A new system for three-dimensional gait recording using electromagnetic tracking

A new methodology for three-dimensional gait recording was tested. It was based upon an electromagnetic tracking instrument. It repeatedly generates three different magnetic fields from orthogonal coils in a transmitter. A sensor in these fields measures the magnetic flux in three orthogonal coils. From the resulting nine signals of magnetic flux, sensor position in x, y and z coordinates, and orientation in sagittal, coronal and transverse planes can be obtained. The errors in records of position and orientation were determined from recordings with a sensor in a series of well-defined positions within an area sufficiently large to record the movements of a stride. Due to environmental disturbances of the generated magnetic fields, the errors were too large to allow relevant recordings of gait movements. After compensation for the local environmental disturbances, the errors of x, y and z coordinates were < 2.0 cm, and the error of angle in the sagittal, coronal and transverse planes < 1.0 degree. Measurements of rotations with the sensor in unchanged position had an error < 2.5%. With four sensors fixed to pelvis and leg segments, records of three-dimensional gait movements were obtained with well-defined precision in all dimensions.