ULTRASOUND VELOCITY MEASUREMENTS ON HEALING BONES USING THE EXTERNAL FIXATION PINS: A TWO-DIMENSIONAL SIMULATION STUDY

Quantitative ultrasound has been largely used for the evaluation of fracture healing in long bones. The propagation velocity across the fracture has been proved to be a quantitative indicator of healing. In this work, we perform a feasibility study of an alternative ultrasonic configuration in which two of the pins of an already applied external fixation device are used as a means of ultrasound transmission and reception. To test and evaluate the applicability of the technique in monitoring the fracture healing course, velocity measurements are performed on two-dimensional (2D) models of intact and healing bones. Comparisons are then made with the traditional percutaneous application and a newer one, the so-called transosseous application. The effect of a non-perpendicular pin insertion on the velocity is finally investigated by assuming various combinations of pin inclination angles. It was found that measurements of the ultrasound velocity through the pins result in higher values due to the fact that the waves travel also along the metal pins whose bulk velocity is higher that of the bone. However, the velocity was increased during healing and this trend was unaffected by any pin inclination angle. In conclusion, the proposed method can offer practical advantages in-vivo but also suffers from highly attenuated received signals. Therefore, clinical trials are needed before it is proposed for clinical use.