Carlos Quental

Critical analysis of musculoskeletal modelling complexity in multibody biomechanical models of the upper limb

The inverse dynamics technique applied to musculoskeletal models, and supported by optimisation techniques, is used extensively to estimate muscle and joint reaction forces. However, the solutions of the redundant muscle force sharing problem are sensitive to the detail and modelling assumptions of the models used. This study presents four alternative biomechanical models of the upper limb with different levels of discretisation of muscles by bundles and muscle paths, and their consequences on the estimation of the muscle and joint reaction forces. The muscle force sharing problem is solved for the motions of abduction and anterior flexion, acquired using video imaging, through the minimisation of an objective function describing muscle metabolic energy consumption. While looking for the optimal solution, not only the equations of motion are satisfied but also the stability of the glenohumeral and scapulothoracic joints is preserved. The results show that a lower level of muscle discretisation provides worse estimations regarding the muscle forces. Moreover, the poor discretisation of muscles relevant to the joint in analysis limits the applicability of the biomechanical model. In this study, the biomechanical model of the upper limb describing the infraspinatus by a single bundle could not solve the complete motion of anterior flexion. Despite the small differences in the magnitude of the forces predicted by the biomechanical models with more complex muscular systems, in general, there are no significant variations in the muscular activity of equivalent muscles.

Bone remodelling analysis of the humerus after a shoulder arthroplasty

The shoulder arthroplasty has become an efficient treatment for some pathologies. However there are complications that can compromise its success. Among them, the stress shielding effect on the humerus has been reported as a possible cause of failure. The objective of this work was to investigate the bone remodelling in the humerus after a shoulder arthroplasty. For this purpose, computational models were developed to analyse the stress shielding contribution to the humeral component failure of shoulder arthroplasties, with a cemented and an uncemented prosthesis. A computational remodelling model was used to characterize the bone apparent density at each site of the humerus. The density distribution was obtained by the solution of a problem that takes into account both structural stiffness and the metabolic cost of bone maintenance. Bone was subjected to 6 load cases that include the glenohumeral reaction force and the action of 10 muscles. In the implanted models, different interface conditions were tested for the bone-implant and the cement-implant interfaces. Moreover, a pathological case defined by a poorer quality of bone was considered. In the healthy situation, the models that better model in vivo conditions showed no significant changes in bone mass. However, the results for the pathological case showed some bone resorption which supports the importance given to the quality of bone in the success of the joint replacement. Bearing in mind the conditions addressed, the results lead to conclude that the stress shielding is not a key factor for the humeral component failure of shoulder arthroplasties in a healthy situation though several issues, including muscle function and bone quality, may heighten its effect.

Multibody System of the Upper Limb Including a Reverse Shoulder Prosthesis

The reverse shoulder replacement, recommended for the treatment of several shoulder pathologies such as cuff tear arthropathy and fractures in elderly people, changes the biomechanics of the shoulder when compared to the normal anatomy. Although several musculoskeletal models of the upper limb have been presented to study the shoulder joint, only a few of them focus on the biomechanics of the reverse shoulder. This work presents a biomechanical model of the upper limb, including a reverse shoulder prosthesis, to evaluate the impact of the variation of the joint geometry and position on the biomechanical function of the shoulder. The biomechanical model of the reverse shoulder is based on a musculoskeletal model of the upper limb, which is modified to account for the properties of the DELTA® reverse prosthesis. Considering two biomechanical models, which simulate the anatomical and reverse shoulder joints, the changes in muscle lengths, muscle moment arms, and muscle and joint reaction forces are evaluated. The muscle force sharing problem is solved for motions of unloaded abduction in the coronal plane and unloaded anterior flexion in the sagittal plane, acquired using video-imaging, through the minimization of an objective function related to muscle metabolic energy consumption. After the replacement of the shoulder joint, significant changes in the length of the pectoralis major, latissimus dorsi, deltoid, teres major, teres minor, coracobrachialis, and biceps brachii muscles are observed for a reference position considered for the upper limb. The shortening of the teres major and teres minor is the most critical since they become unable to produce active force in this position. Substantial changes of muscle moment arms are also observed, which are consistent with the literature. As expected, there is a significant increase of the deltoid moment arms and more fibers are able to elevate the arm. The solutions to the muscle force sharing problem support the biomechanical advantages attributed to the reverse shoulder design and show an increase in activity from the deltoid, teres minor, and coracobrachialis muscles. The glenohumeral joint reaction forces estimated for the reverse shoulder are up to 15% lower than those in the normal shoulder anatomy. The data presented here complements previous publications, which, all together, allow researchers to build a biomechanical model of the upper limb including a reverse shoulder prosthesis.

