Anatomy, Abdomen and Pelvis, Obturator Nerve

The location of the bifurcation of the obturator nerve is variable between sites within the pelvic cavity, obturator canal, or medial thigh. Typically, the obturator nerve enters the thigh after passing through the obturator canal and divides into the anterior and posterior divisions. However, the bifurcation of the obturator nerve can be within the obturator canal (51.78%), in the thigh (25%), or intrapelvic (23.22%). Additionally, the anterior branch can form anywhere from two to four branches, with three branches being the most predominant. In comparison, the posterior branch can form one to four subdivisions, with two divisions being the dominant variant. The articular branches of the obturator nerve demonstrated nine different branching patterns. In terms of cutaneous innervation, research has shown that the obturator nerve provides innervation to the skin surface of the medial thigh, although, has been shown to provide no cutaneous innervation in more than 50% of cases.[4][5]

The obturator nerve is at risk of injury during surgeries that require pelvic dissection and access. In the case of repair of pelvic organ prolapse, the obturator nerve and ureter are particularly at risk of injury, regardless of the surgical approach. The obturator nerve may also suffer an injury during laparoscopic pelvic procedures, such as laparoscopic lymphadenectomy. Furthermore, the obturator nerve can get injured in transvaginal mid-urethral sling placements.[6][7][8]

The obturator nerve has particular utility in transurethral resection of bladder tumor (TURBT), which is common in the treatment of bladder wall masses. Because of the obturator nerve's proximity to the inferolateral wall of the bladder, bladder neck, and prostatic urethra, electrical stimulation caused by tumor resection may cause sudden adductor contraction or "adductor jerk." This sudden thigh movement may cause perforation of the bladder and extravesical seeding of the tumor. Additionally, the adductor jerk may result in damage to the obturator artery. By performing an obturator nerve block with a local anesthetic, the adductor jerk can be eliminated and enable a safe and effective TURBT.[9]

Because of the obturator nerve's innervation of the thigh adductor muscles, blocking the obturator nerve has clinical utility. As described previously, the obturator nerve block (ONB) can help to immobilize the adductor musculature during surgery. Furthermore, due to the obturator nerve's articular branches to the hip and knee, ONB can provide analgesia for hip and knee surgeries, improve chronic groin/thigh pain, and treat adductor spasticity. As a result, conditions such as total knee replacement, hip fracture, traumatic brain injury, and multiple sclerosis can benefit from ONB. If a simple ONB is not effective in providing analgesia, some studies have suggested utility in percutaneous radiofrequency lesioning of the articular branches of the obturator nerve in easing hip joint pain.[3][10]

The obturator nerve is relevant in multiple pathologic conditions. Obturator hernias typically occur in elderly, emaciated women or patients with elevated intra-abdominal pressure due to ascites, chronic cough, or COPD. In an obturator hernia, the hernia sac enters the obturator foramen and follows the course of the obturator canal, obstructing the small bowel. The clinical course is characterized by acute small bowel obstruction and pain in the medial aspect of the upper thigh due to compression of the obturator nerve. Computed tomography (CT) is the imaging modality with the highest sensitivity and accuracy for the timely diagnosis of an obturator hernia. Meanwhile, the definitive treatment is a surgical fixation of the hernia. If the bowel is ischemic, bowel resection and/or a colostomy may be required dependent upon the intraoperative findings. In addition to older women, obturator hernias may also occur during pregnancy due to relaxation of the pelvic peritoneum and development of a wider and more horizontal obturator canal.[11]

Just as the obturator nerve can become compressed by a hernia, the obturator nerve can become compressed by fascia or other tissue in the pelvis. Specifically, the nerve can become entrapped at the exit of the obturator canal or more distally by fascia. Entrapment of the obturator nerve causes exercise-induced medial thigh pain, typically in athletes. Hip abduction and extension aggravate the pain, whereas resisted adduction does not elicit pain. Conservative treatment has not been the target of much research, but stretching and strengthening exercises, cognitive behavioral education, neural gliding, and manual therapy may have utility in easing symptoms. Neurolysis or neurectomy may merit consideration if symptoms are refractory to treatment.[12][13]