Xavier Bonnet

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.

Skeletal landmarks for TKR implantations: Evaluation of their accuracy using EOS imaging acquisition system

INTRODUCTION Lower extremity alignment remains one essential objective during total knee replacement. Implants positioning analysis requires selecting reliable skeletal landmarks. Our objective was to in vivo evaluate the precision of the implemented skeletal landmarks. This evaluation was based on multiple three-dimensional (3D) computer reconstructions of the lower extremity derived from an EOS biplanar low-dose X-ray system acquisition. A 3D angle measurement protocol was used. HYPOTHESIS Currently defined landmarks carry a tolerable uncertainty margin, which can still probably be further improved. MATERIAL AND METHODS Nine lower extremity 3D computer reconstructions were obtained from an EOS protocol based on seven simultaneous A-P and lateral views performed in standing position. A database was established by four operators; finally, building up a total of 99 in vivo 3D reconstructions of these nine lower extremities. Specific algorithms were used for such 3D reconstructions of lower extremities based on bone points and pre-identified contours on X-ray. Four femoral landmarks and four tibial landmarks were thus defined. For each bone and each landmark studied, a mean landmark for the 11 consecutive series elements was established. The deviation from each constructed landmark to the corresponding mean landmark was calculated based on the anteroposterior (x), longitudinal (y) and mediolateral axes (z), in translation (Tx, Ty, Tz) and in rotation (Rx, Ry, Rz). Uncertainty was estimated by the 95% confidence interval (95% CI). RESULTS The landmarks located at the middle of the segment joining the center of each posterior condyle and at the barycenter of the plateaux showed a greater reliability; these landmarks uncertainty (95% CI) of Tx, Ty, Tz was less than 1, 0.5, 1.5 mm for the femur and 1.5, 0.6, 0.6 mm for the tibia, respectively. The femoral landmarks using the center or posterior edge of the posterior condyles to define the mediolateral axis were retained; for rotations Rx, Ry, and Rz, uncertainty remained less than 0.3, 4, and 0.5 degrees. All of the tibial landmarks had a comparable reliability in rotation, 95% of the Rx and Rz deviations were under 0.5 and 1.3 degrees, respectively, with a mean error less than 1 degrees . For the tibial rotation Ry, the mean error was greater (4 degrees), with uncertainty (95% CI) at 11.2 degrees. All tibial translations showed a mean error of 1 mm. The 3D implantation angles were measured on two patients using preoperative 3D skeletal reconstructions and 3D geometric models of the implants repositioned on postoperative EOS knee X-rays. DISCUSSION The posterior condyles are rarely involved in the arthritic wear process, making them an anatomic landmark of choice in the analysis of the femoral component positioning. The femoral landmarks using the posterior condyles were sufficiently reliable for clinical use. However, the posterior contours of the tibial plateaux were less precise. The knees should be staggered from an anteroposterior perspective on the EOS lateral images so that they can be visualized separately. The anatomic zones on which the skeletal landmarks are based are usually removed by the bone cuts, making it preferable to save the preoperative computer reconstructions to analyze the postimplantation 3D reconstruction. CONCLUSION The lower extremity skeletal landmarks precision relates to the quality of the corresponding 3D reconstructions. Except for tibial rotation, all the translation and rotation parameters were estimated within a mean error margin inferior to 1.2 mm and 1.3 degrees, respectively. Making the reconstruction algorithms more robust would render certain anatomic zones even more precise. Biplanar low-dose EOS X-ray system is a tool of the future to generate 3D knee X-rays that can improve the evaluation and follow-up of total knee arthroplasty patients.

Influence of the Geometry of a Ball-and-socket Intervertebral Prosthesis at the Cervical Spine: A Finite Element Study

Study Design. A conceptual study of the influence of the geometry of an articulated disc prosthesis at the cervical level using a 3-dimensional nonlinear finite element model. Objective. To investigate how the mechanical behavior of the functional spinal unit is affected by the position of the center and the size of the radius of a ball-and-socket design at the cervical level. Summary of Background Data. Little is known about the changes in kinematics and internal efforts after intervertebral disc replacement at the cervical spine, specifically regarding the influence of the geometry of the articulated prosthesis. Methods. A ball-and-socket artificial disc was integrated in a validated 3-dimensional nonlinear finite element model of the cervical spine (posterior geometric center, large radius). The model was loaded in flexion, extension, lateral bending, and axial torsion. Two variant designs were investigated: anterior center and small radius. The intervertebral range of motion, the mean center of rotation, and the contact forces in the facet joints and in the bearing surface of the prosthesis were investigated. Results. The range of motion was similar with all prostheses. The posterior geometric center was associated with an adequate mean center of rotation in flexion/extension. The large radius of curvature was associated with the partial unloading of the facet joints and the redistribution of the constraints at the ball-and-socket interface. Conclusion. Our data estimate the influence of the geometrical parameters of a ball-and-socket total disc replacement on kinematics and constraints at the cervical functional spinal unit. Under the experimental conditions, the facet forces were kept below their normal range in the case of the posterior center and a large radius.

