-arises from posterior divisions of Ventral Rami of L2, L3, L4
-see innerv. musc. lower limb;
-passes inferolaterally thru psoas, & then runs between this muscle & iliacus;
-it passes over Iliacus muscle to enter thigh underneath the inguinal ligament;
-it supplies quadriceps & anteromedial thigh, & then continues on as the saphenous nerve;
Pectineus : arises at the level of the inguinal ligament;
Femoral Nerve Palsy:
may result from iliacus hematoma (either from anticoagulation or hemophilia);
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.
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.
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.
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
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).
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 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 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.
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