Obturator Neuropathy

Obturator neuropathy is a rare injury of the obturator nerve (L2 to L4), causing weakness of hip adduction and sensory loss over the medial thigh. Causes are pelvic surgery (gynaecological, urological, colorectal, hernia repair), childbirth, pelvic malignancy, hip arthroplasty, obturator hernia, pelvic fracture, retroperitoneal haematoma, endometriosis and sports injuries (athletic pubalgia).

Pathophysiology. Compression, transection or traction of the nerve in the pelvis, obturator canal or thigh.

Medial thigh pain and numbness, weakness of hip adduction with a wide based gait, difficulty crossing the legs and circumduction on walking. Pain in the groin may radiate to the knee. In obturator hernia there is intestinal obstruction (pain down the medial thigh on extension, abduction and medial rotation of the hip).

Red flags.

• Bowel obstruction with medial thigh pain.
• Rapid onset after pelvic surgery.

Examine adduction strength and medial thigh sensation, with the femoral nerve spared. Electromyography of adductors (longus, brevis and magnus) with nerve conduction studies at 2 to 3 weeks shows denervation. CT or MRI of the pelvis for mass, haematoma or hernia. Ultrasound can show nerve injury.

Differential diagnosis.

• L2 to L4 radiculopathy, lumbar plexopathy and femoral neuropathy.
• Hip pathology, adductor strain and sports hernia.
• Diabetic amyotrophy.

Treat the cause. Surgical repair of obturator hernia (urgent for strangulation), decompression of haematoma, treatment of tumour, and exploration of nerve for suspected transection with repair or grafting.

Conservative. Most iatrogenic injuries are neurapraxia and recover over weeks to months. Physiotherapy for hip adductor strengthening, gait training, and avoidance of provocative activity.

Pain. Gabapentin 300 mg three times daily, increased as tolerated, amitriptyline, topical lidocaine, and in severe cases obturator nerve block with local anaesthetic and corticosteroid.

Monitoring. Strength and electromyography at 3 months.

Referral and escalation. Refer to neurology and surgery, with urgent referral for hernia obstruction.