Differences in biomechanics of abdominal wall closure with and without mesh reinforcement: A study in post mortem human specimens

Self-organising maps in the analysis of strains of human abdominal wall to identify areas of similar mechanical behaviour

The study refers to the application of a type of artificial neural network called the Self-Organising Map (SOM) for the identification of areas of the human abdominal wall that behave in a similar mechanical way. The research is based on data acquired during in vivo tests using the digital image correlation technique (DIC). The mechanical behaviour of the human abdominal wall is analysed during changing intra-abdominal pressure. SOM allow to study simultaneously three variables in four time/load steps. The variables refer to the principal strains and their directions. SOM classifies all the abdominal surface data points into clusters that behave similarly in accordance with the 12 variables. The analysis of the clusters provides a better insight into abdominal wall deformation and its evolution under pressure than when observing a single mechanical variable. The presented results may provide a better understanding of the mechanics of the living human abdominal wall. It might be particularly useful when selecting proper implants as well as for the design of surgical meshes for the treatment of abdominal hernias, which would be mechanically compatible with identified regions of the human anterior abdominal wall, and possibly open the way for patient-specific solutions.

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.

Study of the biomechanical response of a prosthetic mesh secured with penetrating and non-penetrating fixations in IPOM ventral hernia repair

INTRODUCTION

Sutures or tacks are commonly used to secure a mesh in intraperitoneal onlay mesh (IPOM) hernia repair, but such penetrating fixations can cause local damage, that can be associated with pain. The use of an adhesive could be an alternative to reduce complications. However, a risk associated with this approach has been identified, particularly when the defect cannot be closed. A mesh glued to the peritoneum only might not provide as much mechanical reinforcement to the abdominal wall (AW) as a mesh anchored to the myofascial structure with penetrating fixations, which could lead to an increased recurrence rate. Additionally, the high elasticity of the peritoneum may increase mesh bulging. Leveraging an ex vivo approach, the objective of this study was to investigate the impact of mesh fixation using glue versus barbed sutures, on its biomechanical response for IPOM surgery.

METHODS

An experimental method was developed using ex vivo porcine abdominal wall samples (n = 12). A 4-cm centered circular defect was created by dissecting the skin and the subcutaneous tissue and removing muscle and extraperitoneal fat, while keeping the peritoneum intact. A 14-cm diameter mesh was secured (Dermabond™ cyanoacrylate adhesive or V-Loc™ barbed sutures) to the AW. The mesh was placed on the peritoneum to remain consistent with the IPOM placement. The sample was then subjected to some inflation tests to simulate increased levels of intra-abdominal pressure (IAP) representing daily activities. For each test, mesh bulging into the defect was assessed as a function of the pressure using Digital Image Correlation (DIC) analysis.

RESULTS

Mesh bulging was studied for 2 configurations: suture fixation and glue. Glued meshes exhibited significantly higher bulging values than when sutured with a significant difference (p = 0.013) observed at 252 mmHg and a certain trend for statistical difference (p < 0.1) for stair climbing or coughing activities. Additionally, the stiffness of the repair was also significantly higher when the mesh was sutured compared to when it was glued to the peritoneum (p < 0.05).

CONCLUSION

This study demonstrated that a mesh glued to the peritoneum exhibited higher bulging and a behavior of the repair less stiff compared to when it was sutured to the myofascial structure of the AW, particularly for high intra-abdominal pressures. However, the impact of these differences remains to be evaluated over time. Further preclinical investigations are needed to quantify their impact post-operatively.

Full-field in vivo experimental study of the strains of a breathing human abdominal wall with intra-abdominal pressure variation

The presented study aims to assess the mechanical behaviour of the anterior abdominal wall based on an in vivo experiment on humans. Full-field measurement of abdominal wall displacement during changes of intra-abdominal pressure is performed using a digital image correlation (DIC) system. Continuous measurement in time enables the observation of changes in the strain field during breathing. The understanding of the mechanical behaviour of a living human abdominal wall is important for the proper design of surgical meshes used for ventral hernia repair, which was also a motivation for the research presented below. The research refers to the strain field of a loaded abdominal wall and presents the evolution of principal strains and their directions in the case of 12 subjects, 8 male and 4 female. Peritoneal dialysis procedure allows for the measurement of intra-abdominal pressure after fluid introduction. High variability among patients is observed, also in terms of principal strain direction. Subjects exhibit intra-abdominal pressure of values from 11 to 21 cmH2O. However, the strain values are not strongly correlated with the pressure value, indicating variability of material properties.

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.

A novel in vivo approach to assess strains of the human abdominal wall under known intraabdominal pressure

The study concerns mechanical behaviour of a living human abdominal wall. A better mechanical understanding of a human abdominal wall and recognition of its material properties is required to find mechanically compatible surgical meshes to significantly improve the treatment of ventral hernias. A non-invasive methodology, based on in vivo optical measurements is proposed to determine strains of abdominal wall corresponding to a known intraabdominal pressure. The measurement is performed in the course of a standard procedure of peritoneal dialysis. A dedicated experimental stand is designed for the experiment. The photogrammetric technique is employed to recover the three-dimensional surface geometry of the anterior abdominal wall at the initial and terminal instants of the dialysis. This corresponds to two deformation states, before and after filling the abdominal cavity with dialysis fluid. The study provides information on strain fields of living human abdominal wall. The inquiry is aimed at principal strains and their directions, observed at the level from -10% to 17%. The intraabdominal pressure related to the amount of introduced dialysis fluid measured within the medical procedure covers the range 11-18.5 cmH₂O. The methodology leads to the deformation state of the abdominal wall according to the corresponding loading conditions. Therefore, the study is a step towards an identification of mechanical properties of living human abdominal wall.