Spinopelvic sagittal alignment of patients with transfemoral amputation.

PURPOSE: This study aims to describe the spinopelvic sagittal alignment in transfemoral amputees (TFAs) from a radiologic study of the spine with a postural approach to better understand the high prevalence of low back pain (LBP) in this population. METHODS: TFAs underwent X-rays with 3-D reconstructions of the full spine and pelvis. Sagittal parameters were analyzed and compared to the literature. Differences between TFAs with and without LBP were also observed. RESULTS: Twelve subjects have been prospectively included (TFA-LBP group (n = 5) and TFA-NoP group (n = 7)). Four of the five subjects of the TFA-LBP group and two of the seven in TFAs-NoP group had an imbalanced sagittal posture, especially regarding the T9-tilt, significantly higher in the TFA-LBP group than in the TFA-NoP (p = 0.046). Eight subjects (6 TFA-NoP and 2 TFA-LBP) had abnormal low value of thoracic kyphosis (TK). Moreover, the mean angle of TK in the TFA-NoP group was lower than in the TFA-LBP group (p = 0.0511). CONCLUSION: In the considered sample, TFAs often present a sagittal imbalance. A low TK angle seems to be associated with the absence of LBP. It can be hypothesized that this compensatory mechanism of the sagittal imbalance is the most accessible in this population. This study emphasizes the importance of considering the sagittal balance of the pelvis and the spine in patients with a TFA to better understand the high prevalence of LBP in this population. It should be completed by the analysis of the spinopelvic balance and the lower limbs in 3D. These slides can be retrieved under Electronic Supplementary Material.

Axial plane dissimilarities of two identical Lenke-type 6C scoliosis cases visualized and analyzed by vertebral vectors.

PURPOSE: The global appearance of scoliosis in the horizontal plane is not really known. Therefore, the aims of this study were to analyze scoliosis in the horizontal plane using vertebral vectors in two patients classified with the same Lenke group, and to highlight the importance of the information obtained from these vertebral vector-based top-view images in clinical practice. METHODS: Two identical cases of scoliosis were selected, based on preoperative full-body standing anteroposterior and lateral radiographs obtained by the EOS™ 2D/3D system. Three-dimensional (3D) surface reconstructions of the spinal curves were performed by using sterEOS™ 3D software before and after surgery. In both patients, we also determined the vertebral vectors and horizontal plane coordinates for analyzing the curves mathematically before and after surgery. RESULTS: Despite the identical appearance of spinal curves in the frontal and sagittal planes, the horizontal views seemed to be significantly different. The vertebral vectors in the horizontal plane provided different types of parameters regarding scoliosis and the impact of surgical treatment: reducing lateral deviations, achieving harmony of the curves in the sagittal plane, and reducing rotations in the horizontal plane. CONCLUSIONS: Vertebral vectors allow the evolution of scoliosis curve projections in the horizontal plane before and after surgical treatment, along with representation of the entire spine. The top view in the horizontal plane is essential to completely evaluate the scoliosis curves, because, despite the similar representations in the frontal and sagittal planes, the occurrence of scoliosis in the horizontal plane can be completely different. These slides can be retrieved under Electronic Supplementary Material.

Cross-Slope and Level Walking Strategies During Swing in Individuals With Lower Limb Amputation.

OBJECTIVE: To quantitatively analyze prosthetic limb swing phase gait strategies used to adapt to cross slopes compared with flat surfaces. DESIGN: Cross-sectional study. SETTING: Gait laboratory. PARTICIPANTS: A volunteer sample (N=49) of individuals with transfemoral amputation (n=17), individuals with transtibial amputation (n=15), and able-bodied individuals (n=17). INTERVENTIONS: Participants walked on flat and 6° (10%) inclined cross-slope surfaces at a self-selected walking speed. MAIN OUTCOME MEASURES: Gait speed, step width, sagittal plane kinematics (ankle, knee, hip) on the prosthetic side during swing (uphill limb) and on the contralateral side during stance (downhill limb), frontal plane pelvic kinematics on the prosthetic side during swing, contralateral side ankle power during stance, and timing of gait events. RESULTS: All groups reduced gait speed and downhill limb knee flexion during the stance phase. Able-bodied participants adjusted their uphill limb ankle flexion during the swing phase. Participants with lower limb amputation used additional adjustments during the swing phase of the prosthetic limb when positioned uphill on cross slopes. Transtibial amputee participants mainly adapted with increased flexion of the residual hip and knee joints. Transfemoral amputee participants primarily compensated using increased pelvic hiking and vaulting gait strategies. CONCLUSIONS: The swing phase of the uphill limb during cross-slope walking results in compensatory mechanisms that should be addressed during rehabilitation to gain confidence and reduce avoidance when encountering cross slopes in daily life.

