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F Lavaste

Publications and source records attributed to F Lavaste.

At least 19 recordsLinked to original sources
PubMed2006

A functional evaluation of prosthetic foot kinematics during lower-limb amputee gait.

This paper reports on a functional evaluation of prosthetic feet based on gait analysis. The aim is to analyse prosthetic feet behaviour under loads applied during gait in order to quantify user benefits for each foot. Ten traumatic amputees (six trans-tibial and four trans-femoral) were tested using their own prosthetic foot. An original protocol is presented to calculate the forefoot kinematics together with the overall body kinematics and ground reaction forces during gait. In this work, sagittal motion of the prosthetic ankle and the forefoot, time-distance parameters and ground reaction forces were examined. It is shown that an analysis of not only trans-tibial but also trans-femoral amputees provides an insight in the performance of prosthetic feet. Symmetry and prosthetic propulsive force were proved to be mainly dependant on amputation level. In contrast, the flexion of the prosthetic forefoot and several time-distance parameters are highly influenced by foot design. Correlations show influential of foot and ankle kinematics on other parameters. These results suggest that prosthetic foot efficiency depends simultaneously on foot design and gait style. The evaluation, proposed in this article, associated to clinical examination should help to achieve the best prosthetic foot match to a patient.

Adult↗
PubMed2006

Finite element model of the human neck during omni-directional impacts. Part II: relation between cervical curvature and risk of injury.

A detailed 3D FE model of the human neck was used to assess a possible relationship between risk of injury and cervical spine curvature for various impacts. A FE model was previously developed, representing the head and neck of a 50th percentile human with a normal lordotic curvature. The model behaviour was omni-directionally validated for various impacts using published results. For the present study, the model was deformed in order to obtain a straight and a kyphotic curvature, and for each geometry, rear-end, frontal, lateral and oblique impact were simulated. Although results showed similar kinematic patterns, significant differences were found in the distribution and peak values of ligament elongations, forces and moments along the cervical spine for the three configurations. It was concluded that the variability observed on the curvature of the human cervical spine may have a significant influence both on the behaviour and on the risk of injury of the neck during impact.

Cervical Vertebrae↗
PubMed2004

Three-dimensional rotations of human three-joint fingers: an optoelectronic measurement. Preliminary results.

Longitudinal axial rotations of phalanges during flexion motions of digits have scarcely been analyzed with current anatomical or radiological methods. Recent optoelectronic systems were developed for three-dimensional (3D) kinematic analysis of human motion. These systems have the advantages of being non-invasive and non-irradiating. The current study was based on the VICON optoelectronic system. A validation of the protocol was made among a sample of volunteers for further direct clinical applications. An experimental protocol was set up with adaptations to the requirements of finger analyses (multiple infrared markers inside small-sized capture volumes). The set-up and the protocol details are described. Kinematic studies consisted in recording the movements of the right hand of six volunteers (free from any visible pathology). Results were displayed for the joints of each three-joint finger with calculation of 3D rotations. Metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) flexion angles ranged from 78 degrees to 118 degrees, 72 degrees to 119 degrees and 9 degrees to 66 degrees respectively. Lateral angles ranged from 5 degrees to 39 degrees (MCP), 4 degrees to 39 degrees (PIP) and 4 degrees to 30 degrees (DIP). Mean longitudinal axial rotations of MCP, PIP and DIP joints ranged from 11 degrees pronation to 26 degrees supination. The index finger was in a global pronation position (five of the six specimens). The fourth and fifth fingers were in a global supination position in every case. The third finger was in a more variable global rotation (pronation in four of the six specimens). An experimental protocol using an optoelectronic system (VICON) has been developed for a kinematic analysis of three-joint finger. A global measure study should be initiated among a wider sample of adults. A database should be created with direct clinical applications. Patients' kinematic deficits could be graded either for standard movements (flexion/extension and abduction/adduction) or for longitudinal axial rotations.

Adult↗
PubMed2004

Rotations of three-joint fingers: a radiological study.

