New method of studying joint kinematics from three-dimensional reconstructions of MRI data

An Imaged-Based Three-Dimensional Study of First Metatarsal Protrusion Distance in Women with and Without Hallux Valgus

BACKGROUND

First metatarsal protrusion distance (MPD) has been commonly studied as a characteristic of hallux valgus deformity. To date, the majority of investigations have used radiographic methods, with most reporting first metatarsal (ray) protrusion to be associated with deformity. As an alternative, this study used a three-dimensional (3-D) image acquisition and data analysis method to quantify MPD.

METHODS

Magnetic resonance images were acquired in weightbearing on 29 women (19 with hallux valgus; 10 controls). After the 3-D images were reconstructed into virtual bone models, two examiners measured MPD in relation to the navicular. In addition to a reliability analysis, a t test assessed for group differences in demographics, foot posture (hallux valgus, intermetatarsal angles), and MPD.

RESULTS

Group demographics were not different, while measures of hallux valgus and intermetatarsal angles were different ( P < 0.01) between groups. The measurement of MPD was highly reliable (ICC [Formula: see text] 0.99; SEM [Formula: see text] 0.78 mm). Metatarsal protrusion averaged approximately -2.0 mm in both groups. There was no statistical group difference ( P = 0.89) in MPD.

CONCLUSIONS

The reconstructed image datasets captured the 3-D spatial relationship of the anatomy. Measurements of MPD were reliable. The first ray measured 2 mm shorter than the second ray in both the hallux valgus and control groups. Though unexpected, this result may prompt future study of the pathokinematics associated with hallux valgus that include the quantification of metatarsal protrusion with 3-D methods, instead of relying solely on single-plane radiograph reports.

Terminology and forensic gait analysis

The use of appropriate terminology is a fundamental aspect of forensic gait analysis. The language used in forensic gait analysis is an amalgam of that used in clinical practice, podiatric biomechanics and the wider field of biomechanics. The result can often be a lack of consistency in the language used, the definitions used and the clarity of the message given. Examples include the use of 'gait' and 'walking' as synonymous terms, confusion between 'step' and 'stride', the mixing of anatomical, positional and pathological descriptors, and inability to describe appropriately movements of major body segments such as the torso. The purpose of this paper is to share the well-established definitions of the fundamental parameters of gait, common to all professions, and advocate their use in forensic gait analysis to establish commonality. The paper provides guidance on the selection and use of appropriate terminology in the description of gait in the forensic context. This paper considers the established definitions of the terms commonly used, identifies those terms which have the potential to confuse readers, and suggests a framework of terminology which should be utilised in forensic gait analysis.

In vivo three-dimensional analysis of hindfoot kinematics in stage II PTTD flatfoot

BACKGROUND

This study aims to evaluate the rotation and translation of each joint in the hindfoot and compare the differences in healthy foot with that in stage II PTTD flatfoot by analyzing the reconstructive three-dimensional (3D) computed tomography (CT) image data during several extreme positions.

METHODS

CT scans of 20 healthy feet and 20 feet with stage II PTTD flatfoot were taken in maximal positions of plantarflexion, dorsiflexion, inversion, eversion, external rotation and internal rotation conditions. The images of the hindfoot bones were reconstructed into 3D models. The "twice registration" method was used to calculate the spatial changes of the talus relative to the calcaneus in the talocalcaneal joint, the navicular relative to the talus in talonavicular joint, and the cuboid relative to the calcaneus in the calcaneocuboid joint.

RESULTS

Compared with normal participants, with the calcaneus relative to the talus, participants with stage II PTTD flatfoot presented more dorsiflexion (p < 0.05), adduction (p < 0.05), and eversion (p < 0.05) in rotation, and more anterior (p < 0.05) and distal translation (p < 0.05) from maximal plantarflexion to maximal dorsiflexion; more dorsiflexion (p < 0.05), eversion (p < 0.05), and abduction (p < 0.05) in rotation and more lateral translation (p < 0.05) from maximal inversion to maximal eversion; and a greater degree of adduction (p < 0.05) in rotation, and more lateral (p < 0.05) and posterior translation (p < 0.05) from maximal internal rotation to maximal external rotation condition. For navicular relative to the talus, they demonstrated more eversion (p < 0.05) and adduction (p < 0.05) in rotation, and more lateral (p < 0.05), anterior (p < 0.05), and distal translation (p < 0.05) from maximal plantarflexion to maximal dorsiflexion; more eversion (p < 0.05) and adduction (p < 0.05) in rotation, and more lateral (p < 0.05) and proximal (p < 0.05) translation from maximal inversion to maximal eversion; more eversion (p < 0.05) and abduction (p < 0.05) in rotation and more lateral (p < 0.05) translation from maximal internal to maximal external rotation condition. The cuboid position relative to the calcaneus in the calcaneocuboid joint did not change significantly in rotation and translation in different positions (p > 0.05).

CONCLUSIONS

As previous studies shown, regarding both of the cadaveric foot and the live foot, hindfoot joint instability occurred in patients with stage II PTTD flatfoot.