Evaluation of force plate-less estimation of the trajectory of the centre of pressure during gait. Comparison of two anthropometric models

The estimation of the trajectory of the centre of pressure during gait is possible without using force plate by modelling the whole body as a multi-segment chain. The kinematics and inertial parameters of each segment are necessary to determine the ground reaction forces and moments. The position of the centre of pressure can then be calculated at each frame of time. The objective of the study was to evaluate the accuracy of the estimation of the position of the centre of pressure during gait obtained without force plate data. Segment inertial parameters were determined using a proportional model and a geometric model. The modelling and calculations were computed for six volunteers and the estimated centres of pressure were compared to the centre of pressure measured using force plates considered as the gold standard. The estimation was better using the geometric model with an accuracy of 33 mm (4.1% of the peak-to-peak amplitude) on the longitudinal axis and 14.2 mm (12.9% of the peak-to-peak amplitude) on the lateral axis.

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 3 J for SSWS and 7 J for FWS at the end of the first double support phase. The second maximum appears at the end of the single support phase, reaching 15 J for SSWS and 18 J 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.

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.

Whole limb push-off work in people with transtibial amputation during slope ascent.

Unilateral transtibial amputation impairs locomotion, especially in daily living outdoor situations. As an example, slope ascent requires specific gait adjustments such as hip power generation during single support followed by ankle power generation during second double support. Hip extensor strengthening could help people with transtibial amputation for hip propulsion in slope ascent (Langlois et al. 2014). Energy storage and return (ESAR) foot-ankle prostheses have been designed to absorb and release elastic energy in an attempt to restore some functions of the amputated limb. However, it remains unclear how ESAR feet contribute to center of mass propulsion, especially during slope ascent. Simple models were recently developed to globally analyze gait in an energetic point of view by computing the center of mass mechanical work (Donelan et al. 2002; Kuo et al. 2005). Particularly, several hypotheses permit to estimate for each lower limb the whole limb push-off work during double support (Kuo et al. 2005). Using this approach, step-to-step transition was investigated during level walking, in ablebodied subjects wearing prosthetic foot (Caputo & Collins 2014) and in people with transtibial and transfemoral amputation (Houdijk et al. 2009; Bonnet et al. 2014), and in slopes in able-bodied subjects (Franz et al. 2012). Up to now, no study quantified prosthetic and contralateral push-off work during slope ascent in a below-knee amputee population. Thus, the aim of the study is to investigate center of mass mechanical work adjustments during the propulsion period during slope ascent for two inclinations of slopes compared to level walking in people with transtibial amputation.

Analysis of ankle stiffness for asymptomatic subjects and transfemoral amputees in daily living situations

in daily living situations X. Drevelle*, C. Villa, X. Bonnet, J. Bascou, I. Loiret and H. Pillet INI, Centre d’Etude et de Recherche sur l’Appareillage des Handicapés, BP 50719 57147 Woippy Cedex, France; Arts et Métiers ParisTech, LBM, 151 boulevard de l’Hôpital, 75013 Paris, France; PROTEOR, 6 rue de la redoute 21250 Seurre, France; Centre de médecine physique et de réadaptation Louis Pierquin IRR-UGECAM Nord – Est 75, Boulevard Lobau, CS 34209, 54042 Nancy Cedex, France

Foot-flat period estimation during daily living situations of asymptomatic and lower limb amputee subjects.

his work was supported by the French National Research Agency [grant number ANR-292 2010-TECS-020].

Apport du système EOS® dans l’analyse expérimentale de la cinématique fémoropatellaire : évaluation de l’incertitude ☆

BACKGROUND Accurate knowledge of knee joint kinematics, especially patellofemoral joint kinematics,is essential for prosthetic evaluation so as to further improve total knee arthroplasty performances. Improving the evaluation of the functioning of the extensor apparatus appears,in this respect, particularly important in this optimization effort. OBJECTIVES The aim of this study was to propose a new experimental setup for the analysis of knee joint kinematics and to validate its relevance in terms of accuracy and uncertainty.The technique developed herein combines 3D reconstruction imaging with the use of a motion capture system. MATERIAL AND METHODS Eight pairs of fresh-frozen cadaver specimens with no evidence of previous knee surgery were studied using a new test rig where the femur remains fixed and the tibia is free to rotate. The flexion-extension cycles were executed using computer-controlled traction of the quadriceps tendon combined with an antagonist force applied to the distal part of the tibia. Knee joint kinematics were tracked using an optoelectronic motion capture system after a preliminary stage of data acquisition of bone geometry and markers position. This stage was carried out using a new digital stereophotogrammetric system, EOS, combined with specific 3D reconstruction software that also determined the coordinate system used in the kinematic analysis. The resulting uncertainty was assessed as was its impact on the estimated kinematics. RESULTS Test results on eight knees validated the setup designed for the analysis of knee joint kinematics during the flexion-extension cycle. More specifically, the statistical results show that measurement uncertainty for rotations and translations remains below 0.4 and 1.8 mm,respectively, for the tibia and 0.4 and 1.2 mm for the patella (+/- 2 S.D. for all four measurements). DISCUSSION The combination of 3D imaging and motion capture enables the proposed method to track the real-time motion of any bone segment during knee flexion-extension cycle. In particular,the new test rig introduced in this paper allows in vitro measurements of the patello femoral and tibiofemoral kinematics with a good level of accuracy. Moreover, this personalized experimental analysis can provide a more objective approach to the evaluation of knee implants as well as the validation of the finite-elements-based models of the patellofemoral joint.