Ambulatory measurement of 3D knee joint angle

• Published in: Journal of biomechanics 2008-01, Vol.41 (5), p.1029-1035
• Main Authors: Favre, J, Jolles, B.M, Aissaoui, R, Aminian, K
• Format: Article
• Language: English
• Subjects: 3D kinematics; Accelerometer; Accelerometers; Adult; Gyroscope; Hip Joint - physiology; Humans; Inertial sensors; Knee; Knee Joint - physiology; Magnetic fields; Male; Monitoring, Ambulatory - methods; Orientation measurement; Physical Medicine and Rehabilitation; Posture; Posture - physiology; Range of Motion, Articular - physiology; Studies; Walking - physiology
• ISSN: 0021-9290; 1873-2380
• DOI: 10.1016/j.jbiomech.2007.12.003

Abstract Three-dimensional measurement of joint motion is a promising tool for clinical evaluation and therapeutic treatment comparisons. Although many devices exist for joints kinematics assessment, there is a need for a system that could be used in routine practice. Such a system should be accurate, ambulatory, and easy to use. The combination of gyroscopes and accelerometers (i.e., inertial measurement unit) has proven to be suitable for unrestrained measurement of orientation during a short period of time (i.e., few minutes). However, due to their inability to detect horizontal reference, inertial-based systems generally fail to measure differential orientation, a prerequisite for computing the three-dimentional knee joint angle recommended by the Internal Society of Biomechanics (ISB). A simple method based on a leg movement is proposed here to align two inertial measurement units fixed on the thigh and shank segments. Based on the combination of the former alignment and a fusion algorithm, the three-dimensional knee joint angle is measured and compared with a magnetic motion capture system during walking. The proposed system is suitable to measure the absolute knee flexion/extension and abduction/adduction angles with mean (SD) offset errors of −1° (1°) and 0° (0.6°) and mean (SD) root mean square (RMS) errors of 1.5° (0.4°) and 1.7° (0.5°). The system is also suitable for the relative measurement of knee internal/external rotation (mean (SD) offset error of 3.4° (2.7°)) with a mean (SD) RMS error of 1.6° (0.5°). The method described in this paper can be easily adapted in order to measure other joint angular displacements such as elbow or ankle.