AUTHOR INFORMATION

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Authored by Elizabeth A Sekul, MD, Associate Professor, Department of Neurology, Medical College of Georgia

Elizabeth A Sekul, MD, is a member of the following medical societies: American Academy of Neurology, American Association of Neuromuscular and Electrodiagnostic Medicine, and Child Neurology Society

Edited by Aashit K Shah, MD, Associate Professor of Neurology, Wayne State University; Program Director, Clinical Neurophysiology Fellowship, Department of Neurology, Detroit Medical Center; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Neil A Busis, MD, Chief, Division of Neurology, Department of Medicine, University of Pittsburgh Medical Center - Shadyside, Clinical Associate Professor, Department of Neurology, University of Pittsburgh School of Medicine; Matthew J Baker, MD, Consulting Staff, Collier Neurologic Specialists, Naples Community Hospital; and Nicholas Lorenzo, MD, Chief Editor, eMedicine Neurology; Consulting Staff, Neurology Specialists and Consultants

Author's Email:	Elizabeth A Sekul, MD
Editor's Email:	Aashit K Shah, MD

eMedicine Journal, March 20 2007, VOLUME 8, Number 3

INTRODUCTION

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Background: Femoral neuropathies can occur secondary to direct trauma, compression, stretch injury, or ischemia. Femoral neuropathy causes weakness predominantly of the quadriceps, which results in difficulty with ambulation.

Pathophysiology: Knowledge of femoral nerve anatomy is essential to understanding the mechanism of its injury and to localizing the lesion.

The femoral nerve is part of the lumbar plexus. It is formed by L2-4 roots and reaches the front of the leg by penetrating the psoas muscle before it exits the pelvis by passing beneath the medial inguinal ligament to enter the femoral triangle just lateral to the femoral artery and vein. Approximately 4 cm proximal to passing beneath the inguinal ligament, the femoral nerve is covered by a tight fascia at the iliopsoas groove. The nerve can be compressed anywhere along its course, but it is particularly susceptible within the body of the psoas muscle, at the iliopsoas groove, and at the inguinal ligament.

The main motor component innervates the iliopsoas (a hip flexor) and the quadriceps (a knee extensor). The motor branch to the iliopsoas originates in the pelvis proximal to the inguinal ligament. The sensory branch of the femoral nerve, the saphenous nerve, innervates skin of the medial thigh and the anterior and medial aspects of the calf.

Frequency:

• In the US: Femoral mononeuropathies account for approximately 1% of all mononeuropathies seen in the author’s active electrodiagnostic laboratory.

Race: No racial predilection has been noted.

Sex: No gender preponderance is known.

Age: Femoral mononeuropathy is reported in all age groups.

CLINICAL

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History:

• Patients with femoral neuropathy complain of difficulty with stairs and frequent falling secondary to "knee buckling."


• • This weakness is typically of acute or subacute onset.
  
  
  
  • This contrasts with a myopathic process in which the weakness is subacute to chronic in onset and bilateral in nature.
  
  
  
• Acute severe pain in the groin, thigh, and/or lower abdomen may occur if the neuropathy is associated with a retroperitoneal hematoma. Otherwise the associated pain is usually mild and located near the inguinal ligament.



• Patients may complain of medial leg and calf numbness. Sensory symptoms in saphenous nerve distribution are rare with injury to the main trunk of the femoral nerve.

Physical:

• Weakness of the quadriceps muscle and decreased patellar reflex are the most striking examination findings.



• If the neuropathy is advanced and chronic, wasting of the quadriceps may be noted.



• In some patients, the iliopsoas muscle is involved. In such cases, the lesion must be above the inguinal ligament, as the motor branch to this muscle comes off before the inguinal ligament.



• In isolated femoral neuropathies, the thigh adductors are normal. Although the thigh adductors share common lumbar roots with the muscles innervated by the femoral nerve, they are innervated by the obturator nerve along with the sciatic nerve and therefore are spared. Sensory deficits consist of numbness of the medial thigh and the anteromedial calf.



• If a retroperitoneal hematoma is present, hip extension may cause pain.

Causes:

• The femoral nerve is predisposed to compression within the psoas muscle. This commonly is associated with hemorrhage into this muscle due to hemophilia, anticoagulation therapy, or trauma.



• Direct trauma to the femoral nerve can occur as a result of penetrating wounds or fractures of the hip or pelvis.



• Lithotomy positioning during delivery or gynecological/urological procedures also has been associated with compressive femoral neuropathies. In this position, the sharp flexion of the hip can compress the nerve at the inguinal ligament. Excessive hip abduction and external rotation cause additional stretch on the nerve.



• Compression of the femoral nerve also can be due to aortic or iliac aneurysms or tumors.



• Diabetic patients have an unusual predilection for femoral and proximal mononeuropathies. The etiology is suspected to be a vasculitic.



• Iatrogenic causes of femoral mononeuropathy include direct pressure or trauma to the nerve during pelvic or abdominal surgery or focal damage at the femoral triangle due to a difficult femoral line placement.

DIFFERENTIALS

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Vasculitic Neuropathy

Other Problems to be Considered:

Lumbar plexopathies
Lumbosacral disk syndromes

WORKUP

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Imaging Studies:

• In cases of suspected retroperitoneal hematoma, an emergent CT scan of the pelvis should be performed.



