It is estimated that more than 700,000 inguinal hernia repairs are done annually in the United States, and an equal or greater number go untreated. Recent trends in surgical therapy include the development of hernia centers, the placement of mesh, and the introduction of laparoscopic techniques. The majority of operations are done as outpatient procedures, and good long-term results are seen regardless of the technique utilized.
Relatively few complications are observed and include early local wound complications and long-term problems, including recurrent hernias, testicular atrophy, and inguinal neuropathies. The latter problem, although infrequent, may be annoying or even debilitating. The true incidence of postherniorrhaphy neuropathic pain is not known, but published reports present incidence rates from 0% to more than 30%. A review of surgical reports of postherniorrhaphy incisional pain since 1994 presents incidence rates following open hernia repair of all types at 11.8%, while laparoscopic rates are lower at an average of 6.7%. These reports totaled more than 20,000 hernia patients of all types. The variation in incidence rates seems to be related to the method of data collection. Telephone interviews or mailed questionnaires suggest a much higher chronic pain incidence than those reported by surgical groups. However, the majority of questionnaire-generated reports do not have confirmation of the reported symptoms by a physical examination or any other diagnostic or therapeutic procedures. The surgeons’ reports generally do not follow patients for a long period of time.
The ilioinguinal and iliohypogastric nerves arise from the first and second lumbar nerves, with variable contribution from the 12th thoracic nerve. These nerves exit the internal oblique muscle near the anterior iliac spine and traverse
the suprainguinal region going medially where they penetrate the external oblique fascia near the midline (Fig. 1
). The ilioinguinal and iliohypogastric nerves are the most frequently entrapped, and the mechanism seems to be injury by suture, adherence to overlying implanted mesh, or involvement by scar tissue.
Fig. 1. The nerves of the lower abdomen with the external oblique muscle and fascia removed. The ilioinguinal and iliohypogastric nerves exit laterally from the internal oblique muscle and traverse the lower abdomen toward the midline, where they penetrate the external oblique muscle and fascia. The genital branch of the genitofemoral nerve enters the internal ring with the cord structures.
The genitofemoral nerve has its origin from the first and second lumbar nerves and passes through the iliopsoas muscle, where it eventually exits on the ventral surface before branching into its femoral and genital components. The genital branch enters the internal ring along with the spermatic cord or round ligament and accompanies these structures medially, while the femoral branch enters the anterior thigh beneath the inguinal ligament. The genital branch might be compromised by too tight a closure of the internal ring, inadvertent inclusion in sutures used to repair the internal ring, or adherence to mesh inserted into the internal ring orifice as is done in the mesh plug technique. This branch might also be enveloped by preperitoneal mesh placed laparoscopically.
The three nerves may share interconnecting fibers and therefore, exact preoperative identification of the entrapped nerve(s) may be difficult. Local anesthetic injection fanned out cephalad and medial to the anterior iliac spine may implicate the entrapped ilioinguinal and iliohypogastric nerves, while a more inferior-medial injection along the distal inguinal canal might suggest a genitofemoral nerve cause for the symptoms (Fig. 2
). Starling et al. proposed a paravertebral block at L1–L2 to help distinguish the specific nerves involved, but this has not been widely used.
Fig. 2. An injection above and medial to the anterior iliac spine penetrating the external oblique fascia should provide numbness of the ilioinguinal and iliohypogastric nerves. An injection distally along the inguinal canal produces anesthesia in the distribution of the genital branch of the genitofemoral nerve.
One or more of these inguinal nerves may be entrapped by procedures other than inguinal herniorrhaphy. In females, the Pfannenstiel or transverse suprapubic incision is frequently used for cesarean section, hysterectomy, and other gynecologic operations, and reports of postoperative incisional pain are found in general surgical and gynecologic literature. Other operations resulting in such pain include iliac crest bone harvest, lower abdominal midline incisions, abdominoplasty, appendectomy, and various urologic procedures. A series of debilitating and career-threatening complaints occurring in professional hockey players following tears of the external oblique fascia have been reported in Canada and successfully treated surgically.
These patients usually present with groin pain for varying lengths of time. While most report pain immediately after their inguinal operation, a delay in onset of symptoms from a few weeks to several years is seen. In a recent investigation of 100 patients by the author, 59% had pain that radiated to the leg, thigh, genital areas, or flank and an equal number complained of activity-related symptoms. The truncal motions inciting the pain were bending, lifting, walking, and twisting of the trunk. Only a few males reported pain with an erection or intercourse. Nine patients had been diagnosed with depression or other neuropsychiatric disorders, but this did not seem to affect their final outcome. Reports in the literature suggest a less favorable response in individuals who are actively pursuing legal action because of their pain, but this was seen in the author’s experience.
