Numerical modelling of abdominal wall mechanics: The role of muscular contraction and intra-abdominal pressure

Redefining Abdominal Contours: An Analysis of Medium Definition Liposuction Abdominoplasty

INTRODUCTION

This study elucidates the application of Medium Definition Liposuction Abdominoplasty, a novel technique for achieving well-defined abdominal contours. The technique focuses on revealing the patient's inherent muscular volume and form by creating thinner flaps compared to traditional liposuction methodologies.

METHODS

Objective evaluations of the abdominal wall's configuration were systematically executed both pre- and post-intervention for each participant. Digital image measurements facilitated by an image software constituted the basis for these assessments. The Body Fat Index was computed using precise measurements from seven distinct anatomical sites, with two measurements taken at each site and subsequently averaged.

RESULTS

Over a span of 63 months, 300 patients underwent this combined procedure, resulting in discernible enhancements in the configuration of their abdominal walls in 97.6% of cases. However, complications such as partial diminution of tension in the muscular wall (2%), distal flap necrosis (0.6%), and minor muscular hernia (0.3%) were observed.

CONCLUSION

The employment of combined muscle plication emerges as an efficacious methodology in meticulously rectifying alterations inherent within the muscular aponeurotic abdominal wall. This technique ensures the preservation of the original anatomical structure and functional dynamics, thereby circumventing the manifestation of local distortions that may arise from inadequate or excessive corrections.

BULLET POINTS

The study introduces a novel technique, Medium Definition Liposuction Abdominoplasty, for achieving well-defined abdominal contours. This technique focuses on revealing the patient's inherent muscular volume and form by creating thinner flaps compared to traditional liposuction methodologies. Objective evaluations of the abdominal wall's configuration were systematically executed both pre- and post-intervention for each participant. The Body Fat Index was computed using precise measurements from seven distinct anatomical sites. Over a span of 63 months, 300 patients underwent this combined procedure, resulting in discernible enhancements in the configuration of their abdominal walls in 97.6% of cases. This technique ensures the preservation of the original anatomical structure and functional dynamics, thereby circumventing the manifestation of local distortions that may arise from inadequate or excessive corrections.

LEVEL OF EVIDENCE III

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The role of the extracellular matrix in the reduction of lateral force transmission in muscle bundles: A finite element analysis

BACKGROUND AND OBJECTIVE

Aging is associated with a reduction in muscle performance, but muscle weakness is characterized by a much greater loss of force loss compared to mass loss. The aim of this work is to assess the contribution of the extracellular matrix (ECM) to the lateral transmission of force in humans and the loss of transmitted force due to age-related modifications.

METHODS

Finite element models of muscle bundles are developed for young and elderly human subjects, by considering a few fibers connected through an ECM layer. Bundles of young and elderly subjects are assumed to differ in terms of ECM thickness, as observed experimentally. A three-element-based Hill model is adopted to describe the active behavior of muscle fibers, while the ECM is modeled assuming an isotropic hyperelastic neo-Hookean constitutive formulation. Numerical analyses are carried out by mimicking, at the scale of a bundle, two experimental protocols from the literature.

RESULTS

When comparing numerical results obtained for bundles of young and elderly subjects, a greater reduction in the total transmitted force is observed in the latter. The loss of transmitted force is 22 % for the elderly subjects, while it is limited to 7.5 % for the young subjects. The result for the elderly subjects is in line with literature studies on animal models, showing a reduction in the range of 20-34 %. This can be explained by an alteration in the mechanism of lateral force transmission due to the lower shear stiffness of the ECM in elderly subjects, related to its higher thickness.

CONCLUSIONS

Computational modeling allows to evaluate at the bundle level how the age-related increase of the ECM amount between fibers affects the lateral transmission of force. The results suggest that the observed increase in ECM thickness in aging alone can explain the reduction of the total transmitted force, due to the impaired lateral transmission of force of each fiber.