The horizontal plane appearances of scoliosis: what information can be obtained from top-view images?

PURPOSE: A posterior-anterior vertebral vector is proposed to facilitate visualization and understanding of scoliosis. The aim of this study was to highlight the interest of using vertebral vectors, especially in the horizontal plane, in clinical practice. METHODS: We used an EOS two-/three-dimensional (2D/3D) system and its sterEOS 3D software for 3D reconstruction of 139 normal and 814 scoliotic spines-of which 95 cases were analyzed pre-operatively and post-operatively, as well. Vertebral vectors were generated for each case. Vertebral vectors have starting points in the middle of the interpedicular segment, while they are parallel to the upper plate, ending in the middle of the segment joining the anterior end plates points, thus defining the posterior-anterior axis of vertebrae. To illustrate what information could be obtained from vertebral vector-based top-view images, representative cases of a normal spine and a thoracic scoliosis are presented. RESULTS: For a normal spine, vector projections in the transverse plane are aligned with the posterior-anterior anatomical axis. For a scoliotic spine, vector projections in the horizontal plane provide information on the lateral decompensation of the spine and the lateral displacement of vertebrae. In the horizontal plane view, vertebral rotation and projections of the sagittal curves can also be analyzed simultaneously. CONCLUSIONS: The use of posterior-anterior vertebral vector facilitates the understanding of the 3D nature of scoliosis. The approach used is simple. These results are sufficient for a first visual analysis furnishing significant clinical information in all three anatomical planes. This visualization represents a reasonable compromise between mathematical purity and practical use.

Finite element modelling of an energy-storing prosthetic foot during the stance phase of transtibial amputee gait.

Energy-storing prosthetic feet are designed to store energy during mid-stance motion and to recover it during late-stance motion. Gait analysis is the most commonly used method to characterize prosthetic foot behaviour during walking. In using this method, however, the foot is generally modelled as a rigid body. Therefore, it does not take into account the ability of the foot to deform. However, the way this deformation occurs is a key parameter of various foot properties under gait conditions. The purpose of this study is to combine finite element modelling and gait analysis in order to calculate the strain, stress and energy stored in the foot along the stance phase for self-selected and fast walking speeds. A finite element model, validated using mechanical testing, is used with boundary conditions collected experimentally from the gait analysis of a single transtibial amputee. The stress, strain and energy stored in the foot are assessed throughout the stance phase for two walking speed conditions: a self-selected walking speed (SSWS), and a fast walking speed (FWS). The first maximum in the strain energy occurs during heel loading and reaches 3J for SSWS and 7J for FWS at the end of the first double support phase. The second maximum appears at the end of the single support phase, reaching 15J for SSWS and 18J for FWS. Finite element modelling combined with gait analysis allows the calculation of parameters that are not obtainable using gait analysis alone. This modelling can be used in the process of prosthetic feet design to assess the behaviour of a prosthetic foot under specific gait conditions.

Distribution of joint work during walking on slopes among persons with transfemoral amputation.

Persons with above-knee amputation have increased energy consumption and greater difficulty in negotiating uphill and downhill slopes. Walking on slopes requires an adaptation of the positive and negative work performed by the joints of the lower limb to propel the center of mass. Modern prosthetic feet and knees can only partially adapt to changes in inclination, and the redistribution of joint work among persons with above-knee amputation is not described in the literature. Level, upslope and downslope walking (at 5% and 12% inclinations) were investigated for twelve subjects with transfemoral amputation fitted with an Energy Storing And Return foot (ESAR) and a Microprocessor controlled Prosthetic Knee (MPK) versus a control group of seventeen asymptomatic subjects. Lower limb joint and individual limb power and work were compared between prosthetic, contralateral and control limbs. The prosthesis dissipates less energy than the joints of the lower limb of the control group when descending the slope, but the demand on the contralateral limb is limited by a lower speed and step length. The huge deficit of positive work produced by the prosthetic ankle cannot be compensated by the residual hip during level and slope ascent which transfers the demand for energy production to the contralateral limb up to 40% on a 12% slope. This study highlights that prosthetic devices (ESAR foot and MPK) for persons with above-knee amputation present some limitations during slope walking that cannot be compensated by the residual hip and increase the work performed by the contralateral limb.

