Comparison of medial proximal femur shape by measurement used ultrasound probe with two stem models

In total hip arthroplasty, a placement of stem, which is one of the parts of the artificial hip joint, is even difficult for skilled operators. An optimum location of stem is different for each patient. No system for specifying the optimum location has been established. We pay attention to the method using ultrasound in consideration of portability and high introduction ratio to the medical field. The purpose of this study is to compare the measurement results of different stems in specifying the shape of femur by ultrasound through stem. In this study, we developed a femur model and two stem models to reproduce bone condition which is similar to actual surgery. The femur model is made to hold only one stem tightly. Measurement was performed by two probes method, and two probes were placed on the back side of the stem. Reflected ultrasound echoes were measured by moving with a constant interval. By using these echoes, the reflected echoes from the outside surface of femur model were identified. The reflected position was coordinated to create a contour. The contour was compared to the theoretical value in each size of stem, and the error was calculated for them. As a result of the experiment, the small error was observed at any size, however, the result with the suitable size stem shows proper fitting. Therefore, the proposed method using ultrasound will be useful for identifying the curve shape of femur, and it can contribute to quantify the fixation rate by size.