Soft tissue material properties based on human abdominal in vivo macro-indenter measurements

Simulations of human-technology interaction in the context of product development require comprehensive knowledge of biomechanical in vivo behavior. To obtain this knowledge for the abdomen, we measured the continuous mechanical responses of the abdominal soft tissue of ten healthy participants in different lying positions anteriorly, laterally, and posteriorly under local compression depths of up to 30 mm. An experimental setup consisting of a mechatronic indenter with hemispherical tip and two time-of-flight (ToF) sensors for optical 3D displacement measurement of the surface was developed for this purpose. To account for the impact of muscle tone, experiments were conducted with both controlled activation and relaxation of the trunk muscles. Surface electromyography (sEMG) was used to monitor muscle activation levels. The obtained data sets comprise the continuous force-displacement data of six abdominal measurement regions, each synchronized with the local surface displacements resulting from the macro-indentation, and the bipolar sEMG signals at three key trunk muscles. We used inverse finite element analysis (FEA), to derive sets of nonlinear material parameters that numerically approximate the experimentally determined soft tissue behaviors. The physiological standard values obtained for all participants after data processing served as reference data. The mean stiffness of the abdomen was significantly different when the trunk muscles were activated or relaxed. No significant differences were found between the anterior-lateral measurement regions, with exception of those centered on the linea alba and centered on the muscle belly of the rectus abdominis below the intertubercular plane. The shapes and areas of deformation of the skin depended on the region and muscle activity. Using the hyperelastic Ogden model, we identified unique material parameter sets for all regions. Our findings confirmed that, in addition to the indenter force-displacement data, knowledge about tissue deformation is necessary to reliably determine unique material parameter sets using inverse FEA. The presented results can be used for finite element (FE) models of the abdomen, for example, in the context of orthopedic or biomedical product developments.

Numerical investigation of a finite element abdominal wall model during breathing and muscular contraction

BACKGROUND AND OBJECTIVE

Ventral hernia repair is faced with high recurrence rates. The personalization of the diagnosis, the surgical approach and the choice of the prosthetic implant seem relevant axes to improve the current results. Numerical models have the potential to allow this patient-specific approach, yet currently existing models lack validation. This work extensively investigated a realistic finite element abdominal wall model including the implementation of muscle activation.

METHODS

A parametric 3D finite element model composed of bone, muscle and aponeurotic structures was introduced. Hyperelastic anisotropic materials were implemented. Two loading scenarios were simulated: passive inflation of the abdominal cavity to represent, e.g., breathing, and passive inflation followed by muscular activation to simulate other daily activities such as cough. The impact of the inter-individual variability (e.g., BMI, tissue thickness, material properties, intra-abdominal pressure (IAP) and muscle contractility) on the model outputs was studied through a sensitivity analysis.

RESULTS

The overall model predictions were in good agreement with the experimental data in terms of shape variation, muscles displacements, strains and midline forces. A total of 34 and 41 runs were computed for the passive and active sensitivity analysis respectively. The regression model fits rendered high R-squared in both passive (84.0 ± 6.7 %) and active conditions (82.0 ± 8.3 %). IAP and muscle thickness were the most influential factors for the selected outputs during passive (breathing) activities. Maximum isometric stress, muscle thickness and pre-activation IAP were found to drive the response of the simulations involving muscular contraction. The material properties of the connective tissue were essential contributors to the behaviour of the medial part of the abdominal wall.

CONCLUSIONS

This work extensively investigated a realistic abdominal wall model and evaluated its robustness using experimental data from literature. Such a model could improve patient-specific simulation for ventral hernia surgical planning, prevention, and repair or implant evaluation. Further investigations will be conducted to evaluate the impact of the surgical technique and the mechanical characteristic of prosthetic meshes on the model outputs.

Patient-specific computational simulations of wound healing following midline laparotomy closure

In the current study, we developed a new computational methodology to simulate wound healing in soft tissues. We assumed that the injured tissue recovers partially its mechanical strength and stiffness by gradually increasing the volume fraction of collagen fibers. Following the principles of the constrained mixture theory, we assumed that new collagen fibers are deposited at homeostatic tension while the already existing tissue undergoes a permanent deformation due to the effects of remodeling. The model was implemented in the finite-element software Abaqus® through a VUMAT subroutine and applied to a complex and realistic case: simulating wound healing following midline laparotomy closure. The incidence of incisional hernia is still quite significant clinically, and our goal was to investigate different conditions hampering the success of these procedures. We simulated wound healing over periods of 6 months on a patient-specific geometry. One of the outcomes of the finite-element simulations was the width of the wound tissue, which was found to be clinically correlated with the development of incisional hernia after midline laparotomy closure. We studied the impact of different suturing modalities and the effects of situations inducing increased intra-abdominal pressure or its intermittent variations such as coughing. Eventually, the results showed that the main risks of developing an incisional hernia mostly depend on the elastic strains reached in the wound tissue after degradation of the suturing wires. Despite the need for clinical validation, these results are promising for establishing a digital twin of wound healing in midline laparotomy incision.

