A finite element model of the lower limb during stance phase of gait cycle including the muscle forces

Development of a three-dimensional muscle-driven lower limb model developed using an improved CFD-FE method

Analysis of the musculoskeletal movements (gait analysis) is needed in many scenarios. The in vivo method has some difficulties. For example, recruiting human subjects for the gait analysis is challenging due to many issues. In addition, when plenty of subjects are required, the follow-up experiments take a long period and the dropout of subjects always occurs. An efficient and reliable in silico simulation platform for gait analysis has been desired for a long time. Therefore, a technique using three-dimensional (3D) muscle modeling to drive the 3D musculoskeletal model was developed and the application of the technique in the simulation of lower limb movements was demonstrated. A finite element model of the lower limb with anatomically high fidelity was developed from the MRI data, where the main muscles, the bones, the subcutaneous tissues, and the skin were reconstructed. To simulate the active behavior of 3D muscles, an active, fiber-reinforced hyperelastic muscle model was developed using the user-defined material (VUMAT) model. Two typical movements, that is, hip abduction and knee lifting, were simulated by activating the responsible muscles. The results show that it is reasonable to use the improved CFD-FE method proposed in the present study to simulate the active contraction of the muscle, and it is feasible to simulate the movements by activating the relevant muscles. The results from the present technique closely match the physiological scenario and thus the technique developed has a great potential to be used in the in silico human simulation platform for many purposes.

Computation of physiological loading induced interstitial fluid motion in muscle standardized femur: Healthy vs. osteoporotic bone

BACKGROUND AND OBJECTIVES

Physiological loading-induced mechanical environments regulate bone modeling and remodeling. Thus, loading-induced normal strain is typically considered a stimulus to osteogenesis. However, several studies noticed new bone formation near the sites of minimal normal strain, e.g., the neutral axis of bending in long bones, which raises a question on how bone mass is maintained near these sites. Secondary mechanical components such as shear strain and interstitial fluid flow also stimulate bone cells and regulate bone mass. However, the osteogenic potential of these components is not well established. Accordingly, the present study estimates the distribution of physiological muscle loading-induced mechanical environments such as normal strain, shear strain, pore pressure, and interstitial fluid flow in long bones.

METHODS

A poroelastic finite element muscle standardized femur (MuscleSF) model is developed to compute the distribution of the mechanical environment as a function of bone porosities associated with osteoporotic and disuse bone loss.

RESULTS

The results indicate the presence of higher shear strain and interstitial fluid motion near the minimal strain sites, i.e., the neutral axis of bending of femoral cross-sections. This suggests that secondary stimuli may maintain the bone mass at these locations. Pore pressure and interstitial fluid motion reduce with the increased porosity associated with bone disorders, possibly resulting in diminished skeletal mechano-sensitivity to exogenous loading.

CONCLUSIONS

These outcomes present a better understanding of mechanical environment-mediated regulation of site-specific bone mass, which can be beneficial in developing prophylactic exercise to prevent bone loss in osteoporosis and muscle disuse.

Changes in hip joint contact stress during a gait cycle based on the individualized modeling method of "gait-musculoskeletal system-finite element"

OBJECTIVE

To construct a comprehensive simulation method of "gait-musculoskeletal system (MS)-finite element (FE)" for analysis of hip joint dynamics characteristics and the changes in the contact stress in the hip throughout a gait cycle.

METHODS

Two healthy volunteers (male and female) were recruited. The 3D gait trajectories during normal walking and the CT images including the hip and femur of the volunteers were obtained. CT imaging data in the DICOM format were extracted for subjected 3D hip joint reconstruction. The reconstructed 3D model files were used to realize the subject-specific registration of the pelvis and thigh segment of general musculoskeletal model. The captured marker trajectory data were used to drive subject-specific musculoskeletal model to complete inverse dynamic analysis. Results of inverse dynamic analysis were exported and applied as boundary and load settings of the hip joint finite element in ABAQUS. Finally, the finite element analysis (FEA) was performed to analyze contact stress of hip joint during a gait cycle of left foot.

RESULTS

In the inverse dynamic analysis, the dynamic changes of the main hip-femoral muscle force with respect to each phase of a single gait cycle were plotted. The hip joint reaction force reached a maximum value of 2.9%BW (body weight) and appeared at the end of the terminal stance phase. Twin peaks appeared at the initial contact phase and the end of the terminal stance phase, respectively. FEA showed the temporal changes in contact stress in the acetabulum. In the visual stress cloud chart, the acetabular contact stress was mainly distributed in the dome of the acetabulum and in the anterolateral area at the top of the femoral head during a single gait cycle. The acetabular contact area was between 293.8 and 998.4 mm², and the maximum contact area appear at the mid-stance phase or the loading response phase of gait. The maximum contact stress of the acetabulum reached 6.91 MPa for the model 1 and 6.92 MPa for the model 2 at the terminal stance phase.

