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At least 433 records · Page 24Linked to original sources

PubMed2005

An active shape model for the reconstruction of scoliotic deformities from back shape data.

OBJECTIVE: The objective of the present study is to improve the accuracy and reliability of the spinal midline reconstructions in scoliosis from back shape data. Design. An active shape model which covers the variety of scoliotic curves with a minimum of adjustable parameters is designed for the reconstruction of the spinal midline based on rasterstereographic back surface measurements. BACKGROUND: To reduce the number of X-rays needed for patients with a scoliosis, an automatic method was developed for the reconstruction of spinal deformities from back shape data. METHODS: 264 digital X-rays of 264 patients with scoliosis were used as a training set. By examining the statistics of the vertebral body centres a point distribution model was derived. The model is used as a basis to reconstruct the spinal midline from back shape data (active shape model). RESULTS: 478 rasterstereographs of 114 scoliotic patients have been evaluated with this new procedure and with an existing procedure. Both procedures deliver a three-dimensional curve of the spinal midline. The frontal projections of these spinal midlines are compared with the vertebral centres of the corresponding 478 X-rays. The active shape model improved the results as compared to the existing procedure from sigma(x)=3.4mm to sigma(x)=3.0mm. CONCLUSION: The use of the active shape model improves the overall accuracy of the spinal midline reconstructions in scoliosis from back shape data.RELEVANCE. Improvements to the accuracy and the reliability of the three-dimensional spinal reconstruction based on back shape data, can lead to an additional reduction of X-rays for patients with a scoliosis.

Artificial Intelligence↗

PubMed2005

Quantification of soft tissue artefact in motion analysis by combining 3D fluoroscopy and stereophotogrammetry: a study on two subjects.

BACKGROUND: Soft tissue artefact is the most invalidating source of error in human motion analysis using optoelectronic stereophotogrammetry. It is caused by the erroneous assumption that markers attached to the skin surface are rigidly connected to the underlying bones. The quantification of this artefact in three dimensions and the knowledge of how it propagates to relevant joint angles is necessary for the interpretation of gait analysis data. METHODS: Two subjects, treated by total knee replacement, underwent data acquisition simultaneously with fluoroscopy and stereophotogrammetry during stair climbing, step up/down, sit-to-stand/stand-to-sit, and extension against gravity. The reference 3D kinematics of the femur and tibia was reconstructed from fluoroscopy-based tracking of the relevant prosthesis components. Soft tissue artefact was quantified as the motion of a grid of retro-reflecting makers attached to the thigh and shank with respect to the underlying bones, tracked by optoelectronic stereophotogrammetry. The propagation of soft tissue artefact to knee rotations was also calculated. FINDINGS: The standard deviation of skin marker trajectory in the corresponding prosthesis-embedded anatomical frame was found up to 31 mm for the thigh and up to 21 mm for the shank. The ab/adduction and internal/external rotation angles were the most affected by soft tissue artefact propagation, with root mean square errors up to 192% and 117% of the corresponding range, respectively. INTERPRETATIONS: In both the analysed subjects the proximal thigh showed the largest soft tissue artefact. This is subject- and task-specific. However, larger artefact does not necessarily produce larger propagated error on knee rotations. Propagated errors were extremely critical on ab/adduction and internal/external rotation. These large errors can nullify the usefulness of these variables in the clinical interpretation of gait analysis.

Aged↗

PubMed2005

In vivo validation of a new technique that compensates for soft tissue artefact in the upper-arm: preliminary results.

BACKGROUND: Soft tissue artefact is the dominant error source for upper extremity motion analyses that use skin-mounted markers, especially in humeral axial rotation. METHODS: A new in vivo technique is presented that is based on the definition of a humerus bone-embedded frame almost "artefact free" but influenced by the elbow orientation in the measurement of the humeral axial rotation, and on an algorithm designed to solve this kinematic coupling. The technique was validated in vivo in a study of six healthy subjects who performed five arm-movement tasks. For each task the similarity between a gold standard pattern and the axial rotation pattern before and after the application of the compensation algorithm was evaluated in terms of explained variance, gain, phase and offset. In addition the root mean square error between the patterns was used as a global similarity estimator. FINDINGS: After the application, for four out of five tasks, patterns were highly correlated, in phase, with almost equal gain and limited offset; the root mean square error decreased from the original 9 degrees to 3 degrees . INTERPRETATION: The proposed technique appears to help compensate for the soft tissue artefact affecting axial rotation. A further development is also proposed to make the technique effective also for the pure prono-supination task.