Muscle-driven forward dynamic active hybrid model of the lumbosacral spine: combined FEM and multibody simulation

Most spine models belong to either the musculoskeletal multibody (MB) or finite element (FE) method. Recently, coupling of MB and FE models has increasingly been used to combine advantages of both methods. Active hybrid FE-MB models, still rarely used in spine research, avoid the interface and convergence problems associated with model coupling. They provide the inherent ability to account for the full interplay of passive and active mechanisms for spinal stability. In this paper, we developed and validated a novel muscle-driven forward dynamic active hybrid FE-MB model of the lumbosacral spine (LSS) in ArtiSynth to simultaneously calculate muscle activation patterns, vertebral movements, and internal mechanical loads. The model consisted of the rigid vertebrae L1-S1 interconnected with hyperelastic fiber-reinforced FE intervertebral discs, ligaments, facet joints, and force actuators representing the muscles. Morphological muscle data were implemented via a semi-automated registration procedure. Four auxiliary bodies were utilized to describe non-linear muscle paths by wrapping and attaching the anterior abdominal muscles. This included an abdominal plate whose kinematics was optimized using motion capture data from upper body movements. Intra-abdominal pressure was calculated from the forces of the abdominal muscles compressing the abdominal cavity. For the muscle-driven approach, forward dynamics assisted data tracking was used to predict muscle activation patterns that generate spinal postures and balance the spine without prescribing accurate spinal kinematics. During calibration, the maximum specific muscle tension and spinal rhythms resulting from the model dynamics were evaluated. To validate the model, load cases were simulated from -10° extension to +30° flexion with weights up to 20 kg in both hands. The biomechanical model responses were compared with in vivo literature data of intradiscal pressures, intra-abdominal pressures, and muscle activities. The results demonstrated high agreement with this data and highlight the advantages of active hybrid modeling for the LSS. Overall, this new self-contained tool provides a robust and efficient estimation of LSS biomechanical responses under in vivo similar loads, for example, to improve pain treatment by spinal stabilization therapies.

Polypropylene mesh combined with electrospun poly (L-lactic acid) membrane in situ releasing sirolimus and its anti-adhesion efficiency in rat hernia repair

This study developed, a novel polypropylene (PP) mesh combined with poly (L-lactic acid) (PLA) electrospun nanofibers loaded sirolimus (SRL). The PP mesh was combined with PLA/SRL (1/0, 1/0.01, 1/0.02; mass ratios) composed electrospun membrane characterized by FTIR spectroscopy, XPS and SEM, and evaluated for cytocompatibility in vitro. In an in vivo study, a total of 84 Sprague-Dawley rats were employed to evaluate the efficacy of the novel composite PP mesh anti-adhesion, mechanical properties and inflammation. As a results, the PLA/SRL membrane could compound with PP mesh stably and load SRL. Although tensile testing showed that the mechanical properties of composite mesh decreased in vivo, the integration strength between the tissue and mesh was still able to counteract intra-abdominal pressure. Compared with the native PP mesh group, the novel PP mesh group showed a lower score for abdominal adhesion and inflammation. More importantly, the novel PP mesh completely integrated with the abdominal wall and had sufficient mechanical strength to repair abdominal wall defects.

Essential anatomical landmarks in placement of an adequate size mesh for a successful ventral hernia repair

Safe and effective hernia repair requires a surgeon to have the appropriate knowledge necessary to learn details of the surgical technique. Long-term results of treatment, even with the use of synthetic implants, have shown that recurrences were still a significant clinical problem concerning up to every fourth patient. Therefore, it was pointed out that the mere presence of synthetic material is not a solitary circumstance sufficient for a successful repair. A key finding in recurrence prevention has been to focus surgeons' attention on the relationship between the size of the hernia orifice and the mesh surface. An optimal ratio of these values has not been established yet, however, it is considered that the mesh surface area should be at least sixteen times larger than the area of the abdominal wall defect. In cases of medium and large hernias, in order to place an extensive mesh sheet in the appropriate anatomical space of the abdominal wall, an extensive dissection needs to be performed, including several different compartments. Therefore, a surgeon undertaking a hernia repair needs to know perfectly the anatomy and function of all the myofascial structures involved. Performing an incorrect dissection of a mistaken structure may lead to catastrophic abdominal deformities. Depriving the patient of the natural support of the abdominal wall provided by the muscles may lead to total or partial destabilization of the trunk and lead to disability. In this paper a detailed description of anatomical structures and its practical use has been presented.

