3D Printed Wearable Sensor for the Evaluation of Joint Movement Planes

Musculoskeletal disorders of the shoulder are among the main causes of pain and functional limitation, significantly affecting the quality of life and the ability to perform daily activities. Among these, rotator cuff injuries are particularly common and, in the most severe cases, may require surgery followed by a long rehabilitation program. The correct execution of rehabilitation exercises, which often involve movements in different planes, is essential to ensure effective recovery. However, the assessment methods currently used have several limitations: manual clinical tests are subjective and depend on the experience of the professional, while motion capture technologies, although very precise, are expensive and complex to apply in daily clinical practice. In this context, wearable solutions represent a promising option for monitoring shoulder movements. This study presents an innovative sensor based on fiber Bragg grating sensors, integrated into a 3D printed structure. The device has been designed to detect the shoulder motion plane. After the design and manufacturing phase, the sensor was subjected to a metrological characterization to evaluate its reliability. The results showed a strain sensitivity of $0.08 \mathrm{~nm} / \mathrm{m} \varepsilon$, a temperature sensitivity of $0.015 \mathrm{~nm} /{ }^{\circ} \mathrm{C}$ and a hysteresis error between 34% and 36%. Furthermore, the device was tested on three healthy volunteers, demonstrating the ability to distinguish shoulder movements in the sagittal, scapular and frontal planes. These results suggest a possible use of the system as a support tool in shoulder rehabilitation, offering a practical and effective solution for patient monitoring.