Adult↗

PubMed2005

Auto-adjusted 3-D optic disk viewing from low-resolution stereo fundus image.

Three-dimensional (3-D) visualization of the optic nerve head (optic disk) is very useful for clinical applications. It allows clinicians to measure the disk parameters more accurately and thus make the pathological diagnosis and progression monitoring easier. This paper describes an automatic, precise, 3-D optic nerve head reconstruction method from a pair of stereo images for which efficient steps including sparse-image registration and dense-depth recovery are used. A combination of two registration methods is used to detect the sub-pixel correspondences. The proposed method takes advantages of both the correlation methods which is robust to noise and the feature-based method on its accuracy. The searching range in image registration is auto-adjusted based on the previous iteration result. Only sparse matched points are computed to speed up the processing and the sub-pixel matching is used to overcome the problem of low resolution in the image. This is followed by the piecewise cubic interpolation to obtain the dense disparities and depths. Multiple windowing is applied here by first using the large window to obtain basic disparities followed by the small window and previous basic disparities to measure details. The result is then smoothed and displayed as the final 3-D shape.

Algorithms↗

PubMed2005

Human movement analysis using stereophotogrammetry. Part 1: theoretical background.

This paper sets the stage for a series of reviews dealing with the problems associated with the reconstruction and analysis of in vivo skeletal system kinematics using optoelectronic stereophotogrammetric data. Instantaneous bone position and orientation and joint kinematic variable estimations are addressed in the framework of rigid body mechanics. The conceptual background to these exercises is discussed. Focus is placed on the experimental and analytical problem of merging the information relative to movement and that relative to the morphology of the anatomical body parts of interest. The various global and local frames that may be used in this context are defined. Common anatomical and mathematical conventions that can be used to describe joint kinematics are illustrated in a comparative fashion. The authors believe that an effort to systematize the different theoretical and experimental approaches to the problems involved and related nomenclatures, as currently reported in the literature, is needed to facilitate data and knowledge sharing, and to provide renewed momentum for the advancement of human movement analysis.

Biomechanical Phenomena↗

PubMed2005

Soft tissue artefact assessment in humeral axial rotation.

The accuracy of upper-limb kinematic data acquired from optoelectronic systems with retro-reflective markers is poor, mainly due to soft tissue artefact (STA). For the upper-arm, humeral internal/external rotation (HIER) is the movement most affected by STA, which is measured as a percentile fraction (K) of the effective humeral axial rotation performed. The aim of this work was to quantify STA during HIERs, with independently varying attitude of the humerus and elbow flexion, and to test the possibility of estimating its mean value over the tested upper-limb orientations using one simple trial. Six able-bodied subjects performed a series of HIERs in combination with elbow flexion for different humeral planes and degrees of elevation. During the trials the instantaneous attitudes of two humeral anatomical frames were compared, one being affected by the STA to be measured, and the other assumed as the gold standard. K was found to range from 20% to 48% of the effective humeral axial rotation performed, depending on the subject, humeral attitude and elbow flexion. These last two factors comparably affect STA and resulted in mean K coefficients of variation among the subjects of about 9% and 7%, respectively. Common patterns of K with elbow flexion and humerus elevation are discussed. The data also show that the mean of K of a subject is very close to the value assessed in a specific upper-limb configuration consistent among the subjects. This result from this study could be used to build up a time-saving STA compensation procedure suitable for clinical applications.

Adult↗

PubMed2005

Human movement analysis using stereophotogrammetry. Part 2: instrumental errors.

This paper reviews the main aspects involved with the management of instrumental errors associated with video-based optoelectronic stereophotogrammetry. Insights on how such errors propagate to kinematic quantities are of great interest in the field of human movement analysis to improve the precision and reliability of measurements. The review focuses on the technical assessment and analytical compensation procedures to cope with instrumental errors. Relevant contributions dealing with intrinsic sources of systematic and random errors, such as the issues concerning camera calibration and filtering and smoothing of marker position data, are presented. Procedures for marker imaged processing, and missing marker recovery are also surveyed. Methods for checking the accuracy and precision of stereophotogrammetric systems are then reviewed. Finally, since the desired outcome of the movement measurements is a reliable estimate of body segment kinematics, state-of-the-art techniques proposed for minimization of error propagation arising from a cluster of external markers are described.

