Understanding the Passive Mechanical Behavior of the Human Abdominal Wall

A virtual simulation study of the effects of laparotomy incision location and wound stiffness on abdominal wall mechanics

Incisional hernia (IH) is a common complication of laparotomy surgical procedures, influenced by factors such as incision location and surgical wound (SW) tissue strength, and the intra-abdominal pressure (IAP) levels the patient is subject to. In this study we use finite element simulations to investigate how these factors affect the abdominal wall (AW) deformation and the stress distribution on the tissues. Comprehensive geometric models of the AW were generated for five laparotomy incisions, namely midline, paramedian, pararectus, transverse supraumbilical, and subcostal oblique. Finite element simulations for IAP values between 4 and 20 kPa and with the SW tissue strength ranging from very soft to very stiff were conducted using the code Aster open-source software. Simulations revealed that as a general rule laparotomy incisions significantly impact AW mechanics when the SW tissue is soft. In particular, AW mechanics is more sensitive to SW strength in vertical incisions (midline, paramedian, pararectus). The resulting change of the SW dimensions with increasing IAP was also investigated. Softening the SW tissue led to substantial volume increases of the vertical incisions for a given IAP level. In addition, we analyzed stress levels in the SW tissue as well as in the surrounding muscles. A very soft SW may induce the appearance of regions with very high stress levels in the surrounding muscle tissue, heightening their rupture risk. This effect was especially noticeable for the midline incision. On the overall, we found that when the SW tissue is too tender transverse supraumbilical and subcostal incisions present the lowest risk of tissue ruptures whereas the midline incision is the most vulnerable one and the paramedian and pararectus incisions stand midway. In summary, the results of the present simulation provide full support for the clinical guidelines' recommendation to avoid midline incisions in abdominal surgeries whenever possible.

[Remodeling of muscular layer of abdominal wall in patients with postoperative ventral hernia]

OBJECTIVE

To compare the musculature of anterior abdominal wall in healthy people and patients with large or gigantic ventral hernia.

MATERIAL AND METHODS

A retrospective study included 200 patients between January 2020 and September 2024. Two groups were formed for subsequent analysis. The first group consisted of 100 participants without postoperative ventral hernia who underwent examination and treatment. The second group consisted of 100 patients diagnosed with large or giant ventral hernias. All participants underwent computed tomography (CT) of the abdomen, retroperitoneal space and pelvic region. Analysis of anterior abdominal wall muscles was based on CT findings. Thickness, length, area, density, symmetry, structural integrity, volume and circumference were measured.

RESULTS

There were significant differences in muscle length along the inner and outer contours on the right side and area of anterior abdominal wall muscles on both sides. These findings suggest potential changes of these parameters in the 2nd group. Thickness of anterior abdominal muscles differed significantly (p-value ~0.017).

CONCLUSION

There are significant structural differences in anterior abdominal wall musculature between healthy individuals and people with large and giant ventral hernias. This information can improve preoperative management and surgical techniques aimed at restoring the integrity and function of abdominal wall.

Numerical modeling of the abdominal wall biomechanics and experimental analysis for model validation

The evaluation of the biomechanics of the abdominal wall is particularly important to understand the onset of pathological conditions related to weakening and injury of the abdominal muscles. A better understanding of the biomechanics of the abdominal wall could be a breakthrough in the development of new therapeutic approaches. For this purpose, several studies in the literature propose finite element models of the human abdomen, based on the geometry of the abdominal wall from medical images and on constitutive formulations describing the mechanical behavior of fascial and muscular tissues. The biomechanics of the abdominal wall depends on the passive mechanical properties of fascial and muscle tissue, on the activation of abdominal muscles, and on the variable intra-abdominal pressure. To assess the quantitative contribution of these features to the development and validation of reliable numerical models, experimental data are fundamental. This work presents a review of the state of the art of numerical models developed to investigate abdominal wall biomechanics. Different experimental techniques, which can provide data for model validation, are also presented. These include electromyography, ultrasound imaging, intraabdominal pressure measurements, abdominal surface deformation, and stiffness/compliance measurements.

