Expected scapula orientation error regarding scapula-locator uncertainty while studying wheelchair locomotion

Abstract

Shoulder complex motion is a fundamental aspect of wheelchair locomotion. However, this motion is difficult to capture with skin marker methods due to soft tissue artefacts (Bourne et al., 2011). To overcome this issue, scapula locators (SL), which are external devices equipped with reflective markers and manually registered on the scapula, have been designed (Brochard et al. 2012) To track scapula motion, the SL first needs to be configured as to simultaneously palpate three anatomical landmarks of the scapula: the acromial angle, inferior angle and root of the scapular spine. For static poses, de Groot et al. (1997) and Jafarian Tangrood et al. (2020) studied the impact of palpation incertitude and inter-observer variability on scapula position reconstruction. They reported a scapula angle error in the range of 3.5 – 5 degrees. However, shoulder motions have not been studied yet and the angle error remains unpredictable. The issue raised in this study was to determine the impact of palpation errors of the scapula’s anatomical landmarks when configuring the SL on the reconstruction of a motion-tracking task. Four angles were studied through a constrained multibody kinematics optimization. The study used a Monte Carlo approach and a statistic analysis.