The inguinal, iliohypogastric, and genitofemoral nerves can be injured anywhere along their course (Fig. 20.2); however, the point of injury is usually associated with the inciting operation. The mechanisms of injury may involve partial or complete section, stretch, contusion, crush, or electrocoagulation [26]. Secondary damage may also occur from scar and/or neuroma formation or irritation by an adjacent inflammatory process, i.e., suture granuloma [27]. The procedure that most commonly results in postoperative inguinal neuralgia is the inguinal hernia repair, and the two most commonly affected nerves are the ilioinguinal and iliohypogastric [26]. The ilioinguinal nerve is most at risk for entrapment as it courses immediately beneath the external oblique fascia [25]. Here, it is subject to inclusion by suture, adherence to incorporated mesh, or encasement by scar [25]. The iliohypogastric nerve is also at risk for mesh adherence due to its close proximity, and both nerves are subject to stretching during transposition at the time of hernia sac dissection [25, 28]. Low Pfannenstiel incisions are also implicated in inguinal neuralgia for some of the same reasons [26]. The genitofemoral nerve is less commonly involved but may also be injured by suture inclusion, mesh adherence, or excessive tightening of the internal ring during herniorrhaphy [25]. Although these patterns of injury are likely responsible for the associated neuralgia, postoperative histological examination of the excised nerve segments frequently shows normal nervous architecture [25]. Occasionally, microscopic examination will reveal perineural fibrosis, cicatricial neuroma formation, and/or evidence of foreign bodies, i.e., suture material [25, 26].

Entrapments of these nerves present similarly with chronic, disabling postoperative pain that is out of proportion to findings on clinical exam [26]. The pain is usually characterized as burning and constant with associated hyperesthesia [26]. It is exacerbated by forcible stretching of the hip joint, twisting of the torso, and movements that increase intra-abdominal pressure [25, 26]. Some patients even adopt a position of hip flexion with a slight forward truncal bend to alleviate the symptoms [26]. The time of presentation varies from immediately post-op to months or even years after surgery [25, 29]. Radiation of pain, however, is what helps to distinguish which nerves are involved. The pain from inguinal neuralgia will frequently radiate along the associated area of innervation (Fig. 20.3); however, neuroanatomic variability can complicate the diagnosis [30]. Pain from ilioinguinal or iliohypogastric neuralgia may be localized to the area of a hernia repair or radiate down to the medial thigh [26, 30]. Perceived deep pelvic pain, rectal, and even proximal vaginal pain may be referred from entrapment of the iliohypogastric nerve [31]. The genitofemoral nerve innervates the testicle and labia and thus may have associated pain in those areas [30]. Pain with deep pressure at the external ring or palpation of the spermatic cord/round ligament against the pubic bone may also elicit pain consistent with genitofemoral neuralgia [30]. Obviously, the differential diagnosis of groin/pelvic pain is vast, and additional imaging modalities are frequently employed to rule out other causes [29, 32]. Nevertheless, groin pain 1–2 months post-op should be further investigated for consideration of inguinal neuralgia.

The diagnosis of inguinal neuralgia relies heavily on history and physical, with special attention to be paid to the presenting symptoms mentioned previously [25]. The diagnostic triad of nerve entrapment or postoperative neuroma formation is as follows: (1) burning or lancinating pain near the precipitating operation’s incision site that radiates is the sensory distribution of that particular nerve, (2) clear evidence of impaired sensory perception in the involved nerve territory, and (3) pain that is relieved by infiltration with anesthetic [33–35]. Inguinal neuralgia can also be reproduced and confirmed in some patients by truncal hyperextension and torso rotation in either direction [25]. As per the triad, subcutaneous anesthetic nerve blocks result in at least temporary relief for most patients [26]. These blocks can be used to target the culprit nerves; however, anatomic variation and cross innervation may complicate the diagnostic process [25]. The inguinal and iliohypogastric nerves can usually be blocked with local anesthetic superomedially to the anterior superior iliac spine [25]. Pain not relieved by this block may suggest genitofemoral neuralgia, which some surgeons confirm with a paravertebral block at L1/L2 [36]. Few studies report the use of electromyography, mainly to assess denervation of the pyramidalis muscle, which is specific for ilioinguinal nerve injury [26]. However, the utility of electromyography is still a matter of debate [37–39].