Gender Equality in Diastasis Rectus Abdominis in Chronic Back Pain: A Model of M. Transversus Abdominis Motor Control Impairment

Introduction: Diastasis rectus abdominis (DRA) is defined as an increased distance between the left and right muscle of the m. rectus abdominis. Pregnancy-related factors are assumed to be dominant factors in the occurrence of DRA. However DRA is not only found in peri-partum women but also in men and nulliparous women with back or pelvic pain. This study provides an inventory of the incidence of DRA in subjects with chronic back and pelvic pain. If DRA is common in both men and women then other factors besides pregnancy, like impaired motor control, should be explored as cause for DRA. Material and Methods: This study was conducted with data from 849 back pain patients. Results from ultrasound assessment of the abdominal wall were combined with anamnestic data on age, gender, medical history and pregnancies (in women). Results: There was no difference in Inter Rectus Distance cranial of the umbilicus (IRD above umbilicus) between men and women. Almost half of all women and men (45% and 43%, respectively) exhibit an increased IRD above umbilicus. The incidence of an increased IRD above umbilicus is twice as high in women below 30 years, compared to men below 30 years old. This difference is not observed for men and women above 30 years old. Discussion: DRA occurs in women during pregnancy and increases with an increasing number of pregnancies. However, this condition does not affect significantly more women than men. Increased IRD above umbilicus already occurs in young men (mean age 30). Over 30 years of age, cranial of the umbilicus there is no difference in IRD between women and men. An alternative etiological mechanism is suggested.

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.

Shape-Configurable Mesh for Hernia Repair by Synchronizing Anisotropic Body Motion

Continuous progress has been made in elucidating the relationship between material property, device design, and body function to develop surgical meshes. However, an unmet need still exists wherein the surgical mesh can handle the body motion and thereby promote the repair process. Here, the hernia mesh design and the advanced polymer properties are tailored to synchronize with the anisotropic abdominal motion through shape configuration. The thermomechanical property of shape configurable polymer enables molding of mesh shape to fit onto the abdominal structure upon temperature shift, followed by shape fixing with the release of the heat energy. The microstructural design of mesh is produced through finite element modeling to handle the abdominal motion efficiently through the anisotropic longitudinal and transverse directions. The design effects are validated through in vitro, ex vivo, and in vivo mechanical analyses using a self-configurable, body motion responsive (BMR) mesh. The regenerative function of BMR mesh leads to effective repair in a rat hernioplasty model by effectively handling the anisotropic abdomen motion. Subsequently, the device-tissue integration is promoted by promoting healthy collagen synthesis with fibroblast-to-myofibroblast differentiation. This study suggests a potential solution to promote hernia repair by fine-tuning the relationship between material property and mesh design.

Biomechanical stability of hernia-damaged abdominal walls

Hernia occurs when the peritoneum and/or internal organs penetrate through a defect in the abdominal wall. Implanting mesh fabrics is a common way to reinforce the repair of hernia-damaged tissues, despite the risks of infection and failure associated with them. However, there is neither consensus on the optimum mesh placement within the abdominal muscles complex nor on the minimum size of hernia defect that requires surgical correction. Here we show that the optimum position of the mesh depends on the hernia location; placing the mesh on the transversus abdominis muscles reduces the equivalent stresses in the damaged zone and represents the optimum reinforcement solution for incisional hernia. However, retrorectus reinforcement of the linea alba is more effective than preperitoneal, anterectus, and onlay implantations in the case of paraumbilical hernia. Using the principles of fracture mechanics, we found that the critical size of a hernia damage zone becomes severe at 4.1 cm in the rectus abdominis and at larger sizes (5.2-8.2 cm) in other anterior abdominal muscles. Furthermore, we found that the hernia defect size must reach 7.8 mm in the rectus abdominis before it influences the failure stress. In other anterior abdominal muscles, hernia starts to influence the failure stress at sizes ranging from 1.5 to 3.4 mm. Our results provide objective criteria to decide when a hernia damage zone becomes severe and requires repair. They demonstrate where mesh should be implanted for a mechanically stable reinforcement, depending on the type of hernia. We anticipate our contribution to be a starting point for sophisticated models of damage and fracture biomechanics. For example, the apparent fracture toughness is an important physical property that should be determined for patients living with different obesity levels. Furthermore, relevant mechanical properties of abdominal muscles at various ages and health conditions would be significant to generate patient specific results.

The plasticity of biocompatibility

Biocompatibility concerns the phenomena that occur within the interactions between biomaterials and human patients, which ultimately control the performance of many facets of medical technology. It involves aspects of materials science, many different forms of engineering and nanotechnology, chemistry, biophysics, molecular and cellular biology, immunology, pathology and a myriad of clinical applications. It is not surprising that an overarching framework of mechanisms of biocompatibility has been difficult to elucidate and validate. This essay discusses one fundamental reason for this; we have tended to consider biocompatibility pathways as essentially linear sequences of events which follow well-understood processes of materials science and biology. The reality, however, is that the pathways may involve a great deal of plasticity, in which many additional idiosyncratic factors, including those of genetic, epigenetic and viral origin, exert influence, as do complex mechanical, physical and pharmacological variables. Plasticity is an inherent core feature of the performance of synthetic materials; here we follow the more recent biological applications of plasticity concepts into the sphere of biocompatibility pathways. A straightforward linear pathway may result in successful outcomes for many patients; we may describe this in terms of classic biocompatibility pathways. In other situations, which usually command much more attention because of their unsuccessful outcomes, these plasticity-driven processes follow alternative biocompatibility pathways; often, the variability in outcomes with identical technologies is due to biological plasticity rather than material or device deficiency.

