Post-Inguinal Hernia Repair Chronic Pain

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Pain following hernia surgery is common, generally subsiding within approximately two months. However, a proportion of patients experience sustained pain, potentially leading to disability or affecting sexual function. This pain, lasting over three months and unrelated to other causes, is referred to as post-herniorrhaphy neuralgia.

Anatomy

Nerve	Root	Location	Innervation
Ilioinguinal	T12, L1	Accompanies spermatic cord	Proximal and medial thigh
			Mons pubis and labia majora
			Root of penis and upper scrotum
Iliohypogastric	T12, L1	Divides into two branches:
Anterior cutaneous branch		Passes between the aponeurosis and internal oblique; accompanies spermatic cord	Skin of hypogastric region
Lateral cutaneous branch		Pierces the internal and external oblique above the iliac crest	Skin of the gluteal region
Genitofemoral	L1, L2	Divides into two branches:
Genital branch		Through internal ring, joins spermatic cord	Mons and labia/scrotum
Femoral branch		With external iliac artery	Anterior lateral thigh
Lateral femoral cutaneous	L2, L3	Beneath inguinal ligament	Anterior lateral thigh
Femoral nerve	L2, L3	Beneath inguinal ligament	Primarily motor nerve to quadriceps femoris
			Sensory branch anterior thigh

Pathophysiology

The persistent pain following hernia repair often involves the cutaneous nerves of the lower abdomen and groin, specifically the ilioinguinal, iliohypogastric, genitofemoral, and lateral femoral cutaneous nerves. These nerves, originating from the lumbar plexus, provide sensory innervation to the groin, upper hip, and thigh regions. Injuries to these nerves during hernia repair, either primary (occurring during surgery with or without neuroma formation) or secondary (resulting from an inflammatory process adjacent to the nerve, often caused by mesh, or entrapment from staples or sutures), could lead to chronic neuropathic pain.

Epidemiology and Risk Factors

Persistent pain post-groin hernia surgery is relatively common, with up to half of patients reporting some degree of residual groin pain one year after surgery. Risk factors for persistent pain include younger age, history of preoperative pain, interval less than three years from a prior surgery, severe early postoperative pain, postoperative complications, preoperative sensory disorder, female sex, iliohypogastric nerve excision during hernia repair, recurrent hernia repair, and anterior hernia repair. Of the above risk factors, younger age is the strongest.

Prevention

While mesh placement is a standard in hernia repair, the choice of mesh and fixation methods can play a role in the prevention of post-herniorrhaphy neuralgia. Research indicates that the use of light mesh, absorbable sutures, and fibrin glue to secure a mesh can reduce postoperative pain. The practice of prophylactic neurectomy, which involves the deliberate severing of nerves during surgery to prevent future neuralgia, is also considered, though it may lead to sensory changes and should be decided on a patient-by-patient basis after a thorough discussion of potential outcomes.

Clinical Features

A detailed patient history should cover the onset and quality of the pain, radiation pattern, what has affected the pain (both positively and negatively), the type of hernia surgery undergone, and any postoperative complications. Any history of preoperative pain, including pain from previous surgical procedures, should also be noted. Men should be specifically asked about pain related to sexual activity.

Post hernia repair pain can vary greatly in its onset. Some patients may have mild pain postoperatively or may become pain-free, only to experience new-onset pain weeks, months, or even years later. It's also worth noting that some patients may report recurrent or worsened pain due to the development of resistance to analgesics

Inflammatory pain typically subsides over an expected time course, and is characterized by a throbbing quality and heat hyperalgesia. It does not usually present with sensory or motor deficits. On the other hand, neuropathic pain after surgery may manifest as episodic, burning, stabbing, or pricking sensations with a trigger point. It's often aggravated by activity and hyperextension of the hip and relieved with recumbency and hip and thigh flexion. Certain actions like touching the wound site, breathing, coughing, and bowel activity may trigger this pain, and it may radiate to the hemiscrotum, upper leg, or back. Some patients may also report numbness over the groin or thigh.

Neuropathic symptoms and signs are typically distributed along the sensory pathway of the affected nerve(s). However, identifying the specific nerve causing the pain can be challenging due to the overlap of sensory innervation in the groin and the presence of scarring. Pain may be triggered by tapping the skin medial to the anterior superior iliac spine or over an area of local tenderness. Some patients may also report tenderness at the pubic tubercle.

Imaging

MRI can be performed to assess for mesh infection, recurrent hernia, fluid collection, displaced mesh, osteitis pubis. Sometimes neural oedema or sutures/staples can be seen near a groin nerve. Imaging, while important for identifying other sources of pain that may require immediate surgical management, does not reliably highlight nerve abnormalities in this setting. Only on rare occasions does imaging detect nerve swelling or other anatomic abnormalities consistent with nerve injury.

Diagnosis

The clinical triad for diagnosis is as follows:

1. Specific Pain Characteristics: The patient experiences burning or stabbing pain near the incision or the region of the surgery. This pain often radiates along a specific groin nerve distribution.
2. Impaired Sensation: There is evidence of impaired sensory perception in the distribution of the groin nerve.
3. Response to Nerve Block: The pain is relieved when an anesthetic is infiltrated into the groin nerve.

Imaging can also be performed to exclude other non-neuropathic causes of pain.

While a positive response to a peripheral nerve block supports the diagnosis of post-herniorrhaphy neuralgia, a negative response does not necessarily exclude it. This is because mesh-related fibrosis and inflammation can limit the spread of the injected anesthetic, which means that nerve block may be more effective in identifying nerve involvement in repairs that do not involve the use of mesh.

Management

Postoperative pain typically subsides within six to eight weeks. Management of chronic cases can be challenging.

A groin nerve block can be beneficial (see Ilioinguinal and Iliohypogastric Nerve Injection) with breaking the pain cycle. Some patients may find long-term relief from a nerve block, while others may need repeated injections.

Nerve ablation or surgical neurectomy ("groin nerve sacrifice") may be an option when there is failure to respond to repeated nerve blocks but where there is temporary relief from the anaesthetic. Nerve ablation involves injecting a neurolytic solution such as phenol or alcohol to destroy the nerve endings, however this is only temporary as the nerve endings regrow while the cell body is alive. Surgical neurectomy involves surgically removing the affected nerve. It is often difficult to determine which nerve exactly is involved and some surgeons will remove all three (ilioinguinal, iliohypogastric, and genitofemoral) for higher success rates traded against increased sensory loss.

Surgical intervention may be considered for persistent groin pain that does not respond to medications and nerve block or ablation. This can involve groin exploration and neurectomy with mesh removal and replacement. Recommendations around timing for surgical intervention varies. Surgery is more successful than repeated nerve blocks.

Neuromodulatory medications may also be an option.

References

Janina B Bonwich, MD, FACS. Uptodate. Post-herniorrhaphy groin pain. Mar 29, 2022

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