Foot drop and common peroneal nerve palsy

What it is

Foot drop is dorsiflexion weakness, and the gait it produces carries several names: foot drop gait, slap gait, neuropathic gait and steppage gait. The neuropathic, high steppage gait is an LMN lesion sign, with the knee and hip held in flexion because the foot cannot be dorsiflexed. Common peroneal neuropathy is the most common cause.

Causes and risk

Foot drop is thought through by level.

• Muscular: no sensory involvement, muscular tenderness, and a distribution that depends on the compartment involved. Etiology is inflammatory or drug-induced.
• Peripheral nerve lesions: lower motor signs and patchy sensory deficits based on the nerves involved, in the common peroneal nerve or the sciatic nerve. Causes are trauma, post fracture or iatrogenic; compression, from a cast or abnormal posturing; metabolic, from diabetes, B12 deficiency, alcohol or heavy metals; infectious, from polio, leprosy or syphilis; and hereditary, Charcot's-Marie-Tooth.
• Nerve roots and plexuses: radicular pain, spine tenderness, and a dermatome and myotome distribution of the deficits based on the roots involved, in the lumbosacral roots. Causes are mechanical lesions, that is disc herniation, spinal stenosis, a compressive tumor, vertebral fracture or abscess, and the inflammatory GBS.

For common peroneal neuropathy itself the causes are compressive at the fibular head, from crossed legs or prolonged kneeling, or from a Baker's cyst, and trauma at the knee. For L5 radiculopathy they are lumbar: disc herniation and spondylosis. For sciatic neuropathy they are compressive at the buttock, from a toilet seat or being bedbound, and trauma, from an intragluteal injection or at the pelvis and hip.