Split Tummy Exercise Program for Reducing Diastasis Recti in Postpartum Primigravidae: A Randomized Controlled Trial

BACKGROUND

Diastasis rectus abdominis (DRA) involves the separation of the midline abdominal muscles and linea alba and affects more than half of postpartum women. This study aimed to assess the effect of a split tummy exercise program (STEP) on DRA closure in postpartum mothers.

METHODS

A randomized controlled trial was conducted from 2008 to 2020 at the Obstetrics and Gynaecology Clinic of the Universiti Kebangsaan Malaysia Medical Centre. Primigravida mothers diagnosed with DRA were selected and randomly assigned to the intervention (n=21) or control (n=20) group. The intervention group underwent a home-based STEP consisting of three phases of nine abdominal exercises. DRA size was assessed at baseline and at 8 weeks postpartum using two-dimensional ultrasound.

RESULTS

The mean age of the participants was 28 years (standard deviation, 3.6), with the majority of Malay ethnicity (87.8%) and working mothers (78%). After 8 weeks, the intervention group showed a significant reduction in DRA size of up to 27% (mean difference, 6.17 mm; 95% confidence interval, 3.7-8.7; P<0.001). No significant intergroup DRA changes were observed after 8 weeks of follow-up.

CONCLUSION

Early postpartum screening for DRA should be advocated to allow early STEP intervention to ensure favorable outcomes. STEP intervention is an effective postnatal training program for managing DRA.

New Insights into the Application of 3D-Printing Technology in Hernia Repair

Abdominal hernia repair using prosthetic materials is among the surgical interventions most widely performed worldwide. These materials, or meshes, are implanted to close the hernial defect, reinforcing the abdominal muscles and reestablishing mechanical functionality of the wall. Meshes for hernia repair are made of synthetic or biological materials exhibiting multiple shapes and configurations. Despite the myriad of devices currently marketed, the search for the ideal mesh continues as, thus far, no device offers optimal tissue repair and restored mechanical performance while minimizing postoperative complications. Additive manufacturing, or 3D-printing, has great potential for biomedical applications. Over the years, different biomaterials with advanced features have been successfully manufactured via 3D-printing for the repair of hard and soft tissues. This technological improvement is of high clinical relevance and paves the way to produce next-generation devices tailored to suit each individual patient. This review focuses on the state of the art and applications of 3D-printing technology for the manufacture of synthetic meshes. We highlight the latest approaches aimed at developing improved bioactive materials (e.g., optimizing antibacterial performance, drug release, or device opacity for contrast imaging). Challenges, limitations, and future perspectives are discussed, offering a comprehensive scenario for the applicability of 3D-printing in hernia repair.

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.

Testing meshes in a computer model of a laparoscopic ventral hernia repair

BACKGROUND

The ideal mesh for hernia repair has yet to be found, in addition our knowledge of the biomechanics of the abdominal wall is poor. The aim of this study was to develop a computer model of a laparoscopic ventral hernia repair and to test different meshes in that model at various intra-abdominal pressures.

METHODS

Four meshes were tested in a computer model of a ventral hernia. Mechanical failure testing of each mesh was performed in both the longitudinal and transverse directions. A CT scan of a patient with a 5 cm umbilical hernia was used to generate a 3 dimensional model. Meshes were then applied to the model in an intraperitoneal onlay position with a 5 cm overlap. The model was then tested with intraabdominal pressures for standing, coughing and jumping with and without meshes.

RESULTS

Meshes varied significantly (p < 0.001) in both rupture force 14.8 (5.6) to 78 (5) n/cm and force in which they changed from elastic to plastic 1.6 (0.1) to 14.2 (0.2) n/cm. When applied to the computer model all significantly reduced the strain on the abdominal wall from 17.5% without mesh to less than 1% with mesh. All meshes prevented the hernia from bulging in the model.

CONCLUSIONS

We have developed a computer model of laparoscopic ventral hernia repair based on engineering principles. This model demonstrated that meshes tested significantly reduced the strain on the abdominal wall. Further studies are required to refine this model in order to best simulate the biomechanics of the abdominal wall.

Exercises, Tubigrip and taping: can they reduce rectus abdominis diastasis measured three weeks post-partum?

BACKGROUND

Rectus abdominis diastasis is regarded as a risk factor for abdominal muscle dysfunction and reduced quality of life postpartum. It is thought that specific exercises and additional physical support might reduce the diastasis, with a need to establish efficacy in doing so.

