Abstract
BackgroundThe Opti_Knee system, a marker-based motion capture system, tracks and analyzes the 6 degrees of freedom (6DOF) motion of the knee joint. However, the validation of the accuracy of this gait system had not been previously reported. The objective of this study was to validate and the system. Two healthy subjects were recruited for the study.MethodsThe 6DOF kinematics of the knee during flexion–extension and level walking cycles of the knee were recorded by Opti_Knee and compared to those from a biplanar fluoroscopy system. The root mean square error (RMSE) of knee kinematics in flexion–extension cycles were compared between the two systems to validate the accuracy at which they detect basic knee motions. The RMSE of kinematics at key events of gait cycles (level walking) were compared to validate the accuracy at which the systems detect functional knee motion. Pearson correlation tests were conducted to assess similarities in knee kinematic trends between the two systems.ResultsIn flexion–extension cycles, the average translational accuracy (RMSE) was between 2.7 and 3.7 mm and the average rotational accuracy was between 1.7 and 3.8°. The Pearson correlation of coefficients for flexion–extension cycles was between 0.858 and 0.994 for translation and 0.995-0.999 for angles. In gait cycles, the RMSEs of angular knee kinematics were 2.3° for adduction/abduction, 3.2° for internal/external rotation, and 1.4° for flexion/extension. The RMSEs of translational kinematics were 4.2 mm for anterior/posterior translation, 3.3 mm for distal/proximal translation, and 3.2 mm for medial/lateral translation. The Pearson correlation of coefficients values was between 0.964 and 0.999 for angular kinematics and 0.883 and 0.938 for translational kinematics.ConclusionThe Opti_Knee gait system exhibited acceptable accuracy and strong correlation strength compared to biplanar fluoroscopy. The Opti _Knee may serve as a promising portable clinical system for dynamic functional assessments of the knee.
Highlights
The motion analysis of human joints has been frequently investigated in clinical practice, such as in the areas of orthopedics, sports medicine, and rehabilitation [1]
The Opti_knee gait system was used to collect gait data, and the biplanar fluoroscopy system was used to collect the data at the same time
The biplanar fluoroscopy system captured perspective bone images from two views and calculated joint kinematics through a semi-automatic 3D–2D matching process described in great detail in several publications [15]
Summary
The motion analysis of human joints has been frequently investigated in clinical practice, such as in the areas of orthopedics, sports medicine, and rehabilitation [1]. A portable motion analysis system, Opti_ Knee (Innomotion Inc, Shanghai), was developed to track and analyze the 6DOF motion of the knee joint in a convenient and user-friendly clinical setup. The kinematic characteristics of knee diseases have been widely explored using this gait analysis system, such as ACL deficiency, knee osteoarthritis, and general joint hypermobility syndrome [6,7,8,9,10]. The accuracy of this gait system has not been previously validated. The objective of this study is to validate the accuracy of the Opti_Knee system. The Opti_Knee system, a marker-based motion capture system, tracks and analyzes the 6 degrees of freedom (6DOF) motion of the knee joint. The validation of the accuracy of this gait system had not been previously reported.
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