Cardan angle rotation sequence effects on first-metatarsophalangeal joint kinematics: implications for measuring hallux valgus deformity

Background

There currently are no recommended standards for reporting kinematics of the first-metatarsophalangeal joint. This study compared 2 different rotation sequences of Cardan angles, with implications for understanding the measurement of hallux valgus deformity.

Methods

Thirty-one women (19 hallux valgus; 12 controls) participated. All were scanned in an open-upright magnetic resonance scanner, their foot posed to simulate the gait conditions of midstance, heel-off, and terminal stance. Using computer processes, selected tarsals were reconstructed into virtual bone models and embedded with principal-axes coordinate systems, from which the rotation matrix between the hallux and first metatarsal was decomposed into Cardan angles. Joint angles were then compared using a within factors (rotation sequence and gait condition) repeated-measures analysis of variance (ANOVA).

Results

Only the transverse plane-first sequence consistently output incremental increases of dorsiflexion and abduction across gait events in both groups. There was an interaction (F ≥ 25.1; p < 0.001). Follow-up comparisons revealed angles were different (p < 0.05) at terminal stance.

Conclusions

Different rotation sequences yield different results. Extracting the first rotation in the transverse plane allows for the resting alignment of the hallux to deviate from the sagittal plane. Therefore, representing first-metatarsophalangeal joint kinematics with the transverse plane-first rotation sequence may be preferred, especially in cases of hallux valgus deformity.

3D analysis of the proximal interphalangeal joint kinematics during flexion

Background. Dynamic joint motion recording combined with CT-based 3D bone and joint surface data is accepted as a helpful and precise tool to analyse joint. The purpose of this study is to demonstrate the feasibility of these techniques for quantitative motion analysis of the interphalangeal joint in 3D. Materials and Method. High resolution motion data was combined with an accurate 3D model of a cadaveric index finger. Three light-emitting diodes (LEDs) were used to record dynamic data, and a CT scan of the finger was done for 3D joint surface geometry. The data allowed performing quantitative evaluations such as finite helical axis (FHA) analysis, coordinate system optimization, and measurement of the joint distances in 3D. Results. The FHA varies by 4.9 ± 1.7° on average. On average, the rotation in adduction/abduction and internal/external rotation were 0.3 ± 0.91° and 0.1 ± 0.97°, respectively. During flexion, a translational motion between 0.06 mm and 0.73 mm was observed. Conclusions. The proposed technique and methods appear to be feasible for the accurate assessment and evaluation of the PIP joint motion in 3D. The presented method may help to gain additional insights for the design of prosthetic implants, rehabilitation, and new orthotic devices.

An image-based gait simulation study of tarsal kinematics in women with hallux valgus

BACKGROUND

Although not well understood, foot kinematics are changed with hallux valgus.

OBJECTIVE

The purpose of this study was to examine tarsal kinematics in women with hallux valgus deformity.

DESIGN

A prospective, cross-sectional design was used.

METHODS

Twenty women with (n=10) and without (n=10) deformity participated. Data were acquired with the use of a magnetic resonance scanner. Participants were posed standing to simulate gait, with images reconstructed into virtual bone datasets. Measures taken described foot posture (hallux angle, intermetatarsal angle, arch angle). With the use of additional computer processes, the image sequence was then registered across gait conditions to compute relative tarsal position angles, first-ray angles, and helical axis parameters decomposed into X, Y, and Z components. An analysis of variance model compared kinematics between groups and across conditions. Multiple regression analysis assessed the relationship of arch angle, navicular position, and inclination of the first-ray axis.

RESULTS

Both the hallux and intermetatarsal angles were larger with deformity; arch angle was not different between groups. The calcaneus was everted by ≥6.6 degrees, and the first ray adducted (F=44.17) by ≥9.3 degrees across conditions with deformity. There was an interaction (F=5.06) for the first-ray axis. Follow-up comparisons detected increased inclination of the first-ray axis over middle stance compared with late stance in the group with deformity.

LIMITATIONS

Gait was simulated, kinetics were not measured, and sample size was small.

CONCLUSIONS

There were group differences. Eversion of the calcaneus and adduction of the first ray were increased, and the first-ray axis was inclined 24 degrees over middle stance in women with deformity compared with 6 degrees in control participants. Results may identify risk factors of hallux valgus and inform nonoperative treatment (orthoses, exercise) strategies.

Human hand modelling: kinematics, dynamics, applications

An overview of mathematical modelling of the human hand is given. We consider hand models from a specific background: rather than studying hands for surgical or similar goals, we target at providing a set of tools with which human grasping and manipulation capabilities can be studied, and hand functionality can be described. We do this by investigating the human hand at various levels: (1) at the level of kinematics, focussing on the movement of the bones of the hand, not taking corresponding forces into account; (2) at the musculotendon structure, i.e. by looking at the part of the hand generating the forces and thus inducing the motion; and (3) at the combination of the two, resulting in hand dynamics as well as the underlying neurocontrol. Our purpose is to not only provide the reader with an overview of current human hand modelling approaches but also to fill the gaps with recent results and data, thus allowing for an encompassing picture.

