Tsung-Yuan Tsai

In vivo three-dimensional kinematics of the normal knee during active extension under unloaded and loaded conditions using single-plane fluoroscopy

Measurement of the changes of the three-dimensional (3D) motion and surface kinematics of the knee under different external loading conditions is essential for the understanding and evaluation of the function of the joint, as well as for relevant clinical applications. Knee extension exercise (KEE) has been applied extensively in the rehabilitation programs of patients with various knee disorders. This study measured the 3D knee kinematics of eight normal subjects during active knee extension for unloaded and loaded conditions using a voxel-based method for the registration of fluoroscopic images with CT bone data. The knee kinematics during unloaded conditions were found to be similar to previous findings. A mass of 5 kg at the ankle did not affect the joint angles but significantly altered the lateral contact positions during knee extension, especially at knee flexion angles higher than 75 degrees, and also reduced the asymmetry of the surface kinematics between the medial and lateral condyles. The results of the current study may be useful for knee replacement design and for developing guidelines for the use of KEEs for the rehabilitation of patients with knee disorders.

A volumetric model-based 2D to 3D registration method for measuring kinematics of natural knees with single-plane fluoroscopy.

PURPOSE Accurate measurement of the three-dimensional (3D) rigid body and surface kinematics of the natural human knee is essential for many clinical applications. Existing techniques are limited either in their accuracy or lack more realistic experimental evaluation of the measurement errors. The purposes of the study were to develop a volumetric model-based 2D to 3D registration method, called the weighted edge-matching score (WEMS) method, for measuring natural knee kinematics with single-plane fluoroscopy to determine experimentally the measurement errors and to compare its performance with that of pattern intensity (PI) and gradient difference (GD) methods. METHODS The WEMS method gives higher priority to matching of longer edges of the digitally reconstructed radiograph and fluoroscopic images. The measurement errors of the methods were evaluated based on a human cadaveric knee at 11 flexion positions. RESULTS The accuracy of the WEMS method was determined experimentally to be less than 0.77 mm for the in-plane translations, 3.06 mm for out-of-plane translation, and 1.13 degrees for all rotations, which is better than that of the PI and GD methods. CONCLUSIONS A new volumetric model-based 2D to 3D registration method has been developed for measuring 3D in vivo kinematics of natural knee joints with single-plane fluoroscopy. With the equipment used in the current study, the accuracy of the WEMS method is considered acceptable for the measurement of the 3D kinematics of the natural knee in clinical applications.

QUANTIFICATION OF THREE-DIMENSIONAL MOVEMENT OF SKIN MARKERS RELATIVE TO THE UNDERLYING BONES DURING FUNCTIONAL ACTIVITIES

Skin marker-based stereophotogrammetry has been widely used in the in vivo, noninvasive measurement of three-dimensional (3D) joint kinematics in many clinical applications. However, the measured poses of body segments are subject to errors called soft tissue artifacts (STA). No study has reported the unrestricted STA of markers on the thigh and shank in normal subjects during functional activities. The purpose of this study was to assess the 3D movement of skin markers relative to the underlying bones in normal subjects during functional activities using a noninvasive method based on the integration of 3D fluoroscopy and stereophotogrammetry. Generally, thigh markers had greater STA than shank ones and the STA of the markers were in nonlinear relationships with knee flexion angles. The STA of a marker also appeared to vary among subjects and were affected by activities. This suggests that correction of STA in human motion analysis may have to consider the multijoint nature of functional activities such as using a global compensation approach with individual anthropometric data. The results of the current study may be helpful for establishing guidelines of marker location selection and for developing STA compensation methods in human motion analysis.

Intervertebral anticollision constraints improve out-of-plane translation accuracy of a single-plane fluoroscopy-to-CT registration method for measuring spinal motion.