CONCLUSIONS

The "Gait-MS-FE" technology is integrated to construct a comprehensive simulation framework. Based on human gait trajectories and their CT images, individualized simulation modeling can be achieved. Subject-specific gait in combination with an inverse dynamic analysis of the MS provides pre-processing parameters for FE simulation for more accurate biomechanical analysis of hip joint.

A Comparative Study on the Multiscale Mechanical Responses of Human Femoral Neck Between the Young and the Elderly Using Finite Element Method

Background: Femoral neck fracture (FNF) is the most serious bone disease in the elderly population. The multiscale mechanical response is a key to predicting the strength of the femoral neck, assessing the risk of FNF, and exploring the role of mechanosensation and mechanotransmission in bone remodeling, especially in the context of aging bone.

Methods: Multiscale finite element (FE) models of the proximal femur for both young and elderly people were developed. The models included organ scale (proximal femur), tissue scale (cortical bone), tissue element scale (osteon), and cell scale [osteocyte lacuna-canalicular network (LCN) and extracellular matrix (ECM), OLCEM]. The mechanical responses of cortical bone and osteocytes in the mid-femoral neck and the differences in mechanical responses between these two scales were investigated.

Results: The mechanical responses of cortical bone and osteocyte showed significant differences between the elderly and the young. The minimum principal strains and mean SEDs of cortical bone in the elderly were 2.067–4.708 times and 3.093–14.385 times of the values in the young, respectively; the minimum principal strains and mean SEDs of osteocyte in the elderly were 1.497–3.246 times and 3.044–12 times of the values in the young, respectively; the amplification factors of minimum principal strain in the inferior (Inf), anterior (Ant), and posterior (Post) quadrants in the young were 1.241–1.804 times of the values in the elderly, but the amplification factor of minimum principal strain in the superior (Sup) quadrant was 87.4% of the value in the elderly; the amplification factors of mean SED in the young were 1.124–9.637 times of the values in the elderly.

Conclusion: The mass and bone mineral density (BMD) of cortical bone in the femoral neck is closely related to the mechanical response of osteocytes, which provides a new idea for improving cortical bone quality. Perhaps cortical bone quality could be improved by stimulating osteocytes. Quadrantal differences of bone quality in the mid-femoral neck should be considered to improve fracture risk prediction in the future.

Biomechanical effect of intertrochanteric curved varus osteotomy on stress reduction in femoral head osteonecrosis: a finite element analysis

Background

Intertrochanteric curved varus osteotomy (CVO) has been widely used to remove the necrotic bone away from the weight-bearing portion in the treatment of osteonecrosis of the femoral head (ONFH). However, whether all types of necrosis will benefit from CVO, in terms of the stress level, the effect of different center-edge (CE) angles of acetabulum on stress distribution of necrosis after CVO, and the relationship between the intact ratio and the stress of necrosis, has never been addressed. The purpose of the study was to evaluate the influence of CVO on the stress reduction in necrotic bone using a finite element analysis (FEA) with different CE angles.

Methods

CVO finite element models of the hip joint were simulated with a lesion of 60°. The osteotomy angles were divided into four configurations (15°, 20°, 25°, and 30°), and three types (A, B, and C1) of lesions were established based on the Japanese Investigation Committee (JIC) classification. In addition, two CE angles (18° and 33°) of acetabulum were considered. The maximum and mean von Mises stress were analyzed in terms of the necrotic bone by a physiological loading condition. Moreover, the correlation of the intact ratio measured in 3D and the stress distribution after CVO was analyzed.

Results

Stress reduction was obtained after CVO. For type B, the CVO angle was 20° (0.61 MPa), and for type C1, the CVO angle was 30° (0.77 MPa), if the mean stress level was close to type A (0.61 MPa), as a standard. The maximum and mean von Mises stress were higher in the CE angle of 18°models, respectively. The intact ratio measured in 3D had a good negative correlation with stress after CVO and had more influence on stress distribution in comparison to other geometric parameters.

Conclusions

For making decisions about the biomechanics of CVO, a CVO angle of > 20° was recommended for type B and > 30° was safe for type C1. The risk of progressive collapse was increased in the insufficient situation of the weight-bearing portion after CVO. The intact ratio could provide information about clinical outcomes and stress distribution after CVO.

