Visual and quantitative analysis of lower limb 3D gait posture using accelerometers and magnetometers

An approach using a physical-sensor difference and virtual-sensor difference based algorithm to visually and quantitatively confirm 3D lower limb posture was proposed. Three accelerometers attached on the hip, thigh and shank and two MAG³s (inertial sensor module) fixed on the thigh and shank were used to measure the accelerations and magnetic field data for the calculation of flexion/extension (FE) and abduction/adduction (AA) angles of hip joint and FE, AA and internal/external rotation (IE) angles of knee joint then the trajectories of knee and ankle joints were obtained with the joint angles and segment lengths. There was no integration of acceleration or angular velocity for the joint rotations and positions, and just accelerometers and magnetometers were used in this technique. This is an improvement on the previous method in recent literatures. Compared with the camera motion capture system, the correlation coefficients in five trials were above 0.91 and 0.92 for the hip FE and AA respectively, and higher than 0.94, 0.93 and 0.93 for the knee joint FE, AA and IE respectively. The results show that the technique was suitable for visually and quantitatively estimating the lower limb posture using simple calculation and fewer sensors with satisfactory degree of accuracy during different walking speeds.