• In other cases in which the etiology is not apparent, MRI or CT scan of the pelvis may be beneficial to aid in localizing the site of compression and may define the etiology (eg, tumor, abdominal aneurysm, iliac aneurysm).

Other Tests:

• Evaluation for femoral nerve dysfunction includes nerve conduction studies (NCS) and needle electromyography (EMG).



• NCS should include sensory studies of the saphenous nerve and motor studies of the femoral nerve.



• When evaluating femoral NCS, results on the symptomatic side should be compared to those on the asymptomatic side.



• On EMG, the quadriceps should show neuropathic changes.



• The iliopsoas is involved if the lesion is in the pelvis (above the inguinal ligament).



• The adductor magnus and brevis, which share lumbar innervation with quadriceps and iliopsoas, are spared since they are innervated primarily by the obturator and sciatic nerves.

TREATMENT

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Medical Care: Treatment is dependent on the etiology of the lesion.

• Most patients with a femoral mononeuropathy can be treated conservatively with physical therapy, avoidance of excessive hip abduction and external rotation, and knee bracing to prevent buckling of the knee.



• In patients with femoral neuropathy associated with positional compression or retraction compression during surgery or delivery, recovery typically occurs over 3-4 months.



• When the cause of the neuropathy is a retroperitoneal hematoma, evacuation of the hematoma may be indicated, but this is controversial.



• In patients on anticoagulation therapy, anticoagulant agents must be stopped until the hematoma has resolved. Outcomes for these patients are worse than for those with a hematoma due to trauma.



• If the compression is due to a tumor, then therapy, either surgery or chemotherapy, is directed at the neoplasm.



• When the neuropathy is due to diabetes or vasculitic causes, immunosuppressive therapy may be warranted.

Surgical Care:

• Surgical decompression of the nerve sometimes is performed secondary to hematomas or mass lesions.



• Occasionally, surgical exploration for other reasons (eg, penetrating wounds, fascia bands) is indicated.

TEST QUESTIONS

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CME Question 1: In femoral neuropathies, which of the following muscles is not involved?

A: Quadriceps
B: Iliopsoas
C: Thigh adductors
D: Sartorius
E: Pectineus

The correct answer is C: The thigh adductors share common lumbar roots with the femoral innervated muscles. However, they are innervated by the obturator nerve and, along with the sciatic nerve, are spared in femoral neuropathies.

CME Question 2: Which of the following is a common cause of femoral neuropathy?

A: Difficult femoral line placement
B: Lithotomy position
C: Hip fracture
D: Abdominal or pelvic surgery
E: All of the above

The correct answer is E: Another prominent cause is retroperitoneal bleeding.

Pearl Question 1 (T/F): Anticoagulation therapy does not predispose an individual to femoral neuropathies.

The correct answer is False: A complication of anticoagulation is hemorrhage into the retroperitoneal space, including the psoas muscle. The femoral nerve courses through the psoas muscle, making compression likely when a hematoma is present. Recognizing this problem in patients on anticoagulation is imperative so that anticoagulation can be stopped until the hematoma is resolved. Surgical treatment for this condition is controversial.

Pearl Question 2 (T/F): The lithotomy position can be associated with a femoral neuropathy.

The correct answer is True: Prolonged maintenance of the lithotomy position during urological/gynecological procedures or delivery is associated with compression of the nerve against the inguinal ligament with additional stretch to the nerve due to the abducted and externally rotated position of the leg.

Pearl Question 3 (T/F): A femoral nerve lesion can be localized if iliopsoas involvement is confirmed.

The correct answer is True: Such lesions are likely to be above the inguinal ligament in the pelvis if the iliopsoas muscle is involved.

Pearl Question 4 (T/F): The sensory distribution of the femoral nerve is primarily in the lateral thigh.

The correct answer is False: The main sensory branch of the femoral nerve is the saphenous nerve. It is responsible for sensation to the medial thigh and anteromedial calf.

BIBLIOGRAPHY

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• al Hakim M, Katirji B: Femoral mononeuropathy induced by the lithotomy position: a report of 5 cases with a review of literature. Muscle Nerve 1993 Sep; 16(9): 891-5[Medline].
• Azuelos A, Coro L, Alexandre A: Femoral nerve entrapment. Acta Neurochir Suppl 2005; 92: 61-2[Medline].
• Krendel DA, Zacharias A, Younger DS: Autoimmune diabetic neuropathy. Neurol Clin 1997 Nov; 15(4): 959-71[Medline].
• Llewelyn JG, Thomas PK, King RH: Epineurial microvasculitis in proximal diabetic neuropathy. J Neurol 1998 Mar; 245(3): 159-65[Medline].
• Olesen LL: Femoral neuropathy secondary to anticoagulation. J Intern Med 1989 Oct; 226(4): 279-80[Medline].
• Williams FH, Johns JS, Weiss JM: Neuromuscular rehabilitation and electrodiagnosis. 1. Mononeuropathy. Arch Phys Med Rehabil 2005 Mar; 86(3 Suppl 1): S3-10[Medline].

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