A novel method for measuring in-shoe navicular drop during gait

Analysis of foot movement is essential in the treatment and prevention of foot-related disorders. Measuring the in-shoe foot movement during everyday activities, such as sports, has the potential to become an important diagnostic tool in clinical practice. The current paper describes the development of a thin, flexible and robust capacitive strain sensor for the in-shoe measurement of the navicular drop. The navicular drop is a well-recognized measure of foot movement. The position of the strain sensor on the foot was analyzed to determine the optimal points of attachment. The sensor was evaluated against a state-of-the-art video-based system that tracks reflective markers on the bare foot. Preliminary experimental results show that the developed strain sensor is able to measure navicular drop on the bare foot with an accuracy on par with the video-based system and with a high reproducibility. Temporal comparison of video-based, barefoot and in-shoe measurements indicate that the developed sensor measures the navicular drop accurately in shoes and can be used without any discomfort for the user.

In vivo three-dimensional analysis of hindfoot kinematics

BACKGROUND

Knowledge of normal bone motion of the foot is important for understanding the gait as well as for various pathologies; however, the pattern of 3D motion is not completely understood. The aim of this study was to quantify the in vivo motion of the tibiotalar joint, talocalcaneal joint, and talonavicular joint in normal adult feet using a noninvasive (e.g., nonsurgical) measurement technique.

MATERIALS AND METHODS

CT images were taken of both feet of ten normal young adults (six males, four females) in neutral, plantarflexion, and dorsiflexion positions of the ankle joint, from which 3D virtual models were made of each mid-hind foot bones. The 3D bone motion of these models was calculated using volume merge methods in three major planes. These data were used to analyze the relationship between the motion of the ankle joint and each other joint.

RESULTS

Tibiotalar rotation was observed in dorsiflexion, abduction, and eversion during maximal dorsiflexion of the ankle joint. Talocalcaneal and talonavicular rotation was very small because the ankle joint motion was limited to the sagittal plane. Tibiotalar rotation was also observed in plantarflexion and adduction during maximal plantarflexion of the ankle joint, and talocalcaneal rotation was very small. Talonavicular rotation was observed in plantarflexion and inversion. The motion of the x-axis and the z-axis of tibiotalar joint, and the x-axis and the y-axis of the talonavicular and talocalcaneal joint were associated with the ankle motion.

CONCLUSION

Bone motion could be easily and accurately calculated using volume merge methods more effectively than it could with other methods.

CLINICAL RELEVANCE

The data elucidates the baseline segmental motion for comparison with symptomatic subjects which could help us to better understand pathokinematics of various foot and ankle pathologies.

Determination of consistent patterns of range of motion in the ankle joint with a computed tomography stress-test

BACKGROUND

Measuring the range of motion of the ankle joint can assist in accurate diagnosis of ankle laxity. A computed tomography-based stress-test (3D CT stress-test) was used that determines the three-dimensional position and orientation of tibial, calcaneal and talar bones. The goal was to establish a quantitative database of the normal ranges of motion of the talocrural and subtalar joints. A clinical case on suspected subtalar instability demonstrated the relevance the proposed method.

METHODS

The range of motion was measured for the ankle joints in vivo for 20 subjects using the 3D CT stress-test. Motion of the tibia and calcaneus relative to the talus for eight extreme foot positions were described by helical parameters.

FINDINGS

High consistency for finite helical axis orientation (n) and rotation (theta) was shown for: talocrural extreme dorsiflexion to extreme plantarflexion (root mean square direction deviation (eta) 5.3 degrees and theta: SD 11.0 degrees), talorucral and subtalar extreme combined eversion-dorsiflexion to combined inversion-plantarflexion (eta: 6.7 degrees , theta: SD 9.0 degrees and eta:6.3 degrees , theta: SD 5.1 degrees), and subtalar extreme inversion to extreme eversion (eta: 6.4 degrees, theta: SD 5.9 degrees). Nearly all dorsi--and plantarflexion occurs in the talocrural joint (theta: mean 63.3 degrees (SD 11 degrees)). The inversion and internal rotation components for extreme eversion to inversion were approximately three times larger for the subtalar joint (theta: mean 22.9 degrees and 29.1 degrees) than for the talocrural joint (theta: mean 8.8 degrees and 10.7 degrees). Comparison of the ranges of motion of the pathologic ankle joint with the healthy subjects showed an increased inversion and axial rotation in the talocrural joint instead of in the suspected subtalar joint.

INTERPRETATION

The proposed diagnostic technique and the acquired database of helical parameters of ankle joint ranges of motion are suitable to apply in clinical cases.

Three-dimensional in vivo kinematics of the subtalar joint during dorsi-plantarflexion and inversion-eversion

BACKGROUND

It is difficult to determine the kinematics of the subtalar joint because of its anatomical and functional complexity. The purpose of the study was to clarify the 3D kinematics of the subtalar joint in vivo.

MATERIALS AND METHODS

Subjects were four healthy female volunteers. Magnetic resonance imaging (MRI) sequences were acquired in seven positions during dorsi-plantarflexion (DPF) and in 10 positions during inversion-eversion (IE) at intervals of 10 degrees. MRI data of the talus and calcaneus in the neutral position were superimposed on images of the other positions using voxel-based registration, and relative motions and axes of rotation were visualized and quantitatively calculated.