Biomechanical Phenomena↗

PubMed2005

Human movement analysis using stereophotogrammetry. Part 3. Soft tissue artifact assessment and compensation.

When using optoelectronic stereophotogrammetry, skin deformation and displacement causes marker movement with respect to the underlying bone. This movement represents an artifact, which affects the estimation of the skeletal system kinematics, and is regarded as the most critical source of error in human movement analysis. A comprehensive review of the state-of-the-art for assessment, minimization and compensation of the soft tissue artifact (STA) is provided. It has been shown that STA is greater than the instrumental error associated with stereophotogrammetry, has a frequency content similar to the actual bone movement, is task dependent and not reproducible among subjects and, of lower limb segments, is greatest at the thigh. It has been shown that in in vivo experiments only motion about the flexion/extension axis of the hip, knees and ankles can be determined reliably. Motion about other axes at those joints should be regarded with much more caution as this artifact produces spurious effects with magnitudes comparable to the amount of motion actually occurring in those joints. Techniques designed to minimize the contribution of and compensate for the effects of this artifact can be divided up into those which model the skin surface and those which include joint motion constraints. Despite the numerous solutions proposed, the objective of reliable estimation of 3D skeletal system kinematics using skin markers has not yet been satisfactorily achieved and greatly limits the contribution of human movement analysis to clinical practice and biomechanical research. For STA to be compensated for effectively, it is here suggested that either its subject-specific pattern is assessed by ad hoc exercises or it is characterized from a large series of measurements on different subject populations. Alternatively, inclusion of joint constraints into a more general STA minimization approach may provide an acceptable solution.

Adipose Tissue↗

PubMed2005

Human movement analysis using stereophotogrammetry. Part 4: assessment of anatomical landmark misplacement and its effects on joint kinematics.

Estimating the effects of different sources of error on joint kinematics is crucial for assessing the reliability of human movement analysis. The goal of the present paper is to review the different approaches dealing with joint kinematics sensitivity to rotation axes and the precision of anatomical landmark determination. Consistent with the previous papers in this series, the review is limited to studies performed with video-based stereophotogrammetric systems. Initially, studies dealing with estimates of precision in determining the location of both palpable and internal anatomical landmarks are reviewed. Next, the effects of anatomical landmark position uncertainty on anatomical frames are shown. Then, methods reported in the literature for estimating error propagation from anatomical axes location to joint kinematics are described. Interestingly, studies carried out using different approaches reported a common conclusion: when joint rotations occur mainly in a single plane, minor rotations out of this plane are strongly affected by errors introduced at the anatomical landmark identification level and are prone to misinterpretation. Finally, attempts at reducing joint kinematics errors due to anatomical landmark position uncertainty are reported. Given the relevance of this source of errors in the determination of joint kinematics, it is the authors' opinion that further efforts should be made in improving the reliability of the joint axes determination.

Biomechanical Phenomena↗

PubMed2004

Assessment of sub-division of plantar pressure measurement in children.

Methods for the measurement of plantar pressure are poorly defined particularly when describing sub-sections of the plantar surface of the foot in the presence of deformity. The aim of this study was to assess foot pressure measurement in healthy children, using an automatic technique of sub-area definition that has the potential for objective evaluation of treatment of foot deformity. Twelve healthy children were examined on three occasions. Plantar pressure data were collected and time synchronised with force plate and stereophotogrammetric data. The footprint was divided into five sub-sections by using the position of the markers on the foot at mid-stance projected onto the pressure footprint. Repeatability for peak pressure and peak force was assessed. Automatic sub-area definition based on marker placement was found to be reliable in healthy children. A comparison of results revealed that peak vertical force was a more consistent measure than peak pressure for each of the five sub-areas. This suggests that force may be a more appropriate measurement for outcome studies.

Adolescent↗

PubMed2005

Effect of skin movement artifact on knee kinematics during gait and cutting motions measured in vivo.

Eight healthy male subjects had intra-cortical bone-pins inserted into the proximal tibia and distal femur. Three reflective markers were attached to each bone-pin and four reflective markers were mounted on the skin of the tibia and thigh, respectively. Roentgen-stereophotogrammetric analysis (RSA) was used to determine the anatomical reference frame of the tibia and femur. Knee joint motion was recorded during walking and cutting using infrared cameras sampling at 120Hz. The kinematics derived from the bone-pin markers were compared with that of the skin-markers. Average rotational errors of up to 4.4 degrees and 13.1 degrees and translational errors of up to 13.0 and 16.1mm were noted for the walk and cut, respectively. Although skin-marker derived kinematics could provide repeatable results this was not representative of the motion of the underlying bones. A standard error of measurement is proposed for the reporting of 3D knee joint kinematics.