Functionalized Strategies and Mechanisms of the Emerging Mesh for Abdominal Wall Repair and Regeneration

Meshes have been the overwhelmingly popular choice for the repair of abdominal wall defects to retrieve the bodily integrity of musculofascial layer. Broadly, they are classified into synthetic, biological and composite mesh based on their mechanical and biocompatible features. With the development of anatomical repair techniques and the increasing requirements of constructive remodeling, however, none of these options satisfactorily manages the conditional repair. In both preclinical and clinical studies, materials/agents equipped with distinct functions have been characterized and applied to improve mesh-aided repair, with the importance of mesh functionalization being highlighted. However, limited information exists on systemic comparisons of the underlying mechanisms with respect to functionalized strategies, which are fundamental throughout repair and regeneration. Herein, we address this topic and summarize the current literature by subdividing common functions of the mesh into biomechanics-matched, macrophage-mediated, integration-enhanced, anti-infective and antiadhesive characteristics for a comprehensive overview. In particular, we elaborate their effects separately with respect to host response and integration and discuss their respective advances, challenges and future directions toward a clinical alternative. From the vastly different approaches, we provide insight into the mechanisms involved and offer suggestions for personalized modifications of these emerging meshes.

Biomechanics applied to incisional hernia repair - Considering the critical and the gained resistance towards impacts related to pressure

BACKGROUND

Incisional hernia repair is burdened with recurrence, pain and disability. The repair is usually carried out with a textile mesh fixed between the layers of the abdominal wall.

METHODS

We developed a bench test with low cyclic loading. The test uses dynamic intermittent strain resembling coughs. We applied preoperative computed tomography of the abdomen at rest and during Valsalva's maneuver to the individual patient to analyze tissue elasticity.

FINDINGS

The mesh, its placements and overlap, the type and distribution of fixation elements, the elasticity of the tissue of the individual and the closure of the abdominal defect-all aspects influence the reconstruction necessary. Each influence can be attributed to a relative numerical quantity which can be summed up into a characterizing value. The elasticity of the tissues within the abdominal wall of the individual patient can be assessed with low-dose computed tomography of the abdomen with Valsalva's maneuver. We established a procedure to integrate the results into a surgical concept. We demonstrate potential computer algorithms using non-rigid b-spline registration and artificial intelligence to further improve the evaluation process.

INTERPRETATION

The bench test yields relative values for the characterization of hernia, mesh and fixation. It can be applied to patient care using established procedures. The clinical application in the first ninety-six patients shows no recurrences and reduced pain levels after one year. The concept has been spread to other surgical groups with the same results in another fifty patients. Future efforts will make the abdominal wall reconstruction more predictable.

Modeling of muscular activation of the muscle-tendon complex using discrete element method

The tearing of a muscle-tendon complex (MTC) is caused by an eccentric contraction; however, the structures involved and the mechanisms of rupture are not clearly identified. The passive mechanical behavior the MTC has already been modeled and validated with the discrete element method. The muscular activation is the next needed step. The aim of this study is to model the muscle fiber activation and the muscular activation of the MTC to validate their active mechanical behaviors. Each point of the force/length relationship of the MTC (using a parabolic law for the force/length relationship of muscle fibers) is obtained with two steps: 1) a passive tensile (or contractile) test until the desired elongation is reached and 2) fiber activation during a position holding that can be managed thanks to the Discrete Element model. The muscular activation is controlled by the activation of muscle fiber. The global force/length relationship of a single fiber and of the complete MTC during muscular activation is in agreement with literature. The influence of the external shape of the structure and the pennation angle are also investigated. Results show that the different constituents of the MTC (extracellular matrix, tendon), and the geometry, play an important role during the muscular activation and enable to decrease the maximal isometric force of the MTC. Moreover, the maximal isometric force decreases when the pennation angle increases. Further studies will combine muscular activation with a stretching of the MTC, until rupture, in order to numerically reproduce the tearing of the MTC.

In vivo performance of intraperitoneal onlay mesh after ventral hernia repair

BACKGROUND

Ventral hernia repair needs to be improved since recurrence, postoperative pain and other complications are still reported in many patients. The behavior of implants in vivo is not sufficiently understood to design a surgical mesh mechanically compatible with the human abdominal wall.

