Inguinodynia: review of predisposing factors and management

Herniorrhaphy is one of the most common surgical procedures, with an estimated 20 million operations performed annually worldwide. One of the common complications associated with this procedure is inguinodynia, defined as pain beyond three months after inguinal hernia surgery. In this review, we have addressed the main aspects of this complication with current articles, published in the last five years. Inguinodynia has a multifactorial nature and studies have shown that its development is related to the surgical technique and intrinsic factors of the patient that imply greater predisposition to this phenomenon. In this regard, it has been discussed which surgical techniques imply a lower incidence of this complication. Many studies have focused on understanding intrinsic features of each patient, both in physical and cognitive aspects, and how the approach of these factors can favor a better post-surgical recovery. The treatment of this condition is still challenging, and there are no established universal guidelines. We believe that due to its multifactorial nature, the treatment is hampered due to the individuality inguinodynia presentations.

The advent of these techniques has enabled a significant reduction in inguinal hernias' recurrence rates, one of the main postoperative complications. On the other hand, there has been a significant increase in the incidence of inguinodynia, currently the most frequent complication after herniorrhaphy 4,5 .
The International Association for the Study of Pain (IASP) defines Inguinodynia, also called chronic inguinal pain after herniorrhaphy, as pain lasting greater than three months after herniorrhaphy. The incidence of inguinodynia varies between 10% and 12% in the world and, although the pain intensity in most cases is mild, it can be severe and disabling, compromising quality of life [6][7][8][9] .
Annually, about 20 million operations for inguinal hernia repair are performed worldwide. This emphasizes the need to understand and identify the etiological factors involved and to define guidelines for the management of affected patients. Therefore, we propose a narrative review with current scientific evidence, to explore this theme further [9][10][11] .

METHOD
In this study, we adopted the literature review as a methodological strategy. We performed a search for articles in the Latin American and Caribbean Health Sciences (LILACS), Scientific Electronic Library Online (SciELO), and National Library of Medicine (PubMed) Herniorrhaphy is one of the most common surgical procedures, with an estimated 20 million operations performed annually worldwide.
One of the common complications associated with this procedure is inguinodynia, defined as pain beyond three months after inguinal hernia surgery. In this review, we have addressed the main aspects of this complication with current articles, published in the last five years. Inguinodynia has a multifactorial nature and studies have shown that its development is related to the surgical technique and intrinsic factors of the patient that imply greater predisposition to this phenomenon. In this regard, it has been discussed which surgical techniques imply a lower incidence of this complication. Many studies have focused on understanding intrinsic features of each patient, both in physical and cognitive aspects, and how the approach of these factors can favor a better post-surgical recovery. The treatment Original studies (case reports, clinical trials, and observational studies), published between 2015 and 2020, in English and in Portuguese were eligible. We did not include non-systematic reviews, book chapters, and conference proceedings.
We initially selected the articles by title and abstract, and then proceeded with critical reading and synthesis. The search resulted in 154 articles, of which we included 24 for this work. The flowchart in Figure 1 shows the study selection process, as well as the reasons for exclusions. by the suture, mesh, staples, or other fixation devices.
When injured, the interrupted axons try to regenerate to restore innervation. However, some become atrophic, and others form a neuroma, a scar tissue. These last two events are implicated in the etiology of neuropathic pain 9,11 .
In nociceptive pain, on the other hand, the damage affects the tissue adjacent to the nervous structures and is due to the inflammatory reaction and muscle and tendon injuries. This type of pain is commonly reported as continuous and inaccurate, with little intensity. It is also characterized as localized, diffuse, or projected pain in the surrounding areas, and can occur weeks or months after surgery 5,10,12 .
Polypropylene, a synthetic material of meshes usually used in tension-free techniques, can trigger granulomatous reactions around the individual fibers of the material, which unite and encapsulate the mesh, producing a rigid scar with little elasticity, which it is related to pain 1,13 .
There are also cases in which these symptoms affect the penis and testicles beyond the inguinal region, causing pain before, during, and after ejaculation.
Though often ignored, this symptom is common in one third of men with chronic post-herniorrhaphy pain. The migration of the mesh has been associated with the appearance of these symptoms in this group 9,14 .
The differentiation of chronic inguinal pain into nociceptive and neuropathic pain has little clinical significance, since there are no diagnostic methods that make it possible to distinguish the pain. In addition, symptoms, presentations, and findings overlap, which also hampers clinical differentiation 5 .
No study has investigated whether the two types of pain can be safely distinguished. Some authors, however, describe nociceptive pain as acute, tending to decrease over time, while neuropathic pain can persist for long periods 8,15 .

Risk factors
The identification of risk factors is of great

Etiology
Inguinodynia is multifactorial and can be caused by damage to one or more nerves in the region

Management
There are no universally accepted guidelines for the management of patients with inguinodynia.
Correct diagnosis is essential, ruling out other causes of pain and recurrence. Currently, watchful waiting, associated or not with analgesia, can be considered the first line of treatment, which results in pain improvement in most cases. Injections with local anesthetics can be used to relieve pain, although they are more used during diagnosis, in identifying which nerve is injured 7,10,11 .
The persistence of pain after a few months warrants systemic pharmacological interventions. Among the drugs commonly used, there are non-steroidal anti-inflammatory drugs, tricyclic antidepressants, and serotonin reuptake inhibitors. For these cases, treatment is more challenging, requiring multi-professional approaches and even surgery to remove the mesh or neurectomy 7,11,19 .
In many cases, the removal of the mesh is sufficient to reverse the chronic pain. However, during the procedure, damage to nerve structures may occur that is not visible to the surgeon, causing pain to persist.
Thus, the recommendation is removal of the mesh followed by neurectomy 10 .
Selective or triple neurectomy has a high success rate. The neurological deficit is negligible, comprising the impairment of the cremasteric reflex and anesthesia of the area of the inguinoscrotal fold, with about 3 to 5 cm in diameter. It is important to note that, in women, the genital branch of the genitofemoral nerve must be preserved, as it is the sensory nerve for the labia majora.
In addition, as with other more conservative treatments, there is the possibility of side effects after neurectomy and there is also a risk that the treatment may not be effective, or even worsen the pain, although it is a rare event. This technique can be ineffective especially due to scarring and neuropathy near the inguinal canal 10,20,21 .
Triple neurectomy is the safest option and has been recommended the most, but it is a more aggressive Several systematic reviews and meta-analyzes compared heavy versus light meshes [27][28]