Predicting longitudinal changes in joint contact forces in a juvenile population: Scaled generic versus subject-specific musculoskeletal models

Subject-specific musculoskeletal model use in clinical settings is limited due to development-associated time and effort burdens together with potential medical imaging unavailability. As an alternative, this study investigated consistency in estimating longitudinal changes in joint contact forces (JCF) between scaled generic and subject-specific models. For 11 children, joint kinematics and JCF were calculated using subject-specific and scaled generic models. JCF changes estimated by both models were strongly correlated for the hip and knee although JCF estimates varied between models. Findings suggest that within specified limits of accuracy, scaled generic models are sensitive enough to detect JCF changes consistent with subject-specific models

Reliability of an integrated ultrasound and stereophotogrammetric system for lower limb anatomical characterisation

Background. Lower extremity analysis for preoperative total knee and hip arthroplasty routines can increase surgery success rate and hence reduce associated costs. Current tools are limited by being invasive, limited to supine analysis, or too expensive. This study aimed to propose and validate a device, OrthoPilot®, based on the combined use of a stereophotogrammetric and ultrasound system which can in vivo and noninvasively measure varus/valgus, flexion/extension, femur and tibia torsion, and femur and tibia lengths. Methods. A phantom was measured by four operators to determine the resolution of the system. Interoperator variability was measured on three operators who measured the above six variables on both legs of three subjects in standing and supine positions. Intraoperator variability was assessed on data from three repeats from 9 subjects (18 legs). Results. All 6 variables were reliably detected on a phantom, with a resolution of 1 mm and 0.5° . Inter- and intraoperator consistency was observed for varus/valgus, flexion/extension, and length measurements on the healthy subjects in standing and supine positions (all ICC > 0.93). For torsion measurements, there was a considerable variation. Conclusion. The proposed system, when used on healthy subjects, allowed reliable measurements of key parameters for preoperative procedures in both supine and standing positions. Accuracy testing and further validation on patient populations will be the next step toward its clinical adoption

Muscle recruitment strategies can reduce joint loading during level walking

Joint inflammation, with consequent cartilage damage and pain, typically reduces functionality and affects activities of daily life in a variety of musculoskeletal diseases. Since mechanical loading is an important determinant of the disease process, a possible conservative treatment is the unloading of joints. In principle, a neuromuscular rehabilitation program aimed to promote alternative muscle recruitments could reduce the loads on the lower-limb joints during walking. The extent of joint load reduction one could expect from this approach remains unknown. Furthermore, assuming significant reductions of the load on the affected joint can be achieved, it is unclear whether, and to what extent, the other joints will be overloaded. Using subject-specific musculoskeletal models of four different participants, we computed the muscle recruitment strategies that minimised the hip, knee and ankle contact force, and predicted the contact forces such strategies induced at the other joints. Significant reductions of the peak force and impulse at the knee and hip were obtained, while only a minimal effect was found at the ankle joint. Adversely, the peak force and the impulse in non-targeted joints increased when aiming to minimize the load in an adjacent joint. These results confirm the potential of alternative muscle recruitment strategies to reduce the loading at the knee and the hip, but not at the ankle. Therefore, neuromuscular rehabilitation can be targeted to reduce the loading at affected joints but must be considered carefully in patients with multiple joints affected due to the potential adverse effects in non-targeted joints

Investigation of the dependence of joint contact forces on musculotendon parameters using a codified workflow for image-based modelling