OBJECTIVES

Determine the effect of four abdominal exercises as well as Tubigrip or taping in reducing rectus abdominis diastases three weeks postpartum.

DESIGN

Cross-sectional repeated measures comparison.

METHODS

32 women undertook a single session of ultrasound imaging. Ultrasound measurements of inter-rectus distance were taken at rest and during: 1) crook lying abdominal "drawing in" exercise; 2) crook lying trunk curl-up; 3) early Sahrmann level leg raise; 4) McGill side lying plank. The curl-up and abdominal "drawing in" exercises were assessed under two further conditions: a) wearing Tubigrip, b) taping across the diastasis. Data analyses involved repeated measures ANOVA.

RESULTS

At rest the mean inter-rectus distance above and below the umbilicus was 3.5 cm (SD:1.1) and 2.6 cm (SD:1.2) respectively. A significant decrease (19%, p < 0.05) was observed at both measurement points during the curl-up exercise. No other exercises elicited a significant difference compared to resting. At rest, wearing Tubigrip reduced the inter-rectus distance (7%, p < 0.05). During exercise, there was no additional change in the inter-rectus distance (p > 0.05) with supports.

CONCLUSION

The curl-up exercise was most effective in reducing inter-rectus distance. As no exercises invoked an increase in the rectus diastasis, they could not be regarded as potentially detrimental. Tubigrip and taping did not add to the effects of these exercises.

Regulatory science for hernia mesh: Current status and future perspectives

Regulatory science for medical devices aims to develop new tools, standards and approaches to assess the safety, effectiveness, quality and performance of medical devices. In the field of biomaterials, hernia mesh is a class of implants that have been successfully translated to clinical applications. With a focus on hernia mesh and its regulatory science system, this paper collected and reviewed information on hernia mesh products and biomaterials in both Chinese and American markets. The current development of regulatory science for hernia mesh, including its regulations, standards, guidance documents and classification, and the scientific evaluation of its safety and effectiveness was first reported. Then the research prospect of regulatory science for hernia mesh was discussed. New methods for the preclinical animal study and new tools for the evaluation of the safety and effectiveness of hernia mesh, such as computational modeling, big data platform and evidence-based research, were assessed. By taking the regulatory science of hernia mesh as a case study, this review provided a research basis for developing a regulatory science system of implantable medical devices, furthering the systematic evaluation of the safety and effectiveness of medical devices for better regulatory decision-making. This was the first article reviewing the regulatory science of hernia mesh and biomaterial-based implants. It also proposed and explained the concepts of evidence-based regulatory science and technical review for the first time.

The extraperitoneal French AmbUlatory cesarean section technique leads to improved pain scores and a faster maternal autonomy compared with the intraperitoneal Misgav Ladach technique: A prospective randomized controlled trial

Objective

To determine whether the French AmbUlatory Cesarean Section (FAUCS) technique reduces postoperative pain and promotes maternal autonomy compared with the Misgav Ladach cesarean section (MLCS) technique in elective conditions.

Study design

One hundred pregnant women were randomly, but in a non-blinded manner, assigned to undergo FAUCS or MLCS. The primary outcome was a postoperative mean pain score (PMPS), and secondary outcomes were a combined pain/medication score, time to regain autonomy, surgical duration, calculated blood loss, surgical complications, and neonatal outcome.

Results

Women in the FAUCS group experienced less pain than those in the MLCS group (PMPS = 1.87 [1.04–2.41] vs. 2.93 [2.46–3.75], respectively; p < 0.001). Six hours after surgery, the combined pain/medication score for FAUCS patients was 33% lower than that for MLCS patients (p < 0.001). FAUCS patients more rapidly regained autonomy, with 94% reaching autonomy within 12 h vs. 4% of MLCS patients (p < 0.001). There were no differences in maternal surgical or neonatal complications between groups.

Conclusions

Our results indicate that FAUCS can reduce postoperative pain and accelerate recovery, suggesting that this technique might be superior to MLCS and should be more widely used. One potentially key difference between FAUCS and MLCS is that MLCS includes 100 mcg spinal morphine anesthesia in addition to the same anesthesia used by FAUCS. Any interpretation of apparent differences must take the presence/absence of morphine into account.

