Obturator Neuralgia – The Clinical Syndrome
Obturator neuralgia is an uncommon cause of medial thigh pain that does not extend below the knee and occurs most often after trauma. Pelvic fractures, gunshot wounds, and occasionally childbirth have been implicated in the evolution of obturator neuralgia.
With the increased number of total hip arthroplasties being performed, trauma to the branches of the obturator nerve may occur, producing pain and numbness over the medial thigh. Obturator neuralgia also may be due to compression of the nerve by tumor, hemorrhage, bone cement from total hip arthroplasties, endometriosis, or abscess.
Stretch injuries to the obturator nerve can cause the symptoms of obturator neuralgia. Diabetes can affect the obturator nerve, but this is usually in conjunction with neuropathy of the other nerves of the lower extremity, especially the femoral nerve.
What are the Symptoms of Obturator Neuralgia
A patient with obturator neuralgia presents with pain that radiates into the medial thigh and, except in rare patients, does not extend below the knee. This pain may be paresthetic or burning, and the intensity is moderate to severe. No significant feeling of sunburn over the distribution of the obturator nerve has been reported.
How is Obturator Neuralgia diagnosed?
Electromyography can help identify the exact source of neurological dysfunction and clarify the differential diagnosis and should be the starting point of the evaluation of all patients thought to have obturator neuralgia. Plain radiographs of the spine, hip, pelvis, and proximal femur are indicated in all patients with obturator neuralgia to rule out occult bony pathology. Based on the patient’s clinical presentation, additional tests, including complete blood cell count, uric acid level, erythrocyte sedimentation rate, and antinuclear antibody testing, may be indicated. Magnetic resonance imaging (MRI) of the spine, pelvis, and proximal lower extremity is indicated if tumor or hematoma is suspected. Ultrasound imaging may also provide useful information regarding the status of the nerve. Injection of the obturator nerve with a local anesthetic and steroid serves as a diagnostic and therapeutic maneuver.
It is sometimes difficult to separate obturator neuralgia from a lumbar plexopathy or radiculopathy on purely clinical grounds, and electromyography is strongly recommended. Electromyography and nerve conduction testing also help rule out the presence of peripheral neuropathy. Intrapelvic or retroperitoneal tumor or hematoma may compress the lumbar plexus and mimic the clinical presentation of obturator neuralgia.
Mild cases of obturator neuralgia usually respond to conservative therapy, and surgery should be reserved for more severe cases. Initial treatment of obturator neuralgia should consist of treatment with simple analgesics, nonsteroidal antiinflammatory drugs (NSAIDs), or cyclooxygenase-2 (COX-2) inhibitors and avoidance of repetitive activities that exacerbate the symptoms. If diabetes is thought to be the cause of the patient’s obturator neuralgia, tight control of blood glucose levels is mandatory. Avoidance of repetitive activities thought to be responsible for the exacerbation of obturator neuralgia also helps ameliorate the symptoms. The use of gabapentin or a tricyclic antidepressant such as nortriptyline as an adjuvant analgesic also may help ameliorate the symptoms of obturator neuralgia. If the patient fails to respond to these conservative measures, a reasonable next step is injection of the obturator nerve with a local anesthetic and steroid. Ultrasound imaging may improve the accuracy of needle placement and decrease the incidence of needle-related complications.
Complications and Pitfalls
It is imperative that the clinician rule out causes of obturator neuralgia that, if undiagnosed, could harm the patient, such as uncontrolled diabetes and retroperitoneal or pelvic tumor. The main side effect of obturator nerve block is postblock ecchymosis and hematoma. Potential exists for needle-induced trauma to the obturator nerve. By advancing the needle slowly and then withdrawing the needle slightly away from the nerve, needle-induced trauma to the obturator nerve can be avoided.
Obturator neuralgia always should be differentiated from lumbar plexopathy and radiculopathy of the nerve roots that may sometimes mimic obturator nerve compression. Lumbar radiculopathy and obturator nerve entrapment may coexist in the “double crush” syndrome. The double crush syndrome is seen most commonly with median nerve entrapment at the wrist.
Injection of the obturator nerve is a simple and safe technique in the evaluation and treatment of the previously mentioned painful conditions. Careful neurological examination to identify preexisting neurological deficits that may later be attributed to the nerve block should be performed on all patients before beginning obturator nerve block, especially in patients with clinical symptoms of diabetes or clinically significant obturator neuralgia.