Knee kinematics of ACL-deficient patients: A development of a portable motion analysis system

This study is to compare the knee kinematic measurements between the novel portable skin marker-based motion analysis system (Opti-Knee (R)) and a conventional system (Vicon (R)). Nineteen subjects were recruited and asked to perform stair descent with lower limb placed with skin markers. Knee kinematic data was computed from the trajectories of the skin markers. Pearson's correlation coefficient and Root-mean-square deviation (RMSD) were used to analyse the data. For the waveform, sagittal plane rotation is strongly positive correlated between systems, while for axial and coronal plane rotation, it was moderately to strongly positive correlated in both normal (ACLN) and ACL-deficient (ACLD) group. Substantial difference between two groups was found in correlation of abduction/ adduction in both stance and swing phase, as well as in external/ internal rotation in all selected regions of interest. Moreover, the RMSD was larger in ACLN than in ACLD in three planes of rotation. The capability of Opti-Knee (R) in tracking lower limb sagittal plane rotation was comparable to Vicon (R). However, for coronal and axial plane rotation, although the correlation to Vicon (R) in kinematic waveforms was moderately high, their ROM and peak values substantially deviated from the values in Vicon (R).