RESULTS

The calcaneus always rotated from dorsolateral to medioplantar during DPF and IE, and the motion plane was very similar to that of the entire foot in IE. The axes of rotation of the calcaneus relative to the talus during DPF and IE had a very close spatial relationship, running obliquely from antero-dorso-medial to postero-planto-lateral and penetrating the talar neck. The rotation angle around each of these calcaneal axes tended to be greater in IE (20 degrees +/- 2 degrees) than in DPF (16 degrees +/- 3 degrees). In DPF, motion of the calcaneus relative to the talus occurred predominantly around maximum dorsiflexion and plantarflexion, with little movement observed at intermediate positions. During IE, the calcaneus exhibited uninterrupted motion related to foot movement.

CONCLUSION

The subtalar joint is essentially a uniaxial joint with a motion plane almost identical to that of IE of the entire foot.

CLINICAL RELEVANCE

Knowledge of normal subtalar kinematics may be helpful when evaluating pathologic conditions.

Performing accurate joint kinematics from 3-D in vivo image sequences through consensus-driven simultaneous registration

This paper addresses the problem of the robust registration of multiple observations of the same object. Such a problem typically arises whenever it becomes necessary to recover the trajectory of an evolving object observed through standard 3-D medical imaging techniques. The instances of the tracked object are assumed to be variously truncated, locally subject to morphological evolutions throughout the sequence, and imprinted with significant segmentation errors as well as significant noise perturbations. The algorithm operates through the robust and simultaneous registration of all surface instances of a given object through median consensus. This operation consists of two interwoven processes set up to work in close collaboration. The first one progressively generates a median and implicit shape computed with respect to current estimations of the registration transformations, while the other refines these transformations with respect to the current estimation of their median shape. When compared with standard robust techniques, tests reveal significant improvements, both in robustness and precision. The algorithm is based on widely-used techniques, and proves highly effective while offering great flexibility of utilization.

In vivo three-dimensional skeletal alignment analysis of the hindfoot valgus deformity in patients with rheumatoid arthritis

The purpose of this study was to analyze the skeletal alignment of the hindfoot valgus deformity in patients with rheumatoid arthritis using bone models reconstructed from three-dimensional computerized tomography data. Computed tomography was performed on 21 feet of patients with rheumatoid arthritis, and magnetic resonance imaging was taken of 10 normal feet of eight volunteers. An image processing system was used to create bone models and analyze the three-dimensional displacement of the calcaneus, talus, navicular, and cuboid bones. With a standard coordinate system in the distal tibia and a local coordinate system in each bone of the hindfoot, three rotational parameters and three translational parameters were used to evaluate the relative displacement. The talus showed plantar flexion. Both the calcaneus and navicular bones had valgus and lateral shift displacements. However, the cuboid had no displacement relative to the calcaneus, and the navicular showed no displacement relative to the cuboid. The calcaneus, navicular, and cuboid bones have the same pattern of deformity in patients with rheumatoid arthritis. This three-dimensional image-based technique successfully quantified the hindfoot valgus deformity resulting from rheumatoid arthritis and is beneficial for better understanding the deformity pathomechanism.

Intrinsic foot kinematics measured in vivo during the stance phase of slow running

An accurate kinematic description of the intrinsic articulations of the foot during running has not previously been presented, primarily due to methodological limitations. An invasive method based upon reflective marker arrays mounted on intracortical pins drilled into the bones was used in this study. Four male volunteers participated as subjects. Pins (1.6mm diameter) were inserted under local anaesthetic in the tibia, fibula, calcaneus, talus, navicular, cuboid, medial cuneiform and metatarsals I and V. A 10 camera motion analysis system was used for kinematic data capture and the ground reaction force was simultaneously measured. Segment motion relative to adjacent proximal segments was determined using helical axes projected into the coordinate system of the proximal segment. Coefficients of multiple correlation calculated to determine the strength of association between running style with and without the pins inserted indicated that the subjects had little restriction due to the inserted pins. Individual and mean results were presented for rotations defined in the planes of the proximal segment's coordinate system and showed frontal plane rotation of the talocrural joint (12.2+/-7.1 degrees ), which exceeded that of the subtalar joint (8.9+/-3.2 degrees ). Considerable mobility of the talonavicular joint was found (6.5+/-2.9 degrees , 13.5+/-4.1 degrees and 8.7+/-1.4 degrees in the sagittal, frontal and transverse planes, respectively). Furthermore, little, but non-negligible motion between the fibula and tibia was found (3.3+/-2.4 degrees in the sagittal plane). The presented data are of interest as input for future biomechanical modelling and clinical decision making in particular, concerning joint fusion.