The generation of subject-specific musculoskeletal models of the lower limb has become a feasible taskthanks to improvements in medical imaging technology and musculoskeletal modelling software.Nevertheless, clinical use of these models in paediatric applications is still limited for what concernsthe estimation of muscle and joint contact forces. Aiming to improve the current state of the art, amethodology to generate highly personalized subject-specific musculoskeletal models of the lower limbbased on magnetic resonance imaging (MRI) scans was codified as a step-by-step procedure and appliedto data from eight juvenile individuals. The generated musculoskeletal models were used to simulate 107gait trials using stereophotogrammetric and force platform data as input. To ensure completeness of themodelling procedure, muscles’ architecture needs to be estimated. Four methods to estimate muscles’maximum isometric force and two methods to estimate musculotendon parameters (optimal fiber lengthand tendon slack length) were assessed and compared, in order to quantify their influence on the models’output. Reported results represent the first comprehensive subject-specific model-based characterizationof juvenile gait biomechanics, including profiles of joint kinematics and kinetics, muscle forces and jointcontact forces. Our findings suggest that, when musculotendon parameters were linearly scaled from areference model and the muscle force-length-velocity relationship was accounted for in the simulations,realistic knee contact forces could be estimated and these forces were not sensitive the method used tocompute muscle maximum isometric force

Frequent use of emergency departments: an application to the paediatric context.

Frequent users of Emergency Departments (EDs) represent a particularly interesting category of users since they account to a small percentage of patients but they affect considerably accesses, overcrowding and the overall costs of ED activities. The literature on the topic is vast and it allows to delineate a profile of frequent users identifying socio-demographic (age, gender, nationality) and clinical (chronic diseases, drugs and alcohol abuse; psychic illnesses) risk factors. However, most of the studies on the topic limit the analysis to one-year period or to a single study site and there is no consensus on the definition of frequent use. Frequent users are generally defined as those patients reporting a number of accesses per year beyond a certain threshold. The selection of the threshold is often based on previous literature or on percentiles but the definitions vary considerably and the choice tends to be subjective. In this study, the focus will be placed on paediatric patients, with reference to which the contributions in the literature are still very limited. The objective is to identify the most important drivers of ED frequent use in the 19 EDs of Liguria region (Italy) during a three-year period (2013-2015). The dataset contains 287,242 accesses referred to 144,895 under 14 patients and it includes information on patients\u2019 characteristics and on their clinical pathway. To overcome the limitations connected to previous definitions of frequent use, we exploit the availability of data on three years; this allows to define, not only frequent use, but also its duration (i.e. One-shot / Multiple shot frequent use) and intensity (Normal, High, Very high). By the use of logit and multinomial logit regressions we identify a set of risk factors associated to frequent use and to the different forms of frequent use. Results show that even if frequent users represent a small share of patients (9%) they contribute to roughly 25% of accesses. Chronic conditions are the most relevant determinants of frequent use (particularly mental disorders, diseases of the respiratory system) but also foreign nationality turns out to be an important predictor. Differences emerge in the impact of regressors on the different forms of frequent use defined according to its duration and intensity. The study represents an important tool to support policy-making and to discriminate between the potentially preventable frequent use (i.e. inapFrequent users of Emergency Departments (EDs) represent a particularly interesting category of users since they account to a small percentage of patients but they affect considerably accesses, overcrowding and the overall costs of ED activities. The literature on the topic is vast and it allows to delineate a profile of frequent users identifying socio-demographic (age, gender, nationality) and clinical (chronic diseases, drugs and alcohol abuse; psychic illnesses) risk factors. However, most of the studies on the topic limit the analysis to one-year period or to a single study site and there is no consensus on the definition of frequent use. Frequent users are generally defined as those patients reporting a number of accesses per year beyond a certain threshold. The selection of the threshold is often based on previous literature or on percentiles but the definitions vary considerably and the choice tends to be subjective. In this study, the focus will be placed on paediatric patients, with reference to which the contributions in the literature are still very limited. The objective is to identify the most important drivers of ED frequent use in the 19 EDs of Liguria region (Italy) during a three-year period (2013-2015). The dataset contains 287,242 accesses referred to 144,895 under 14 patients and it includes information on patients\u2019 characteristics and on their clinical pathway. To overcome the limitations connected to previous definitions of frequent use, we exploit the availability of data on three years; this allows to define, not only frequent use, but also its duration (i.e. One-shot / Multiple shot frequent use) and intensity (Normal, High, Very high). By the use of logit and multinomial logit regressions we identify a set of risk factors associated to frequent use and to the different forms of frequent use. Results show that even if frequent users represent a small share of patients (9%) they contribute to roughly 25% of accesses. Chronic conditions are the most relevant determinants of frequent use (particularly mental disorders, diseases of the respiratory system) but also foreign nationality turns out to be an important predictor. Differences emerge in the impact of regressors on the different forms of frequent use defined according to its duration and intensity. 150 05 March 2018, IISES Annual Conference, Sevilla ISBN ISBN 978-80-87927-45-8, IISES The study represents an important tool to support policy-making and to discriminate between the potentially preventable frequent use (i.e. inapFrequent users of Emergency Departments (EDs) represent a particularly interesting category of users since they account to a small percentage of patients but they affect considerably accesses, overcrowding and the overall costs of ED activities. The literature on the topic is vast and it allows to delineate a profile of frequent users identifying socio-demographic (age, gender, nationality) and clinical (chronic diseases, drugs and alcohol abuse; psychic illnesses) risk factors. However, most of the studies on the topic limit the analysis to one-year period or to a single study site and there is no consensus on the definition of frequent use. Frequent users are generally defined as those patients reporting a number of accesses per year beyond a certain threshold. The selection of the threshold is often based on previous literature or on percentiles but the definitions vary considerably and the choice tends to be subjective. In this study, the focus will be placed on paediatric patients, with reference to which the contributions in the literature are still very limited. The objective is to identify the most important drivers of ED frequent use in the 19 EDs of Liguria region (Italy) during a three-year period (2013-2015). The dataset contains 287,242 accesses referred to 144,895 under 14 patients and it includes information on patients\u2019 characteristics and on their clinical pathway. To overcome the limitations connected to previous definitions of frequent use, we exploit the availability of data on three years; this allows to define, not only frequent use, but also its duration (i.e. One-shot / Multiple shot frequent use) and intensity (Normal, High, Very high). By the use of logit and multinomial logit regressions we identify a set of risk factors associated to frequent use and to the different forms of frequent use. Results show that even if frequent users represent a small share of patients (9%) they contribute to roughly 25% of accesses. Chronic conditions are the most relevant determinants of frequent use (particularly mental disorders, diseases of the respiratory system) but also foreign nationality turns out to be an important predictor. Differences emerge in the impact of regressors on the different forms of frequent use defined according to its duration and intensity. 150 05 March 2018, IISES Annual Conference, Sevilla ISBN ISBN 978-80-87927-45-8, IISES The study represents an important tool to support policy-making and to discriminate between the potentially preventable frequent use (i.e. inapappropriate use) and that associated to complex medical conditions, such as chronic conditions

