Spine kinematic analysis using digital videofluoroscopy and image processing
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The author has examined spine kinematics using videofluoroscopy imaging combined with digital image processing. The parameters studied were instantaneous centres of rotation, intervertebral angles, angles of rotation and displacement for each vertebral joint. Parallel computation, using an array of transputers, was used. The method can be used to produce an efficient display to aid clinical diagnosis. >Cite
These studies were aimed at developing an image processing method for the measurement of intervertebral movement using video fluoroscopy. The technique is directed primarily at the assessment of patients with suspected mechanical dysfunction of the spine. The accuracy was established using a calibration model of spinal segments. The method was then applied to lumbar images obtained from motion X-rays of asymptomatic volunteers. The results suggest that it is possible to create a rapid clinical method for accurately defining spine kinematics with a level of X-ray dosage acceptable for screening and investigation in patients where conventional levels are not justified by the severity of the disability.< >
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This paper presents a fully automatic algorithm evaluating the knee joint kinematics on the basis of X-ray images. The practical instantaneous center of rotation (ICR) path acts as the main feature of interest. The X-ray images taken from unhealthy child subject while knee flexion, are used as an input data. A clear description of each step of the procedure is provided in the paper, i.e. the image preprocessing, morphological operations, object labeling, image stabilization, determination of bone landmarks, and calculation of ICR. The output information can be used as a basis in the design stage of lower limb rehabilitation manipulator.
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Dynamic assessment of three-dimensional (3D) skeletal kinematics is essential for understanding normal joint function as well as the effects of injury or disease. This paper presents a novel technique for measuring in-vivo skeletal kinematics that combines data collected from high-speed biplane radiography and static computed tomography (CT). The goals of the present study were to demonstrate that highly precise measurements can be obtained during dynamic movement studies employing high frame-rate biplane video-radiography, to develop a method for expressing joint kinematics in an anatomically relevant coordinate system and to demonstrate the application of this technique by calculating canine tibio-femoral kinematics during dynamic motion. The method consists of four components: the generation and acquisition of high frame rate biplane radiographs, identification and 3D tracking of implanted bone markers, CT-based coordinate system determination, and kinematic analysis routines for determining joint motion in anatomically based coordinates. Results from dynamic tracking of markers inserted in a phantom object showed the system bias was insignificant (−0.02 mm). The average precision in tracking implanted markers in-vivo was 0.064 mm for the distance between markers and 0.31° for the angles between markers. Across-trial standard deviations for tibio-femoral translations were similar for all three motion directions, averaging 0.14 mm (range 0.08 to 0.20 mm). Variability in tibio-femoral rotations was more dependent on rotation axis, with across-trial standard deviations averaging 1.71° for flexion/extension, 0.90° for internal/external rotation, and 0.40° for varus/valgus rotation. Advantages of this technique over traditional motion analysis methods include the elimination of skin motion artifacts, improved tracking precision and the ability to present results in a consistent anatomical reference frame.
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The increasing use of motion preserving devices in the spine has highlighted the need for accurate kinematic measurement tools to evaluate the performance of these new implants. In addition to quantifying the motion of the implant itself, it is also desirable to measure how implants affect the motion at adjacent vertebral levels. Single plane fluoroscopy has been used for over 15 years to analyze the in vivo motions of total knee replacement implants, with reported accuracies of 0.5–1.0 deg for rotations and 0.5 mm for in plane translations1,2. It is our goal to apply this type of image registration technique to the spine, so that accurate 3D kinematics of vertebral motion can be measured in vivo. This involves a significant extension to previous work, instead of tracking silhouettes of implants, we proposed to use digitally reconstructed radiograph images generated from a CT as the basis for image registration. The purpose of this project was to develop a methodology that would enable the 3D position and orientation (pose) of a vertebral body to be accurately measured from a single plane fluoroscopic image.