Six DOF in vivo kinematics of the ankle joint complex: Application of a combined dual-orthogonal fluoroscopic and magnetic resonance imaging technique

Accurate knowledge of in vivo ankle joint complex (AJC) biomechanics is critical for understanding AJC disease states and for improvement of surgical treatments. This study investigated 6 degrees-of-freedom (DOF) in vivo kinematics of the human AJC using a combined dual-orthogonal fluoroscopic and magnetic resonance imaging (MRI) technique. Five healthy ankles of living subjects were studied during three in vivo activities of the foot, including maximum plantarflexion and dorsiflexion, maximum supination and pronation, and three weight-bearing positions in simulated stance phases of walking. A three-dimensional (3D) computer model of the AJC (including tibia, fibula, talus, and calcaneus) was constructed using 3D MR images of the foot. The in vivo AJC position at each selected position of the foot was captured using two orthogonally positioned fluoroscopes. In vivo AJC motion could then be reproduced by coupling the orthogonal images with the 3D AJC model in a virtual dual-orthogonal fluoroscopic system. From maximum dorsiflexion to plantarflexion, the arc of motion of the talocrural joint (47.5 +/- 2.2 degrees) was significantly larger than that of the subtalar joint (3.1 +/- 6.8 degrees). Both joints showed similar degrees of internal-external and inversion-eversion rotation. From maximum supination to pronation, all rotations and translations of the subtalar joint were significantly larger than those of the talocrural joint. From heel strike to midstance, the plantarflexion contribution from the talocrural joint (9.1 +/- 5.3 degrees) was significantly larger than that of the subtalar joint (-0.9 +/- 1.2 degrees). From midstance to toe off, internal rotation and inversion of the subtalar joint (12.3 +/- 8.3 degrees and -10.7 +/- 3.8 degrees, respectively) were significantly larger than those of the talocrural joint (-1.6 +/- 5.9 degrees and -1.7 +/- 2.7 degrees). Strong kinematic coupling between the talocrural and subtalar joints was observed during in vivo AJC activities. The contribution of the talocrural joint to active dorsi-plantarflexion was higher than that of the subtalar joint, whereas the contribution of the subtalar joint to active supination-pronation was higher than that of the talocrural joint. In addition, the talocrural joint demonstrated larger motion during the early part of stance phase while the subtalar joint contributes more motion during the later part of stance phase. The results add quantitative data to an in vivo database of normals that can be used in clinical diagnosis, treatment, and evaluation of the AJC after injuries.

Three-dimensional in vivo motion of adult hind foot bones

Knowledge of hind foot bone motion is important for understanding gait as well as various foot pathologies, but the three-dimensional (3D) motion of these bones remains incompletely understood. The purpose of this study was to quantify the motion of the talus, calcaneus, navicular, and cuboid in normal adult feet during open chain quasi-static uniplanar plantar flexion motion. Magnetic resonance images of the right feet of six normal young adult males were taken from which 3D virtual models were made of each hind foot bone. The 3D motion of these models was analyzed. Each hind foot bone rotated in the same plane about half as much as the foot (mean 0.54 degrees of bone rotation per degree of foot motion, range 0.40-0.73 degrees per degree of foot motion as measured relative to the fixed tibia). Talar motion was primarily uniaxial, but the calcaneus, navicular, and cuboid bones exhibited biplanar (sometimes triplanar) translation in addition to biaxial rotation. Net translational motions of these bones averaged 0.39 mm of bone translation per degree of foot motion (range 0.06-0.62 mm per degree of foot motion). These data reflect the functional anatomy of the foot, extend the findings of prior studies, provide a standard for comparison to patients with congenital or acquired foot deformities, and establish an objective reference for quantitatively assessing the efficacy of various hind foot therapies.

A method for measurement of joint kinematics in vivo by registration of 3-D geometric models with cine phase contrast magnetic resonance imaging data

A new method is presented for measuring joint kinematics by optimally matching modeled trajectories of geometric surface models of bones with cine phase contrast (cine-PC) magnetic resonance imaging data. The incorporation of the geometric bone models (GBMs) allows computation of kinematics based on coordinate systems placed relative to full 3-D anatomy, as well as quantification of changes in articular contact locations and relative velocities during dynamic motion. These capabilities are additional to those of cine-PC based techniques that have been used previously to measure joint kinematics during activity. Cine-PC magnitude and velocity data are collected on a fixed image plane prescribed through a repetitively moved skeletal joint. The intersection of each GBM with a simulated image plane is calculated as the model moves along a computed trajectory, and cine-PC velocity data are sampled from the regions of the velocity images within the area of this intersection. From the sampled velocity data, the instantaneous linear and angular velocities of a coordinate system fixed to the GBM are estimated, and integration of the linear and angular velocities is used to predict updated trajectories. A moving validation phantom that produces motions and velocity data similar to those observed in an experiment on human knee kinematics was designed. This phantom was used to assess cine-PC rigid body tracking performance by comparing the kinematics of the phantom measured by this method to similar measurements made using a magnetic tracking system. Average differences between the two methods were measured as 2.82 mm rms for anterior/posterior tibial position, and 2.63 deg rms for axial rotation. An intertrial repeatability study of human knee kinematics using the new method produced rms differences in anterior/posterior tibial position and axial rotation of 1.44 mm and 2.35 deg. The performance of the method is concluded to be sufficient for the effective study of kinematic changes caused to knees by soft tissue injuries.

