The aim of this study was to investigate the mechanical behavior of the Physiomesh™/Securestrap™ system, which experienced high failure rates and adverse clinical outcomes. The authors conducted a set of mechanical experiments and numerical simulations to gain insight into the potential cause of system failures and understand the mechanics of the implant fixed to the anterior abdominal wall.
Figure 1b shows geometry of the Physiomesh™/Securestrap™ system. It can be noticed, the staple is so narrow that it can easily miss any thread of the mesh while being applied. Then, the staple fixes absorbable barrier layers only to abdominal tissue, which gives no fixation of the mesh because this layer hardly has any load bearing capacity and is damaged by the staple due to any load acting on the implanted mesh (intraabdominal pressure or body movement). This incompatibility of the sizes of the staple and the mesh pores is a first, basic drawback of the Physiomesh™/Securestrap™ system. When move to the mechanical analysis of the system, subsequent drawbacks are found.
The elasticity modulus of the Physiomesh™ was determined through uniaxial tension tests, showing nonlinearity, anisotropy, and non-homogeneity of the material. These properties were considered in the numerical model, which accurately represented the behavior of the implant. However, the analysis of the uni-axial tests results revealed a second major drawback of the mesh, which is the idea of using PDO strip as an orientation marker. The values of the elasticity modulus in the initial tension state identified in ‘1’ and ‘2’ directions of the mesh and also for the PDO strip show that this strip is approximately 3-times stiffer than the mesh itself in the ‘1’ direction (parallel to the strip). The strip changes a basic demanded property of the mesh, which states the mesh stiffness should be smaller in the cranio-caudal direction (after implantation) than in the lateral direction [28]. That property would be preserved for Physiomesh™ without the strip. As Fig. 4a also shows, the strip has the lowest limit force and limit strain among other tested mesh samples. Physiomesh™ implanted according to the manufacturer recommendation causes a mismatch between the mesh properties and natural kinematic properties of the abdominal wall, which induce increased reaction forces in the mesh fixation points and may cause the failure [11]. Former studies show the mesh orientation importance on the reaction forces in the mesh fixation points [27].
The uni-axial tests of the mesh-staples-tissue system provided valuable information about the strength of the mesh-tissue junction. The results indicated that the limit load of the junction was identified as 4 N, with failure primarily occurring due to the staple pull-out from the tissue. This finding suggests that the fixation strength of the Physiomesh™/Securestrap™ system may not be sufficient, especially under higher loads.
The ex-vivo experiments on the porcine abdominal wall models implanted with the Physiomesh™/Securestrap™ system under simulated intra-abdominal pressure load provided insights into the mechanical behavior of the system. The models exhibited failure, such as staple breakage or pull-out, particularly under higher pressure loads. The failure modes consistently occurred in an oblique direction relative to the PDO strip of the mesh.
The numerical simulations further supported the experimental findings, demonstrating reaction forces on the staples and maximum displacements under different pressure scenarios. The results indicated that the forces in the fixation points exceeded their experimentally determined strength, particularly under higher pressure loads.
The numerical simulations showed how the PDO strip itself seems to influenced negatively the implanted mesh behaviour, causing a stress concentration along this stiffer part of the material under pressure (Fig. 5b). It may be important in particular, when it is oriented along a direction of the largest abdominal strains generated in patient’s postoperative life.
The mesh exhibited high flexibility in transverse projection – probably intended to compensate for rotation movements of the torso. In turn, in the longitudinal projection the flexibility was insufficient. The reason for that is the strengthening of the mesh with the extra strip which influenced negatively overall behaviour of the implanted mesh.
On the other hand there are assumptions and hypotheses encountered in the literature which try to explain the mechanism of recurrence cases of Physiomesh™/Securestrap™ system usage. One, partially true, assumes the lack of strength of the non-absorbable implant layer to the breaking forces generated by the maximum intra-abdominal pressure [22]. This is also confirmed by experimental research conducted by our team. There are not enough strong threads within the knitting pattern, which directly contributed to breakage of the implant from the fixation system. To be strict, the mesh is knitted out of threads of two diameters (see Fig. 1b). Our preliminary study showed that when staple embraces thinner thread, the thread can be ruptured while the system is loaded by pressure. Thus, in our tests we placed staples always around the thicker threads to simulate best surgical situation of the considered system. Besides, the staple itself was made without proper consideration of the tissue specificity. It was brittle and broke several times when placed in the physical model.