Modeling intra-abdominal volume and respiratory driving pressure during pneumoperitoneum insufflation-a patient-level data meta-analysis

During pneumoperitoneum, intra-abdominal pressure (IAP) is usually kept at 12-14 mmHg. There is no clinical benefit in IAP increments if they do not increase intra-abdominal volume IAV. We aimed to estimate IAV (ΔIAV) and respiratory driving pressure changes (ΔP_RS) in relation to changes in IAP (ΔIAP). We carried out a patient-level meta-analysis of 204 adult patients with available data on IAV and ΔP_RS during pneumoperitoneum from three trials assessing the effect of IAP on postoperative recovery and airway pressure during laparoscopic surgery under general anesthesia. The primary endpoint was ΔIAV, and the secondary endpoint was ΔP_RS. The endpoints' response to ΔIAP was modeled using mixed multivariable Bayesian regression to estimate which mathematical function best fitted it. IAP values on the pressure-volume (PV) curve where the endpoint rate of change according to IAP decreased were identified. Abdomino-thoracic transmission (ATT) rate, that is, the rate ΔP_RS change to ΔIAP was also estimated. The best-fitting function was sigmoid logistic and linear for IAV and ΔP_RS response, respectively. Increments in IAV reached a plateau at 6.0 [95%CI 5.9-6.2] L. ΔIAV for each ΔIAP decreased at IAP ranging from 9.8 [95%CI 9.7-9.9] to 12.2 [12.0-12.3] mmHg. ATT rate was 0.65 [95%CI 0.62-0.68]. One mmHg of IAP raised ΔP_RS 0.88 cmH₂O. During pneumoperitoneum, IAP has a nonlinear relationship with IAV and a linear one with ΔP_RS. IAP should be set below the point where IAV gains diminish.NEW & NOTEWORTHY We found that intra-abdominal volume changes related to intra-abdominal pressure increase reached a plateau with diminishing gains in commonly used pneumoperitoneum pressure ranges. We also found a linear relationship between intra-abdominal pressure and respiratory driving pressure, a known marker of postoperative pulmonary complications.

Comparative study of collagen and elastin content of abdominal wall fascia in inguinal hernia and non-hernia patients in an African population

PURPOSE

Altered composition of collagen and elastin in abdominal fascia has been linked with the pathogenesis of hernias. This has not been studied amongst Africans who have hernia presentations which vary significantly from Caucasian cohorts. The aim of this study was to determine, and compare, the collagen and elastin contents of the transversalis fascia and rectus sheath of inguinal hernia patients with non-hernia controls.

METHODS

Twenty-five patients with solitary, primary, uncomplicated inguinal hernia and twenty-five non-hernia controls were evaluated. Biopsies of the transversalis fascia and anterior rectus sheath were stained with Masson Trichrome and Verhöeff van-Gieson to isolate collagen and elastin respectively, which were quantified using the ImageJ/Fiji® image analysis software.

RESULTS

Inguinal hernia patients were aged 19-85 years with a mean age of 45.2 years, mean body mass index (BMI) of 23.3 kg/m² and mean duration of hernia of 42.5 months. Lateral hernias with no hernia defect or posterior wall defect [PL0] were the predominant clinical type. There were significantly lower collagen and higher elastin content in the transversalis fascia and rectus sheath of inguinal hernia patients [P < 0.001]. Regression analysis identified smoking and long duration of hernias as independent predictors of low collagen levels in this study CONCLUSION: Inguinal hernia patients in the study population demonstrated depleted collagen in the connective tissue of the inguinal canal. This might justify the routine use of prosthetic mesh for the reinforcement of the posterior wall during hernia repair.

Age-related changes in mechanical properties of human abdominal fascia

The purpose of this study is to assess and model age-related changes in the mechanical properties of human fascia. The samples were divided into three age groups: group A-up to 60 years (mean age 52.5 ± 6 years), group B-61-80 years (mean age 70.4 ± 5.2 years), and group C-81-90 years (mean age 83.2 ± 2 years). A uniaxial tensile test was applied to fascia specimens cut perpendicular and parallel to fibers. The secant modulus at 5% strain, the maximum stress, and the stretch at maximum stress were calculated from the stress-stretch ratio curves. The results indicated an increase in the secant modulus with the increased age. The trend is clearer in the longitudinal direction. Considering the strain energy function which accounts the isotropic and non-isotropic response of the fascia where isotropic and anisotropic parts are split, we evaluated which material model is the most suitable to present isotropic mechanical behavior of the tissue. The experimental stress-stretch ratio curves were approximated using Mooney-Rivlin, Yeoh, and neo-Hookean strain energy functions and a good match between theoretical and experimental results was obtained. On the basis of objective function values and normalized mean square root error, we recommend using the Yeoh model to describe the isotropic mechanical behavior of human abdominal fascia. Graphical abstract .

Abdominal wall morphometric variability based on computed tomography: Influence of age, gender, and body mass index

INTRODUCTION

Ventral hernia surgery does not usually account for the individuality of the abdominal wall anatomy. This could be both because medical imaging is rarely performed before surgery and because data on abdominal wall variability are limited. The objective of the present study was to perform an exhaustive morphometric analysis of abdominal wall components based on computed tomography (CT) scans.