A new shoulder model with a biologically inspired glenohumeral joint.

Kinematically unconstrained biomechanical models of the glenohumeral (GH) joint are needed to study the GH joint function, especially the mechanisms of joint stability. The purpose of this study is to develop a large-scale multibody model of the upper limb that simulates the 6 degrees of freedom (DOF) of the GH joint and to propose a novel inverse dynamics procedure that allows the evaluation of not only the muscle and joint reaction forces of the upper limb but also the GH joint translations. The biomechanical model developed is composed of 7 rigid bodies, constrained by 6 anatomical joints, and acted upon by 21 muscles. The GH joint is described as a spherical joint with clearance. Assuming that the GH joint translates according to the muscle load distribution, the redundant muscle load sharing problem is formulated considering as design variables the 3 translational coordinates associated with the GH joint translations, the joint reaction forces associated with the remaining kinematic constraints, and the muscle activations. For the abduction motion in the frontal plane analysed, the muscle and joint reaction forces estimated by the new biomechanical model proposed are similar to those estimated by a model in which the GH joint is modeled as an ideal spherical joint. Even though this result supports the assumption of an ideal GH joint to study the muscle load sharing problem, only a 6 DOF model of the GH joint, as the one proposed here, provides information regarding the joint translations. In this study, the biomechanical model developed predicts an initial upward and posterior migration of the humeral head, followed by an inferior and anterior movement, which is in good agreement with the literature.

Computational design and fabrication of a novel bioresorbable cage for tibial tuberosity advancement application

Tibial tuberosity advancement (TTA) is a promising method for the treatment of cruciate ligament rupture in dogs that usually implies the implantation of a titanium cage as bone implant. This cage is non-biodegradable and fails in providing adequate implant-bone tissue integration. The objective of this work is to propose a new process chain for designing and manufacturing an alternative biodegradable cage that can fulfill specific patient requirements. A three-dimensional finite element model (3D FEM) of the TTA system was first created to evaluate the mechanical environment at cage domain during different stages of the dog walk. The cage microstructure was then optimized using a topology optimization tool, which addresses the accessed local mechanical requirements, and at same time ensures the maximum permeability to allow nutrient and oxygen supply to the implant core. The designed cage was then biofabricated by a 3D powder printing of tricalcium phosphate cement. This work demonstrates that the combination of a 3D FEM with a topology optimization approach enabled the design of a novel cage for TTA application with tailored permeability and mechanical properties, that can be successfully 3D printed in a biodegradable bioceramic material. These results support the potential of the design optimization strategy and fabrication method to the development of customized and bioresorbable implants for bone repair.

A simple controller to overcome the lack of correlation between forward and inverse dynamic analysis of human motion tasks

The majority of biomechanical analyses of human motions, including those with musculoskeletal models, use inverse dynamic approaches due to its ability to deal with experimentally acquired kinematic and kinetic data. Yet, a forward dynamic approach can be more powerful and provide better insights on the transmission of forces in the internal biomechanical systems and structures of the human body. Although both approaches may use the same biomechanical model the results achieved do not necessarily correlate with each other. The aim of this study is to demonstrate the source of the lack of correlation between inverse and forward dynamics methodologies providing, in the process, insights on how to overcome such differences. Two types of problems involving the biomechanics of the spatial human motion are used to evaluate the correlation between the forward and inverse dynamic approaches: a gait analysis of a deterministic biomechanical model of the lower limbs, and, a full musculoskeletal model of the upper limb, which is characterised by the solution of a redundant muscle force sharing problem. For that purpose, an inverse dynamic model is applied to estimate the forces responsible for two experimentally acquired motions that are, afterwards, given as input to the forward dynamics model, which is used, in turn, to compute the kinematics of the biomechanical model. The comparison between the reference kinematics, acquired experimentally, and that resulting from the forward dynamic analysis supports that a lack of correlation between the inverse and forward dynamic analysis is always observed. It is proposed here, and demonstrated, that a controller implemented in a feedback loop is able to enhance numerical stability of the forward dynamics solution, leading to the ability of the forward dynamics approach to successfully simulate the acquired motions.

