3D-Printed Wearable Sensors for the Identification of Shoulder Movement Planes.

Rotator cuff injuries are a leading cause of shoulder disability, directly impacting joint mobility and overall quality of life. Effective recovery in these patients depends not only on surgical intervention, when necessary, but also on accurate and continuous monitoring of joint movements during rehabilitation, especially across multiple anatomical planes. Traditional tools, such as clinical assessments or motion capture systems, are often subjective or expensive and impractical for routine use. In this context, wearable devices are emerging as a viable alternative, offering the ability to collect real-time, non-invasive, and repeatable data, both in clinical and home settings. This study presents innovative wearable sensors, developed through 3D printing and integrated with fiber Bragg grating technology, designed to detect the shoulder's planes of motion (sagittal, scapular, and frontal) during flexion-extension movements. Two wearable sensors made of thermoplastic polyurethane (TPU 85A and 95A) were fabricated and subjected to metrological characterization, including strain and temperature sensitivity, hysteresis error, and tear resistance, and tested on eight healthy volunteers. The results demonstrated high discriminative ability, with sensitivity values up to 0.76 nm/mε and low hysteresis errors. The proposed system represents a promising, cost-effective, and customizable solution for motion monitoring during shoulder rehabilitation.