Florent Moissenet

A 3D lower limb musculoskeletal model for simultaneous estimation of musculo-tendon, joint contact, ligament and bone forces during gait

Musculo-tendon forces and joint reaction forces are typically estimated using a two-step method, computing first the musculo-tendon forces by a static optimization procedure and then deducing the joint reaction forces from the force equilibrium. However, this method does not allow studying the interactions between musculo-tendon forces and joint reaction forces in establishing this equilibrium and the joint reaction forces are usually overestimated. This study introduces a new 3D lower limb musculoskeletal model based on a one-step static optimization procedure allowing simultaneous musculo-tendon, joint contact, ligament and bone forces estimation during gait. It is postulated that this approach, by giving access to the forces transmitted by these musculoskeletal structures at hip, tibiofemoral, patellofemoral and ankle joints, modeled using anatomically consistent kinematic models, should ease the validation of the model using joint contact forces measured with instrumented prostheses. A blinded validation based on four datasets was made under two different minimization conditions (i.e., C1 - only musculo-tendon forces are minimized, and C2 - musculo-tendon, joint contact, ligament and bone forces are minimized while focusing more specifically on tibiofemoral joint contacts). The results show that the model is able to estimate in most cases the correct timing of musculo-tendon forces during normal gait (i.e., the mean coefficient of active/inactive state concordance between estimated musculo-tendon force and measured EMG envelopes was C1: 65.87% and C2: 60.46%). The results also showed that the model is potentially able to well estimate joint contact, ligament and bone forces and more specifically medial (i.e., the mean RMSE between estimated joint contact force and in vivo measurement was C1: 1.14BW and C2: 0.39BW) and lateral (i.e., C1: 0.65BW and C2: 0.28BW) tibiofemoral contact forces during normal gait. However, the results remain highly influenced by the optimization weights that can bring to somewhat aphysiological musculo-tendon forces.

Influence of joint models on lower-limb musculo-tendon forces and three-dimensional joint reaction forces during gait:

Several three-dimensional (3D) lower-limb musculo-skeletal models have been developed for gait analysis and different hip, knee and ankle joint models have been considered in the literature. Conversely to the influence of the musculo-tendon geometry, the influence of the joint models - i.e. number of degrees of freedom and passive joint moments - on the estimated musculo-tendon forces and 3D joint reaction forces has not been extensively examined. In this paper musculo-tendon forces and 3D joint reaction forces have been estimated for one subject and one gait cycle with nine variations of a musculoskeletal model and outputs have been compared to measured electromyographic signals and knee joint contact forces. The model outputs are generally in line with the measured signals. However, the 3D joint reaction forces were higher than published values and the contact forces measured for the subject. The results of this study show that, with more degrees of freedom in the model, the musculo-tendon forces and the 3D joint reaction forces tend to increase but with some redistribution between the muscles. In addition, when taking into account passive joint moments, the 3D joint reaction forces tend to decrease during the stance phase and increase during the swing phase. Although further investigations are needed, a five-degree-of-freedom lower-limb musculo-skeletal model with some angle-dependent joint coupling and stiffness seems to provide satisfactory musculo-tendon forces and 3D joint reaction forces.

Effect of various upper limb multibody models on soft tissue artefact correction: A case study

Soft tissue artefacts (STA) introduce errors in joint kinematics when using cutaneous markers, especially on the scapula. Both segmental optimisation and multibody kinematics optimisation (MKO) algorithms have been developed to improve kinematics estimates. MKO based on a chain model with joint constraints avoids apparent joint dislocation but is sensitive to the biofidelity of chosen joint constraints. Since no recommendation exists for the scapula, our objective was to determine the best models to accurately estimate its kinematics. One participant was equipped with skin markers and with an intracortical pin screwed in the scapula. Segmental optimisation and MKO for 24-chain models (including four variations of the scapulothoracic joint) were compared against the pin-derived kinematics using root mean square error (RMSE) on Cardan angles. Segmental optimisation led to an accurate scapula kinematics (1.1°≤RMSE≤3.3°) even for high arm elevation angles. When MKO was applied, no clinically significant difference was found between the different scapulothoracic models (0.9°≤RMSE≤4.1°) except when a free scapulothoracic joint was modelled (1.9°≤RMSE≤9.6°). To conclude, using MKO as a STA correction method was not more accurate than segmental optimisation for estimating scapula kinematics.