MATERIALS AND METHODS

A retrospective study was performed on 120 abdominopelvic CT scans of clinically normal adults aged 18-86 years equally divided between women and men and into four age groups. Each abdominal wall muscle was evaluated in terms of area, thickness, shape ratio, fat infiltration, and aponeuroses width. The influence of age, gender, and body mass index (BMI) was investigated, as well as muscular asymmetry.

RESULTS

The abdominal wall muscle area represented 8.5 ± 2.5% of the abdominal area. The internal oblique muscle had the largest area, the rectus abdominis was the thickest, the transversus abdominis was the narrowest and had the smallest area. The width of the linea alba was 20.3 ± 12.0 mm. The evolution of the abdominal wall with age was quantified, as well as the large differences between the sexes and BMI groups, resulting in strong correlations and highlighting the specific pattern of the transversus abdominis. The asymmetry of the left and right muscle areas oscillated around 17%.

CONCLUSIONS

The various components of the abdominal wall have been precisely described. Knowledge of their variability could be used to enhance the planning of ventral hernia surgery or to develop numerical modeling of the abdominal wall.

Anterior and posterior rectus abdominis sheath stiffness in relation to diastasis recti: Abdominal wall training or not?

INTRODUCTION

This study explores the anatomical relation of the rectus abdominis muscles with the anterior and posterior rectus sheaths. The elastic behavior of these fascial sheets is also assessed. Both of these analyses form an anatomic-biomechanical basis for diagnosis and treatment, especially in relation to diastasis recti abdominis (DRA).

METHOD

Fundamental observational, biomechanical study. Seven post-mortem, embalmed human specimens were dissected. The abdominal muscles and the fascial sheets of the abdominal wall were dissected. 4 × 4 cm samples of the anterior and posterior rectus sheaths were loaded in longitudinal and transverse direction, while recording elongation by means of a displacement sensor. The main outcome measures were anatomical descriptions and elongation of fascia samples in mm (mean and standard ± deviation).

RESULTS

In longitudinal direction the posterior rectus sheath samples stretched over 1.67 ± 0.48 mm, while in transverse direction the mean stretch was 0.29 ± 0.18 mm (p = 0.001). In contrast, no significant difference between longitudinal (0.78 ± 0.43 mm) and transversal displacement (0.50 ± 0.23 mm) was observed in the anterior rectus sheath (p = 0.56).

DISCUSSION AND CONCLUSION

The posterior rectus sheath is functionally more related to the transverse abdominis muscle than to the rectus abdominis muscle. From this connection, in combination with the specific stiffness of the posterior fascia in the lateral direction, it is assumed that the transverse abdominis muscles play an important role in the etiology but also in reduction of DRA. The transverse abdominis and rectus abdominis muscles collaborate in support of the abdominal wall.

Abdominal Compliance and Laparoscopy: A Review

Background and Objectives

Creating and maintaining a pneumoperitoneum to perform laparoscopy is governed by gas laws and the limiting physical constraints of the abdomen.

Methods

A review of how gas, biomechanical and physical properties affect the abdomen and a systematic structured Medline and PubMed search was conducted to identify relevant studies related to the topic.

Results

Abdominal compliance is a measure of ease of abdominal expansion and is determined by the elasticity of the abdominal wall and diaphragm. It is the change in intra-abdominal volume per change in intra-abdominal pressure. Caution should be exercised with pressures exceeding 12 millimeters mercury since this is defined as intra-abdominal hypertension.

Conclusions

Abdominal compliance has its limits, is unique for each patient and pressure-volume curves cannot be easily predicted. Using the lowest possible pressure to accomplish the surgical task without compromising surgical outcome is the desired goal. The clinical importance is caution and knowing there is a point where more pressure does not increase working space and only increases pressure.

Diastasis Recti Abdominis-diagnosis, Risk Factors, Effect on Musculoskeletal Function, Framework for Treatment and Implications for the Pelvic Floor

Background:

Diastasis Recti Abdominis (DRA) can occur during pregnancy and postpartum. It is defined as an increase of the inter-recti distance (IRD) beyond normal values. The diagnosis of DRA is inconsistent within the literature and varies depending on measurement instrument and activity during measurement (rest versus active curl-up). DRA is characterized by the stretching of linea alba (LA) and contributes to a protrusion of the anterior abdominal wall due to increased laxity in the myofascial system that supports abdominal viscera. DRA has been postulated to affect lumbopelvic support and function due to laxity of the LA and altered angle of muscle insertion, but recent studies have not confirmed this. Risk factors for the development of DRA have been investigated in pregnancy to 12-months postpartum.

