Regardless of the use of mesh, there are many factors that affect the risk of development of CGP in inguinal hernia repair. The presence of preoperative pain, psychosocial issues, and aberrant nerve anatomy can all contribute to postoperative CGP development. Furthermore, perioperative factors such as tissue and nerve trauma, seroma, hematoma, and infection can all contribute to chronic pain. Some or all of these factors can be present regardless of a mesh or non-mesh inguinal hernia repair [1]. One must consider all of these risk factors when trying to determine the reason for the development of CGP, but the focus of this chapter is the role synthetic mesh may or may not play in the development of postoperative CGP.

There is no question that all synthetic mesh elicits an inflammatory response. Whether that response is clinically significant is debatable. Animal studies have shown that mesh in contact with nerves does cause inflammatory changes characterized by an increase in fiber diameter and increased nerve demyelination [2]. However, the clinical significance of these findings in animals alone cannot be substantiated.

A translational study, “Mesh-Related SIN Syndrome. A Surreptitious Irreversible Neuralgia and its Morphologic Background in the Etiology of Post-Herniorrhaphy Pain” by Bendavid et al., has recently been published. Given the title alone, one can surmise that the mesh is perceived as the sole instigator of chronic pain, though perhaps not in the traditional manner of being a foreign body that causes inflammation. In this study, a scientific model was implemented comparing 10 explants of virgin tissue of the posterior inguinal wall, 10 explants of scar tissue from tissue repairs, and 10 explants from mesh repairs. Mesh was not found to significantly inhibit or promote nerve growth in scar. However, deformation of mesh was found to provide potential compartments for entrapment of nerves and to create more surfaces for random nerve ingrowth into the mesh. These issues can be further potentiated by contraction and migration of mesh, which can occur after it is implanted [3].

Objective scientific findings from implanted mesh provide data to support a convincing case for mesh-related chronic pain. However, based on these findings, one should expect CGP to be an even larger problem than it is currently. In fact, much of the existing clinical data support the contrary. Therefore, despite evidence of the foreign body reaction seen after synthetic mesh implantation, one must understand the contemporary history and clinical data surrounding CGP to gain a full perspective of this complex and multifactorial problem.

Perceptions about mesh use for inguinal hernia repair can vary greatly; trying to understand the thoughts and biases of surgeons, patients, and research data can be challenging. Some believe the use of mesh in and of itself is the cause for the apparent increase in CGP. Others believe there has not been an objective increase in CGP due to mesh, but at the same time they recognize that mesh can play a role in the development of CGP postoperatively.

Fischer recently wrote a commentary on the continued use of mesh for inguinal hernia repair despite the “human toll of inguinodynia” [4]. He comments that “conventional” tissue repairs had sound results, including acceptable recurrence rates of 4–6 % and CGP in 2–4 % of patients. Along the way, mesh repairs became more popular and with it his personal perception of increased incidence of inguinodynia . These complications were superimposed with issues of pending litigation, potential malingering by patients for secondary gain, and “ruined lives.” After evaluating the data, including mesh use and nerve management, he concludes that there has been little gained by the use of mesh in inguinal hernia repair due to the risk of chronic debilitating pain and really no improvement of recurrence rates. He contributes the etiology of CGP to the inflammatory response of mesh as it involves the three inguinal nerves (ilioinguinal, iliohypogastric, and genital branch of the genitofemoral nerve). His recommendation is that it would be better to learn to do tissue repairs, similar to the Shouldice repair, so as to not “create” inguinodynia in patients, as it has significant societal and economic implications. He also notes that the U.S. Food and Drug Administration has become increasingly concerned about the issue of CGP and the use of mesh.

The opposite view was expressed by Gilbert, a hernia surgeon specialist and originator of a commonly used mesh prosthesis for inguinal hernia repair. He wrote a response to Fischer’s article with a perception that was strikingly different, starting with the issue of inflammation due to a foreign body [5]. He states, “Ordinarily reactions to inert mesh are minimal and short lived.” He goes on to interpret the existing data that incriminate mesh to have bias, as they are not the result of randomized controlled trials. His personal experience includes both Shouldice tissue-based repairs and thousands of mesh-based repairs. His perceptions of CGP were that it occurred in his patients with recurrences and not necessarily in those with mesh. He further states that the mesh repair decreases the incidence of recurrence. His feeling is that CGP is due to inadequate knowledge of the groin and is directly related to surgical technique and not necessarily due to the use of mesh. He states the cause of CGP is due to the “absence of careful technique.”

There is a difference of opinion between two expert and well-respected surgeons regarding the issue of CGP after inguinal hernia repair. As with most controversial issues, the answer lies somewhere between these two extremes.

One of the first papers to describe inguinodynia after mesh repair as a clinical syndrome was from Heise and Starling [6]. They reviewed 117 patients with inguinodynia, 20 of whom had mesh removal, neurectomy (when involved), and tissue repair (modified Bassini or McVay). Sixty percent of patients had favorable results with their technique. Most importantly, the authors did a review of CGP in non-mesh repairs and reported that it was as high as 10.6 % with certain tissue repairs (McVay), and that the etiology most commonly was entrapment of nerves. They concluded by noting, “We strongly believe that mesh inguinodynia does occur, [and] will occur more frequently than anticipated now that mesh is used with impunity.” This conclusion about mesh in the study is interesting, given the historical data provided about certain tissue repair techniques having a predicted rate of chronic pain of 10.6 %. It also points out the fact that since mesh is now used much more often than autogenous repairs, it is only natural that we speak about CGP in relation to the use of mesh.

Since Starling’s work there have been other reviews of CGP and the use of mesh in inguinal hernia repair. Poobalan et al. reviewed CGP and hernia repair in 2001 [7]. They defined chronic pain as pain that persists for greater than 3 months. Forty studies were reviewed and they found that the incidence of chronic pain ranged from 0 to 53 %. Moderate to severe pain was experienced by up to 10 % of patients. Within the review, they found three studies that looked at mesh versus non-mesh repairs and the development of CGP. They found that two of the three studies evaluated reported less CGP with the mesh-based repairs.

Aasvang and Kehlet also reviewed chronic postoperative pain in inguinal hernia in 2004 [8]. In their review, they specifically looked at studies comparing mesh versus non-mesh repairs, and they showed no increase in the incidence of CGP with the use of mesh.

A more recent randomized clinical trial of mesh versus non-mesh methods of inguinal hernia repair was done by van Veen et al. [9]. Three hundred patients were reviewed with follow-up in 153 of the patients out to a median of 129 months. None of the patients in either group had pain as defined by persistent pain or pain interfering with daily activities. Autogenous repairs including Bassini, McVay, and Shouldice techniques were compared to the Lichtenstein repair. At all time points, pain was similar with mesh repair trending toward less pain compared to non-mesh repairs, except at 10 years when neither group had chronic pain. This agrees with most comparative studies that have found the incidence of CGP to be similar between the open mesh repairs versus the autogenous repairs. The Hernia Trialists reviewed 20 trials and over 5000 repairs comparing mesh-based and non-mesh-based repairs for inguinal hernia [10]. The incidence of CGP was equal in both groups. Nordin et al. found similar results when comparing the mesh-based Lichtenstein repair versus the autogenous Shouldice repair [11]. At 3-year follow-up, the incidence of CGP was 4.2 % in the Shouldice repair and 5.6 % in the Lichtenstein group.