Variations of lower-limb joint kinematics associated with the use of different ankle joint models

Skeletal computational models relying on global optimisation are widely used alongside gait analysis for the estimate of joint kinematics, but the degrees of freedom (DOFs) and axes definitions to model the ankle complex are still debated. The aim of this paper is to establish whether ankle modelling choices would also critically affect the estimate of the other joints' kinematics. Gait and MRI data from fifteen juvenile participants were used to implement three ankle joint models (M1, one-DOF sagittal motion; M2, two-DOFs sagittal and frontal motions; M3, three-DOFs) as part of a full lower-limb skeletal model. Differences in lower-limb joint and foot progression angles calculated using global optimisation were evaluated both at individual and group level. Furthermore, the influence of these differences on the correlations between joints and on the calculations of the root mean square deviation (RMSD) were investigated. Inter-model variations at individual level reached up to 4.2°, 9.1°, and 15.0° for hip flexion, adduction, and rotation, respectively, and up to 6.5° for knee flexion. Despite the tibiotalar axis being the same for all models, up to 19.3° (9.1° on average) larger dorsiflexion was found at push-off with M2. A stronger correlation between foot progression and ankle and knee sagittal movements was found for M1. Finally, RMSD led to inconsistent ranking of the participants when using different models. In conclusion, the choice of the ankle joint model affects the estimates of proximal lower-limb joint kinematics, which should discourage comparisons across datasets built with different models

Reducing the complexity of musculoskeletal models using gaussian process emulators

