The investigation of the lower limb geometry using 3D sonography and magnetic resonance

► We developed a method to calibrate navigated ultrasound probe. ► We performed comparative tests of system on probands using ultrasound and MRI. ► Navigated ultrasound probe enables bone diagnosing for patients with limb deformity. ► Navigated ultrasound probe enables control of treatment (Ilizarov External Fixator). The main aim of this work was to test the developed system of a free hand sonographic probe in the clinical conditions. The measuring system consists of navigation system tracking the position of a linear ultrasound probe and the self-developed software to control the tools and analyse the recorded data. It enables both measurement of geometrical parameters according to the self-designed template and the identification of the three dimensional shape of bone. Moreover the software provides virtual planning of surgery and supports the surgeon to execute the planned scenario in the reality. The paper describes the three methods of the ultrasound probe calibration and the obtained results of calibration affecting the accuracy of measurement. There have been performed tests of the femur and tibia mechanical axes, the mechanical axis of the lower limb and the neck-shaft angle using 3D ultrasound imaging and magnetic resonance imaging, on a group of five probands. The results revealed high Pearson’s correlation coefficient and small deviations estimated to 0.4–3.5mm and 2°. The 3D ultrasound tests of limb geometry were performed on seven patients suffering from limb deformities and three patients treated with Ilizarov External Fixator. The measurements enable planning and post-operative diagnosing of limb corrections with lengthening. The results of measurements are analyzed in terms of applicability in clinical conditions.