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Lumbar Plexus Nerve Entrapment Syndromes as a Cause of Groin Pain in Athletes

Rassner, Leslie MD

doi: 10.1249/JSR.0b013e318214a045
Abdominal Conditions
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In athletes, groin pain is not uncommon and can be severe and activity-limiting. Nerve entrapment syndromes of the lumbar plexus are a rare but important etiology that should be considered when evaluating athletes. Diagnosis can be made based on patterns of pain and hypoesthesia following the sensory distribution of the involved nerve and by pain relief with nerve block. Conservative therapies, including nerve blocks, neurodestructive procedures, and medications, may provide long-term pain relief. If nonsurgical therapies fail, referral should be made for surgical exploration and neurectomy.

Address for correspondence: Leslie Rassner, MD, St. Mark's Family Medicine Residency, 1250 East 3900 South, Suite 260, Salt Lake City, UT 84124 (E-mail: lrassner@gmail.com).

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Introduction

Groin pain in athletes is not uncommon. Sports injuries to the hip and groin region have been noted in 5% to 9% of high school athletes (19). Groin pain among professional sports players has an estimated incidence of 0.5% to 6.2% (8). In the most difficult cases, groin pain can be severe and activity-limiting (19). Because of the complex anatomy of the region and nerve anatomic variability, the diagnosis of groin pain can be challenging, and an exact diagnosis of chronic pain can be elusive (15,23). Nerve entrapment syndromes are a rare but important etiology that should be considered when evaluating athletes as they may provide a pathological diagnosis and definitive treatment while avoiding more invasive and costly investigations (15,22).

This article focuses on the evaluation and management of the most common nerve entrapments of the lumbar plexus, with a focus on athletes, and it includes relevant literature developments of the past decade. In 1999, McCrory and Bell completed an excellent comprehensive review of nerve entrapment syndromes of the lumbar and sacral plexuses causing hip, groin, and buttock pain in athletes, including surgical techniques (15). The reader is advised to consult McCrory's review for nerve entrapments not covered in this article and for surgical technique.

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Differential Diagnosis of Groin Pain in Athletes

A focused history and physical is necessary to search for athletic and nonathletic causes of groin pain (13). A differential diagnosis of groin pain in athletes is well summarized in Table 1 (13). Particular notice should be made to overlapping history and physical findings, as two or more coexisting injuries may be found in 27% to 90% of patients with groin pain (4,12). It is theorized that the proximity of anatomical structures in the groin region predisposes an insulting force to cause more than one injury. Alternately, an initial injury may result in a mechanical dysfunction of the hip, pelvis, and sacroiliac joints, predisposing an athlete to a secondary overuse injury (19). Regardless, the proper diagnosis and treatment of groin pain is crucial for return to function and sport.

TABLE 1

TABLE 1

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Anatomy of the Nerves of the Lumbar Plexus

The lumbar plexus is formed by the ventral rami of the first four lumbar nerves plus a branch of T12. Branches of the lumbar plexus include the iliohypogastric, ilioinguinal, genitofemoral, lateral femoral cutaneous, femoral, and obturator nerves (Fig. 1) (27). Most of the branches of the plexus are related to the psoas major muscle, passing through it or behind it or being formed within it. Within the psoas muscle, the rami of the lumbar plexus are connected to the sympathetic plexus by rami communicantes (17).

FIGURE: Dee

FIGURE: Dee

The iliohypogastric and ilioinguinal nerves originate from T12 through L2 nerve roots. They pass together laterally through the psoas muscle, extend diagonally along the ventral surface of the quadratus lumborum muscle above the iliac crest. Both nerves continue their course to the deep inguinal ring on the inner surface of the transversus abdominis muscle, then pierce this muscle to run between it and the internal oblique for a short distance (17). The iliohypogastric nerve has been cited to pierce the transversus abdominis near the anterior superior iliac spine (ASIS), while the ilioinguinal nerve takes a similar but slightly more caudal course (27). The iliohypogastric nerve provides motor innervation to the abdominal wall muscles, while the ilioinguinal nerve provides motor innervation to the lowermost portions of the transversus abdominis and internal oblique muscles (15). In a cadaver study by Rab et al., the iliohypogastric and ilioinguinal nerves were found to branch off motor fibers within these abdominal muscle layers and to share several branches (23).

Between the transversus abdominis and internal oblique, the iliohypogastric divides into the lateral and anterior cutaneous bxranches (17). The lateral cutaneous branch pierces the internal and external oblique and supplies the skin of the upper buttock. The anterior cutaneous branch pierces the internal oblique 2 to 3 cm medial to the ASIS and thereafter runs for a distance between the two obliques. It finally pierces the aponeurosis of the external oblique above the superficial inguinal ring and innervates a small area of skin above the pubis (15,17).

