It is very important in marker-based motion capture systems that cameras can follow markers attached to anatomical points without any obstruction. Based on marker positions the computer program can reconstruct movement of the body’s biomechanical model by calculating typical distances, angles and trajectories.

Analysis becomes complicated when the person wears a rigid and opaque orthotic device (e.g. a plastic corset), through which cameras can not see markers attached to the body surface.

We had to find a marker attachment method, so that infrared motion capture cameras can follow movement of markers attached to certain anatomical points on scoliosis patients wearing their corsets, when analyzing the effects of corsets on posture and movement.

Infrared cameras in the Gait Analysis Laboratory of Semmelweis University’s Department of Orthopedics can not „see through” polyethylene corsets. Markers have to be attached directly to the body surface, because a corset is a rigid body, therefore it moves differently, than the human body under it. Multiple considerations have to be made, when choosing markers. There is limited room between body and corset, markers can not affect wearer’s movement and can not cause discomfort. The chosen method uses magnets attached to the skin with medical tape. Size and properties of magnets were verified by simulation. Infrared cameras can follow the painted magnet counterparts on the outer surface of the corset.

Magnets attached to the corset’s outer surface follow the movement of magnets taped to the body, so cameras can follow movement of anatomical points under the opaque corset, without the need of providing direct visibility by destructing corset material. Holes larger than the size of markers would be required, to avoid the shading effects of the corset resulting from body-corset and body-camera distance and angle.

According to measurement results of patients with and without corsets, magnetic markers sufficiently follow the body’s movement under the corset. In the meantime with markers attached immovably to the corset’s outer surface, movement of the corset as a rigid body can be tracked, as well.

The presented method allows further detailed investigation, concerning the movement altering effects of not just corsets, but other orthotics, too.

 

DOI: 10.17489/biohun/2013/1/11