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Foot drop, a disorder of the distal aspect of a lower extremity, like most foot ailments, has little to do with the
intrinsic function of the foot. This neurological disturbance, like most common to the foot, is caused by nerves
proximal to it's location. This impairment is a malfunction of either a peripheral nerve or a part of the central
nervous system.

The innervation of the foot and ankle are by the spinal segments of L4, L5, S1, S2, and S3. These segments make
up the sciatic nerve that proceeds out of the low back and descends under the gluteal and hamstring
musculature (1). The sciatic nerve divides at the lower third of the posterior thigh into the posterior tibial nerve
and the common peroneal nerve. The common peroneal nerve, about half the size of the posterior tibial nerve,
descends obliquely along the outside of the popliteal space to the head of the fibula (2). It can be palpated just
under the skin behind the head of the fibula. It then winds around the neck of the fibula where it divides again
into the deep peroneal nerve, and the superficial peroneal nerve. The deep peroneal nerve innervates the
tibialis anterior muscle with the innervation stemming from the L4, L5, and S1 levels (3). The deep peroneal
nerve is primarily motor, where the superficial peroneal nerve supplies both sensation to the anterolateral
aspect of the leg and foot and also motor innervation to the peroneus longus and peroneal brevis muscles in
the lateral compartment (4). Therefore, injury to the common peroneal nerve causes functional impairment of
the dorsum of the foot and toes. This impairment creates foot drop resulting in a steppage gait (3). Sensory
involvement is confined to a small area of the foot between the first and second toes. Motor involvement is a
more difficult diagnosis in determining if it is at the anterior horn cell level, root level, spinal nerve level, or
peripheral nerve level (3). Causes that must be taken into account for this condition range from anterior
compartment syndrome, percutaneous laser-assisted diskectomy, labor and delivery, total hip arthroplasty,
acute and chronic trauma, disc injuries, interneural ganglionic cyst, mononeuropathy, entrapment neuropathy,
nerve lesion, lipomas and/or masses, and spinocerebellar diseases. The use of manual muscle testing, sensory
pattern mapping, EMGS, and SSEPS studies are tools in locating the site of impairment (3).


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