Abstract
Model-based 3D/2D image registration using single-plane fluoroscopy is a common setup to determine knee joint kinematics, owing to its markerless aspect. However, the approach was subjected to lower accuracies in the determination of out-of-plane motion components. Introducing additional kinematic constraints with an appropriate anatomical representation may help ameliorate the reduced accuracy of single-plane image registration. Therefore, this study aimed to develop and evaluate a multibody model-based tracking (MbMBT) scheme, embedding a personalized kinematic model of the tibiofemoral joint for the measurement of tibiofemoral kinematics. The kinematic model was consisted of three ligaments and an articular contact mechanism. The knee joint activities in six volunteers during isolated knee flexion, lunging, and sit-to-stand motions were recorded with a biplane X-ray imaging system. The tibiofemoral kinematics determined with the MbMBT and mediolateral view fluoroscopic images were compared against those determined using biplane fluoroscopic images. The MbMBT was demonstrated to yield tibiofemoral kinematics with precision values in the range from 0.1 mm to 1.1 mm for translations and from 0.2° to 1.3° for rotations. The constraints provided by the kinematic model were shown to effectively amend the nonphysiological tibiofemoral motion and not compromise the image registration accuracy with the proposed MbMBT scheme.
Highlights
Accurate measurement of the three-dimensional motion and arthrokinematics of the knee is essential for the functional assessment of the joint
The lengths of the ACL, PCL, and MCL predicted with the random forest regression model were compared with standard reference values derived using the biplane MBTdetermined tibiofemoral kinematics and the predicted values using a uniform scaling factor φCT (Figure 5A–C) and were shown to have average RMS errors of 0.55 mm, 0.21 mm and 0.14 mm, respectively (Figure 5D)
The mean absolute differences (MAD) of 6 degrees of freedom (6-DOF) of individual bone obtained using single-body model-based tracking (SbMBT, equivalent to step-1 of multibody model-based tracking (MbMBT)) and the proposed MbMBT are shown in Figure 6, in which the median values of MAD for in-plane translations (X-axis, Y-axis) and rotation (Z-axis) were all below 0.3 mm and 0.2◦, respectively
Summary
Accurate measurement of the three-dimensional motion and arthrokinematics of the knee is essential for the functional assessment of the joint. To this end, skin marker-based stereophotogrammetry is commonly used to measure the spatial poses of the thigh and shank. Appropriate kinematic models, either at the segment level [3] or at the multibody level [4], can be applied with the measured skin markers to better reproduce the spatial poses of the body segment of interest and thereafter more accurately estimate joint angles. The spatial parallel mechanism represented by rigid links connecting adjacent joint articular surfaces is one of the most popular models in the community [6,11,12,13,14]. The feasibility of replicating accurate knee kinematics during various weight-bearing activities using the precise knee model remains unclear
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