Musculoskeletal models (MSKMs) are used to estimate the muscle and joint forces involved in human locomotion, often associated with the onset of degenerative musculoskeletal pathologies (e.g., osteoarthritis). Subject-specific MSKMs offer more accurate predictions than their scaled-generic counterparts. This accuracy is achieved through time-consuming personalisation of models and manual tuning procedures that suffer from potential repeatability errors, hence limiting the wider application of this modelling approach. In this work we have developed a methodology relying on Sobol’s sensitivity analysis (SSA) for ranking muscles based on their importance to the determination of the joint contact forces (JCFs) in a cohort of older women. The thousands of data points required for SSA are generated using Gaussian Process emulators, a Bayesian technique to infer the input–output relationship between nonlinear models from a limited number of observations. Results show that there is a pool of muscles whose personalisation has little effects on the predictions of JCFs, allowing for a reduced but still accurate representation of the musculoskeletal system within shorter timeframes. Furthermore, joint forces in subject-specific and generic models are influenced by different sets of muscles, suggesting the existence of a model-specific component to the sensitivity analysis

MRI-based anatomical characterisation of lower-limb muscles in older women

The ability of muscles to produce force depends, among others, on their anatomical features and it is altered by ageing-associated weakening. However, a clear characterisation of these features, highly relevant for older individuals, is still lacking. This study hence aimed at characterising muscle volume, length, and physiological cross-sectional area (PCSA) and their variability, between body sides and between individuals, in a group of post-menopausal women. Lower-limb magnetic resonance images were acquired from eleven participants (69 (7) y. o., 66.9 (7.7) kg, 159 (3) cm). Twenty-three muscles were manually segmented from the images and muscle volume, length and PCSA were calculated from this dataset. Personalised maximal isometric force was then calculated using the latter information. The percentage difference between the muscles of the two lower limbs was up to 89% and 22% for volume and length, respectively, and up to 84% for PCSA, with no recognisable pattern associated with limb dominance. Between-subject coefficients of variation reached 36% and 13% for muscle volume and length, respectively. Generally, muscle parameters were similar to previous literature, but volumes were smaller than those from in-vivo young adults and slightly higher than ex-vivo ones. Maximal isometric force was found to be on average smaller than those obtained from estimates based on linear scaling of ex-vivo-based literature values. In conclusion, this study quantified for the first time anatomical asymmetry of lower-limb muscles in older women, suggesting that symmetry should not be assumed in this population. Furthermore, we showed that a scaling approach, widely used in musculoskeletal modelling, leads to an overestimation of the maximal isometric force for most muscles. This heavily questions the validity of this approach for older populations. As a solution, the unique dataset of muscle segmentation made available with this paper could support the development of alternative population-based scaling approaches, together with that of automatic tools for muscle segmentation

An extended discrete element method for the estimation of contact pressure at the ankle joint during stance phase

Abnormalities in the ankle contact pressure are related to the onset of osteoarthritis. In vivo measurements are not possible with currently available techniques, so computational methods such as the finite element analysis (FEA) are often used instead. The discrete element method (DEM), a computationally efficient alternative to time-consuming FEA, has also been used to predict the joint contact pressure. It describes the articular cartilage as a bed of independent springs, assuming a linearly elastic behaviour and absence of relative motion between the bones. In this study, we present the extended DEM (EDEM) which is able to track the motion of talus over time. The method was used, with input data from a subject-specific musculoskeletal model, to predict the contact pressure in the ankle joint during gait. Results from EDEM were also compared with outputs from conventional DEM. Predicted values of contact area were larger in EDEM than they were in DEM (4.67 and 4.18 cm2, respectively). Peak values of contact pressure, attained at the toe-off, were 7.3 MPa for EDEM and 6.92 MPa for DEM. Values predicted from EDEM fell well within the ranges reported in the literature. Overall, the motion of the talus had more effect on the extension and shape of the pressure distribution than it had on the magnitude of the pressure. The results indicated that EDEM is a valid methodology for the prediction of ankle contact pressure during daily activities