Adult↗

PubMed2006

Rear-foot, mid-foot and fore-foot motion during the stance phase of gait.

This paper proposes a new protocol designed to track a large number of foot segments during the stance phase of gait with the smallest possible number of markers, with particular clinical focus on coronal plane alignment of the rear-foot, transverse and sagittal plane alignment of the metatarsal bones, and changes at the medial longitudinal arch. The shank, calcaneus, mid-foot and metatarsus were assumed to be 3D rigid bodies. The longitudinal axis of the first, second and fifth metatarsal bones and the proximal phalanx of the hallux were also tracked independently. Skin markers were mounted on bony prominences or joint lines, avoiding the course of main tendons. Trajectories of the 14 markers were collected by an eight-camera motion capture system at 100 Hz on a population of 10 young volunteers. Three-dimensional joint rotations and planar angles were calculated according to anatomically based reference frames. The marker set was well visible throughout the stance phase of gait, even in a camera configuration typical of gait analysis of the full body. The time-histories of the joint rotations and planar angles were well repeatable among subjects and consistent with clinical and biomechanical knowledge. Several dynamic measurements were originally taken, such as elevation/drop of the medial longitudinal arch and of three metatarsal bones, rear-foot to fore-foot rotation and transverse plane deformation of the metatarsus. The information obtained from this protocol, consistent with previous clinical knowledge, enhanced our understanding of the dynamics of the human foot during stance.

Adult↗

PubMed2006

Propagation of anatomical landmark misplacement to knee kinematics: performance of single and double calibration.

Soft tissue artefact and anatomical landmark misplacement have been recognized as the most critical sources of error in gait analysis. The double calibration method was recently proposed to compensate for soft tissue artefact in knee kinematics. This compensation method resulted very effective in the absence of anatomical landmark misplacement. The purpose of the present work was to assess the effectiveness of double calibration in reducing the effects of skin motion artefact on knee rotations and translations when anatomical landmark misplacement is present on the thigh and shank. The double calibration method was used to calculate knee kinematics of two subjects while they performed several motor tasks. The results were compared with those from conventional single calibration. The soft tissue artefact propagated to knee kinematics was quantified by simulating different misplacement errors using both single and double calibration. The double calibration method performed much better than the single calibration one in quantifying knee rotations and particularly translations, with misplacement error up to 15mm superimposed on the anatomical coordinates of the epicondyles. If misplacement errors were limited to just 5mm, the double calibration would be effective in providing kinematics accurate enough for orthopaedic biomechanic applications.

Adult↗

PubMed2006

Reliability of the intrinsic and extrinsic patterns of level walking in older women.

The aim of the study was to assess short- and long-term reliability of the harmonic analysis of the trajectories of head, upper trunk, and pelvis during walking in healthy older women, which reveals mechanisms to coordinate upper body segments and control head stability in the search for a safer gait. A stereophotogrammetric system was used to measure the displacement of markers located at head, shoulder, and pelvis level in 11 healthy older women (77+/-2 years) walking on an oval shaped 20-m walkway circuit, in three experimental sessions separated by 6 weeks. The harmonic analysis of the time-curves was highly reliable both within and between sessions (standard error of measurement ranging between 0.15 mm and 1.50mm for the amplitudes and 0.03 rad and 0.41 rad for the phases) and revealed different oscillatory patterns for the pelvis, head, and upper trunk. An intrinsic pattern, representing the natural overall movement symmetry of the whole population of older women of this study, was described by the first medio-lateral harmonic and second antero-posterior and vertical harmonics. An extrinsic pattern, characteristic of each individual in the population, was described by the first antero-posterior and vertical harmonics. The intrinsic pattern was both intra- and inter-subject repeatable (coefficient of multiple correlation, CMC, ranging between 0.82 and 0.99), while the extrinsic pattern was only intra-subject repeatable (CMC ranging between 0.70 and 0.90). Harmonic analysis reliably describes upper body kinematics in older women for detecting the intrinsic and extrinsic patterns of gait, which reveal fundamental mechanisms governing their walking.