The aim of the current study was to test a protocol of quantification of phalangeal three-dimensional (3D) rotations during flexion of three-joint digits. Three-dimensional-specific software was developed to analyze CT reconstruction images. A protocol was carried out with six fresh-frozen upper limbs from human cadavers free from any visible pathology (three females, three males). CT millimetric slices were done for reconstruction of hand bone units. Orthonormal coordinate systems of inertia were calculated for each unit. Three-dimensional phalangeal rotations were estimated between two static positions (fingers in extension and in a fist position). Results were displayed for the joints of each three-joint finger with calculation of 3D rotations. Mean longitudinal axial rotations of metacarpophalangeal (MCP), proximal interphalangeal (PIP) and distal interphalangeal (DIP) joints ranged from 14 degrees pronation to 19 degrees supination. The index finger was in a global pronation position (4/6 specimens). The fourth and fifth fingers were in a global supination position in every case. The third finger was in a more variable global rotation (pronation in 2/6 specimens). MCP, PIP and DIP flexion angles ranged respectively from 71 degrees to 89 degrees, 65 degrees to 87 degrees, and 41degrees to 77 degrees. Lateral angles ranged from 19 degrees (ulnar angulation) to 23 degrees (radial angulation). The study of phalangeal rotations was possible in spite of a heavy protocol. This protocol could be partially automatated to speed up the analyses. Longitudinal axial rotations could be analyzed, in addition to flexion/extension or abduction/adduction rotations. CT scan reconstructions would be helpful for investigating pathological fingers. Abnormal rotations of digits could be quantified more precisely than during a current clinical examination of the hand.

Aged↗
PubMed2004

A proprioception based regulation model to estimate the trunk muscle forces.

Evaluation of loads acting on the spine requires the knowledge of the muscular forces acting on it, but muscles redundancy necessitates developing a muscle forces attribution strategy. Optimisation, EMG, or hybrid models allow evaluating muscle force patterns, yielding a unique muscular arrangement or/and requiring EMG data collection. This paper presents a regulation model of the trunk muscles based on a proprioception hypothesis, which searches to avoid the spinal joint overloading. The model is also compared to other existing models for evaluation. Compared to an optimisation model, the proposed alternative muscle pattern yielded a significant spine postero-anterior shear decrease. Compared to a model based on combination of optimisation criteria, present model better fits muscle activation observed using EMG (38% improvement). Such results suggest that the proposed model, based on regulation of all spinal components, may be more relevant from a physiologic point of view.

Abdomen↗
PubMed2004

3D finite element simulation of Cotrel-Dubousset correction.

The Cotrel-Dubousset (CD) scoliosis surgery was simulated for 10 patients with idiopathic scoliosis using a 3D finite element model (FEM) of the patient's entire spine. The geometry of the FEM was extracted from a 3D stereo-radiographic reconstruction, and mechanical properties were personalized using lateral bending films. Finally, each step of the CD correction was simulated and results were compared with the post-operative 3D stereo-radiographic reconstruction. The whole procedure was applied for 10 patients, and quantitative comparison was performed between post-operative spine configuration and predicted configuration. For all patients, mean differences between post-operative measurements and predicted values of vertebral rotation were estimated at 5 degrees (max: 13 degrees) and those for linear position at 6 mm (max: 12 mm). Furthermore, intermediate steps of surgery simulation were consistent with the literature. Then, for one scoliotic patient, the model was used to investigate three alternative surgical strategies. It was found that a one-level change in the instrumentation limit may have a significant effect on spine alignment and correction.

Biomechanical Phenomena↗
PubMed2003

Dynamic stiffness and damping of human intervertebral disc using axial oscillatory displacement under a free mass system.

The aim of this study was to analyse the dynamic response of the human intervertebral disc to vibration in a physiologically relevant frequency spectrum. Eight lumbar intervertebral discs were harvested. After preparation, each sample was subjected to a pre-loading and then dynamic compression (from 5 to 30 Hz). The dynamic compression was applied using an experimental set-up comprising a free weight loading from above and a driving oscillatory displacement from below (closest to the in vivo loading). A viscoelastic model enabled the calculation of stiffness and damping from the transfer function. From 5 Hz to 30 Hz the stiffness values are between 0.19 and 3.66 (MN/m) and the damping values between 32 and 2094 (Ns/m). The mean resonant frequency was found at 8.7 Hz. These dynamic characteristics of the intervertebral disc could be used in a three-dimensional finite elements model of the human body to study its response to vibration in the driving position.