Three-dimensional hindfoot motion in adolescents with surgically treated unilateral clubfoot

Advances in imaging and computerized analyses have enabled three-dimensional bone motion in the treated clubfoot to be measured precisely. Three-dimensional translations and rotations of the talus, calcaneus, navicular, and cuboid of surgically treated clubfeet were less in magnitude and sometimes different in direction (or without motion in a specific plane) compared with the contralateral normal feet. Surgical techniques used for clubfoot treatment do not restore normal hindfoot bone motion when examined with high-resolution magnetic resonance imaging, computer reconstruction, and image analysis techniques. These data advance the knowledge of hindfoot bone motion and establish a new and quantitative objective.

Relation of jaw sounds and kinematics visualized and quantified using 3-D computer animation

The management of jaw pain or temporomandibular disorders (TMD) has been controversial regarding temporomandibular joint (TMJ) sounds and their implication regarding TMD prognosis. 3-D computer animation was used to visualize and quantify the internal mechanics of natural mandibular motion synchronized with TMJ sounds. Mandibular movements of four TMD patients and two healthy subjects were recorded using CCD cameras and reflective markers. Sounds were recorded with electret microphones. Magnetic resonance imaging was used to create 3-D geometric models. Visualization of the internal anatomy, mandibular condyle and glenoid fossa, revealed that the condyle initially rotated within the fossa and then moved out of the fossa along, and well beyond, the articular eminence. Power in the opening sound recordings after the condyle moved out of the fossa was significantly greater than when the condyle was within the fossa (p<0.001). The louder opening sounds were often classified as TMJ clicks, implying that clicks occur after the condyle moves out of the fossa. The 3-D computer animation should help resolve the implication of TMJ sounds regarding TMD prognosis by providing visualization and quantization of the TMJ internal mechanics during sound production.

Data representation for joint kinematics simulation of the lower limb within an educational context

Three-dimensional (3D) visualization is becoming increasingly frequent in both qualitative and quantitative biomechanical studies of anatomical structures involving multiple data sources (e.g. morphological data and kinematics data). For many years, this kind of experiment was limited to the use of bi-dimensional images due to a lack of accurate 3D data. However, recent progress in medical imaging and computer graphics has forged new perspectives. Indeed, new techniques allow the development of an interactive interface for the simulation of human motions combining data from both medical imaging (i.e., morphology) and biomechanical studies (i.e., kinematics). Fields of application include medical education, biomechanical research and clinical research. This paper presents an experimental protocol for the development of anatomically realistic joint simulation within a pedagogical context. Results are shown for the lower limb. Extension to other joints is straightforward. This work is part of the Virtual Animation of the Kinematics of the Human project (VAKHUM) (http://www.ulb.ac.be/project/vakhum).

Knee surgery assistance: patient model construction, motion simulation, and biomechanical visualization

We present a new system that integrates computer graphics, physics-based modeling, and interactive visualization to assist knee study and surgical operation. First, we discuss generating patient-specific three-dimensional (3-D) knee models from patient's magnetic resonant images (MRIs). The 3-D model is obtained by deforming a reference model to match the MRI dataset. Second, we present simulating knee motion that visualizes patient-specific motion data on the patient-specific knee model. Third, we introduce visualizing biomechanical information on a patient-specific model. The focus is on visualizing contact area, contact forces, and menisci deformation. Traditional methods have difficulty in visualizing knee contact area without using invasive methods. The approach presented here provides an alternative of visualizing the knee contact area and forces without any risk to the patient. Finally, a virtual surgery can be performed. The constructed 3-D knee model is the basis of motion simulation, biomechanical visualization, and virtual surgery. Knee motion simulation determines the knee rotation angles as well as knee contact points. These parameters are used to solve the biomechanical model. Our results integrate 3-D construction, motion simulation, and biomechanical visualization into one system. Overall, the methodologies here are useful elements for future virtual medical systems where all the components of visualization, automated model generation, and surgery simulation come together.

Reconstruction of the articular facets of the subtalar and talonavicular joints from volumetric magnetic resonance data

Image processing methods have been used to visualize the articular surfaces of an intact foot from an MR scan and to allow the relationship between the joint surfaces to be studied. The MR protocol employed would be applicable in the living foot. Several standard image-processing methods have been used to develop protocols for manual and automated editing of a volumetric MR scan. The result is a volume-rendered foot, displaying the articular surfaces of the tarsal and metatarsal joints. The methods employed are discussed and reconstructions of the subtalar and talonavicular joints presented, thereby enabling a qualitative analysis of the facets on the talus, calcaneus and navicular.

An in vivo analysis of the motion of the peri-talar joint complex based on MR imaging

The purpose of this work is to characterize the three-dimensional (3-D) motion of the peritalar joint complex in vivo using magnetic resonance imaging (MRI). Each image data set utilized in this study is made of 60 longitudinal MR slices of the foot in each of eight positions from extreme pronation to extreme supination. We acquired and analyzed ten such data sets from normal subjects, seven data sets from pathological joints and two postoperative data sets. We segmented and formed the surfaces of the calcaneus, talus, cuboid and navicular from all data sets. About 30 geometrical parameters are computed for each joint in each position. The results present features of normal motion and show how normal and abnormal motion can be distinguished. They also show the consequences of surgery on the motion. This non- invasive method offers a unique tool to characterize and quantify the 3-D motion of the rearfoot in vivo from MR images.

