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

BackgroundKnee injuries form a large part of musculoskeletal trauma 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 measurement of knee flexion angles would greatly improve the evaluation of the rehabilitation process and the subsequent planning procedure, with meaningful reduction of recovery time and cost.MethodsA novel tool for nonstop measurements of knee flexion angles based on the adoption of an elastic sensor embedded in an easy-to-realize wearable kneepad has been proposed. We fully characterized this tool in terms of accuracy, repeatability, and reliability of measure, and validated it against the gold-standard Vicon.ResultsOur 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 good reliability (intraclass correlation coefficient between 0.80 and 0.91).ConclusionsThe proposed tool demonstrates good performance, is portable, cheap, easy to use, and allows automatic measurements, so as to be a valuable system for accurate nonstop measurement of knee angles.Clinical RelevanceOur sensor-based measurement system is suitable for the evaluation of the rehabilitation course after knee traumas, because it furnishes a low-cost but accurate monitor of knee flexion movements, during an amount of time as long as desired.