Aged↗
PubMed2003

Explicit calibration method and specific device designed for stereoradiography.

The three-dimensional geometry of the human spine is noteworthy information that can be obtained by stereoradiographic methods. These methods are based on the identification of anatomical structures in several views which are obtained by rotation of a patient standing on a turntable. Calibration algorithms for computer vision or photogrammetry are well documented, but they generally yield calibration devices which are cumbersome for the use in clinical stereoradiography. This paper presents a calibration method adapted to a two-view stereoradiography calibration (frontal and lateral incidences) and based on a simplified geometric modeling of the radiological environment. The a priori knowledge yields four calibration equations related to the vertical and horizontal planes of both views, leading to a specific calibration procedure and device. Moreover this device is attached to the stereoradiographic system (directly integrated on the turntable) in order to facilitate clinical applications. A validation was performed on 26 dried lumbar vertebrae in order to evaluate clinical situation. The mean accuracy of the stereoradiographic reconstruction was 1.2mm.

Aged↗
PubMed2003

Dynamic stiffness and damping of porcine muscle specimens.

The aim of this study was to quantify the mechanical properties of the muscles of the buttock, using dynamic compression (5-->30 Hz). Tests were conducted in vitro on porcine muscles, using a lever arm device, which applied a dynamic load onto cylindrical samples. A two-parameter viscoelastic model allowed the calculation of stiffness and damping of the samples with respect to frequency. The average stiffness curve showed a monotonous increase (5 Hz: 8.5 kN/m-->30 Hz: 347 kN/m). Concerning damping, between 5 and 20 Hz, values were typically inferior to 300 Ns/m, which then increased till 30 Hz (556 Ns/m). The lever arm device may be used to evaluate dynamic properties of other biological tissues also.

Animals↗
PubMed2003

A biplanar reconstruction method based on 2D and 3D contours: application to the distal femur.

A three-dimensional (3D) reconstruction algorithm based on contours identification from biplanar radiographs is presented. It requires, as technical prerequisites, a method to calibrate the biplanar radiographic environment and a surface generic object (anatomic atlas model) representing the structure to be reconstructed. The reconstruction steps consist of: the definition of anatomical regions, the identification of 2D contours associated to these regions, the calculation of 3D contours and projection onto the radiographs, the associations between points of the X-rays contours and points of the projected 3D contours, the optimization of the initial solution and the optimized object deformation to minimize the distance between X-rays contours and projected 3D contours. The evaluation was performed on 8 distal femurs comparing the 3D models obtained to CT-scan reconstructions. Mean error for each distal femur was 1 mm.

Algorithms↗
PubMed2003

[Influence of proximal stem geometry and stem-cement interface characteristics on bone and cement stresses in femoral hip arthroplasty: finite element analysis].

PURPOSE OF THE STUDY: The combined effects of proximal canal filling and stem-cement surface characteristics on stresses in the cement and bone in femoral hip arthrosplasty were investigated by finite element analysis. MATERIAL AND METHODS: Our finite element study of a femoral implant fitted with a stainless steel stem was based on a set of 4 models with decreasing metaphyseal fill, designed to simulate loading before the occurrence of any deterioration in the cement-bone interface. Thus, the cement was represented fully bonded to the bone. The implant-cement interface was modeling in the bonded and debonded states. First a vertical load was applied to the implant to simulate the conditions of the bearing phase of gait. Second, a rotational load was applied to the implant. Torsional loading tests were found to be satisfactory for studying variations in shape of the proximal portion of femoral implants because they simulate the most critical loading conditions such as stair climbing or chair rising. RESULTS: With the bonded implant-cement surface, bone stresses were rather distal, whereas they were mainly proximal with the debonded implant-cement interface. Under rotational loading, debonded implants produced less normal tensile and shear stresses in the proximal portion of the cement mantle. In contrast, compressive cement stresses were higher with debonded implants. In the debonded state, the rotational stability of the implant was found to be closely related to the degree of metaphyseal fill. CONCLUSION: In conclusion, the use of implants with a debonded metal-cement interface and with optimal metaphyseal filling should preserve the cement-bone interface from excessive shear and tensile stresses, while providing good rotational stability.

