title: The inaccuracy of surface-measured model-derived tibiofemoral kinematics.
abstract: This study assessed the accuracy of surface-measured OpenSim-derived tibiofemoral kinematics in functional activities. Ten subjects with unilateral, isolated grade II PCL deficiency performed level running and stair ascent. A dynamic stereo radiography (DSX) system and a Vicon motion capture system simultaneously measured their knee or lower extremity movement. Surface marker motion data from the Vicon system were used to create subject-specific models in OpenSim and derive the tibiofemoral kinematics. The surface-measured model-derived tibiofemoral kinematics in all six degrees of freedom (DOFs) were then compared with those measured by the DSX as the benchmarks. The differences between surface- and DSX-measured tibiofemoral kinematics were found to be substantial: the overall mean (±SD) RMS differences during running were 9.1±3.2°, 2.0±1.2°, and 6.4±4.5° for the flexion-extension, abduction-adduction, and internal-external rotations, respectively, and 7.1±3.2 mm, 8.8±3.7 mm, and 1.9±1.2 mm for anterior-posterior, proximal-distal, and medial-lateral translations, respectively. The differences were more pronounced in relatively higher speed running than in stair ascent. It was also found that surface-based measures significantly underestimated the mean as well as inter-subject variability of the differences between PCL-injured and intact knees in abduction-adduction, internal-external rotations, and anterior-posterior translation.
authors.affiliation: Department of Industrial and Systems Engineering, Rutgers, The State University of New Jersey, USA.
authors.forename: Kang
authors.initials: K
authors.lastname: Li
authors.forename: Liying
authors.initials: L
authors.lastname: Zheng
authors.forename: Scott
authors.initials: S
authors.lastname: Tashman
authors.forename: Xudong
authors.initials: X
authors.lastname: Zhang
mesh_terms: D000328:Adult; D001696:Biomechanical Phenomena; D003198:Computer Simulation; D005269:Femur / Q000000981:diagnostic imaging / Q000502:physiology*; D006801:Humans; D008954:Models, Biological; D016119:Posterior Cruciate Ligament / Q000000981:diagnostic imaging / Q000503:physiopathology*; D011859:Radiography; D015203:Reproducibility of Results; D012420:Running / Q000502:physiology; D013977:Tibia / Q000000981:diagnostic imaging / Q000502:physiology*; D016138:Walking / Q000502:physiology; D055815:Young Adult