Kinematic models of the upper limb joints for multibody kinematics optimisation: An overview

Soft tissue artefact (STA), i.e. the motion of the skin, fat and muscles gliding on the underlying bone, may lead to a marker position error reaching up to 8.7cm for the particular case of the scapula. Multibody kinematics optimisation (MKO) is one of the most efficient approaches used to reduce STA. It consists in minimising the distance between the positions of experimental markers on a subject skin and the simulated positions of the same markers embedded on a kinematic model. However, the efficiency of MKO directly relies on the chosen kinematic model. This paper proposes an overview of the different upper limb models available in the literature and a discussion about their applicability to MKO. The advantages of each joint model with respect to its biofidelity to functional anatomy are detailed both for the shoulder and the forearm areas. Models capabilities of personalisation and of adaptation to pathological cases are also discussed. Concerning model efficiency in terms of STA reduction in MKO algorithms, a lack of quantitative assessment in the literature is noted. In priority, future studies should concern the evaluation and quantification of STA reduction depending on upper limb joint constraints.

EMG-based validation of musculo-skeletal models for gait analysis

Musculo-skeletal models are the useful biomechanical tools for a better understanding and treatment of orthopaedic and neurological pathologies. However, the difficulty of validating the results of such models is a wellknown issue (Prilutsky and Zatsiorsky 2002). On the one hand, quantitative validation is possible at the level of tendon forces, bone forces or joint contact forces using invasive devices, e.g. instrumented prosthesis (Kinney et al. 2013). However, this quantitative validation deals with few patients. On the other hand, qualitative validation is possible at the level of musculo-tendon forces (or muscular activations) with the surface electromyography (EMG) envelopes. This is possible for any subject, but only for superficial muscles and the quality of the EMG measurements is crucial. In dynamic tasks, subjective comparison is commonly performed although assessment of the pattern correlations may be applicable (Prilutsky and Zatsiorsky 2002). Otherwise, the active/inactive state concordance between musculo-tendon forces and EMG envelopes (Pedersen et al. 1987; Dickerson et al. 2008) seems a promising semi-quantitative validation approach. This study proposes a specific application of the active/ inactive state concordance to the gait analysis. The semiquantitative validation of a previously developed musculoskeletal model of the lower limb is carried out using the data of patients equipped with instrumented knee prostheses. Therefore, a quantitative validation of the medial and lateral knee contact forces is also performed.

Influence of the Level of Muscular Redundancy on the Validity of a Musculoskeletal Model

While recent literature has clearly demonstrated that an extensive personalization of the musculoskeletal models was necessary to reach high accuracy, several components of the generic models may be further investigated before defining subject-specific parameters. Among others, the choice in muscular geometry and thus the level of muscular redundancy in the model may have a noticeable influence on the predicted musculotendon and joint contact forces. In this context, the aim of this study was to investigate if the level of muscular redundancy can contribute or not to reduce inaccuracies in tibiofemoral contact forces predictions. For that, the dataset disseminated through the Sixth Grand Challenge Competition to Predict In Vivo Knee Loads was applied to a versatile 3D lower limb musculoskeletal model in which two muscular geometries (i.e., two different levels of muscular redundancy) were implemented. This dataset provides tibiofemoral implant measurements for both medial and lateral compartments and thus allows evaluation of the validity of the model predictions. The results suggest that an increase of the level of muscular redundancy corresponds to a better accuracy of total tibiofemoral contact force whatever the gait pattern investigated. However, the medial and lateral contact forces ratio and accuracy were not necessarily improved when increasing the level of muscular redundancy and may thus be attributed to other parameters such as the location of contact points. To conclude, the muscular geometry, among other components of the generic model, has a noticeable impact on joint contact forces predictions and may thus be correctly chosen even before trying to personalize the model.

Alterations of musculoskeletal models for a more accurate estimation of lower limb joint contact forces during normal gait: A systematic review

Musculoskeletal modelling is a methodology used to investigate joint contact forces during a movement. High accuracy in the estimation of the hip or knee joint contact forces can be obtained with subject-specific models. However, construction of subject-specific models remains time consuming and expensive. The purpose of this systematic review of the literature was to identify what alterations can be made on generic (i.e. literature-based, without any subject-specific measurement other than body size and weight) musculoskeletal models to obtain a better estimation of the joint contact forces. The impact of these alterations on the accuracy of the estimated joint contact forces were appraised. The systematic search yielded to 141 articles and 24 papers were included in the review. Different strategies of alterations were found: skeletal and joint model (e.g. number of degrees of freedom, knee alignment), muscle model (e.g. Hill-type muscle parameters, level of muscular redundancy), and optimisation problem (e.g. objective function, design variables, constraints). All these alterations had an impact on joint contact force accuracy, so demonstrating the potential for improving the model predictions without necessarily involving costly and time consuming medical images. However, due to discrepancies in the reported evidence about this impact and despite a high quality of the reviewed studies, it was not possible to highlight any trend defining which alteration had the largest impact.

