Mechanical Axis Estimation System for Total Knee Arthroplasty Using a Three-Axis Inertial Measurement Unit Sensor

In Japan, the number of total knee arthroplasties (TKA) has been increasing as the society is progressively aging. TKA is an operation consisting in removing the damaged surface of a patient ’ s knee joint and implanting an artificial one. The implantation angle of the artificial knee joint depends on the mechanical axis crossing the hip joint of the patient. However, it ’ s difficult for medical doctors to accurately visualize a patient ’ s mechanical axis in a clinical setting during the operation. Because the existing systems that can estimate the mechanical axis present several disadvantages such as cost, size, and complexity, they have not been widely used. The aim of this research is to develop a simple and low cost system to estimate a patient ’ s mechanical axis in a clinical setting. A three-axis inertial measurement unit (IMU) is attached to the bone cutting guide. When the femur is swung, either horizontally or vertically, the angular difference in roll, pitch and yaw is proportional to the angular difference between the mechanical and sensor ’ s axis. From this, the angular difference between mechanical and sensor ’ s axis can be calculated. In our experiments, the angular differences were 0°,  ,  , and  , with calculated angle errors below 1.0  . These results indicate the effectiveness of our system