The diagnosis is made by a careful history of typical symptoms and physical examination of groin tenderness. Inspection of previous operative reports usually demonstrates potential causes for the symptoms. Confirmation of inguinal nerve entrapment can be made by asking the patient to stand and hyperextend his or her trunk and rotate both toward and away from the symptomatic inguinal site (Fig. 3
). This “arch and twist” maneuver acutely stretches the distally tethered nerves and usually reproduces the typical pain. Subcutaneous injection of the inguinal region with 0.5% bupivacaine HCl transiently relieves the pain, even when the arch and twist maneuver is repeated. The bupivacaine injection may also assist
in detection of which nerve or nerves are involved. Fanning the injection anterior and superior to the anterior iliac spine and beneath the external oblique fascia should anesthetize the ilioinguinal and iliohypogastric nerves. A more distal injection parallel to the inguinal ligament should produce numbness in the distribution of the genital branch of the genitofemoral nerve along its course with the spermatic cord or the round ligament in females.
Fig. 3. Asking the patient to stand and arch his or her back while twisting the trunk both toward and away from the symptomatic side will replicate pain when the patient turns away from the affected side by putting the entrapped nerve on more tension.
There are no imaging studies or nerve conduction studies that have been reported to make the diagnosis independently, especially after the use of mesh.
The most successful method available to relieve postincisional pain is surgical resection of the involved nerves with reasonably good long-term pain relief. Whether or not a patient complaining of postincisional pain is returned to the operating room depends upon the experience and interest of the surgeon. Since there are no reliable, sophisticated investigative studies to provide absolute evidence of nerve entrapment, many surgeons refuse to become involved with a surgical procedure for a complaint of pain without objective evidence.
Once a surgical procedure is thought to be indicated, the question of the most effective and reliable technique arises. It is tempting to think that identification and neurolysis of an entrapped nerve to free it from surrounding scar tissue will suffice. However, this approach usually results in the nerve being re-entrapped with recurrent symptoms. Traditionally, surgeons have been taught that severance of the ilioinguinal or genital branch of the genitofemoral nerve will result in annoying hypesthesia of the external genitalia in both men and women and perhaps lead to litigation.
It is occasionally stated publically that prophylactic neurectomy of the inguinal nerves at the time of herniorrhaphy, especially with mesh prostheses, will prevent postincisional neuropathy. Only two studies in the surgical literature address this issue in a prospective randomized fashion and both report identical occurrence of postincisional pain, but the neurectomized patients frequently developed annoying and occasionally disabling numbness. This is not a frequent complaint when neurectomies are done for pain symptoms, since most, if not all, patients are happy to trade numbness for pain relief.
Neurectomy appears to be a more definitive method to alleviate such symptoms. The most frequent nerves involved are the ilioinguinal and iliohypogastric nerves, and these may be trapped by sutures used to repair the hernia or close the abdominal wall, or more commonly in the sutures used to reapproximate the external oblique fascia. Although this problem is occasionally attributed to a “neuroma,” it is unusual to find a neuroma at operation, especially if the nerve has not been divided. The diagnosis of the genital branch nerve being involved can frequently be presumed by the pain pattern of discomfort and/or numbness at the lateral scrotum/labia majora and/or upper medial thigh. Several surgeons, including the author, suggest searching for and dividing all three inguinal nerves to eliminate all sources for future pain and accepting any numbness that might occur. The potential loss of the cremaster reflex in males from division of the genital branch of the genitofemoral nerve, although discussed by some authors, has not seemed to be a postoperative problem and is not mentioned as a complication in any of the published articles.
Technically, the previous inguinal incision should be opened and extended laterally toward the anterior iliac spine to allow access to the nerve as it exits the internal oblique muscle. Careful opening of the external oblique fascia should allow visualization of the ilioinguinal and iliohypogastric nerves as they course medially on the surface of the internal oblique fascia and muscle. Implanted mesh may obscure the more medial view of the nerves, but they should be readily evident laterally in unoperated territory. It is not really necessary to dissect out the entire extent of the nerves but only to gain access to it proximally near the anterior iliac spine. Frequently, if the nerve is elevated anteriorly, its medial tethering will be observed, providing evidence of its anchoring by scar tissue, suture, or mesh.
Fig. 4. The ilioinguinal nerve is clamped and divided at its exit from the internal oblique muscle, ligated with fine Mersiline J sutures, and finally sealed with an application of either absolute alcohol or phenol.