Objective:

Rehabilitation for DRA has been traditionally focused on reducing the IRD, but recent research has proposed that a sole focus on closing the DRA is suboptimal.

Results:

It is important alongside the rehabilitation of the abdominal wall that there is the consideration of the pelvic floor (PF). In healthy individuals, with the activation of the transversus abdominis, there is a sub-maximal co-contraction of the PF muscles. This co-contraction can be lost or altered in women with urinary incontinence. An increase in intra-abdominal pressure without simultaneous co-contraction of the PF may cause caudal displacement of the PF.

Conclusion:

The aim of this review is to bring the reader up to date on the evidence on DRA and to propose a rehabilitation framework for the whole abdominal wall in DRA with consideration of the impact on the PF.

Pre-clinical assay of the tissue integration and mechanical adhesion of several types of cyanoacrylate adhesives in the fixation of lightweight polypropylene meshes for abdominal hernia repair

INTRODUCTION

Lightweight (LW) polypropylene (PP) meshes better adapt to host tissue, causing less fibrosis and inflammatory responses than high-density meshes. Mesh fixation using tissue adhesives (TA) that replace conventional sutures may improve the process of hernia repair and tissue trauma. This preclinical study compares the behavior of different cyanoacrylate-based adhesives in the fixation of LW-PP meshes for hernia repair.

METHODS

Partial abdominal wall defects were repaired using LW-PP Optilene meshes in New Zealand rabbits. The following groups were established according to the mesh fixation method: Suture (control), Glubran 2 (n-butyl), Ifabond (n-hexyl), SafetySeal (n-butyl) and Evobond (n-octyl). At 14, 90 and 180 days after surgery, the recovered implants were examined to assess the host tissue integration, the macrophage response and the biomechanical strength.

RESULTS

All the groups showed optimal host tissue incorporation regardless of the fixation procedure. Significantly increased levels of collagen 1 and collagen 3 gene expression (p<0.001) were observed at 14 days compared to the medium- and long-term durations, where the Suture and Glubran groups showed the highest expression of collagen 1. All the adhesives increased the macrophage reaction (p<0.001) compared to sutures at all implant times. Maximal macrophage response was observed in the short-term Glubran group (p<0.01) compared to the rest of the groups. Although SafetySeal and Evobond did not reach the biomechanical resistance of sutures at 14 days, all the adhesives did reach this level in the medium- to long-term periods, providing significantly higher resistance (p<0.05).

CONCLUSIONS

All the cyanoacrylates, despite inducing a significantly increased macrophage response versus sutures, showed optimal host tissue integration and long-term mechanical behavior; thus, they might be good choices for LW-PP mesh hernia repairs.

A numerical investigation of the healthy abdominal wall structures

The present work aims to assess, via numerical modeling, the global passive mechanical behavior of the healthy abdominal wall under the action of pressures that characterize different daily tasks and physiological functions. The evaluation of a normal range of intra-abdominal pressure (IAP) during activities of daily living is fundamental because pressure alterations can cause several adverse effects. At this purpose, a finite element model is developed from literature histomorphometric data and from diagnostic images of Computed Tomography (CT), detailing the different anatomical regions. Numerical simulations cover an IAP up to the physiological limit of 171 (0.0223MPa) mmHg reached while jumping. Numerical results are in agreement with evidences on physiological abdomens when evaluating the local deformations along the craniocaudal direction, the transversal load forces in different regions and the increase of the abdominal area at a IAP of 12mmHg. The developed model can be upgraded for the investigation of the abdominal hernia repair and the assessment of prostheses mechanical compatibility, correlating stiffness and tensile strength of the abdominal tissues with those of surgical meshes.

Immediate Effect of Active Abdominal Contraction on Inter-recti Distance

STUDY DESIGN

Controlled laboratory study.

BACKGROUND

Inter-recti distance (IRD) is the measurement of the linear distance between the medial aspects of the rectus abdominis muscle. Inter-recti distance has been reported to decrease in postpartum women during a curl-up maneuver.

OBJECTIVE

To determine if IRD decreases with active abdominal contraction in men and in nulliparous and parous women.

METHODS

Fifty-six subjects (male, 11; nulliparous female, 22; parous female, 23) participated. Inter-recti distance was measured with the abdominal muscles at rest and during active contraction (curl-up), at 2 locations (above and below the umbilicus), using ultrasound imaging. A mixed-model, repeated-measures analysis of covariance was used for each of the 2 locations, to determine whether IRD differed between contraction states among the 3 groups, with age and umbilicus circumference as covariates. When significant differences were found, planned t test comparisons were made.