After piercing the transversus abdominis muscle near the ASIS and giving off a motor branch, the ilioinguinal nerve pierces the internal oblique muscle medial to the ASIS and supplies motor innervation to the muscle. Before entering the inguinal canal at the lower surface of the spermatic cord, a branch of the ilioinguinal nerve passes posteriorly to innervate a strip of skin over the iliac crest. After passing through the inguinal canal, the nerve emerges through the superficial inguinal ring to supply the skin of the upper inner thigh, the root of the penis, and the scrotal skin or the mons pubis and labium majus.

The genitofemoral nerve originates from L1 and L2 nerve roots and is formed within the psoas muscle (17). It emerges on the anterior surface of the psoas muscle near its medial border at the level of L3 and L4 vertebra (17). It descends retroperitoneally on the psoas muscle until the inguinal ligament, where it divides into the genital and femoral branches (15). The genital branch crosses anteriorly over the external iliac vessels and then enters the inguinal canal through the deep ring, just lateral to the deep inferior epigastric artery and the origin of the cremasteric branch of the deep inferior epigastric artery. Passing through the inguinal canal, it supplies motor innervation to the cremaster muscle and shares sensory innervation to the scrotal skin or the mons pubis and labium majus (15,17). The femoral branch passes under the inguinal ligament and enters the femoral sheath lateral to the femoral artery. Then it pierces the anterior sheath of the femoral sheath and fascia lata and supplies the skin of the triangle of Scarpa (femoral triangle) on the anterior thigh (15,17).

Variability of the terminal course and distribution of the ilioinguinal and genitofemoral nerves has been found in cadaver studies (23). Rab et al. and Akita et al. found the inguinal and ventromedial regions innervated by isolated cutaneous branches of the ilioinguinal, by isolated branches of the genitofemoral, or by cutaneous branches originating from both nerves respectively (1,23).

The obturator nerve arises from the ventral rami of L2, L3, and L4 and descends in the psoas muscle until emerging from its medial aspect at the pelvic brim. Entering the pelvis, it passes on the lateral wall until reaching the fibro-osseous tunnel of the obturator foramen under the pubic ramus (15,17). The obturator nerve passes posterior to the common iliac vessels and lateral to the internal iliac vessels, continuing downward until innervating the adductor muscles and gracilis, the skin of the medial part of the thigh, and the hip and knee joints (17).

The lateral femoral cutaneous nerve forms from the fusion of the dorsal divisions of the ventral primary rami of the L2 and L3 nerve roots and passes retroperitoneally through the psoas until emerging from the lateral border of the psoas muscle approximately at the level of the L4 vertebra (15,17). It runs obliquely across the iliacus muscle toward the ASIS. It supplies sensory fibers to the parietal peritoneum in the iliac fossa. After traveling down the posterior wall of the iliac fossa, posterolateral to the cecum on the right and lower part of the descending colon on the left, it passes below or perforates the inguinal ligament 0.5 cm medial to the ASIS. The lateral femoral cutaneous nerve then courses through or in front of the proximal sartorius muscle where it splits into anterior and posterior branches to supply the skin of the anterolateral aspect of the thigh (15,17).

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Clinical Features

Groin pain of neural origin can be caused by pelvic surgeries, blunt trauma, sports injury, hypertrophy of the abdominal muscles from excessive training, or from unknown causes (5,11,20). In the case of genitofemoral and lateral femoral cutaneous nerve entrapments, the wearing of tight clothing also has been implicated (26). Obturator nerve entrapment can be caused by pelvic trauma and tumors or normal pregnancy (15). Some patients will recall a specific injury, such as weight lifting in the gym (16). Others will describe an insidious onset of symptoms without a remembered mechanism of injury outside of usual sports participation (2). Postoperative neuralgias can occur in the first week following surgery from suture entrapment or direct nerve trauma, or months to years later from scar tissue entrapment and/or neuroma formation (10,14,22). Herniorrhaphy and hysterectomy are the most commonly cited surgeries linked to postoperative neural groin pain, with neural pain following other gynecologic surgeries, vasectomies, appendectomies, soft tissue tumor surgeries, and iliac bone grafts also observed (10,15,20).