Aged↗

PubMed2006

Dysgnathia, orthognathic surgery and spinal posture.

The aim of this study was to evaluate the spine by video rasterstereography before and after orthognathic surgery. Twenty-nine patients (17 patients with a skeletal class III, 7 patients with a skeletal class II, and 5 patients with mandibular asymmetry) were evaluated preoperatively and 1 year postoperatively. Video rasterstereography is a method of back surface measurement and shape analysis using the moire topography. Orthognathic surgery in cases of class III and asymmetry did not lead to significant changes in body posture. In class II patients it led to some changes in body posture, but without orthopaedic consequences. It is concluded that orthognathic surgery causes minimal or no change in body posture.

Adolescent↗

PubMed2006

Comparison of three methods of facial measurement.

The aims of this study were to assess the accuracy of measurements recorded by 3D stereophotogrammetry and to compare three methods of facial measurement: manual anthropometry, 3D stereophotogrammetry and 2D photography. Measurements were taken from 14 landmarks on each of six volunteers and compared. In addition, the variability of the methods was assessed. Three-dimensional measurements were shown to compare well with manual measurements on volunteers as well as test objects for which the mean difference was 0.23 mm (shortest distance) and 0.13 mm (surface). All the three methods of measurement were found to have good levels of repeatability. Two-dimensional measurements were more variable than manual measurements (P=0.021). Three-dimensional stereophotogrammetric measurements were shown to compare well with manual measurements although the values obtained were mostly slightly larger. Stereophotogrammetry allows images to be taken in a Medical Photography Department, facilitating the accurate measurement of facial morphology from digitized data, including changes associated with treatment or growth. There are clear potential benefits of using 3D measurements in the assessment of facial deformity.

Adult↗

PubMed2005

A novel method for in vivo knee prosthesis wear measurement.

Wear remains an important cause of failure in knee replacement. Of the current methods of early performance assessment or prediction, simulators have been un-physiological, single X-ray film analyses remain limited by accuracy and retrieval and survival methods have a prohibitive time scale. An accurate method is needed to allow a timely assessment of polyethylene component wear in vivo, when a new design is introduced, in order to predict likely outcome. We present a new method for measuring wear in vivo that we believe will allow this prediction of long-term wear. X-ray film pairs were taken of implanted prosthetic metal components. When the X-ray system was calibrated, projections of the appropriate Computer Aided Design (CAD) model could be matched to the shapes on the scanned X-ray films to find component positions. Interpenetration of the metal femoral component into the polyethylene component could then be established and represents our estimate of "wear". This method was used to measure in vivo prosthesis wear to an accuracy of 0.11 mm.

Arthroplasty, Replacement, Knee↗

PubMed2005

Marker Configuration Model-Based Roentgen Fluoroscopic Analysis.

It remains unknown if and how the polyethylene bearing in mobile bearing knees moves during dynamic activities with respect to the tibial base plate. Marker Configuration Model-Based Roentgen Fluoroscopic Analysis (MCM-based RFA) uses a marker configuration model of inserted tantalum markers in order to accurately estimate the pose of an implant or bone using single plane Roentgen images or fluoroscopic images. The goal of this study is to assess the accuracy of (MCM-Based RFA) in a standard fluoroscopic set-up using phantom experiments and to determine the error propagation with computer simulations. The experimental set-up of the phantom study was calibrated using a calibration box equipped with 600 tantalum markers, which corrected for image distortion and determined the focus position. In the computer simulation study the influence of image distortion, MC-model accuracy, focus position, the relative distance between MC-models and MC-model configuration on the accuracy of MCM-Based RFA were assessed. The phantom study established that the in-plane accuracy of MCM-Based RFA is 0.1 mm and the out-of-plane accuracy is 0.9 mm. The rotational accuracy is 0.1 degrees. A ninth-order polynomial model was used to correct for image distortion. Marker-Based RFA was estimated to have, in a worst case scenario, an in vivo translational accuracy of 0.14 mm (x-axis), 0.17 mm (y-axis), 1.9 mm (z-axis), respectively, and a rotational accuracy of 0.3 degrees. When using fluoroscopy to study kinematics, image distortion and the accuracy of models are important factors, which influence the accuracy of the measurements. MCM-Based RFA has the potential to be an accurate, clinically useful tool for studying kinematics after total joint replacement using standard equipment.

Arthroplasty, Replacement↗