METHODS

This analysis was based on radiological pictures of patients who underwent laparoscopic ventral hernia repair. The pictures show the trunk of the patient at rest in a standing position and under side bending. The change in the distance between different tacks due to trunk movement was analyzed, which allowed us to determine the in vivo elongation of the mesh incorporated into the abdominal wall.

FINDINGS

The relative elongations of the surgical mesh varied from a few percent to greater than 100% in two cases. The median of the median relative elongations obtained for all patients is 9.5%, and the median of the maximum relative elongations for all patients is 32.6%. The maximum elongation occurs between tacks that are next to each other. Trunk movement causes implant deformation, and this study provides quantitative information regarding changes in the distance between fasteners.

INTERPRETATION

The physiological movement of the human abdomen must be regarded as a very important factor in mesh deformation and should be considered in surgical practice to reduce the hernia recurrence rate and postoperative pain.

Surgical treatment of diastasis recti: the importance of an overall view of the problem

PURPOSE

Diastasis recti (DR) is characterized by an alteration of the linea alba with increased inter-recti distance (IRD). It is more frequent in females, and when symptomatic or associated with midline hernia it needs to be surgically repaired. This retrospective study aims to demonstrate how an overall approach to DR leads to good results in terms of functional and morphological outcomes and quality of life (QoL).

METHODS

From January 2018 to December 2019, 94 patients were operated for DR > 50 mm, with or without midline hernias. Three different surgical approaches were used: complete laparoabdominoplasty, laparominiabdominoplasty and minimally invasive (endoscopic) technique. QoL was assessed with the EuraHS-QoL tool.

RESULTS

All patients were female except two males. We performed 26 endoscopic treatments (27.7%), 39 laparoabdominoplasties (41.5%) and 29 laparominiabdominoplasties (umbilical float procedure) (30.9%). The total median operative time was 160 min. No intraoperative complications were registered. In three (4.2%) cases, major surgical complications occurred, all after open operations. In 13 open surgery cases, vacuum-assisted closure (VAC) therapy was used to repair the cutaneous ischemic defect. No recurrence was registered to date. Minimally invasive surgery showed fewer complications and lower hospital stay than the open approach. The QoL was significantly improved.

CONCLUSION

Our experience shows the importance of an overall view of the functional and cosmetic impairment created by DR. The surgeon should obtain an optimal repair of the function, by open or minimally invasive surgery, also considering the morphological aspects, which are very important for the patients in terms of QoL.

Application of Acellular Tissue Matrix for Enhancement of Weak Abdominal Wall in Animal Model

Background

Abdominal wall weakness occurs when the strength of muscle decreases due to physiological reason or iatrogenic injury. However, the treatment of this disease is complicated.

Aim

To study the therapeutic effect of acellular tissue matrix (ACTM), compared with the polypropylene mesh.

Methods

An abdominal wall weakness model was established in rabbits through motor nerves cutting. The polypropylene mesh and ACTM were implanted in the left and right abdomen sides, respectively. Mechanical testing of abdominal wall muscle and histology and scanning electron microscopy (SEM) evaluation of abdominal tissue explants were performed.

Results

In animal model establishment, the abdominal length of healthy and weakened abdominal wall was 17.0 ± 0.7 cm and 19.0 ± 1.2 cm, respectively (P=0.022), and the weak abdominal wall group showed a significant decrease of 1.116 ± 0.221 MPa in tensile stress (P=0.022), and the weak abdominal wall group showed a significant decrease of 1.116 ± 0.221 MPa in tensile stress (P=0.022), and the weak abdominal wall group showed a significant decrease of 1.116 ± 0.221 MPa in tensile stress (P=0.022), and the weak abdominal wall group showed a significant decrease of 1.116 ± 0.221 MPa in tensile stress (P=0.022), and the weak abdominal wall group showed a significant decrease of 1.116 ± 0.221 MPa in tensile stress (P=0.022), and the weak abdominal wall group showed a significant decrease of 1.116 ± 0.221 MPa in tensile stress (P=0.022), and the weak abdominal wall group showed a significant decrease of 1.116 ± 0.221 MPa in tensile stress (

Conclusion

The abdominal wall weakness model in rabbits was successfully established. ACTM is a promising biological material to be possibly further applied in clinical surgery in patients with abdominal wall weakness.