Proposition of a Classification of Adult Patients with Hemiparesis in Chronic Phase.

Background Patients who have developed hemiparesis as a result of a central nervous system lesion, often experience reduced walking capacity and worse gait quality. Although clinically, similar gait patterns have been observed, presently, no clinically driven classification has been validated to group these patients’ gait abnormalities at the level of the hip, knee and ankle joints. This study has thus intended to put forward a new gait classification for adult patients with hemiparesis in chronic phase, and to validate its discriminatory capacity. Methods and Findings Twenty-six patients with hemiparesis were included in this observational study. Following a clinical examination, a clinical gait analysis, complemented by a video analysis, was performed whereby participants were requested to walk spontaneously on a 10m walkway. A patient’s classification was established from clinical examination data and video analysis. This classification was made up of three groups, including two sub-groups, defined with key abnormalities observed whilst walking. Statistical analysis was achieved on the basis of 25 parameters resulting from the clinical gait analysis in order to assess the discriminatory characteristic of the classification as displayed by the walking speed and kinematic parameters. Results revealed that the parameters related to the discriminant criteria of the proposed classification were all significantly different between groups and subgroups. More generally, nearly two thirds of the 25 parameters showed significant differences (p<0.05) between the groups and sub-groups. However, prior to being fully validated, this classification must still be tested on a larger number of patients, and the repeatability of inter-operator measures must be assessed. Conclusions This classification enables patients to be grouped on the basis of key abnormalities observed whilst walking and has the advantage of being able to be used in clinical routines without necessitating complex apparatus. In the midterm, this classification may allow a decision-tree of therapies to be developed on the basis of the group in which the patient has been categorised.

Control of Stroke-Related Genu Recurvatum With Prolonged Timing of Dorsiflexor Functional Electrical Stimulation: A Case Study.

BACKGROUND AND PURPOSE Abnormal knee hyperextension during the stance phase (genu recurvatum) is a common gait abnormality in persons with hemiparesis due to stroke. While ankle-foot orthoses (AFOs) are often used to prevent genu recurvatum by maintaining ankle dorsiflexion during the stance phase, AFOs reduce ankle joint mobility. Functional electrical stimulation (FES) is an alternative to the use of AFO for producing appropriately timed ankle dorsiflexion and with prolonged timing may also have value for reducing genu recurvatum. CASE DESCRIPTION A 51-year-old man with chronic stroke was the subject of this case study. The patient had excessive plantarflexion during stance phase (ie, dynamic equinus foot), with associated genu recurvatum. INTERVENTION Evaluation included clinical examination, instrumented gait analysis, 10-meter walk test, and 6-minute walk test. The patient underwent a trial of botulinum toxin to the plantarflexor muscles that was not effective for controlling the genu recurvatum. A subsequent trial with surface FES to elicit dorsiflexion during gait was effective, and he subsequently received an implanted FES system. OUTCOMES Stimulation-induced contraction of the dorsiflexors during terminal swing phase resulted in improved ankle dorsiflexion at initial contact. Moreover, extension of stimulation into the loading phase ensured tibial advancement, which limited knee hyperextension. The patient was reevaluated 12 months following implantation with continued positive outcomes. DISCUSSION This case study illustrates the potential value of prolonged timing of dorsiflexor FES to manage genu recurvatum attributed to a dynamic equinus foot in a stroke survivor.

Comparison and validation of five scapulothoracic models for correcting soft tissue artefact through multibody optimisation

Comparison and validation of five scapulothoracic models for correcting soft tissue artefact through multibody optimisation A. Naaim, F. Moissenet, R. Dumas, M. Begon & L. Chèze To cite this article: A. Naaim, F. Moissenet, R. Dumas, M. Begon & L. Chèze (2015) Comparison and validation of five scapulothoracic models for correcting soft tissue artefact through multibody optimisation, Computer Methods in Biomechanics and Biomedical Engineering, 18:sup1, 2014-2015, DOI: 10.1080/10255842.2015.1069561 To link to this article: http://dx.doi.org/10.1080/10255842.2015.1069561