The sciatic nerve derives its supply from the L4-S2 nerve roots. The nerve arises from the lumbosacral plexus, and exits the pelvis through the greater sciatic foramen before traveling under the piriformis muscle. The nerve itself consists of two distinct trunks, the lateral trunk (peroneal) and medial trunk (tibial). Branches originating in the proximal thigh arise predominantly from the tibial division. The tibial division supplies the hamstring muscles, with the exception of the short head of the biceps femoris, which receives its supply from the peroneal division. All muscles below the knee receive innervation from the sciatic nerve through one of its two divisions (peroneal or tibial). Afferent sensory input from the leg also travels in the sciatic nerve, except for that region supplied by the saphenous nerve.
Weakness, numbness, and paresthesias in the lower extremity are common symptoms of sciatic neuropathy. A flail foot is commonly seen with this condition. Weakness of knee flexion and impairment of all ankle and toe movements will be present. Sensory loss may be appreciated in various areas over the posterior calf, ankle, and sole of the foot. Sciatic neuropathy may arise from a myriad of causes, including compression during surgery or coma, tumors (compression or direct nerve invasion), vascular abnormalities, fibromuscular bands, mononeuritis multiplex, piriformis compression, and traumatic injuries arising from gunshot or knife wounds or injections.
The electrodiagnostic evaluation should confirm a sciatic neuropathy and exclude other conditions that mimic this lesion. The nerve conduction studies/needle examination that should be performed are summarized in Table 11.
Imaging studies, especially MRI, are often very helpful in identifying a structural lesion, if present. Angiography may be indicated if an arterial aneurysm or iliac artery thrombosis is a possible cause.
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