A Force Line Trajectory Measuring System and Algorithms for Unicondylar Knee Replacement Surgery.

Abstract

The force line trajectory of the distal femoral prosthesis relative to the prosthesis gasket is an important factor in judging the appropriate position of implants in the Unicondylar Knee Arthroplasty (UKA) surgery, which is critical to the success of the UKA surgery. In this paper, we propose an UKA force line trajectory measurement system, which includes the pressure sensors array, the controlling circuits, the transceivers, and the receiving recorder. Data from twenty sensors are obtained by a multi-channel analog switch. The data is transmitted wirelessly and the force line trajectory is calculated and displayed on the screen in real-time. Radio frequency transmitter chip and the amplifier work only when the wireless data transmission to save power. The algorithm for force line trajectory fitting is proposed, with which we first get the pressure distribution and the maximum pressure point, and then we use maximum pressure points as the contacting points and fit the force line trajectory of the maximum pressure points by the improved least squares fitting algorithm. From the simulation and experimental results, we can find that the low power system meets the requirement of real-time display force line trajectory. The calculation amount of our algorithm is significantly reduced compared to the finite element analysis method. Compared with the iterative solution method, the calculation time of the thirty maximum pressure points and the force line trajectory fitting is reduced from 1.3ms to 0.018ms. Moreover, the proposed algorithm is easier to be realized in hardware in the future, which will increase data processing speed, transfer less data, and further reduce the system power.