Kinetics Analysis of Ankle, Knee and Hip Joints Using a Wearable Sensor System

Abstract

The kinetics analysis of ankle, knee and hip joints during gait is fundamental for rehabilitation and clinical diagnosis but data are commonly obtained by means of the laboratory-restricted equipment such as a force plate and optical camera system, which usually require complicated computing programs and professional operation. In this study, we have developed a wearable sensor system to facilitate joint kinetics analysis to assess body movement in daily activities. The sensor system is composed of a shoe-based force sensor which measures ground reaction force (GRF) and center of pressure (CoP), and a leg-attached motion sensor consisting of three uniaxial gyroscopes units which detect lower limbs movement. This paper presents a kinetics analysis of ankle, knee and hip joints in the sagittal plane by using the sensor system on human normal level walking during whole gait phases. In order to estimate the joint kinetics, an inverse kinetics method based on the sensing signals and gait characteristics was developed. In the validation experiments with 10 subjects, joint kinetics was calculated using data synchronously measured by the sensor system and a force plate & optical camera system. The root mean square (RMS) differences of the ankle, knee and hip joints moments between the two systems in a gait cycle were (2± 0.34) (mean± standard deviation) Nm, (7.2 ± 1.34) Nm and (11.2 ± 1.3) Nm, being (5.4 ± 0.7)%, (6± 0.32)% and (6.1± 0.25)% of the maximal magnitude of ankle, knee and hip joints moments respectively. The RMS differences of the ankle, knee and hip joints powers between the two systems in a gait cycle were (4.2± 0.4) W, (5.7± 2.1) W and (5.7 ± 0.3) W, being (8.4 ± 0.4)%, (4.1 ± 0.5)% and (6.4 ± 0.4)% of the maximal magnitude of joint powers respectively. The experimental results demonstrate the feasibility and effectiveness of the joint kinetics analysis using the wearable sensor system for a daily application in gait analysis.