RESULTS

The parous group's IRD significantly decreased from rest to contraction at both locations, whereas the nulliparous and male groups' IRD did not significantly change from rest to contraction. The nulliparous group's IRD was significantly narrower than the other groups at rest at both locations, and narrower than the parous group during active contraction.

CONCLUSION

Parous women had a narrower IRD in the curl-up condition than at rest, as hypothesized. However, an unexpected finding of a lack of significant within-group change in IRD in nulliparous women and men occurred. Findings suggest that the IRD in men may only differ from that of nulliparous women.

Incisional and port-site hernias following robotic colorectal surgery

BACKGROUND

The association between extraction site location, robotic trocar size, and the incidence of incisional hernias in robotic colorectal surgery remain unclear. Laparoscopic literature reports variable rates of incisional hernias versus open surgery, and variable rates of trocar site hernias. However, conclusions from these studies are confusing due to heterogeneity in closure techniques and may not be generalized to robotic cases. This study evaluates the effect of extraction site location on incisional hernia rates, as well as trocar hernia rates in robotic colorectal surgery.

MATERIALS AND METHODS

A retrospective review of multiport and single incision robotic colorectal surgeries from a single institution was performed. Patients underwent subtotal, segmental, or proctocolectomies, and were compared based on the extraction site through either a muscle-splitting (MS) or midline (ML) incision. Hernias were identified by imaging and/or physical exam. Demographics and risk factors for hernias were assessed. Groups were compared using a multivariate logistic regression analysis.

RESULTS

The study included 259 colorectal surgery patients comprising 146 with MS and 113 with ML extraction sites. Postoperative computed tomograms were performed on 155 patients (59.8 %) with a mean follow-up of 16.5 months. The overall incisional hernia rate was 5.8 %. A significantly higher hernia rate was found among the ML group compared to the MS group (12.4 vs. 0.68 %, p < 0.0001). Of the known risk factors assessed, only increased BMI was associated with incisional hernias (OR 1.18). No trocar site hernias were found.

CONCLUSION

Midline extraction sites are associated with a significantly increased rate of incisional hernias compared to muscle-splitting extraction sites. There is little evidence to recommend fascia closure of 8-mm trocar sites.

Inter-rectus distance in postpartum women can be reduced by isometric contraction of the abdominal muscles: a preliminary case-control study

OBJECTIVES

To determine the effect of isometric contraction of the abdominal muscles on inter-rectus distance in postpartum women.

DESIGN

Preliminary case-control study.

SETTING

Research laboratory.

PARTICIPANTS

Ten postpartum women {mean age 30 [standard deviation (SD) 4] years; mean weight 58 (SD 7) kg; mean height 159 (SD 4) cm} and 10 nulliparous (control) women [mean age 28 (SD 2) years; mean weight 56 (SD 6) kg; mean height 160 (SD 6) cm].

INTERVENTIONS

Ultrasound images from the anterior abdominal wall were recorded at rest (supine position) and during an abdominal isometric contraction, with the subject actively performing an abdominal crunch (crook lying position). Two-way analysis of variance was used to compare the inter-rectus distance between groups (postpartum vs control) and between levels of abdominal muscle activation (rest vs isometric contraction).

MAIN OUTCOME MEASURES

Inter-rectus distance 2cm above the level of the umbilicus.

RESULTS

The inter-rectus distance was significantly greater in the postpartum group compared with the control group [14.7 (SD 3.1) mm vs 9.6 (SD 2.8) mm; mean difference 5.1mm; 95% confidence interval (CI) 3.4 to 6.8]. The inter-rectus distance was significantly lower during isometric contraction compared with rest [10.7 (SD 3.1) mm vs 13.4 (SD 3.1) mm; mean difference 2.8mm; 95% CI 1.2 to 4.5]. No interaction was found between group and muscle contraction.

CONCLUSIONS

The inter-rectus distance was significantly higher in postpartum women compared with controls, and significantly lower during isometric contraction of the abdominal muscles (abdominal crunch) compared with rest.

Mechanical Response of the Herniated Human Abdomen to the Placement of Different Prostheses

This paper describes a method designed to model the repaired herniated human abdomen just after surgery and examine its static mechanical response to the maximum intra-abdominal pressure provoked by a physiological movement (standing cough). The model is based on the real geometry of the human abdomen bearing a large incisional hernia with several anatomical structures differentiated by MRI. To analyze the outcome of hernia repair, the surgical procedure was simulated by modeling a prosthesis placed over the hernia. Three surgical meshes with different mechanical properties were considered: an isotropic heavy-weight mesh (Surgipro®), a slightly anisotropic light-weight mesh (Optilene®), and a highly anisotropic medium-weight mesh (Infinit®). Our findings confirm that anisotropic implants need to be positioned such that the most compliant axis of the mesh coincides with the craneo-caudal direction of the body.