Impact of alignment and kinematic variation on resistive moment and dislocation propensity for THA with lipped and neutral liners

Instability and dislocation remain leading indications for revision of total hip arthroplasty (THA). Many studies have addressed the links between implant design and dislocation; however, an understanding of the impact of alignment and kinematic variability on constraint of modern THA constructs to provide joint stability is needed. The objective of this study is to provide objective data to be considered in the treatment algorithm to protect against joint instability. Joint contact and muscle forces were evaluated using musculoskeletal models of THA patients performing activities consistent with posterior and anterior dislocation. Position and joint loads were transferred to a finite element simulation with an experimentally calibrated hip capsule representation, where they were kinematically extrapolated until impingement and eventual dislocation. Cup anteversion and inclination were varied according to clinical measurements, and variation in imposed kinematics was included. The resistive moment provided by the contact force and joint capsule, and overall dislocation rate (dislocations/total simulations) were determined with neutral and lipped acetabular liners. Use of a lipped liner did increase the resistive moment in posterior dislocation, by an average of 5.2 Nm, and the flexion angle at dislocation by 1.4° compared to a neutral liner. There was a reduction in similar magnitude in resistance to anterior dislocation. Increased cup anteversion and inclination, hip abduction and internal rotation all reduced the occurrence of posterior dislocation but increased anterior dislocation. A quantitative understanding of tradeoffs in the dislocation risk inherent to THA construct options is valuable in supporting surgical decision making.

Subject-Specific Finite Element Models of the Tibia With Realistic Boundary Conditions Predict Bending Deformations Consistent With In Vivo Measurement

Understanding the structural response of bone during locomotion may help understand the etiology of stress fracture. This can be done in a subject-specific manner using finite element (FE) modeling, but care is needed to ensure that modeling assumptions reflect the in vivo environment. Here, we explored the influence of loading and boundary conditions (BC), and compared predictions to previous in vivo measurements. Data were collected from a female participant who walked/ran on an instrumented treadmill while motion data were captured. Inverse dynamics of the leg (foot, shank, and thigh segments) was combined with a musculoskeletal (MSK) model to estimate muscle and joint contact forces. These forces were applied to an FE model of the tibia, generated from computed tomography (CT). Eight conditions varying loading/BCs were investigated. We found that modeling the fibula was necessary to predict realistic tibia bending. Applying joint moments from the MSK model to the FE model was also needed to predict torsional deformation. During walking, the most complex model predicted deformation of 0.5 deg posterior, 0.8 deg medial, and 1.4 deg internal rotation, comparable to in vivo measurements of 0.5-1 deg, 0.15-0.7 deg, and 0.75-2.2 deg, respectively. During running, predicted deformations of 0.3 deg posterior, 0.3 deg medial, and 0.5 deg internal rotation somewhat underestimated in vivo measures of 0.85-1.9 deg, 0.3-0.9 deg, 0.65-1.72 deg, respectively. Overall, these models may be sufficiently realistic to be used in future investigations of tibial stress fracture.

Numerical comparative study of five currently used implants for high tibial osteotomy: realistic loading including muscle forces versus simplified experimental loading

Background

Many different fixation devices are used to maintain the correction angle after medial open wedge high tibial osteotomy (MOWHTO). Each device must provide at least sufficient mechanical stability to avoid loss of correction and unwanted fracture of the contralateral cortex until the bone heals. In the present study, the mechanical stability of following different implants was compared: the TomoFix small stature (sm), the TomoFix standard (std), the Contour Lock, the iBalance and the second generation PEEKPower. Simplified loading, usually consisting of a vertical load applied to the tibia plateau, is used for experimental testing of fixation devices and also in numerical studies. Therefore, this study additionally compared this simplified experimental loading with a more realistic loading that includes the muscle forces.

Method

Two types of finite element models, according to the considered loading, were created. The first type numerically simulated the static tests of MOWHTO implants performed in a previous experimental biomechanical study, by applying a vertical compressive load perpendicularly to the plateau of the osteotomized tibia. The second type included muscle forces in finite element models of the lower limb with osteotomized tibiae and simulated the stance phase of normal gait. Section forces in the models were determined and compared. Stresses in the implants and contralateral cortex, and micromovements of the osteotomy wedge, were calculated.

Results

For both loading types, the stresses in the implants were lower than the threshold values defined by the material strength. The stresses in the lateral cortex were smaller than the ultimate tensile strength of the cortical bone. The implants iBalance and Contour Lock allowed the smallest micromovements of the wedge, while the PEEKPower allowed the highest. There was a correlation between the micromovements of the wedge, obtained for the simplified loading of the tibia, and the more realistic loading of the lower limb at 15% of the gait cycle (Pearson’s value r = 0.982).

Conclusions

An axial compressive load applied perpendicularly to the tibia plateau, with a magnitude equal to the first peak value of the knee joint contact forces, corresponds quite well to a realistic loading of the tibia during the stance phase of normal gait (at 15% of the gait cycle and a knee flexion of about 22 degrees). However, this magnitude of the knee joint contact forces overloads the tibia compared to more realistic calculations, where the muscle forces are considered. The iBalance and Contour Lock implants provide higher rigidity to the bone-implant constructs compared to the TomoFix and the PEEKPower plates.