A 3D generalization of user-steered live-wire segmentation

We have been developing user-steered image segmentation methods for situations which require considerable human assistance in object definition. In the past, we have presented two paradigms, referred to as live-wire and live-lane, for segmenting 2D/3D/4D object boundaries in a slice-by-slice fashion, and demonstrated that live-wire and live-lane are more repeatable, with a statistical significance level of P < 0.03, and are 1.5-2.5 times faster, with a statistical significance level of P < 0.02, than manual tracing. In this paper, we introduce a 3D generalization of the live-wire approach for segmenting 3D/4D object boundaries which further reduces the time spent by the user in segmentation. In a 2D live-wire, given a slice, for two specified points (pixel vertices) on the boundary of the object, the best boundary segment is the minimum-cost path between the two points, described as a set of oriented pixel edges. This segment is found via Dijkstra's algorithm as the user anchors the first point and moves the cursor to indicate the second point. A complete 2D boundary is identified as a set of consecutive boundary segments forming a "closed", "connected", "oriented" contour. The strategy of the 3D extension is that, first, users specify contours via live-wiring on a few slices that are orthogonal to the natural slices of the original scene. If these slices are selected strategically, then we have a sufficient number of points on the 3D boundary of the object to subsequently trace optimum boundary segments automatically in all natural slices of the 3D scene. A 3D object boundary may define multiple 2D boundaries per slice. The points on each 2D boundary form an ordered set such that when the best boundary segment is computed between each pair of consecutive points, a closed, connected, oriented boundary results. The ordered set of points on each 2D boundary is found from the way the users select the orthogonal slices. Based on several validation studies involving segmentation of the bones of the foot in MR images, we found that the 3D extension of live-wire is more repeatable, with a statistical significance level of P < 0.0001, and 2-6 times faster, with a statistical significance level of P < 0.01, than the 2D live-wire method, and 3-15 times faster than manual tracing.

Normal kinematics of the interosseous membrane during forearm pronation-supination--a three-dimensional MRI study

We studied in vivo dynamic shape changes of the interosseous membrane (IOM) during forearm rotation using three-dimensional magnetic resonance imaging (3D-MRI), and simultaneously analysed 3D-motion of the forearm rotation. Wavy deformities were seen in the IOM in the pronated position, and similar small changes were also seen at maximum supination (average 82 degrees ) and in the neutral position. These dynamic changes mainly occurred in the membranous part of the IOM, whereas the tendinous part demonstrated minimal dynamic changes during rotation in all subjects. On the dorsal aspect, deformity around the dorsal oblique cord was seen at maximum pronation. From this 3D-MRI observation, the tendinous part is considered to be taut during rotation to provide stability between the radius and ulna, because of its straightness and less dynamic changes. The more deformable membranous part is important to allow for smooth rotation, since it lies at a distance from the rotation axis. Inelasticity developing in the membranous part from trauma may pre-dispose to pronation-supination contracture. The radius rotated around the ulna from maximum supination to 45 degrees pronation. At maximum pronation (average 75 degrees ), the radius translated average 1.8 mm palmarly and rotated average 4.0 degrees ulnarward on the ulna. Incongruity of the distal radioulnar joint, contraction of the pronator quadratus and torsion between the radius and ulna at maximum pronation may produce this irregular motion of the radius and cause the dynamic changes of the IOM.

An ultra-fast user-steered image segmentation paradigm: live wire on the fly

We have been developing general user steered image segmentation strategies for routine use in applications involving a large number of data sets. In the past, we have presented three segmentation paradigms: live wire, live lane, and a three-dimensional (3-D) extension of the live-wire method. In this paper, we introduce an ultra-fast live-wire method, referred to as live wire on the fly, for further reducing user's time compared to the basic live-wire method. In live wire, 3-D/four-dimensional (4-D) object boundaries are segmented in a slice-by-slice fashion. To segment a two-dimensional (2-D) boundary, the user initially picks a point on the boundary and all possible minimum-cost paths from this point to all other points in the image are computed via Dijkstra's algorithm. Subsequently, a live wire is displayed in real time from the initial point to any subsequent position taken by the cursor. If the cursor is close to the desired boundary, the live wire snaps on to the boundary. The cursor is then deposited and a new live-wire segment is found next. The entire 2-D boundary is specified via a set of live-wire segments in this fashion. A drawback of this method is that the speed of optimal path computation depends on image size. On modestly powered computers, for images of even modest size, some sluggishness appears in user interaction, which reduces the overall segmentation efficiency. In this work, we solve this problem by exploiting some known properties of graphs to avoid unnecessary minimum-cost path computation during segmentation. In live wire on the fly, when the user selects a point on the boundary the live-wire segment is computed and displayed in real time from the selected point to any subsequent position of the cursor in the image, even for large images and even on low-powered computers. Based on 492 tracing experiments from an actual medical application, we demonstrate that live wire on the fly is 1.3-31 times faster than live wire for actual segmentation for varying image sizes, although the pure computational part alone is found to be about 120 times faster.

