Identifying Internal and External Shoulder Rotation Using a Kirigami-Based Shoulder Patch

Internal and external rotation of the shoulder is often challenging to quantify in the clinic. The current study evaluates a novel, engineered, wearable sensor system for improved internal and external shoulder rotation monitoring, and applies it in healthy individuals. Using the design principles of the Japanese art of kirigami (folding and cutting of paper to design 3D shapes), the sensor platform conforms to the shape of the shoulder with on-board strain gauges to measure movement. Our objective was to examine how well this kirigami-inspired shoulder patch could identify differences in shoulder kinematics between internal and external rotation as healthy individuals moved their humerus through specified movement patterns. Seventeen participants donned the wearable sensor on their right shoulder. Four strain gauges measured skin deformation patterns while participants moved their arm into internal or external rotation based on Codman's paradox. One-dimensional statistical parametric mapping explored differences in strain voltage change of the strain gauges between internally-directed and externally-directed movements. The kirigami shoulder sensor, with its four on-board strain gauges, detected distinct differences in the movement pattern of participants who performed prescribed movements that resulted in either internal or external shoulder rotation. Three of the four strain gauges detected significant temporal differences between internal and external rotation (all p <0.047), particularly for the strain gauges placed distal or posterior to the acromion. These results are clinically significant, as they suggest a new class of wearable sensors conforming to the shoulder can measure differences in skin surface deformation corresponding to the underlying humerus rotation.