Obturator Neuropathy

A Cause of Exercise-Related Groin Pain

Peter Brukner, MBBS; Chris Bradshaw, MBBS; Paul McCrory, MBBS

THE PHYSICIAN AND SPORTSMEDICINE - VOL 27 - NO. 5 - MAY 1999

In Brief: Obturator neuropathy is a cause of exercise-related groin pain, particularly in those who play sports that involve much running, twisting and turning, and kicking. Symptoms include pain that begins insidiously at the adductor origin on the pubic bone and worsens with exercise. Diagnostic measures include reproduction of pain by stretching the pectineus muscle after exercise, electromyography, and a local anesthetic block of the obturator nerve. Surgery allows most patients to resume previous levels of activity.

The list of conditions that can cause acute or chronic groin pain in active patients is long, and the diagnosis and treatment can be complex and challenging. Common causes in athletes include adductor tendinitis, osteitis pubis, and the "sports hernia" (see "When Groin Pain Is More than 'Just a Strain': Navigating a Broad Differential," April 1998, page 78, and "The 'Sports Hernia': A Common Cause of Groin Pain," January 1998, page 36).

Another condition, obturator neuropathy, has recently been added (1) to the list of causes of exercise-related groin pain. In our clinic, we have treated over 150 patients, and all have resumed sports participation following treatment. Knowing the signs and symptoms of this disorder can help physicians diagnose and treat it promptly, so their patients can resume physical activity and sports as soon as possible.

Anatomy

The obturator nerve arises from the posterior division of nerve roots L2 to L4 and runs over the pelvic rim into the lesser pelvis (figure 1). After passing through a fibroosseous tunnel, it divides into the anterior and posterior branches, which exit the pelvis through the obturator foramen. The anterior branch innervates the adductor longus, adductor brevis, and gracilis muscles, and its sensory branch innervates the skin over the medial distal thigh. The posterior branch innervates the obturator externus and portions of the adductor magnus and pectineus muscles.

The mechanism of obturator nerve entrapment is unclear. However, the entrapment does not appear to occur within the fibroosseous obturator tunnel but rather at the level of the obturator foramen and proximal thigh where the fascia entraps the anterior branch of the nerve as it passes over the adductor brevis muscle. The causes of the fascial entrapment are not certain, but inflammatory processes may be involved. Given the clinical progression, which begins with pain of an inflammatory nature that evolves to consistent exercise-related pain, we postulate that chronic adductor tendinopathy develops and leads to fibrosis and fascial adhesions and eventual nerve entrapment. This theory is supported by the isotope bone scan appearance described below.

Clinical Presentation

Our patients were nearly all male, and most were Australian Rules football and soccer players. All presented with groin pain of more than 3 months' duration. Previous treatment included physical therapy, consisting of muscle stimulation, strengthening, stretching, and massage therapy. Five percent to 10% had had surgery, such as an inguinal hernia repair or adductor tendon release, in unsuccessful attempts to alleviate their chronic pain.

Signs and symptoms. Patients who have this condition typically present with an insidious onset of groin pain, which they describe as a deep ache centered on the adductor origin at the pubic bone. During exercise the pain is more severe and may radiate down the medial aspect of the thigh toward the knee. They may also report exercise-related weakness in the affected leg that is especially noticeable when they attempt to jump. Patients seldom report numbness or paresthesia, except in cases lasting longer than 12 months.

Adductor weakness and muscle spasm are more likely to occur after exercise, so the patient should always exercise immediately before being examined. The amount and intensity of the exercise must be sufficient to reproduce the patient's pain. Paresthesia along the medial thigh may also be present after exercise. Pain may be induced in the affected areas by a pectineus muscle stretch (figure 2) or by resisted external rotation of the hip.

Diagnostic studies. Imaging does not play a significant role in confirming the diagnosis, but may be important in excluding other diagnoses, such as stress fracture of the femoral neck or pubic ramus. The typical scintigraphic appearance of obturator neuropathy, unilateral increased uptake over the pubic symphysis (figure 3), is similar to that of osteitis pubis, so scintigraphy cannot be used to distinguish the two conditions.

In cases of obturator neuropathy lasting longer than about 3 months, electromyography (EMG) studies, performed by inserting the needle into the belly of the patient's adductor muscles, show a pattern of denervation in the adductor longus and brevis muscles. A local anesthetic block can confirm the diagnosis; this is performed under radiographic control by inserting the needle into the roof of the obturator foramen and injecting radioopaque dye, which travels along the nerve sheath. If the block reproduces the patient's postexercise weakness and relieves the pain produced by the pectineus muscle stretch and resisted hip external rotation, obturator neuropathy is likely. The nerve block is not necessary to confirm the diagnosis clinically, and our baseline investigation is the needle EMG.

Differential Diagnosis

Physicians must differentiate obturator neuropathy from a number of other disorders (table 1), including the three mentioned above plus stress fractures of the neck of the femur and pubic ramus, osteomyelitis, iliopsoas muscle strain or bursitis, referred pain from the lumbar spine or sacroiliac joints, and hip joint problems such as osteoarthritis or synovitis.

Treatment

Conservative treatment, consisting of electrical stimulation of the adductor and hip flexor muscles, stretching, and myofascial massage, has not been successful in resolving this condition. It is possible, however, that such measures could be effective with early recognition.

Surgery is the preferred treatment for patients who have the clinical features of obturator neuropathy and evidence of denervation on needle EMG. It involves dividing the fascia over the pectineus and adductor longus muscles (figure 1) and dissecting the space between the two muscles to reveal the anterior branch of the nerve beneath a thick fascia. This fascia is divided along the line of the nerve, and the adductor longus-pectineus junction is loosely closed. Routine closure of the subcutaneous tissue and skin completes the procedure.

Rehabilitation and Outcome

Standard postoperative wound management is important and should include gentle stretching after the first week of recovery. Beginning about 10 days after surgery, exercise usually begins with light jogging and, as tolerated, progresses to faster running and gradually to functional activities.

The results of the fascial release have been excellent, with patients returning to full, symptom-free activity within 3 to 4 weeks of surgery. EMG studies normalize within a few weeks to months. Thus far only 1 out of 150 patients has had a recurrence.

We believe that obturator neuropathy is a common cause of exercise-related groin pain, particularly in those who play sports such as soccer or Australian Rules football, which involve a great deal of running, sharp twists and turns, and frequent, powerful kicks. Physicians who recognize its clinical presentation can expedite its diagnosis and treatment and help their patients make a safe and early return to sports activity.

Reference

1. Bradshaw C, McCrory P, Bell S, et al: Obturator nerve entrapment: a cause of groin pain in athletes. Am J Sports Med 1997;25(3):402-408

Drs Brukner, Bradshaw, and McCrory are sports physicians at Olympic Park Sports Medicine Centre in Melbourne, Australia, where Dr McCrory is also a neurologist. They are fellows of the Australian College of Sports Physicians, and Dr McCrory is also a fellow of the Royal Australian College of Physicians. Address correspondence to Peter Brukner, MBBS, Olympic Park Sports Medicine Centre, Swan St, Melbourne, VIC 3004, Australia; e-mail to pbrukner@compuserve.com.