Dynamics of homemade aortic endografts: in vivo study in humans with computed tomography scanner modeling.

BACKGROUND: Several cases of aortic endograft rupture have been described. In most cases, they stem from component wear and perforation of the graft, leading to leakage. Friction of the stents on the graft can cause abrasion and perforate the textile. This friction results from movements inside the endograft implanted in the aorta exposed to blood flow, arterial pressure, and the movements of the aorta itself. METHODS: To study in vivo the movements of homemade stent grafts (HMSGs) designed and constructed by the surgeons at La Pitié Salpêtrière Hospital (Paris), the displacements of the metallic skeleton of the HMSG after implantation were measured using a dynamic CT scanner connected to the patient's ECG. The geometric structure of the HMSG was modeled using MATLAB software to specify the different displacements in the HMSG: angular displacements (A) (in degrees) at the sutures between two eyelets, radial displacements (R) (in millimeters for absolute values and percentile diameter for relative values) describing HMSG pulsation, and longitudinal displacements (L) (in millimeters) reflecting compression movements. These movements differ from the global movements of the aorta in the Windkessel wave: they are movements between the different levels of eyelets in the metallic structure. RESULTS: The results obtained were A = 4.5 + or - 1.5 degrees , R = 0.6 + or - 0.4 mm, R% = 4.2 + or - 2.4, and L = 0.4 + or - 0.2 mm. These values are the maximum displacements measured. They are located close to the junctions between the HMSG necks and body. These transition areas between the neck anchored in the aorta and the body, which not fixed in the aneurysm pouch, seem to be the areas of the maximum displacements, mainly angular and radial. On the other parts of the HMSG, displacements were less pronounced, approaching the CT scan's detection limit (0.1 to 0.2 mm). CONCLUSION: We made videos while modeling the amplitude of the displacements in the HMSG with a color code. This sequence could be a very good way to monitor the progression of HMSG displacements.

Validated finite element analysis of the maverick total disc prosthesis.

STUDY DESIGN: Combining in vitro tests and finite element analysis to provide a more complete picture of the role that a disc prosthesis implant would play in the biomechanics of the spine. OBJECTIVE: Analysis of the disc function after total disc prosthesis insertion with and without antero-posterior or lateral offset and in combination with adjacent fusion. SUMMARY OF BACKGROUND DATA: To avoid the risk of degenerative cascade the total disc replacement may be considered as an alternative. Few finite element analysis combined with cadaver testing under loading conditions have been published today. MATERIALS AND METHODS: In vitro tests were performed using 6 fresh human cadaver specimens to quantify the load-displacement behaviors before and after insertion of a total disc replacement (Maverick, Memphis) implant. A finite element (FE) spine model was validated with the data from the in vitro tests. This model is built on the basis of ANSYS software. The effect of the prosthesis positioning on the motion behavior at L4-L5 and on the inner loads over facets was evaluated in 4 configurations. RESULTS: The study showed that the motion behavior at the levels adjacent to the Maverick prosthesis remained the same as the intact spine, unlike a single level fusion at L5-S1. In the biomechanical study settings, Maverick prosthesis, once properly positioned, does not modify the motion behavior of the spine as compared with its intact state. The less-than-ideal positioning of the prosthesis, especially with anterior offset, affect significantly the range of motion of the spine segment and cause increase of inner load in the facets. Those results indicated a good reliability of the finite element model in representing both intact and instrumented spine segments. DISCUSSION: The in vitro test results demonstrated that Maverick disc prosthesis provides near physiologic function of a natural disc restores stability of the spine and preserves the segmental motion without undue stress on adjacent segments.To our knowledge, this study suggested for the first time the importance of the prosthesis positioning into the spine model.

The third dimension of scoliosis: The forgotten axial plane.

Idiopathic scoliosis is a three-dimensional (3D) deformity of the spine. In clinical practice, however, the diagnosis and treatment of scoliosis consider only two dimensions (2D) as they rely solely on postero-anterior (PA) and lateral radiographs. Thus, the projections of the deformity are evaluated in only the coronal and sagittal planes, whereas those in the axial plane are disregarded, precluding an accurate assessment of the 3D deformity. A universal dogma in engineering is that designing a 3D object requires drawing projections of the object in all three planes. Similarly, when dealing with a 3D deformity, knowledge of the abnormalities in all three planes is crucial, as each plane is as important as the other two planes. This article reviews the chronological development of axial plane imaging and spinal deformity measurement.

Estimation of the walking speed of individuals with transfemoral amputation from a single prosthetic shank-mounted IMU.

