Summary

A study for monitoring bilateral scapular movements by using two polymer-encapsulated textile-based strain sensors has been conducted. Experimental results showed that the developed strain sensors were able to track consecutive repetitions of abduction-adduction and flexion-extension movements performed in the frontal and sagittal plane, respectively.

Abstract

Background

The normal scapular movement is a crucial factor to establish the efficient shoulder joint’s level of functionality. Scapular dyskinesis (SD) is an alteration of scapular position and orientation during shoulder movements. SD incidence is frequent in patients suffering from shoulder musculoskeletal disorders and overhead athletes. In the last years, wearable sensors for monitoring human body motions are assuming great relevance in clinical scenario and rehabilitation. Strain sensors based on conductive textiles represent an emerging generation of wearable sensors for monitoring human movements, thanks to their flexibility, lightweight, and easy adaptability to different anthropometries.

AIMS
To assess the feasibility of using wearable strain sensors based on conductive textile to track scapular movements during shoulder abduction-adduction and flexion-extension.

Methods

Two wearable strain sensors based on conductive textile (EeonTex™ LG-SLPA) and encapsulated in a polymeric matrix (Ecoflex 00-30) were developed and characterized. Bilateral movements were executed at three different velocities and covering the full range of motion. Both sensors were positioned obliquely on the scapular region, in the direction joining the scapular angulus acromialis and T8 vertebra. A kinesiology tape was used to ensure sensors adhesion to the skin.
A Qualysis™ motion capture system (Qualisys Inc., Gothenburg, Sweden) was used as reference to monitor sensors deformation during trials. A total of four spherical markers with a diameter of 8 mm were placed on each sensor.

Results

Results showed that both sensors were able to track all repetitions of bilateral shoulder abduction-adduction and flexion-extension movements at different speeds. In particular, sensors’ output showed a different trend during abduction-adduction and flexion-extension, suggesting the possibility to differentiate scapular movements during the investigated shoulder motions. From motion capture data analysis, sensors maximum elongation ranged from 5.0% to 15.5%. This range falls within the middle-scale of human body deformations and investigated sensors performances. Indeed, sensors electrical behaviour was characterized by straining both sensing elements up to 20% of their initial length.

Discussion

This study was performed to examine the feasibility of applying wearable strain sensors for scapular motion assessment during shoulder abduction-adduction and flexion-extension. Sensors’ output showed a different trend, especially in correspondence of the maximum degrees of flexion and abduction, reached during trials. From a biomechanical perspective, scapula generally experiences upward rotation and abduction during flexion and abduction tasks, although scapular abduction is reduced in the latter case. This could justify the different trend of sensors’ output.
Providing reliable and objective evaluation of scapular motion is a highly demanding task, especially when patients with SD had to be examined. Flexible and wearable strain sensors represent a promising alternative technology to monitor scapular motions.