A Wireless Trajectory Measurement System for Unicondylar Knee Arthroplasty

During unicondylar knee arthroplasty surgery, the tibial prosthesis is fixed and the angle of distal femoral prosthesis relative to the prosthetic gasket is changed to generate the force line trajectory, which is important for doctors to judge the appropriate position of the implants. In this article, we propose a wireless force line trajectory measurement system for unicondylar knee arthroplasty, which includes the pressure sensors array, the control and processing data circuits, the radio frequency transmitter, and the data recorder. Data from 20 sensors are processed and transmitted wirelessly, and the force line trajectory is displayed on the screen in real time. The least squares fitting algorithm is proposed, with which we obtain the pressure distribution, the maximum pressure points, and the force line trajectory. We adopt field programmable gate array to implement the algorithm with lower-upper decomposition to fit the trajectory faster and transmit less data to save power. The average current consumption of the system is 1.37 mA in the operating mode. Dimensions of the data transmission module are length 70 mm, width 35 mm, and height 4 mm. The total uncertainty of the system measurement force line trajectory is 0.92 mm. Experimental results show that the system meets the requirement of real-time measurement of the force line trajectory during the surgery.