Soft tissue artifact distribution on lower limbs during treadmill gait: Influence of skin markers location on cluster design

Segment poses and joint kinematics estimated from skin markers are highly affected by soft tissue artifact (STA) and its rigid motion component (STA(RM)). While four marker-clusters could decrease the STA non-rigid motion during gait activity, other data, such as marker location or STA(RM) patterns, would be crucial to compensate for STA in clinical gait analysis. The present study proposed 1) to devise a comprehensive average map illustrating the spatial distribution of STA for the lower limb during treadmill gait and 2) to analyze STA(RM) from four marker-clusters assigned to areas extracted from spatial distribution. All experiments were realized using a stereophotogrammetric system to track the skin markers and a bi-plane fluoroscopic system to track the knee prosthesis. Computation of the spatial distribution of STA was realized on 19 subjects using 80 markers apposed on the lower limb. Three different areas were extracted from the distribution map of the thigh. The marker displacement reached a maximum of 24.9 mm and 153 mm in the proximal areas of thigh and shank, respectively. STA(RM) was larger on thigh than the shank with RMS error in cluster orientations between 1.2 degrees and 8.1 degrees. The translation RMS errors were also large (3.0 mm to 16.2 mm). No marker-cluster correctly compensated for STA(RM). However, the coefficient of multiple correlations exhibited excellent scores between skin and bone kinematics, as well as for STA(RM) between subjects. These correlations highlight dependencies between STA(RM) and the kinematic components. This study provides new insights for modeling STA(RM) for gait activity. (C) 2015 Elsevier Ltd. All rights reserved.