Pain can be experienced within and outside the groin, referring to the pelvic viscera, buttock, thigh, and hip and knee joints. Table 2 provides a review of the sensory and motor innervations of the commonly entrapped nerves of the lumbar plexus (15). When evaluating the sensory distribution of pain, particular note should be made of the anatomic variability of the iliohypogastric, ilioinguinal, and genitofemoral nerves (23). Pain can be intermittent with activity or constant (26). Pain characteristically is lancing, sharp, or stabbing but may be a burning or deep ache (2,11). In women, pain has been reported during sexual activity (11).

TABLE 2

TABLE 2

In athletes, risk factors and specific sports can be linked to specific nerve entrapments. Among athletes, most cases of entrapment of the ilioinguinal nerve are linked to hypertrophy of the abdominal muscles as a result of excessive training (5). Irshad et al. have described the diagnosis and surgical treatment of "hockey groin syndrome," a tearing of the external oblique combined with entrapment of the ilioinguinal nerve causing debilitating pain in elite hockey athletes (6). Iliohypogastric nerve injury combined with tears in the external oblique aponeurosis has been described in soccer and rugby players (5,28). In athletes, obturator nerve entrapment appears to be the result of a fascial band at the distal end of the obturator canal, most commonly in skaters, Australian Rules football players, and soccer players as a result of adductor muscle development (5).

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Physical Examination

Neurologic symptoms such as hypoesthesia, hyperesthesia, or allodynia may be present along with groin tenderness to palpation (11,14). Hyperextension of the hip and twisting body movements can induce pain and may produce hypoesthesia by means of nerve traction and compression (5,11). If active abdominal muscle contraction intensifies pain (a positive Carnett's sign), nerve entrapment in the abdominal wall should be suspected (11). Tests for radicular lumbar pain, such as a straight leg raise, should be negative, and sciatic notch tenderness should not be present. Motor weakness may be observed or reported postexercise in the corresponding abdominal wall, hip, and thigh musculature. However, frequently no objective findings of motor weakness are present, even when motor innervations exist (2,16,26). It is theorized that sensory nerve fibers are more sensitive to compression and therefore are affected first (26).

Patients with ilioinguinal, iliohypogastric, and genitofemoral neuralgias report body movements as aggravating their pain (stretching the hip joint, coughing, sneezing) (26). Slight hip flexion may improve the pain (26). Tenderness may be noted over or inferomedial to the ASIS with ilioinguinal nerve entrapment and just superior to the deep inguinal ring with iliohypogastric nerve entrapment (5,9). In a series of 100 patients with mixed ilioinguinal, iliohypogastric, and genitofemoral nerve entrapments, Madura et al. described an "arch and twist" maneuver that usually reproduces the pain. The patient is asked to stand and hyperextend his/her trunk while rotating both toward and away from the symptomatic inguinal site. A positive test occurs when turning toward the affected side does not reproduce pain, whereas twisting away from the affected side recreates symptoms (14).

In obturator nerve entrapment, adductor muscle atrophy and weakness and paresthesias may be present (5). Exam findings and symptoms may be aggravated by physical exercise (2,5). With the patient standing, a pectineus stretch, performed by the patient passively externally rotating and abducting the affected hip, will reproduce the pain (2).

Patients with lateral femoral cutaneous nerve entrapment (meralgia paresthetica) have an absence of motor findings (5). Tinel's sign usually is present 1 cm medial and inferior to the ASIS (5).

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Diagnosis

A diagnostic triad for nerve entrapment syndromes includes burning or lancing pain, impaired sensory perception, and pain that is relieved by a nerve block (26). Laboratory and advanced imaging studies should be performed as indicated to rule out other etiologies, but they will not confirm a diagnosis of idiopathic or iatrogenic entrapment of the nerves of the lumbar plexus. Nerve conduction studies may be used mainly for evaluation and localization of paresthesias (numbness, tingling, burning). Electromyography (EMG) may be used when a suspected entrapped nerve supplies skeletal muscle motor innervation.

Patients with suspected ilioinguinal or iliohypogastric neuralgia can undergo EMG. Although EMG studies usually are not confirmatory, denervation of the pyramidalis is specific for ilioinguinal injury and paresthesia in the ilioinguinal sensory distribution may be reproduced (26). Local nerve blocks should be used for diagnosis. The ilioinguinal nerve is blocked approximately 2 inches medial and 2 inches inferior to the ASIS. A 25-gauge needle is inserted and aimed towards the pubic symphysis. As the external oblique fascia is pierced, lidocaine is infiltrated. The iliohypogastric nerve is blocked in similar fashion with injection site 1 inch medial and 1 inch inferior to the ASIS. Corticosteroid may be injected if there is an inflammatory component to the pain (26). Meulen et al. describe a technique using an EMG-guided nerve block to diagnose and treat an idiopathic ilioinguinal neuropathy in a man with onset of pain after weight lifting. They used a monopolar EMG injection needle inserted 1.2 inches inferomedial to ASIS and gently advanced until paresthesias of the scrotum were reported with electrical stimuli of 5 mA, 200 ms duration, and at 1 Hz. The ilioinguinal nerve was then blocked with mixture of lidocaine and corticosteroid, providing immediate pain relief several minutes after injection and at 4 months follow-up (16).