Bone remodelling of the humerus after a resurfacing and a stemless shoulder arthroplasty

Background: New implant designs, such as resurfacing and stemless implants, have been developed to improve the long‐term outcomes of the shoulder arthroplasty. However, it is not yet fully understood if their influence on the bone load distribution can compromise the long‐term stability of the implant due to bone mass changes. Using three‐dimensional finite element models, the aim of the present study was to analyse the bone remodelling process of the humerus after the introduction of resurfacing and stemless implants based on the Global C.A.P. and Sidus Stem‐Free designs, respectively. Methods: The 3D geometric model of the humerus was generated from the CT data of the Visible Human Project and the resurfacing and stemless implants were modelled in Solidworks. Considering a native humerus model, a humerus model with the resurfacing implant, and a humerus model with the stemless implant, three finite element models were developed in Abaqus. Bone remodelling simulations were performed considering healthy and poor bone quality conditions. The loading condition considered comprised 6 load cases of standard shoulder movements, including muscle and joint reaction forces estimated by a multibody model of the upper limb. Findings: The results showed similar levels of bone resorption for the resurfacing and stemless implants for common humeral regions. The regions underneath the head of the resurfacing implant, unique to this design, showed the largest bone loss. For both implants, bone resorption was more pronounced for the poor bone quality condition than for the healthy bone quality condition. Interpretation: The stemless implant lost less density at the fixation site, which might suggest that these implants may be better supported in the long‐term than the resurfacing implants. However, further investigation is necessary to allow definite recommendations.

Full-thickness tears of the supraspinatus tendon: A three-dimensional finite element analysis

Knowledge regarding the likelihood of propagation of supraspinatus tears is important to allow an early identification of patients for whom a conservative treatment is more likely to fail, and consequently, to improve their clinical outcome. The aim of this study was to investigate the potential for propagation of posterior, central, and anterior full-thickness tears of different sizes using the finite element method. A three-dimensional finite element model of the supraspinatus tendon was generated from the Visible Human Project data. The mechanical behaviour of the tendon was fitted from experimental data using a transversely isotropic hyperelastic constitutive model. The full-thickness tears were simulated at the supraspinatus tendon insertion by decreasing the interface area. Tear sizes from 10% to 90%, in 10% increments, of the anteroposterior length of the supraspinatus footprint were considered in the posterior, central, and anterior regions of the tendon. For each tear, three finite element analyses were performed for a supraspinatus force of 100N, 200N, and 400N. Considering a correlation between tendon strain and the risk of tear propagation, the simulated tears were compared qualitatively and quantitatively by evaluating the volume of tendon for which a maximum strain criterion was not satisfied. The finite element analyses showed a significant impact of tear size and location not only on the magnitude, but also on the patterns of the maximum principal strains. The mechanical outcome of the anterior full-thickness tears was consistently, and significantly, more severe than that of the central or posterior full-thickness tears, which suggests that the anterior tears are at greater risk of propagating than the central or posterior tears.

Computational reverse shoulder prosthesis model: Experimental data and verification

The reverse shoulder prosthesis aims to restore the stability and function of pathological shoulders, but the biomechanical aspects of the geometrical changes induced by the implant are yet to be fully understood. Considering a large-scale musculoskeletal model of the upper limb, the aim of this study is to evaluate how the Delta reverse shoulder prosthesis influences the biomechanical behavior of the shoulder joint. In this study, the kinematic data of an unloaded abduction in the frontal plane and an unloaded forward flexion in the sagittal plane were experimentally acquired through video-imaging for a control group, composed of 10 healthy shoulders, and a reverse shoulder group, composed of 3 reverse shoulders. Synchronously, the EMG data of 7 superficial muscles were also collected. The muscle force sharing problem was solved through the minimization of the metabolic energy consumption. The evaluation of the shoulder kinematics shows an increase in the lateral rotation of the scapula in the reverse shoulder group, and an increase in the contribution of the scapulothoracic joint to the shoulder joint. Regarding the muscle force sharing problem, the musculoskeletal model estimates an increased activity of the deltoid, teres minor, clavicular fibers of the pectoralis major, and coracobrachialis muscles in the reverse shoulder group. The comparison between the muscle forces predicted and the EMG data acquired revealed a good correlation, which provides further confidence in the model. Overall, the shoulder joint reaction force was lower in the reverse shoulder group than in the control group.

Dynamics of the Upper Limb with a Detailed Model for the Shoulder

The human muscle-skeletal system has a large number of redundant muscles, implying that the same motion may be obtained by different combination of muscle forces. As a consequence, the modeling of the kinematics of biomechanical models used for human motion task simulations has important implication on the distribution of the muscle forces and joint reaction forces. This work compares the performance and applicability of three biomechanical models, with different levels of complexity, in face of specific kinematic modeling assumptions for the anatomical joints and muscle geometry. The muscle contraction dynamics is simulated by the Hill-type muscle model, being the activation of each muscle a unknown in the redundant force sharing problem. An optimization technique is applied to minimize of an objective function related with muscle metabolic energy consumption. The input for the model analysis comprises the data for an abduction motion, kinematically consistent with the biomechanical models developed, acquired using video imaging at the Laboratory of Biomechanics of Lisbon.