Microprocessor prosthetic knees, able to restore the gait of people with transfemoral amputation, are now often equipped with sensors embedded in the prosthetic shank, which could be used to assess some gait characteristics during real-life activities. In particular, an estimation of the walking speed during the locomotion of those subjects would be a relevant indicator of the performance. However, if methods have already been proposed in the literature to compute this walking speed, none are directly usable in this context and with this population. For these reasons, the current study proposed to estimate the instantaneous walking speed with a shank-embedded Inertial Measurement Units based on a biomechanical model of the prosthetic lower limb. Averaged walking speed estimation has been quantified for nine individuals with transfemoral amputation walking on a treadmill at different speeds and slopes when wearing an instrumented knee ankle prosthesis. Experimental results demonstrated the ability of the model to estimate the walking speed with an accuracy of 9% (normalized root mean squared errors over all the patients), which is consistent with previous reported walking speed estimation errors. In addition, as the walking speed estimation is instantaneous, the proposed method can provide the estimation by the end of the stance phase, which is an originality compared to other methods based on step length estimation. The present method is relevant for the estimation of walking speed during real-life activities of above-knee amputees opening the way to direct activity monitoring from the prosthesis.

Comparison of shoulder kinematic chain models and their influence on kinematics and kinetics in the study of manual wheelchair propulsion.

Several kinematic chains of the upper limbs have been designed in musculoskeletal models to investigate various upper extremity activities, including manual wheelchair propulsion. The aim of our study was to compare the effect of an ellipsoid mobilizer formulation to describe the motion of the scapulothoracic joint with respect to regression-based models on shoulder kinematics, shoulder kinetics and computational time, during manual wheelchair propulsion activities. Ten subjects, familiar with manual wheelchair propulsion, were equipped with reflective markers and performed start-up and propulsion cycles with an instrumented field wheelchair. Kinematic data obtained from the optoelectronic system and kinetic data measured by the sensors on the wheelchair were processed using the OpenSim software with three shoulder joint modeling versions (ellipsoid mobilizer, regression equations or fixed scapula) of an upper-limb musculoskeletal model. As expected, the results obtained with the three versions of the model varied, for both segment kinematics and shoulder kinetics. With respect to the model based on regression equations, the model describing the scapulothoracic joint as an ellipsoid could capture the kinematics of the upper limbs with higher fidelity. In addition, the mobilizer formulation allowed to compute consistent shoulder moments at a low computer processing cost. Further developments should be made to allow a subject-specific definition of the kinematic chain.

Three-dimensional motions of trunk and pelvis during transfemoral amputee gait.

OBJECTIVES: To identify characteristics of upper-body kinematics and torque transmission to the ground during locomotion in a group of patients with transfemoral amputation as compared with a group of asymptomatic subjects; and to investigate the influence of walking velocity and residual limb length on several characteristics of upper-body motion. DESIGN: Three-dimensional gait analysis with an optoelectronic device. SETTING: Gait laboratory. PARTICIPANTS: Twenty-seven patients with transfemoral amputation and a control group of 33 nondisabled subjects. INTERVENTIONS: Not applicable. MAIN OUTCOME MEASURES: Three-dimensional kinematics of the pelvis and the thorax and ground reaction force for amputees and control subjects. RESULTS: For subjects with transfemoral amputation, it was observed that upper-body angular ranges of motion (ROMs) increased globally as walking velocity decreased. For these subjects, specific patterns of pelvic rotation and torque transmission by the lower limbs around the vertical axis were found. The counter-rotation between the pelvic and scapular girdles was reduced. This reduction proved to be linked with the decrease of walking velocity. Walking velocity also affected all the parameters describing the motion of upper body. Pelvic ROM increased with the length of the limb decreasing. CONCLUSIONS: The huge differences found between subjects with and without amputation suggest that the motion of the upper body must be considered to enhance gait.

Is bearing resistance negligible during wheelchair locomotion? Design and validation of a testing device.