Neurophysiologic testing is not indicated for the diagnosis of genitofemoral nerve entrapment. The genital branch of the genitofemoral nerve may be blocked just lateral to the pubic tubercle and below the inguinal ligament with subcutaneous anesthetic infiltration. Alternately, an L1 and L2 paravertebral block can be completed. Pain that does not resolve with an ilioinguinal block but does resolve with the paravertebral block is indicative of genitofemoral nerve entrapment. A successful paravertebral nerve block also can serve as a good prognostic indicator for who will benefit from surgery (26).

Patients with suspected obturator nerve entrapment should undergo EMG. In patients with pain for greater than 3 months, EMG will demonstrate denervation of the adductor muscles (2). A fluoroscopic-guided obturator nerve block will relieve pain, paresthesias, and reproduce postexercise weakness (2).

When diagnosis is in question, EMG can be useful in distinguishing lumbar radiculopathy from lateral femoral cutaneous nerve entrapment. Magnetic resonance imaging (MRI) to rule out lumbar spine pathology is recommended before surgical intervention for lateral femoral cutaneous nerve entrapment. The lateral femoral cutaneous nerve can be blocked at a point 1 inch medial to the ASIS and just inferior to the inguinal ligament (26).

In the pediatric anesthesia literature, a failure rate with "blind" ilioinguinal and iliohypogastric nerve blocks of 10% to 25% has been documented (24). Consideration should be given for a radiologic nerve block where the procedure is available readily. If groin pain from a suspected nerve entrapment is not relieved by a "blind" nerve block, a repeat ultrasound or fluoroscopic-guided injection should be considered.

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Treatment

Diagnostic nerve blocks, with and without corticosteroid, may provide definitive treatment in some patients with mild nerve entrapment syndromes (7,16,21). Nerve blocks that provide short-term or partial pain relief may be repeated to attain long-term relief. Suresh et al. utilized two ultrasound-guided nerve blocks at a 3-month interval to achieve complete resolution of pain at 6 months follow-up in an adolescent with persistent postoperative ilioinguinal neuralgia (25). Other conservative treatments include ice, ultrasound, nonsteroidal antiinflammatory drugs (NSAID), gabapentin, oral tricyclic antidepressants, acupuncture, massage, biofeedback, and altering athletic training (5,25). When tight clothing or weighted belts are implicated in lateral femoral cutaneous or genitofemoral nerve entrapment, alterations in clothing and waist belts may relieve symptoms.

Other neurodestructive procedures may provide long-term relief from chronic nerve entrapment pain, although the potential for axon regeneration may limit long-term results. In a case report, ultrasound-guided cryoablation effectively relieved chronic pain from a genitofemoral nerve entrapment through 2 months follow-up (3). Mitra et al. described a case of ilioinguinal neuropathy treated successfully with pulsed radiofrequency followed immediately by an injection of an anesthetic and corticosteroid solution. This case was limited by a relatively short 3-month follow-up (18).

If conservative treatments fail, referral for surgical exploration and neurectomy is recommended. Short-term pain relief with a nerve block is a good prognostic indicator for patients who will obtain pain relief with surgery. Madura et al. and Loos et al. published retrospective case series on the surgical management of neuralgias and nerve entrapment syndromes. Loos and Madura showed similar results from neurectomy for inguinal neuralgia, with total pain relief in 73% to 75%, moderate pain relief in 14% to 25%, and poor or no relief in 3% to 13% (11,14).

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Conclusion

Nerve entrapment syndromes of the lumbar plexus are a rare but important etiology that should be considered when evaluating athletes with groin pain. A complete and focused history and physical should be performed to exclude other causes of groin pain and indicated laboratory testing and advanced imaging completed. The diagnosis of specific nerve entrapment syndromes can be made based on patterns of pain and hypoesthesia following the sensory distribution of the involved nerve, characteristic physical exam findings, and pain relief with a diagnostic nerve block. Conservative therapies, including nerve blocks, neurodestructive procedures, and medications, may provide long-term pain relief. If nonsurgical therapies fail, referral should be made for surgical exploration with neurectomy when indicated.

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References

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