Inguinal Nerve Block

• Chronic groin pain
• Chronic post surgical groin pain
• Suprapubic pain
• Post hernia surgery pain (post herniorrhaphy pain)

The ilioinguinal and iliohypogastric nerves are branches of the lumbar plexus originating from the ventral ramus of L1 with occasional contributing fibers from T12. They emerge from the lateral border of the psoas major muscle, travel around the abdominal wall, and penetrate the transverse abdominal and the internal oblique muscles to innervate the hypogastric and inguinal areas. The anterior cutaneous branch of the iliohypogastric nerve passes through the internal oblique muscle just medial to the anterior superior iliac spine (ASIS), to lie next to the external oblique muscle. It then passes through the external oblique above the superficial inguinal ring, and supplies the suprapubic area. The ilioinguinal nerve remains between the deeper two muscle layers, it travels through the inguinal canal and supplies the upper medial thigh and superior inguinal region.

The genitofemoral (L1–L2) nerve passes through and along the anterior surface of the psoas major muscle, and it divides into genital and femoral branches above the inguinal ligament. Its genital branch travels with the spermatic cord and innervates the genitalia inferior to the area supplied by the ilioinguinal nerve.

Ilioinguinal and iliohypogastric nerve blocks are used as a diagnostic and therapeutic tools in the management of groin pain and pain in the inguinal region. They are used to discriminate peripheral neuropathies from radiculopathies, as well as to treat both chronic and acute groin pain. In addition, they may help to predict the outcome of procedures like nerve ablations (pulsed radiofrequency) and neurolysis.

In patients with chronic groin pain post surgery, ilioinguinal and iliohypogastric nerve blocks may provide sustained analgesia where conservative therapies have failed.

While inguinal nerve block is generally a safe procedure, complications may occur as with any other injections. Bleeding and hematoma formation can occur, though this is more likely in patients with any existing blood dyscrasia or those on anticoagulants. Infection is an important risk and can be minimized by maintaining a sterile technique. The peritoneum lies just below the fascia and is therefore at risk for penetration. This may subsequently result in peritonitis, bowel perforation, or fistula formation. Other complications include paresthesias of the lower limb, intravascular injection, or inadvertent femoral nerve block.

The accuracy of ultrasound guidance has been validated in a cadaver study with the injection site superior to anterior superior iliac spine and the block success rate was 95%. The success of using ultrasound to guide ilioinguinal and iliohypogastric nerve blockade has been replicated in the clinical setting. Based on visualization of the abdominal muscles, fascial planes, and the deep circumflex iliac artery, a clinically successful block can be reliably achieved in most cases based on sensory loss corresponding to the II and IH nerves following injection.

Use of ultrasound allows real-time soft tissue imaging, greatly improving the success of the ilioinguinal block. It allows reduction in the volume of local anesthetic used and prevention of potential injury to adjacent structures.