PURPOSE: Among the different resistances occurring during wheelchair locomotion and that limit the user autonomy, bearing resistance is generally neglected, based on a few studies carried out in static conditions and by manufacturer's assertion. Therefore, no special attention is generally paid to the mounting and the maintenance of manual wheelchair bearings. However, the effect of inadequate mounting or maintenance on wheelchair bearing resistance has still to be clarified. This study aimed at filling this gap by developing and validating a specific device allowing the measurement of wheelchair bearing friction, characterized by low speed velocities, with an accuracy lower than 0.003 Nm. METHODS: The bearing resistance measured by the device was compared to free deceleration measurement, intra and inter operator reproducibility were assessed. A factorial experiment allowed the effects of various functioning parameters (axial and radial loads, velocity) to be classified. RESULTS: The device allowed significant differences in the bearing resistance of static and rotating conditions to be measured, even if a relatively high proportionality was found between both conditions. The factorial experiment allowed the expected impact of the radial load on bearing resistance as well as the predominant effect of the axial load to be demonstrated. CONCLUSIONS: As a consequence, it appeared that the control of the axial load is compulsory for measurement purposes or during wheel mounting, to avoid significant increase of global resistance during wheelchair locomotion. The findings of this study could help enhancing the models which assess manual wheelchair mechanical power from its settings and use conditions.

[A new 2D and 3D imaging approach to musculoskeletal physiology and pathology with low-dose radiation and the standing position: the EOS system]. / Une nouvelle imagerie ostéo-articulaire basse dose en position debout: le systeme EOS.

Close collaboration between multidisciplinary specialists (physicists, biomecanical engineers, medical radiologists and pediatric orthopedic surgeons) has led to the development of a new low-dose radiation device named EOS. EOS has three main advantages: The use of a gaseous X-ray detector, invented by Georges Charpak (Nobel Prizewinner 1992), the dose necessary to obtain a 2D image of the skeletal system has been reduced by 8 to 10 times, while that required to obtain a 3D reconstruction from CT slices has fallen by a factor of 800 to 1000. The accuracy of the 3D reconstruction obtained with EOS is as good as that obtained with CT. The patient is examined in the standing (or seated) position, and is scanned simultaneously from head to feet, both frontally and laterally. This is a major advantage over conventional CT which requires the patient to be placed horizontally. -The 3D reconstructions of each element of the osteo-articular system are as precise as those obtained by conventional CT. EOS is also rapid, taking only 15 to 30 minutes to image the entire spine.

Evolution of vaulting strategy during locomotion of individuals with transfemoral amputation on slopes and cross-slopes compared to level walking.

BACKGROUND: Vaulting is a walking strategy qualitatively characterized in clinics by the sound ankle plantiflexion in midstance to assist prosthetic foot clearance. Even though potentially harmful, this strategy is often observed among people with transfemoral amputation to secure clearance of the prosthetic limb during swing phase. The aim of the study is to provide a quantitative analysis of the evolution of the vaulting strategy in challenging situations of daily living. METHODS: 17 persons with transfemoral amputation and 17 able-bodied people participated in the study. Kinematic and kinetic gait analyses were performed for level walking, 10% inclined cross-slope walking, 5% and 12% inclined slope ascending. To study vaulting strategy, peak of generated power at the sound ankle at midstance was identified and quantified in the different walking situations. In particular, values were compared to a vaulting threshold corresponding to a peak of generated power superior to 0.15 W/kg. FINDINGS: The vaulting threshold was exceeded for a larger proportion of people with amputation during cross-slope locomotion and slope ascent than during level walking. In addition, magnitude of the peak of generated power increased significantly compared to level walking in these situations. INTERPRETATION: Vaulting seems to be widely used by patients with transfemoral amputation in daily living situations. The number of patients using vaulting increased with the difficulty of the walking situation. Results also suggested that patients could dose the amount of vaulting according to gait environment to secure prosthetic toe clearance. During rehabilitation, vaulting should also be corrected or prevented in daily living tasks.

Morphometric analysis of one anatomic scoliotic specimen.

Idiopathic scoliosis is a 3-D deformation affecting the position of the spine in space. The regional deformity has been studied extensively but the local changes have not been widely investigated and this being mainly due to the rarity of anatomical specimens. The objective of this study was to identify a deformation pattern for idiopathic scoliosis. We thus studied one complete scoliotic specimen using a digitizing protocol developed by our research group. The anatomical specimen was selected from the Hamann-Todd Osteology Collection at the Cleveland Natural History Museum, which contains over 1,300 skeletons. We were also able to match this scoliotic specimen with one normal specimen for age, sex, race, height and weight. Each vertebra was measured by taking approximately 200 points on each surface. Parameters for each vertebra were then calculated from these sets of points. Each scoliotic vertebra was then compared with a corresponding normal vertebra of the matched specimen. We present the first findings of these measurements, which show pedicle and posterior elements changes that are thought to be secondary to the scoliotic deformation.

Mechanical work performed by individual limbs of transfemoral amputees during step-to-step transitions: Effect of walking velocity.

