ASSESSMENT OF AN INERTIAL- AND MAGNETIC-BASED ORIENTATION TRACKER IN LARGE VOLUME CLINICAL APPLICATIONS

Abstract

In many fields, such as orthopedics and rehabilitation, measurement of segment orientation or three-dimensional (3D) joint rotation is highly required. However, even if laboratory systems (e.g., optical-based tracker) are enough accurate for human movement measurement, they have some limitations (e.g., cost, complexity, capture volume) that exclude their uses in routine practice.

Recently, our group proposed an original system fusing a low level magnetic tracker (Minuteman®, Polhemus, USA) and 3D gyroscopes (Physilog®, BioAGM, CH) to measure segments orientation. These complementary devices were selected with the aim to provide real time orientation in clinical environment and without restriction on the acquisition duration. The objective of the present study was to assess the performances of this new system in routine clinical applications.

For this evaluation, five healthy young men were enrolled and the orientation of their left thigh was considered. They were asked to perform two times a long scenario (14 min) which included various postures (standing, sitting and lying) and activities (e.g., walking and stairs climbing). These activities were realized both, in the vicinity and far from the magnetic source. Additionally, different metallic objects were inserted and moved in the capture volume to simulate assisted clinical applications. An optical motion capture system (VICON®, UK) was used as reference.

In the absence of magnetic distortion and independently of the activity, we obtained a RMS orientation error of 1.2°. Generally, during distortion periods we obtained a slow growing orientation error of about 0.1°/s whatever the activity.

In conclusion, the proposed system provided an accurate and real-time measurement of orientation in a large capture volume over a long duration. Furthermore the system performances were tested in an environment including representative distortions of routine clinical uses. In combination with a functional calibration, this system was very promising for routine measurements of 3D joint rotations.