Izabela Lubowiecka

Biomechanics of the front abdominal wall as a potential factor leading to recurrence with laparoscopic ventral hernia repair

BackgroundIntraabdominal pressure often is blamed as the cause of mesh–fascia junction failure after laparoscopic ventral hernia repair. Stretching of the mesh during a cough or defecation may lead to recurrence. Little is known about the movements of mesh in the abdominal cavity after this operation. This study investigated the front abdominal wall to describe its elasticity in vivo and searched for elongations that possibly stretched an implanted mesh, thereby causing fixation failure and subsequent recurrence.MethodsTo measure front abdominal wall elongations, a model of fascia movements was created. Eight healthy volunteers were measured during exercise to determine the extent of elongations in their front abdominal wall. Videos were analyzed in three positions to create a mathematical shell structure. A computerized model based on the net movement of nodes was calculated to determine the axes and values for maximum elongations.ResultsThe largest average elongations were measured for the upper midline (32.08%) and the transverse line in the low lateral area (34.06%). The maximum values for these lines were larger than 100% for the middle line (133.78%) and exceeded 50% for the entire middle line. The values for the horizontal lines did not reach 10% at any level. According to these data, areas of both high and low elasticity were defined.ConclusionsThe presented experiment adds new parameters to the understanding of in vivo mesh behavior. Elongation of the front abdominal wall may stretch implanted mesh and could be a cause of recurrence in cases of insufficient fixation.

Physical and mathematical modelling of implant–fascia system in order to improve laparoscopic repair of ventral hernia

BACKGROUND This paper describes an investigation of biomechanical behaviour of hernia repair, which is focused on the selection of safe linking of certain type of implant with fascia in laparoscopic operation. The strength of various fixations of the implant to the fascia is analysed. METHODS The research is based on experimental observations of operated hernia model behaviour during a dynamic impulse load corresponding to post-operative cough. Fifty seven different types of models of implanted mesh are considered. Five types of implants and five types of connectors are used. Mechanical properties of the implants as well as limit tearing forces of joints are identified in uni-axial tensile tests. Mathematical model of implanted mesh based on finite element method is proposed. The identified mechanical properties of the materials are applied and the model is calibrated using quantities measured during experiments. FINDINGS The presented results point at trans-abdominal sutures and ProTacks (connectors) and at DynaMesh (implant) as the most reliable materials used in ventral hernia operation, in the tested materials group. Desired properties of implants seem to be: elastic properties similar to the properties of tissues and high local strength, as fixation have a local character. The proposed mathematical model can be applied to simulate real behaviour of an implant with appropriate accuracy and to estimate the number of tacks for the implantation of hernia meshes. INTERPRETATION The presented results may help in the deeper understanding of the fascia-mesh system behaviour, and thus may lead to improve the fixation methods.

Mathematical modelling of implant in an operated hernia for estimation of the repair persistence

This paper presents mathematical modelling of an implanted surgical mesh used in the repair process of the abdominal hernia. The synthetic implant is simulated by a membrane structure. The author provides a material modelling of the implant based on the dense net model appropriate for technical fabrics. The accuracy of the proposed solution is evaluated by comparing the simulations of the dynamic behaviour of the system with the experiments carried out on physical models of implanted mesh. The model can be used to estimate the repair persistence for different mesh materials, fixing systems and different numbers of tacks to be provided during the surgery in order to resist the cough pressure and required action to avoid hernia recurrence. The persistence of the repaired hernia is assessed on the basis of the values of the forces in the tissue–implant joints because the usual form of the repair failure is due to as the joint disconnection or tissue failure.

EXPERIMENTS AND SIMULATIONS FOR LAPAROSCOPIC VENTRAL HERNIA REPAIR IMPROVEMENT

The authors conducted a wide experimental and numerical study in order to determine effective approaches in the laparoscopic VH repair. At first the study covered identification of mechanical properties of the abdominal fascia, implants, tacks and transabdominalsutures. Basis on these data, the one and two-dimensional mathematical models were formulated and a number of numerical static and dynamic analyses were carried out. Then various physical models of the fascia-mesh system were built in many configurations, using a porcine fascia, a few kinds of implants and tacks.

Mechanical properties of mosquito nets in the context of hernia repair

The paper deals with issue of applying mosquito nets as implants in hernia repair, which have already been used in resource-poor developing countries. Uniaxial tensile tests have been conducted on polyester mosquito meshes in two orthogonal directions. Non-linear elastic constitutive laws parameters have been identified to be applied in dense net material models. Mechanical performance of tested mosquito nets has been compared with properties of commercial implants used in treatment of hernia and with properties of human tissue. This study contributes to mechanical knowledge of hernia repair issue by investigation of cheaper alternative to commercial implants.

