What is the Obturator nerve?

The obturator nerve is the biggest nerve in the front lumbar plexus, which is a group of nerves or a nerve network present in the lower back region. This cluster of nerves acts as a passageway for electrochemical signals that connect the brain to the abdomen, back, knees, and groin, and are regarded as constituents of the peripheral nervous system, which in turn connects the body to the central nervous system, i.e., the brain and the spinal cord. The obturator nerve is different from the nerve that supplies the obturator internus.

The obturator nerve originates from the 2^nd to 4^th lumbar or the lower back and continues onward in the anterior section of the hip region across the psoas major muscle. This muscle facilitates hip flexion; it commences at the final trunk, vertebral, or trunk spinal bones, joins all the vertebral lumbar bones, and continues onward to the femur’s lesser trochanter or the thigh bone. The femur’s lesser trochanter is an elevated region above the bone present in the inner thigh where the bone attaches to the muscle. The obturator nerve then continues onwards across the thigh and pelvis, thereby providing sensory information to the knee region and the upper section of the leg.

The obturator nerve: Functions and Structure

• The obturator nerve plays an important role in innervating the senses of the skin of the thigh’s medial aspect; sensory innervation of the peritoneum of lateral walls of the pelvis; motor innervation of the pectineus; and motor innervation of the lower limb abductor muscles such as the adductor longus, external obturator, adductor brevis, gracilis, and adductor magnus. Despite having almost similar names, the obturator nerve has no role to play in innervating the obturator internus.
• Initially, the obturator nerve comes out from the medial edge of the psoas major muscle present in the abdomen. Then it runs along the lumbosacral torso downwards into the pelvic area. Out here, it continues posterior to the iliac arteries and passes through the side of the false pelvis wall, in the angle formed between the external and internal iliac vessels.
• Then, the nerve arrives at the obturator canal, the upper section of the obturator foramen that does not contain any obturator membrane. The nerve now divides into posterior and anterior divisions; both of them run across the canal and finally via the obturator canal, enter the obturator area of the thigh. Some people may elicit posterior and anterior division of the nerve in the obturator canal itself.
  • Posterior division/branching of the obturator nerve: The posterior branch of the obturator nerve is located at the back portion of the adductor brevis and runs downwards in a vertical manner. It gets inside the obturator externus and continues onwards down at the back part of the abductor brevis and anterior side of the adductor magnus muscle, onwards to the muscular branches of the adductor section of adductor magnus, obturator externus, and adductor brevis. The articular branch flows to the knee joint.
  • Anterior division/branching of the obturator nerve: The obturator externus in the anterior division of the thigh is located above, while the adductor brevis is placed below. The obturator nerve passes down anteriorly along the adductor brevis and the obturator externus and posteriorly along the adductor longus pectineus muscles to muscular branches of the adductor brevis, gracilis, adductor longus, and pectineus. The sensory braches flow to the thigh’s medial aspect while the articular branches flow to the hip joint.

Obturator nerve injuries and pain

• Pain, damage, and other problems of the obturator nerve can occur due to injuries to the nerve itself or to the nearby tissues and musculature. This may also be accompanied by entrapment, restriction, or impingement of the nerve.
• Obturator nerve pain and injuries often occur due to pelvic injuries that include fractures. Injuries to the nerve and surrounding tissues can happen during motor vehicle or household accidents. Another common cause of obturator nerve injuries and subsequent pain is accidental damage of the nerve during abdominal or pelvic surgery. In rare cases, the obturator nerve may become spontaneously trapped without any known causes, often at the area where it gets out of the pelvic area.
• Patients with obturator nerve damage and injuries may suffer from numbness, pain, and weakness in the thigh area. Some affected people may also complain of continuous dull or acute pain emanating from the thigh area. Groin pain may also occur, which can then radiate along the middle section of the thigh and downwards to the knee. There may be instability or weakness of the leg, particularly with physical activities. Obturator nerve injury can also be accompanied by weakness of the abduction thigh, which in turn can prevent coordinated movement of the thighs thereby causing unstable posture and/or gait.
• The process of healing of nerves in general tends to be very slow. Hence, pain and other symptoms associated with obturator nerve entrapment and damage can persist for many months.

Treatment of obturator nerve injuries

Minor obturator nerve damage can be corrected via physical therapy. Severe instances of obturator nerve injuries may need to be treated via surgery. Healing process is prolonged as the nerve tends to regenerate on its own at the rate of around 1 inch per month.

• If the obturator nerve is entrapped or if there are nerve blocks, then doctors may prescribe the use of steroid injections for a limited time period. It will not only help alleviate associated inflammation and swelling, but will also ease manage the nerve pain. Non-steroidal anti-inflammatory drugs may also be given to manage and control pain and inflammation.
• In case of nerve blocks or nerve entrapment, doctors may sometimes go for decompression procedure of the obturator nerve, at the area where it exits the pelvis. This technique however does not have a high success rate.
• Spinal cord stimulation may be tried in refractory instances.
• Minor nerve damage can be treated with physical therapy that involves a generalized exercise regimen, stretching of the affected area, muscle therapy for alleviation of tightness in the muscles, and use of electrical stimulation, ultrasound, and other modalities to manage pain.
• Severe cases of obturator nerve injuries may be treated via surgery and/or nerve transfer procedures, wherein the branch from a nearby femoral nerve present in the groin is connected to the obturator nerve.