷と代替)  [in Japanese] DESIGN OF SPIRAL STEM IN TOTAL HIP ARTHROPLASTY  [in Japanese]

Methodology for design of the femoral component in total hip arthroplasty is closely related to evaluation of shape of the proximal femoral canal. Shape of a canal in a tubular bone, such as femur, is defined by the shapes of its axis and cross section. In this study we proposed a novel methodology for determination of three-dimensional shape and arrangement of the axis and cross section, using geodesic curves on a surface of a cone as its axis, the cross section of a torus as its cross section, and some measurements obtained from X-ray photographs. Geodesic curves on a surface of a cone are expressed by the following formula: [mumerical formula] Cross section of a torus is expressed as: [mumerical formula] We named a stem designed according to this method a spiral stem. The spiral stem has a smooth surface and has both spiral and taper properties. The spiral stem, which therefore has excellent fit and fill, torsional load, and dispersion of force, is expected to be designed using this novel method.