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The purpose of the present study is to develop a direct and accurate method for measuring knee kinematics by using single-plane fluoroscopy. The 3-dimensional (3D) position of the bone (in other words, the 6 degree-of-freedom (DOF) parameters) was recovered by matching the digitally reconstructed radiographs (DRRs) generated from the 3D volume model of the bone on the basis of the fluoroscopic image. The root-mean-square error (RMSE) of the overall rotation parameters was within 2.1 degrees. For the translation parameters RMSE took its maximal value of 3.6 mm in the out-of-plane direction. This indicates that the present method has potential for clinical application.
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Accurate measurement of three-dimensional knee replacement kinematics using single-plane fluoroscopy
A simple extension of a previously reported object recognition technique has been used to implement a six-degree-of-freedom position/orientation estimator for the measurement of knee replacement motion from two-dimensional (2-D) fluoroscopic images. Computer modeling studies and controlled mechanical tests were performed to assess the accuracy of the technique. The results indicate that knee rotations can be measured with an accuracy of approximately one degree and that sagittal plane translations can be measured with an accuracy of approximately 0.5 mm. The measurement technique is uniquely well suited for performing dynamic kinematic measurements on individuals with knee replacements, and for performing comparative studies among subjects with different designs of knee replacements.
Total Knee Replacement
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Several models exist in the literature to describe knee kinematics. In this paper we propose a morpho-functional approach based on the determination of a simulated kinematics of flexion/extension from a unique CT scan acquisition. We will compare this kinematics to the real one obtained from experiments on one cadaver. In parallel, we have developed quantitative tools for the assessment of the motion. As the computation of these tools depends on the bone morphology, they can describe the state of the joint, which is not classical in the literature. Both tools follow the evolution of the distances between two bones during motion. They are called the Figure of Articular Coherence and the Index of Articular Coherence. In order to verify the relevance of these tools, we have tested them to compare different surgeries of Anterior Cruciate Ligament (ACL) reconstruction.
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The patellofemoral joint is critical in the biomechanics of the knee. The patellofemoral instability is one condition that generates pain, functional impairment and often requires surgery as part of orthopedic treatment. The analysis of the patellofemoral dynamics has been performed by several medical image modalities. The clinical parameters assessed are mainly based on 2D measurements, such as the patellar tilt angle and the lateral shift among others. Besides, the acquisition protocols are mostly performed with the leg laid static at fixed angles. The use of helical multi slice CT scanner can allow the capture and display of the joint´s movement performed actively by the patient. However, the orthopedic applications of this scanner have not yet been standardized or widespread. In this work we present a method to evaluate the biomechanics of the patellofemoral joint during active contraction using multi slice CT images. This approach can greatly improve the analysis of patellar instability by displaying the physiology during muscle contraction. The movement was evaluated by computing its 3D displacements and rotations from different knee angles. The first processing step registered the images in both angles based on the femur´s position. The transformation matrix of the patella from the images was then calculated, which provided the rotations and translations performed by the patella from its position in the first image to its position in the second image. Analysis of these parameters for all frames provided real 3D information about the patellar displacement.
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The paper describes an algorithm to estimate the position and orientation (pose) of artificial knee implants from X-ray fluoroscopy images using computer vision. The resulting information is used to determine the kinematics of bone motion in implanted knees. This determination can be used to support the development of improved prosthetic knee implants, which currently have a limited life span due to premature wear of the polyethylene material at the joint surface. The algorithm determines the full 6 degree of freedom translation and rotation of knee components. This is necessary for artificial knees which have shown significant rotation out of the sagittal plane, in particular internal/external rotations. By creating a library of images of components at known orientation and performing a template matching technique, the 3D pose of the femoral and tibial components are determined. The entire process, when used at certain knee angles, gives a representation of the positions in contact during normal knee motion.
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Four intact human head-neck complexes were fixed between T1 and T2. Reflective target markers were inserted into the exposed cervical vertebra to document the 3D kinematics of the cervical spine and head. A dynamic pulse was delivered to the specimen using a mini-sled pendulum apparatus. Each specimen was examined in five different orientations and with two different pulses, for a total of tens trials. Cervical spine motion was recorded from two high-speed cine cameras. 3D reconstruction of the markers was computed using a triangulation software routine. Preliminary analysis of camera images show that the system is sufficient for high-speed analysis.
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Biomechanics
Motion analysis
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