Arthroplasty, Replacement, Hip↗
PubMed2002

The importance of spinopelvic parameters in patients with lumbar disc lesions.

Using a special software program we measured spinopelvic parameters on digitised radiographs of the entire spine and the pelvis of 50 patients with lumbar disc herniation and compared these with the same measurements on 30 healthy subjects. In the disc hernia group the patients had a relatively straight spine in the sagittal plane. The sacrum was more vertical, and the value of the lumbar lordosis was lower, as was the amplitude of the spinal curvatures, when compared with those of the healthy group. This results in a higher gravitational compressive force which may, in turn, lead to progressive degeneration of the discs. The anterior shift of the line of gravity may cause spinopelvic instability, and contraction of the posterior spinal muscles in trying to balance this disturbed spatial relationship may produce back pain.

Adult↗
PubMed2002

[Validation of an experimental protocol of an optoelectronic analysis of continuous active knee kinematics in vitro].

PURPOSE OF THE STUDY: In vitro experiments are particularly useful for studying kinematic changes in the normal knee exposed to experimental conditions simulating different disease states. We developed an experimental protocol allowing a kinematic analysis of the femorotibial and femoropatellar joints in healthy knees and after implantation of a knee prosthesis, using a central pivot to simulate active loaded movement from the standing to sitting position. EXPERIMENTAL SETUP: An experimental device was designed to apply force to the femur of a cadaveric specimen including the femur, the patella and the tibia. The tibia was angled in the sagittal plane and the femur was free to move in space in response to the geometric movement of the knee joint, the capsuloligamentary structures, the quadriceps tendon and gravity. Variation in the length of the quadriceps tendon controlled the flexion-extension movement. The experimental setup included computer-controlled activation allowing continuous coordinated movement of the femur relative to the tibia and of the tibia relative to the ground. Standard activations simulated movement from the standing to the sitting position. STUDY PROTOCOL: Five pairs of fresh-frozen cadaver specimens including the entire femur, patella, tibia and fibula, the capsuloligamentary and intra-articular structures of the knee, the superior and inferior tibiofibular ligaments and the quadriceps tendon were studied. The quadriceps tendon was connected to the computer-guided activation device. Reflectors were fixed onto the anterior aspect of the femur, the superior tibial epiphysis and the center of the patella. Anatomic landmarks on the femur, the tibia, and the patella were identified to determine the plane of movement of each bone in the three rotation axes and the three translation directions. Three infrared cameras recorded movements of the reflectors fixed on the bony segments and, by mathematical transformation, the movement of the corresponding bony segment, displayed in time-course curves. RESULTS: The precision of the measurements, evaluated in a previous study, was +/- 1.5 degrees for rotation and +/- 0.5 mm for translation movements. Three acquisitions were made for each experiment and produced results differing less than one degree. A qualitative analysis of femorotibial and femoropatellar kinematics was achieved for the normal knee. The automatic internal rotation of the femur during flexion was observed and the patellar kinematics were defined with six degrees of freedom. DISCUSSION: This experimental setup enables a comparison of the kinetics of a normal knee with the kinetics observed after implantation of a prosthesis on the same knee. The kinetic analysis does not involve a succession of static states but rather a continuous movement generated by the action of the quadriceps that can be loaded, simulating partial weight bearing. Using the markers fixed directly on the bones, this in vitro study allowed remarkably precise and reproducible measurements. The movements simulated regularly encountered clinical situations. The quality of the movement recorded for a given prosthesis thus provides an accurate approach to the quality of the prosthesis. The goal is not to define the exact kinematics of the normal knee but rather to compare the kinematics of the normal knee with that of the same knee after prosthesis implantation allowing an accurate method for assessing prosthesis design and studying the influence of different parameters, particularly the ligaments. Concomitant study of femorotibial and femoropatellar kinematics provides further information rarely found in the literature.

Aged↗
PubMed2002

[In vitro analysis of the continuous active patellofemoral kinematics of the normal and prosthetic knee].

