A Novel Tibiafemoral Kinematics Measurement System Based on Multi-Channel A-Mode Ultrasound System

Improving the accuracy of measuring 6 degree of freedom tibiofemoral kinematics is a crucial step in gait analysis. The skin-marker estimated kinematics is subject to soft tissue artefacts. Fluoroscopic systems have been reported to achieve high accurate kinematics, but induced irradiation and a limited field of view and its high cost hampers routine usage on large patient cohorts. The aim of this study is to assess the feasibility of measuring tibiofemoral kinematics using multi-channel A-mode ultrasound system in cadaver experiment and assess its achievable accuracy. A full cadaver was placed on the surgery table and legs were hanging in the air. Upper body was fixated and right leg was pulled by rope to generate a movement. To track the ground truth of the motion, two bone pins with optical markers were mounted to the femur and tibia separately. Six custom A-mode ultrasound holders containing 30 A-mode ultrasound transducers and 18 optical markers were mounted on six anatomical regions. Calculating the bone to each ultrasound transducer distance from ultrasound echo, and using the spatial information of the optical markers on the holders, 30 points were determined. The segmented bone models acquired from CT or MRI were registered to the corresponding points. Then the tibiofemoral kinematics were determined from the positions of registered femur and tibia per frame. This study has presented a multi-channel A-mode ultrasound system and proven its feasibility of reconstructing tibiofemoral kinematics in cadaver experiment. Although the reconstructed tibiofemoral kinematics is less accurate than fluoroscopic system, it outperforms skin-mounted markers system. Thus, this A- mode Ultrasound approach could provide a non-invasive and non-radiative method for measuring tibiofemoral kinematics, which may be used in clinic gait analysis or even computer-aided orthopedic surgery.