• Lateral cutaneous nerve of the thigh (from L2 and L3)—Painful paresthe-sias—burning, tingling discomfort in the anterolateral aspect of the thigh—is the only symptom of a disease of this nerve, called meralgia paresthetica. Symptoms are caused by entrapment or stretching of the nerve under the lateral aspect of the inguinal ligament. The disease is common in people who are gaining or losing weight, during or after pregnancy. Symptoms are often related to one posture only, such as sitting or standing. Examination reveals hyperesthesia or, rarely, hypoesthesia in the anterior lateral thigh. The thigh is strong, the knee reflex is normal, and disease is benign.
• Obturator nerve (from L2, L3, and L4)—Lesions produce weakness of adduction of the thigh and pain on the medial aspect of the thigh to the knee. The nerve may be injured during delivery or labor or may be involved in pelvic neoplasm.
• Femoral nerve (from L2, L3, and L4)—Lesions produce a wasted quadriceps, weakness of leg extension, and, if the lesion is proximal, weakness of thigh flexion (iliopsoas muscle) as well. The knee reflex is absent, and sensory loss extends from the anteromedial thigh to the medial malleolus. Diabetes is the most common cause of femoral neuropathy, although pelvic tumors, femoral hernia, and femoral artery aneurysms are also possible causes. A retroperitoneal hematoma may compress the nerve, and drainage of the hematoma is an emergency if the nerve is to be saved.
• Sciatic nerve (from L4 and L5 and S1 and S2)—The lesion will cause loss of knee flexion (hamstrings) and no movement of any muscle below the knee. Sensory loss will occur in all of the sole of the foot, the dorsum of the foot, and the posterior and lateral leg. Causes are pelvic fractures; penetrating injuries, including misplaced injections; and pelvic tumors. Lying flat on a hard floor while in coma from any cause can produce a compression sciatic palsy.
• Peroneal nerve (the most common peripheral nerve lesion in the lower limb that you will see)—The sciatic nerve divides into the tibial nerve and the common peroneal nerve. The latter winds around the neck of the fibula, a common site of lesions of this nerve. Diabetes, sitting with the legs crossed for long periods, trauma, and sporting injuries (eg, in professional figure skaters or skiers) as well as tightly applied plaster casts account for most of the identifiable causes. There is weakness of dorsiflexion of the toes and foot as well as eversion. The ankle reflex is normal, and although the patient may say he has numbness over the dorsum of the foot, there are usually no sensory abnormalities.
• Posterior tibial nerve (lesions are uncommon)—The nerve may be compromised in its tunnel on the inferomedial aspect of the calcaneus. Pain and paresthesias over the sole of the foot in response to exercise are the only complaints. There are no motor findings.
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