Development and evaluation of a novel low-cost sensor-based knee flexion angle measurement system

Background Knee injuries play a large part of musculoskeletal traumas in sporting activities and the rehabilitation can require a long period, for both the patients and the specialists, to restore healthy condition. A reliable, portable and low cost system that could allow quick, simple and effective measures of knee flexion angles, would greatly improve the evaluation of the rehabilitation process and the subsequent planning procedure, with meaningful reduction of the recovery time and cost. Methods It is proposed a novel tool for the non-stop measurements of the knee flexion angles, based on the adoption of an elastic sensor embedded in an easy-to-realize wearable kneepad. We fully characterized this tool in terms of accuracy, repeatability and reliability of the measure, and validated it against the gold-standard Vicon. Results Our tool demonstrated good reproducibility and repeatability among testers (mean Range of measures = 5.82° ± 1.93°) and high accuracy (root mean square error <1.28°), together with a good reliability (Intraclass Correlation Coefficient between 0.80 and 0.91). Conclusions The proposed tool demonstrates good performances, is portable, cheap, easy to use, and allows automatic measurements, so to be a valuable system for accurate non-stop measurement of knee angles.