PURPOSE OF THE STUDY: In vitro experiments are particularly useful for studying kinematic changes from the normal knee to experimental conditions simulating different disease states. We developed an experimental protocol allowing a kinematic analysis of the femorotibial and femoropatellar joints in the healthy knee and after implantation of a knee prosthesis, according to the central pivot during simulated active loaded movement from the standing to sitting position. EXPERIMENTAL SETUP: An experimental device was designed to apply force to the femur of a cadaveric specimen including the femur, the patella and the tibia. The tibia was angled in the sagittal plane and the femur was free to move in space in response to the geometric movement of the knee joint, the capsuloligamentary structures, the quadriceps tendon and gravity. Variation in the length of the quadriceps tendon controlled the flexion-extension movement. The experimental setup included computer-controlled activation allowing continuous coordinated movement of the femur relative to the tibia and of the tibia relative to the ground. Standard activations simulated movement from the standing to the sitting position. STUDY PROTOCOL: Five pairs of fresh-frozen cadaver specimens including the entire femur, patella, tibia and fibula, the capsuloligamentary and intra-articular structures of the knee, the superior and inferior tibiofibular ligaments and the quadriceps tendon were studied. The quadriceps tendon was connected to the computer-guided activation device. Reflectors were fixed onto the anterior aspect of the femur, the superior tibial epiphysis and the center of the patella. Anatomic landmarks on the femur, the tibia, and the patella were identified to determine the plane of movement of each bone in the three rotation axes and the three translation directions. Three infrared cameras recorded movements of the reflectors fixed on the bony segments and, by mathematical transformation, the movement of the corresponding bony segment, displayed in time-course curves. RESULTS: The patella moved in continuous fashion over the femur, directly following the angle of knee flexion with a ratio of about 60%, which was constant for all knees studied and for all configurations. The patella of healthy knees and knees implanted with a unicompartmental prosthesis exhibited medial rotation during the first 30 degrees of flexion, with a movement of about of 10 degrees, then a lateral rotation of about 10 degrees to 20 degrees when the flexion reached 90 degrees; implantation of a total knee prosthesis led to a medial rotation which was continuous from 5 degrees to 15 degrees. There was a trend towards continuous abduction of about 10 degrees. The patella exhibited a continuous anterior translation of 10 to 20 mm from the tibia with increasing knee flexion, in both normal and prosthetic knees (unicompartmental prosthesis); knees implanted with a total knee prosthesis exhibited 5 to 10 mm anterior translation from 0 degrees to 50 degrees flexion, then an equivalent posterior translation for 50 degrees to 90 degrees flexion. The patella made a continuous 5 to 10 mm medial translation movement over the tibia in both normal and prosthetic (unicompartmental) knees; knees implanted with a total knee prosthesis exhibited 0 to 5 mm lateral translation starting after 50 degrees flexion. The patella also exhibited a continuous distal translation over the tibia of about 20 to 30 mm, for all configurations. DISCUSSION: The experimental set up enables a comparison of the kinetics of a normal knee with the kinetics observed after implantation of a prosthesis on the same knee. Implantation of a unicompartmental medial prosthesis, leaving the posterior cruciate ligament intact and irrespective of the status of the anterior cruciate ligament, did not, in these experimental conditions, exhibit any significant difference in the femorotibial or femoropatellar kinetics compared with the same normal knee. Implantation of a total knee prosthesis had a significant effect on the femoropatellar kinematics, compared with the same knee before implantation. The main anomalies were related to the medial-lateral rotation of the patella which exhibited an abnormal lateral rotation, possibly favorable for subluxation; these changes were directly related to femorotibial rotation after implantation of the total prosthesis and appeared to be related to the symmetry of the femoral condyles of the prosthesis model studied, perturbing the normal automatic rotation of the knee. There is thus a strong relationship between femorotibial and femoropatellar kinetics in the total knee prosthesis.

Arthroplasty, Replacement, Knee↗
PubMed2002

[Influence of the height of the joint space on the three-dimensional kinetics of total knee prostheses and behavior of the lateral ligaments: an in vitro study].

