Normal and shear forces measurements at the interface of the skin–knee distraction orthosis during squatting: A feasibility study

Understanding the mechanical interaction at the skin–orthosis interface is essential for designing assistive devices that are safe and comfortable under high mechanical loads. However, in vivo characterization of these interactions remains limited, as existing approaches do not provide distributed measurements of combined normal and tangential forces during dynamic activities. In this work, we present a dedicated measurement device for the biomechanical characterization of the skin–orthosis interface. The system combines a patient-specific knee distraction orthosis enabling controlled loading with thin, flexible 3D force-sensing taxels arranged in modular strips for distributed contact-force measurements. A pilot experiment was conducted on a healthy participant performing repeated squat trials using a protocol designed for future large-scale studies. The measurements showed high intra-trial repeatability and consistent force patterns across neighboring sensors. Repeated orthosis and sensors repositioning revealed the sensitivity of the measured contact forces to orthosis placement and strap tightening, underlining the importance of standardized sensor positioning and fitting procedures. These promising proof-of-concept results demonstrate the feasibility of acquiring quantitative 3D contact forces between the skin and a knee brace during dynamic activities. To our knowledge, this study provides the first quantitative datasets of 3D contact forces at the skin–knee orthosis interface. Further studies involving larger and more diverse participant cohorts are required to establish the reproducibility and generalizability of the proposed methodology and to investigate common mechanical trends across different morphologies and orthosis configurations.