These findings shed light on the potential biomechanical factors contributing to the high failure rates observed with the Physiomesh™/Securestrap™ system. The inadequate fixation strength, demonstrated by the staple pull-out and breakage, suggests a mechanical limitation of the system. The stress concentration observed in the PDO strip highlights the importance of considering the mechanical properties and design of the implant when assessing its performance. Those factors also recur in other biomechanical studies [28–30].
Physiomesh™ implant with the Securestrap™ fixation system was approved for use in the USA by the Food and Drug Administration (FDA) in 2010. In its application, the manufacturer (Ethicon) declared that it is essentially similar to three other implants of this company, which have been approved for use before. Very quickly, the FDA began receiving information about a disturbingly high complication rate after Physiomesh™/Securestrap™ system use. Physiomesh™ was permanently withdrawn from the market in May 2016 and as of today, the number of court claims has reached nearly 3000 [13]. The whole situation is worth considering, as the concept of the new system seemed to coincide with the commonly used.
The implications of this study extend beyond the specific case of the Physiomesh™/Securestrap™ system. By understanding the mechanical behavior of implant-tissue systems, researchers and clinicians can make informed decisions regarding implant selection, design modifications, and fixation techniques to improve surgical outcomes. This knowledge may guide the development of future generations of implants, with a focus on creating mechanically reliable systems compatible with the mechanics of a healthy abdominal wall [28, 29, 31].
The analysis described above was partially inspired by the discussions with patients who experienced hernia recurrence after surgery with a Physiomesh™/Securestrap™ system. The patients were often able to accurately describe the moment of recurrence. The recurrence most often appeared in a moment of and abrupt sneeze, cough or sudden twisting of the torso accompanied by severe pain and/or feeling of “tearing tissue”. In our model we took into account one of the situations, generating a high intraabdominal pressure, and explain the biophysical reasons for this state of affairs.
In preclinical studies on the porcine and rabbit model, Ethicon presented great results in terms of fixation, maintenance in the operating field, and tissue incorporation [32, 33]. The presented analysis proves that the animal model cannot be directly translated into humans. The reasons include both phylogenesis with the adoption of a vertical body posture by humans, as well as the anatomy of the anterior abdominal wall, and thus a different distribution of forces and directions of their action in the event of a sudden increase of intraabdominal pressure than in the case of four-legged animals.
Comparing with a number of studies referring to biological aspects of mesh implantation based on an animal model, the above results also allow to understand the biomechanical cause of such rapid and spectacular hernia recurrences in patients operated on with the Physiomesh™ implant. We believe that this will prevent similar errors in the future, while also serving as a valuable reference for the development of new implants [17]. Additionally, it shows the complexity and importance of this mechanism in terms of the mesh-fascia system on the level of physics.
It is important to note that this study has certain limitations. The experiments and simulations were conducted under controlled laboratory conditions, which may not fully replicate the complex in vivo environment. There was porcine tissue used in an ex-vivo experiment that may lead to slightly different results comparing to in vivo human tissue behaviour. Additionally, the study focused on mechanical aspects and did not consider other factors that may contribute to the clinical failures observed with the Physiomesh™/Securestrap™ system, such as biological responses and host reactions.
What is interesting, when Physiomesh™/Securestrap™ entered the market in 2013, surgical meshes were classified as category II according to the regulations of the European Union and the USA. This meant that the introduction of a new product for general use required no clinical trials. From October 2021, upon entry into force of the MDR (Medical Device Regulation), hernia meshes have been included in group III, which means that randomized control tests must be carried out before placing the implant on the market [16].
We firmly believe that the presented findings will prevent similar mistakes in the future, but at the same time will allow us to supplement our current knowledge in the field of the anterior abdominal wall mechanics.