The greater metabolic demand during the gait of people with a transfemoral amputation limits their autonomy and walking velocity. Major modifications of the kinematic and kinetic patterns of transfemoral amputee gait quantified using gait analysis may explain their greater energy cost. Donelan et al. proposed a method called the individual limb method to explore the relationships between the gait biomechanics and metabolic cost. In the present study, we applied this method to quantify mechanical work performed by the affected and intact limbs of transfemoral amputees. We compared a cohort of six active unilateral transfemoral amputees to a control group of six asymptomatic subjects. Compared to the control group, we found that there was significantly less mechanical work produced by the affected leg and significantly more work performed by the unaffected leg during the step-to-step transition. We also found that this mechanical work increased with walking velocity; the increase was less pronounced for the affected leg and substantial for the unaffected leg. Finally, we observed that the lesser work produced by the affected leg was linked to the increase in the hip flexion moment during the late stance phase, which is necessary for initiating knee flexion in the affected leg. It is possible to quantify the mechanical work performed during gait by people with a transfemoral amputation, using the individual limb method and conventional gait laboratory equipment. The method provides information that is useful for prosthetic fitting and rehabilitation.

Influence of physical capacities of males with transtibial amputation on gait adjustments on sloped surfaces.

The aim of the study was to investigate how kinematic and kinetic adjustments between level and slope locomotion of persons with transtibial amputation are related to their individual muscular and functional capacities. A quantified gait analysis was conducted on flat and slope surfaces for seven patients with transtibial amputation and a control group of eight subjects to obtain biomechanical parameters. In addition, maximal isometric muscular strength (knee and hip extensors) and functional scores were measured. The results of this study showed that most of the persons with transtibial amputation could adapt to ramp ascent either by increasing ankle, knee, and hip flexion angles of the residual limb and/or by recruiting their hip extensors to guarantee enough hip extension power during early stance. Besides, 6-minute walk test score was shown to be a good predictor of adaptation capacities to slope ascent. In ramp descent, the increase of knee flexion moment was correlated with knee extensor strength and residual-limb length. However, no correlation was observed with functional parameters. Results show that the walking strategy adopted by persons with transtibial amputation to negotiate ramp locomotion mainly depends on their muscular capacities. Therefore, muscular strengthening should be a priority during rehabilitation.

A method for the field assessment of rolling resistance properties of manual wheelchairs.

This article presents an examination and validation of a method to measure the field deceleration of a manual wheelchair (MWC) and to calculate the rolling resistances properties of the front and rear wheels. This method was based on the measurements of the MWC deceleration for various load settings from a 3D accelerometer. A mechanical model of MWC deceleration was developed which allowed computing the rolling resistance factors of front and rear wheels on a tested surface. Four deceleration sets were conducted on two paths on the same ground to test the repeatability. Two other deceleration sets were conducted using different load settings to compute the rolling resistance parameters (RPs). The theoretical decelerations of three load settings were computed and compared with the measured decelerations. The results showed good repeatability (variations of measures represented 6-11% of the nominal values) and no statistical difference between the path results. The rolling RPs were computed and their confidence intervals were assessed. For the last three sets, no significant difference was found between the theoretical and measured decelerations. This method can determine the specific rolling resistance properties of the wheels of a MWC, and be employed to establish a catalogue of the rolling resistance properties of wheels on various surfaces.

Effects of user's actions on rolling resistance and wheelchair stability during handrim wheelchair propulsion in the field.

Currently, rolling resistance and wheelchair stability during manual wheelchair propulsion can be assessed from the loads applied on the front and rear wheels, which are determined in a static condition. However, a user's actions on the wheelchair would change these loads during locomotion, which should affect both the rolling resistance and wheelchair stability. The goal of this study was to verify these assumptions and assess how much the rolling resistance and wheelchair stability are affected by the user's actions during propulsion. For that purpose, a mechanical model was developed using measurements of an instrumented wheelchair equipped with several six-component dynamometers. Experiments were performed by three subjects propelling the instrumented wheelchair over flat ground. The results showed variations over wide ranges of the fore-aft distribution of the total load, rolling resistance, wheelchair stability, wheelchair velocity and mechanical power dissipated by the rolling resistance during the propulsion cycle. In addition, the time courses of all these variables differed with the subject. Finally, this study demonstrated the possibility of assessing intra-cycle values of both rolling resistance and wheelchair stability during manual wheelchair displacements in the field, which provides a technical step towards evaluating a wheelchair user in his daily environment.