PURPOSE OF THE STUDY: The level of the joint space can be modified after implantation of a total knee prosthesis. Likewise, ligament balance is a cardinal point of the surgical technique. The purpose of this in vitro work was to study the influence of the position of the distal tibiofemoral joint space after implantation of a total knee prosthesis on the three-dimensional kinetics of the knee joint and on the behavior of the lateral ligaments. MATERIAL AND METHOD: Total knee arthroplasty (TKA) with a posterior stabilized prosthesis was performed on seven fresh-frozen cadaver specimens. A specially-designed experimental device was used to achieve continuous knee motion simulating hip flexion from a vertical position. The Vicon optoelectronic system was used to record the femorotibial and femoropatellar kinematics in three dimensions. Two electronic goniometers were positioned on the insertions of the lateral ligaments to measure ligament displacements during knee movements. Five configurations were recorded on each knee: healthy knee, same knee after TKA, and 2-mm and 4-mm upward displacement of the prosthetic distal tibiofemoral joint space. Ligament balance at extension was preserved in all configurations. The kinematic curves obtained were compared with the coefficient of multiple correlation. RESULTS: Changing the position of the joint space had a significant effect on the kinematics of the patella (rotation and abduction-rotation) but did not have a significant effect on the femorotibial kinematics. Variations in the length of the lateral ligaments were of small amplitude. Lowering the joint space led to laxity at flexion. Raising the joint space tightened the ligaments at flexion. DISCUSSION: These results confirm our clinical impression when the level of the distal femur cut is set to achieve tension on the ligaments at knee extension. If the joint space is lowered, i.e. with a more sparing distal femur cut, the prosthesis takes up less space during flexion, leading to laxity at flexion. If the joint space is raised, i.e. with an excessive distal femur cut, the prosthesis takes up more space during flexion, tightening the lateral ligaments. CONCLUSION: The position of the joint space must be rigorously reproduced during TKA not only to maintain correct femorotibial kinematics, but most importantly to preserve patellar kinematics and proper behavior of the lateral ligaments. Ideally, the height of the joint space should be restored first, followed by control of the ligament balance. An over- or undercut of the femur can lead to defective femoropatellar kinematics and ligament tension at flexion despite good ligament balance at extension. In addition, ligament balance should not be achieved by displacing the tibial cut or by modifying the thickness of the tibial component, which would have an effect not only at extension but also at flexion.

Anthropometry↗
PubMed2002

Muscular modelling: relationship between postural default and spine overloading.

The objectives of the study are to describe and use a muscular model to compare spinal loads and muscles recruitments between an unbalanced subject (patient) and a normal volunteer. Data collection was performed and imputed into the muscular model: from sagittal X-rays, together with plantar foot pressure measurements, external loads for the L3/L4 level were calculated. Using MRI of the thoraco-lumbar region and muscular testing, a personalized muscular model was constructed. The main results are as follow: external loads for the unbalanced subject were higher because of the postural default, especially for flexion moment. Running the model, simulations showed a higher erector spinae group activation for the patient. This induced a significant difference in joint compression. Setting the maximum admissible stress of the extensor muscles of the patient to an equivalent level as the one found for the volunteer to maintain the posture, a second simulation was performed. Joint compression was reduced, but postero-anterior shear and flexion moment increased drastically. The model suggests that either the muscular system needed a stronger activation, yielding a higher joint compression and probably a muscle fatigue in such an activation level, or the spinal loads increased to a higher and probably dangerous level.

Humans↗
PubMed2002

Comparison of mechanical behaviour of normal and scoliotic vertebral segment: a preliminary numerical approach.

Specific behaviour of the scoliotic spine has already been proven. The aim of this preliminary study is to evaluate if this behaviour is mainly due to geometrical deformities or to mechanical characteristics of soft tissues. We use a kriging technique to obtain a personalized finite element model of scoliotic spine from 3D reconstructions and from an existing detailed model of normal spine. To evaluate if deformed geometry has a share in specific behaviour of scoliotic spine, numerical simulations were performed on an apical segments extracted from normal and scoliotic models and the results were compared. Average mechanical properties of normal spine were considered in both models.

Humans↗