PURPOSE The study aimed to propose a new single-plane fluoroscopy-to-CT registration method integrated with intervertebral anticollision constraints for measuring three-dimensional (3D) intervertebral kinematics of the spine; and to evaluate the performance of the method without anticollision and with three variations of the anticollision constraints via an in vitro experiment. METHODS The proposed fluoroscopy-to-CT registration approach, called the weighted edge-matching with anticollision (WEMAC) method, was based on the integration of geometrical anticollision constraints for adjacent vertebrae and the weighted edge-matching score (WEMS) method that matched the digitally reconstructed radiographs of the CT models of the vertebrae and the measured single-plane fluoroscopy images. Three variations of the anticollision constraints, namely, T-DOF, R-DOF, and A-DOF methods, were proposed. An in vitro experiment using four porcine cervical spines in different postures was performed to evaluate the performance of the WEMS and the WEMAC methods. RESULTS The WEMS method gave high precision and small bias in all components for both vertebral pose and intervertebral pose measurements, except for relatively large errors for the out-of-plane translation component. The WEMAC method successfully reduced the out-of-plane translation errors for intervertebral kinematic measurements while keeping the measurement accuracies for the other five degrees of freedom (DOF) more or less unaltered. The means (standard deviations) of the out-of-plane translational errors were less than -0.5 (0.6) and -0.3 (0.8) mm for the T-DOF method and the R-DOF method, respectively. CONCLUSIONS The proposed single-plane fluoroscopy-to-CT registration method reduced the out-of-plane translation errors for intervertebral kinematic measurements while keeping the measurement accuracies for the other five DOF more or less unaltered. With the submillimeter and subdegree accuracy, the WEMAC method was considered accurate for measuring 3D intervertebral kinematics during various functional activities for research and clinical applications.

THE EFFECTS OF PEDAL RATES ON PEDAL REACTION FORCES DURING ELLIPTICAL EXERCISE

Despite the growing popularity in recent years of elliptical exercise (EE), little is known regarding the loadings applied to the body during EE. Since overloading to the body may lead to early fatigue of the muscles and increase the incidence of overuse injuries, such information is necessary for safe use of the elliptical trainer (ET) as a fitness tool. The current study aimed to determine the typical patterns and loading rates of the measured pedal reaction forces (PRF), and to quantify their differences from those during level walking, and the effects of pedaling rate. Fifteen male adults performed level walking and EE while 3D marker data, right PRFs and ground reaction forces (GRF) were measured. The parameters of the ET were set for two different pedal rates: 50 rpm and 70 rpm. For each pedal rate, the parameters were set to match the variables measured during level walking, with a mean step length of 55% leg length and no workload. During early stance the vertical PRF was smaller than the GRF, while the medial and posterior PRF were greater. PRFs also occurred during swing. Loading rates around heelstrike during EE were all smaller than those during walking. The medial, anterior and posterior PRF, as well as the medial and vertial loading rates increased with increasing pedal rates. The basic force patterns of EE and the effects of pedal rate were established in order to determine the true potential for such instrumentation in locomotion analysis. The results will be helpful for future related studies.

IN VIVO THREE-DIMENSIONAL KINEMATICS OF TOTAL KNEE REPLACEMENTS DURING OPEN AND CLOSED KINETIC CHAIN ACTIVITIES

Measurement of the three-dimensional (3D) motions and surface kinematics of total knee replacements (TKR) during different kinetic activities helps provide necessary knowledge for a better use of these activities for rehabilitation purposes. The 3D kinematics of the knee in eight patients with posterior cruciate ligament-retaining (PCL-retaining) mobile-bearing TKR were measured during sit-to-stand, a closed kinetic chain (CKC) activity, and active knee flexion/extension, an open kinetic chain (OKC) activity, using a single-plane, 3D fluoroscopy method. Angular, translational motions as well as the contact patterns of the prosthesis components were calculated. The joint angular motion patterns were not statistically different between the OKC and CKC activities, but different contact patterns were found. The knee joint center translated more anteriorly during OKC than during CKC activities. Compared to the CKC activity, the more anterior contact positions and smaller total displacements of the medial contact in the OKC activity may indicate a greater loading in PCL and a smaller contact area on the medial tibial plateau. Rehabilitation of patients with mobile-bearing TKR may have to consider the potential negative effects of the greater loadings in the PCL and greater stresses in the medial tibial plateau when using OKC as a training exercise.

Validation of a voxel-based 2D to 3D registration method for measuring 3D natural ankle kinematics with single plane fluoroscopy

In vivo three-dimensional (3D) kinematics of the ankle joint is essential for a better understanding of its biomechanics and for many clinical applications. Several measurement techniques are available for this data, but few allow non-invasive measurements with sub-millimetre accuracy. The purposes of the study were to develop further a voxel-based 2D to 3D registration method [1] for measuring 3D ankle kinematics with single plane fluoroscopy, and to determine experimentally the measurement errors in vitro.