Femoral and Lateral Femoral Cutaneous Nerves

Clinical. An iliacus syndrome (L2, 3) occurs when the femoral nerve is entrapped during its initial course within the pelvis and groin, affecting the iliopsoas and quadriceps femoris muscles. The former leads to unilateral hip flexion weakness and the latter to knee extension weakness. When severe, this leads to total loss of knee extension, precluding walking as leg stability is totally compromised from lack of quadriceps femoris function. With partial lesions, patients first note difficulty going down stairs as their ability to lock their knee to support their weight is compromised. The patellar muscle stretch reflex is diminished or absent. Groin and thigh pain may also occur. Sensory symptoms involve the anteromedial thigh and medial lower leg. A somewhat unusual pure motor syndrome with primary quadriceps weakness occurs with lesions distal to the origin of the saphenous nerve.

Femoral mononeuropathies are infrequent. Acute femoral nerve deficits may occur when an expanding mass, particularly a spontaneous hematoma, develops within the iliopsoas muscle in a medically anticoagulated patient. Diabetes mellitus is the most common associated disorder occurring with a “femoral neuropathy.” Although these lesions clinically mimic a painful femoral neuropathy, electromyography (EMG) studies typically demonstrate that the disorder is more extensive; these lesions are better considered as femoral radiculoplexopathies. Often, there is an autoimmune vasculitic component not unlike polyarteritis nodosa. With either illness, the femoral neuropathy may be the initial sign of mononeuritis multiplex. Occasionally, femoral neuropathies manifest in patients having prolonged pelvic surgery or childbirth requiring a lithotomy position. Other iatrogenic mechanisms include postoperative hematomas or abscesses, misplaced femoral artery or venous puncture, and direct nerve injury subsequent to nephrectomy or hip arthroplasty. Tumors, either benign ones such as neurofibromas, or infiltrating malignant lesions, such as lymphoma, rarely cause femoral neuropathies. Isolated saphenous nerve injuries may result from knee arthroscopy, femoral-popliteal artery bypass surgery, and in the course of coronary artery bypass graft surgery.

Femoral mononeuropathies are extremely rare in children, occurring subsequent to orthopedic or renal transplant surgery, with stretch injuries, spontaneous intrapelvic hemophiliac-related intraneural or extraneural hematomas, perineuromas, and neurofibromas.

Differential Diagnosis. L3 and L4 nerve root and lumbosacral plexus lesions are the two primary possibilities. If there is no pain or sensory loss, early motor neuron disease is always a possibility. Very rarely, a lumbosacral plexitis occurs in children. This mimics the immunologically mediated Parsonage-Turner brachial plexitis.

Evaluation. Electromyelography with computed tomography (CT) and/or magnetic resonance imaging (MRI) is most useful. Relevant blood studies include serum glucose, perhaps a 2-hour glucose tolerance test if there is a lot of pain typical of diabetes, and an erythrocyte sedimentation test and/or C-reactive protein when an autoimmune process, such as polyarteritis nodosa, is a clinical possibility.

Treatment and Prognosis. Rehabilitation, particularly utilizing bracing lending to knee stabilization, is essential. The degree of axonal damage and subsequent reinnervation determines the patient’s outcome. Physical therapy is important.

LATERAL FEMORAL CUTANEOUS NERVE

The lateral femoral cutaneous nerve (LFCN) has a pure sensory function. It is derived from the L2 and L3 nerve roots to emerge from the lateral psoas muscle, passing obliquely over the iliacus, to course toward the anterior superior iliac spine. Eventually, it enters the thigh by passing above or through the most lateral portion of the inguinal ligament. The LFCN next passes over or through the proximal sartorius muscle, descending deep to the fascia lata. After a number of small branches are delivered to the overlying skin, the LCFN pierces the fascia about 10 cm below the inguinal ligament to innervate the anterolateral thigh.

Only gold members can continue reading. Log In or Register to continue