Identification of medial proximal stem shape by measurement of five ultrasound probes inside stem model

Total Hip Arthroplasty (THA) recently becomes more famous in Japan. The number of operations is increasing more and more because of longevity. In the operation, inserting artificial femoral joint is important for clinical outcome (e.g., pain, and loosening.). In addition, femoral stem which is one of the artificial joints, has a shape fitting to femur bone so that the fixation between the femur bone and the artificial joint. The fixation degree of the artificial joint strongly depends on the insertion angle of the artificial joint. However, THA requires fuzzy subjective judgement of surgeons due to the difficulty to define the fixation degree. To evaluate the fuzzy subjective judgement, this study aims to specify the curve shape of medial proximal part of stem by measuring the curve with ultrasound device. This study develops five probes with small size which enables us to embed the probes into inside stem. The probes measure reflected echoes from boundary of the femur contour, then the propagated time of the echo was converted into the distance from the surface of the probes and the femur contour by using ultrasound velocity. The experiments were performed with two femur models. As a result, the proposed system could show the contour which is corresponding with real shape. We indicated usefulness of the method using ultrasound proves for measuring a curve stem inside.