Ambulatory Measurement of 3D Knee Joint Angle. Favre, J., Jolles, B. M., Aissaoui, R., & Aminian, K. Journal of Biomechanics, 41:1029--1035, 2008.
Ambulatory Measurement of 3D Knee Joint Angle [link]Paper  doi  abstract   bibtex   
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.
@Article{Favre2008,
  Title                    = {Ambulatory Measurement of 3D Knee Joint Angle},
  Author                   = {Favre, J. and Jolles, B. M. and Aissaoui, R. and Aminian, K.},
  Journal                  = {Journal of Biomechanics},
  Year                     = {2008},
  Pages                    = {1029--1035},
  Volume                   = {41},

  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.},
  Doi                      = {10.1016/j.jbiomech.2007.12.003},
  ISSN                     = {0021-9290},
  Keywords                 = {Knee},
  Review                   = {Motion type: Assorted. Overlaps on knee flexion
Recovery methodology: 2 6DOF IMU (240 Hz)
Verification technique: Liberty magnetic tracking device
Subject demographics: 10 healthy adults
Error reported: RMS deg. 1.5� (SD = 0.4�)},
  Timestamp                = {2012.02.06},
  Url                      = {http://www.sciencedirect.com/science/article/pii/S0021929007005350}
}
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