At the most proximal point where the nerve exits the internal oblique muscle, the nerve should be grasped gently with a fine mosquito hemostat and divided distal to the clamp. The distal portion of the nerve may be resected and sent for histopathologic examination. The proximal portion of the nerve should be ligated securely with fine synthetic nonabsorbable sutures such as braided polyester (Mersiline J) (Fig. 4
). The proximal divided nerve end should be sealed by applying absolute alcohol or 12% phenol solution to prevent traumatic neuroma formation. The nerve end is then allowed to retract back into the internal oblique muscle layer, which may give further protection against neuroma formation. A similar procedure should be carried out on the iliohypogastric nerve if it seems to be tethered as well.
Next, a search for the genital branch of the genitofemoral nerve should be carried out. If onlay mesh or an internal inguinal ring mesh prosthesis has been placed, finding the nerve may be difficult and require dissection or removal of the prosthesis. In that instance, one may risk injury to the spermatic cord arteries and veins with resultant testicular atrophy. It might also require re-repairing the hernia defect, if present, with sutures or new mesh prosthesis. If the genital nerve is unable to be located and the symptoms strongly suggest its involvement as the source of the pain, several options are available. Since the groin is already open, one may enter the preperitoneal space by dividing the fibers of the internal oblique and transversus abdominus muscles and gaining access to the pelvic fossa, much like a renal transplant incision. The genitofemoral nerve and its bifurcation are readily discernible as it descends along the ventral surface of the iliopsoas muscle and then branches with the genital nerve, ascending with the spermatic cord structures into the internal ring (Fig. 5
). In females it accompanies the round ligament through the internal ring orifice. Once the genital branch is identified, it should be divided, ligated, and treated for neuroma prophylaxis similar to that done for the ilioinguinal and iliohypogastric neurectomies. At this time, the femoral canal and internal ring may be reinforced with sutures if necessary. A second option would be to approach this nerve laparoscopically. While the genital femoral nerve may be relatively easy to locate, finding the ilioinguinal and iliohypogastric nerves via this approach might be a more daunting task. Several anecdotal reports describe a few cases of successful preperitoneal laparoscopic neurectomy.
Fig. 5. A caudal view of the pelvic fossa where the genital branch of the genital femoral nerve can be seen ascending into the internal ring with the cord structures.
Not many reports place much emphasis on neuroma prophylaxis, but this might be a reason for recurrent pain, months to years after neurectomy. There are a number of techniques described, both clinical and experimental, to prevent neuromas following traumatic or planned amputation of major somatic nerves in the upper and lower extremities. It is thought that the nerve ends attempt regeneration with nerve fibers spilling out of the divided nerve sheath, growing in disorganized bundles and causing erratic pain signals. Therefore, ligating and sealing the severed nerve end may prevent this regenerative process. Popularly described methods of prophylaxis of these potentially disabling problems are (a) implanting the severed end into adjacent muscle, (b) implanting into the nerve more
proximally, or (c) various caustic treatments of the divided nerve ends. The later treatments have included laser treatment, electrofulguration, suture ligation, and various denaturing agents such as absolute alcohol and phenol.
There is little literature to support any of these treatments with sensory somatic nerves as described herein, and very few reports of postinguinal neurectomy neuroma occurrence. Nonetheless, a few minutes invested intraoperatively may be well worth the effort to prevent recurrence of the symptoms at a later date postoperatively.
The reported occurrence of typical pain following laparoscopic herniorrhaphy is explained by the same mechanism as the open repair, that is, entrapment or impingement upon these same nerves, particularly the genital branch of the genital femoral nerve. A large “unfurled” piece of mesh is usually tacked or anchored with metallic devices and these may involve not only the genital nerve branch, but also the more ventral inguinal nerves. Should this occur, repeat laparoscopy should reveal the involved nerve(s) and proximal neurectomy carried out. Neuroma prophylaxis might in this instance include suture ligation with or without nerve end fulguration. Application of a potentially harmful substance such as alcohol or phenol may not be justified in proximity to the femoral vessels and nerve.
Removal of implanted mesh and its hardware is a matter of personal preference, and if the entrapped nerves are easily visualized and can be dissected back proximally where they can be easily divided, then tedious dissection of mesh that is adequately controlling a hernia is probably unnecessary. However, if the mesh is large and encompasses one or more nerves, then effective treatment would require its removal.
Results of Treatment
The initial reports of inguinal neurectomy were in small series of patients in the early 1940s and were uniformly successful. Relatively few reports have appeared since then, suggesting either disinterest in reporting such patients or failure to recognize the problems that must predictably occur, given the large number of herniorrhaphies and suprainguinal incisions done each year. Risk factors for therapeutic failure are primarily seen in multiply recurrent hernias or in cases where not all of the nerves are located and divided. Collective reviews of the series that have been reported suggest an 80% to 90% success rate with few, if any, immediate or long-term problems.