Development of a Measuring System for Lateral Translation of the Knee Joint During Walking Using 6-axis Inertial Sensors

The knee joint is a part of the body that supports the entire body during activities such as walking. OA (Osteoarthritis) occurs when the bones of the knee joint directly collide with each other, mainly due to the loss or reduction of cartilage in the knee joint. At present, OA is mainly diagnosed by standing radiography, and physicians use the K-L classification as a criterion for diagnosing the severity of OA. However, although this method is minimally invasive, it is undesirable to perform multiple radiographic examinations because of the radiation effects on the body. In addition, as the severity of OA increases, patients with OA are more likely to have lateral thrust, a movement in which the knee do lateral translation as soon as the foot touches the ground. Therefore, in this study, as a preparation, we develop a device to measure the lateral translation (outward movement) of the knee in the mid-stance of walking in adult males. In this study, a belt with a 6-axis inertial sensor was wrapped around the medial part of the both knee joints, and 3 healthy males were measured to walk 9 and 13 steps 3 times each on a flat surface. In addition, one healthy male subject walked 9 and 13 steps on a flat surface with a piece of wood in the heel of his shoe to make it difficult to walk (rough road experiment). As a result of the measurement, the lateral acceleration of both knees in the middle of the stance phase was greater for the left knee than for the right knee, because the dominant foot was considered to be the left foot in the 3 subjects in the walking experiment on a flat road. As for the degree of varus of knee, subjects #1 and #3 had varus of the knee in the middle of stance, while subject #2 had valgus of the knee, according to the results of the 9 and 13 step walking experiments. In the future, it is necessary to compare the difference in gait between OA patients and healthy subjects by actually measuring their gait, and to collect data on the acceleration and angle of the knee in various cases by increasing the number of subjects and increasing the walking conditions such as walking on a slope.