A characterization of the geometric architecture of the peritalar joint complex via MRI: an aid to the classification of foot type

The purpose of this work is to study the architecture of the rearfoot using in vivo MR image data. Each data set used in this study is made of sixty sagittal slices of the foot acquired in a 1.5-T commercial GE MR system. We use the live-wire method to delineate boundaries and form the surfaces of the bones. In the first part of this work, we describe a new method to characterize the three-dimensional (3-D) relationships of four bones of the peritalar complex and apply this description technique to data sets from ten normal subjects and from seven pathological cases. In the second part, we propose a procedure to classify feet, based on the values of these new architectural parameters. We conclude that this noninvasive method offers a unique tool to characterize the 3-D architecture of the feet in live patients, based on a set of new architectural parameters. This can be integrated into a set of tools to improve diagnosis and treatment of foot malformations.

Three-dimensional magnetic resonance imaging of the interosseous membrane of forearm: a new method using fuzzy reasoning

We now report newly developed three-dimensional magnetic resonance imaging (3D-MRI) system which is based on semiautomatic tissue extraction from the axial MR images utilizing the fuzzy reasoning calculation method and 3D-image reconstruction with surface rendering. We also studied normal in vivo dynamic changes of the interosseous membrane (IOM) of forearm during rotation using this 3D-MRI. Serial axial MRI of right forearms of five healthy volunteers was obtained in five rotational positions, and extraction and 3D-reconstruction of the radius, ulna, and IOM was made using the system. Extraction results were well with the fuzzy reasoning method. 3D-MRI of the radius and ulna, IOM were reconstructed from these images respectively, and their 3D-shapes were almost identical to the anatomic shape. 3D-MRI showed there were wavy deformities on the IOM in pronation position in the all five subjects and dorsiflexion on the most dorsal portion of the IOM at maximum supination in three forearms. In neutral position, the IOM of all five volunteers was almost flat. From anatomic orientation, these dynamic changes of the IOM mainly occurred at the membranous portion, which is soft, thin, and elastic. Otherwise, the tendinous portion which is a thick and strong complex of 5 to 10 bundles run from proximal one third of the radius to distal one fourth of the ulna, demonstrated minimal dynamic changes on the 3D-MRI. Therefore, the tendinous portion is considered to be taut during rotation to provide stability between the radius and the ulna, while the membranous portion is easy to deform and allowing smooth rotation. Furthermore, because of wide-use, our 3D-MRI system is useful for in vivo analysis of soft tissue kinesiology in normal and abnormal musculoskeletal systems.

Analysis of in vivo 3-D internal kinematics of the joints of the foot

This paper describes a methodology for the analysis of three-dimensional (3-D) kinematics of live joints of the foot based on tomographic image data acquired via magnetic resonance (MR) imaging. A mechanical jig facilitates acquisition of MR images corresponding to different positions of the joint in a pronation-supination motion. The surfaces of the individual tarsal bones are constructed by segmenting the MR images. A mathematical description of the motion of the individual bones and of their relative motion is derived by computing the rigid transformation required to match the centroids and the principal axes of the surfaces. The mathematically described motion is animated via surface renditions of the bones. The kinematics of the bones are analyzed based on features extracted from the motion description and on how they vary with motion. Based on 17 joints that have been imaged, which includes an abnormal joint and the same joint after surgical correction, we conclude that this methodology offers a practical tool for measuring internal 3-D kinematics of joints in vivo and for characterizing and quantifying with specificity normal kinematics and their pathological deviations. Some of the 3-D kinematic animations generated using the methods of this paper for normal joints can be seen at: http:(/)/www.mipg.upenn.edu.

An objective comparison of 3-D image interpolation methods

To aid in the display, manipulation, and analysis of biomedical image data, they usually need to he converted to data of isotropic discretization through the process of interpolation. Traditional techniques consist of direct interpolation of the grey values. When user interaction is called for in image segmentation, as a consequence of these interpolation methods, the user needs to segment a much greater (typically 4-10x) amount of data. To mitigate this problem, a method called shape-based interpolation of binary data was developed 121. Besides significantly reducing user time, this method has been shown to provide more accurate results than grey-level interpolation. We proposed an approach for the interpolation of grey data of arbitrary dimensionality that generalized the shape-based method from binary to grey data. This method has characteristics similar to those of the binary shape-based method. In particular, we showed preliminary evidence that it produced more accurate results than conventional grey-level interpolation methods. In this paper, concentrating on the three-dimensional (3-D) interpolation problem, we compare statistically the accuracy of eight different methods: nearest-neighbor, linear grey-level, grey-level cubic spline, grey-level modified cubic spline, Goshtasby et al., and three methods from the grey-level shape-based class. A population of patient magnetic resonance and computed tomography images, corresponding to different parts of the human anatomy, coming from different three-dimensional imaging applications, are utilized for comparison. Each slice in these data sets is estimated by each interpolation method and compared to the original slice at the same location using three measures: mean-squared difference, number of sites of disagreement, and largest difference. The methods are statistically compared pairwise based on these measures. The shape-based methods statistically significantly outperformed all other methods in all measures in all applications considered here with a statistical relevance ranging from 10% to 32% (mean = 15%) for mean-squared difference.