The femoral nerve arises from the posterior divisions of the ventral primary rami of L2, L3, and L4 within the psoas major muscle. These nerves join to form the largest branch of the lumbar plexus. The nerve emerges from the lateral border of the psoas muscle and courses inferiorly in the intermuscular groove between this muscle and the iliacus muscle. One of the major branches is the lateral femoral cutaneous nerve, see meralgia peresthetica. The main femoral nerve then passes under the inguinal ligament lateral to the femoral artery and vein where divides into multiple branches within the femoral triangle.
Branches of the femoral nerve:-
The femoral nerve can have several entrapment locations or causes of injury, including intrapelvic injury or injury in the inguinal region. Diabetic amyotrophy is the most common cause of femoral nerve neuropathy. Open injuries can occur from gunshots, knife wounds, glass shards, or needle puncture in some medical procedures. The most worrisome complication of major trauma to the femoral triangle region is an associated femoral artery injury. The nerve can be injured at the time of the trauma or inadvertently sutured during repair of this injury. Large-blade, self-retaining retractors used during pelvic operations can cause injury to the nerve due to compression.
Conduction of the femoral nerve was measured in diabetic patients without clinical signs of femoral nerve involvement, and there was a statistically significant difference between diabetics and healthy individuals in terms of both femoral nerve motor latency and amplitude. The authors observed that these abnormalities became more evident as the polyneuropathy of the patients became more serious.
Most entrapment neuropathies occur below the inguinal ligament. After passing beneath the inguinal ligament, the femoral nerve is in close proximity to the femoral head, the tendon insertion of the vastus intermedius, the psoas tendon, the hip, and the joint capsule. The femoral nerve does not have significant protection in this area.
Heat developed by methylmethacrylate during a total hip arthroplasty can injure the femoral nerve. Pelvic procedures that require the lower extremity to be positioned in an acutely flexed, abducted, and externally rotated position for long periods can cause compression by angling the femoral nerve beneath the inguinal ligament. The nerve may be compromised by pressure from a fetus in a difficult birth. Pelvic fractures and acute hyperextension of the thigh may also cause an isolated femoral nerve injury. Pelvic radiation, appendix or renal abscesses, and tumours can cause femoral nerve injuries as well. The nerve can also be injured by a compartment-like compression from a hemorrhage (caused by a hemorrhagic disorder or by anticoagulant use).
The symptoms of a femoral neuropathy may include pain in the inguinal region that is partially relieved by flexion and external rotation of the hip, and dysesthesia over the anterior thigh and anteromedial leg. Patients complain of difficulty in walking and of knee buckling, depending on the severity of the injury. The nerve gives rise to the saphenous nerve in the thigh; therefore, numbness in this distribution can be present. Anterior knee pain may also be present because the saphenous nerve supplies the patella.
On examination, patients may present with weak hip flexion, weak knee extension, and impaired quadriceps tendon reflex, as well as sensory deficit in the anteromedial aspect of the thigh. Pain may be increased with hip extension and relieved with external rotation of the hip. If compression occurs at the inguinal region, no hip flexion weakness is present. Sensory loss may occur along the medial aspect of the leg below the knee (saphenous distribution).
Electrodiagnostic testing typically is performed for diagnosis, but is also important to determine the extent of the injury and the prognosis for recovery. With electrodiagnostic testing, either surface or needle electrodes lateral to the femoral artery in the inguinal region are used for stimulation. The stimulation can be performed above and below the inguinal ligament. Disk electrodes from the vastus medialis are used to record stimulation.
A saphenous nerve sensory study may also be performed (continuation of the sensory portion of the femoral nerve over the medial aspect of the leg and ankle). Needle examination should be completed for the paraspinal muscles as well as for the iliopsoas (also L2-3) and hip adductors supplied by the obturator nerve, to determine the presence of root or plexus injury versus peripheral nerve injury. Needle electromyography is usually the most revealing portion of the electrodiagnostic test. The examiner must look not only for denervation potentials but also for any active motor units.
Treatment may be based on symptoms only, or it may be more invasive and include surgical intervention, depending upon the severity of the injury. Quadriceps weakness may be treated with a locking knee brace to prevent instability, and the patient may require an assistive device for walking. Good recovery has been reported in up to 70% of patients with a femoral neuropathy and may take up to a year. The recovery may even occur in the setting of a fairly severe injury, as determined through electrodiagnostic testing and by physical examination. Patients with severe axonal loss have some recovery of function, although it is usually incomplete.
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