Two-criteria optimisation problem for ventral hernia repair

Abstract Two-criteria optimisation problem related to laparoscopic ventral hernia repair is formulated in this paper. An optimal implant from a given set and its orientation is sought. The implant is subjected to kinematic extortions due to a patient’s body movement and intra-abdominal pressure. The first criterion of the optimisation problem deals with the reaction force in the implant fastener, while the deflection of the implant constitutes the second criterion. A two-stage optimization procedure is proposed and the optimal solution is determined with the aid of minimization of an additional objective function. Numerical examples for typical locations of hernia are provided.

Safety and efficacy of a Ventralight ST echo ps implant for a laparoscopic ventral hernia repair - a prospective cohort study with a one-year follow-up.

UNLABELLED Laparoscopic ventral hernia repair has become popular technique. Every year, companies are introducing new products Thus, every mesh prior to introduction in clinical settings should be tested with a dedicated tacker to discover the proper fixation algorithm. The aim of the study was to assess the safety and efficacy of the Ventralight ST implant with an ECHO positioning system and a dedicated fixation device, the SorbaFix stapler, in a prospective cohort of patients. MATERIAL AND METHODS The study was a prospective single centre cohort study with a one-year followup period. Fifty-two patients received operations for a ventral hernia using a laparoscopic IPOM mesh - Ventralight ST ECHO PS. The size of the mesh and the fixation method were based on mathematical considerations. A recurrence of the hernia and pain after 1, 2 and 12 months were assessed as the primary endpoints. RESULTS Two recurrences were noted, one in parastomal and one in a large incisional hernia. Pain was observed in 22 patients (41%) and mostly disappeared after 3 months (7%). The intensity of pain was low (VAS <2). However, 2 patients still experienced severe pain (VAS>6) until the end of the study. CONCLUSION The Ventralight ST Echo PS implant fixed with a Sorbafix stapler is a valuable and safe option for a laparoscopic ventral hernia repair. In our opinion, the implant could be used in all patients due to the hernia ring diameter. According to the mathematical models and clinical practice, we do not recommend this implant in orifices with a width larger than 10 cm.

Towards Understanding of Mechanics of Hernia Managed by Synthetic Mesh in Laparoscopic Operation: A Single Case Study

In this paper a research towards understanding of mechanics of ventral hernia operated with the use of Physiomesh Open image in new window implant and SecureStrap Open image in new window staples is described. Experimental and numerical studies are conducted for that purpose. Experimental works cover uni-axial tension tests of the implant samples and of the implant-staples-tissue system. Also experiments on implant-staples-tissue models, representing operated hernia, subjected to impulse pressure loading are performed. Based on that, constitutive model of the mesh has been identified and failure load of the staples has been determined. In the experiments on the operated hernia systems subjected to pressure loading safe loading level has been determined and failure modes connected to higher pressure values have been observed. Finally, in the numerical simulations of the operated hernia model, built according to FEM rules, it has been proved that failures observed experimentally result from exceeding of the load bearing capacity of the staples considered in this study.

Mechanics of mesh implanted into abdominal wall under repetitive load. Experimental and numerical study: Mesh Implantation into Abdominal Wall

There are a number of papers discussing medical and mechanical aspects of ventral hernia management. Despite intensive work on the problem understanding, recurrences of the sickness still happen too often. For that reason, new aspects of the problem must be considered. In this article, a change in the abdominal implants stiffness is discussed, which is caused by cyclic loading. Such loading influence abdominal implant, for example, while patient is coughing or exercising. For the first time, this stiffness change is quantitatively described for a selected knitted mesh. The influence of mesh stiffness changes on repaired hernia persistence is studied. Then, ex vivo experiments on a repaired hernia model under cyclic pressure loading are performed. Finally, numerical simulations of the experiments are made in which stresses and forces in the system are calculated. The two following cases are considered. In the first case, the mesh has its baseline stiffness, and in the second case, the mesh is preconditioned by former loading; thus, it is stiffened. Reaction forces at the mesh fixation points appear to be approximately twofold higher in the second case than in the first case. That may be a reason for a fixation damage in operated hernia system. The results presented shed new light on the necessary strength of mesh fixation in the abdominal wall. They enlarge the state of the art on laparoscopic hernia management with the use of a synthetic implant.

Dynamic research of masonry vault in a technical scale

The paper presents preliminary results of dynamic tests of the masonry barrel vault in a technical scale. Experimental studies are intended to identify material properties of homogenized masonry vaults under dynamic loads. The aim of the work is to create numerical models to analyse vault’s dynamic response to dynamic loads in a simplest and accurate way. The process of building the vault in a technical scale is presented in the paper. Furthermore a excitation of vibrations with an electrodynamic modal exciter placed on the vault, controlled by an arbitrary waveform function generator, is discussed. Finally paper presents trends in the research for homogenization algorithm enabling dynamic analysis of masonry vaults.Experimental results were compared with outcomes of so-called macromodels (macromodel of a brick masonry is a model in which masonry, i.e. a medium consisting of two different fractions – bricks and mortar, is represented by a homogenized, uniformed, material). Homogenization entail significan...