Current Concepts In Diagnosing And Treating Drop Foot

Nicholas Romansky, DPM, Kelly Scollon-Grieve, MD, and James G. McGinness, CPO

Drop foot can have a complex etiology and the effects of the condition can affect quality of life for patients. These authors provide insights on the workup and diagnosis of drop foot, and discuss treatments ranging from medical therapies and surgery to AFOs and functional electrical stimulation.

Drop foot is a weakness of ankle dorsiflexion and is frequently accompanied by weakness of the extensor hallucis longus and extensor digitorum longus muscles, causing difficulty with dorsiflexion of the toes. This results from a deep fibular (peroneal) nerve compromise. Physical examination findings consistent with a drop foot are difficulty clearing the foot during the swing phase of the gait cycle, a steppage gait, an equinovarus deformity of the foot and ankle, and an uncontrolled foot slap.1

   Motor symptoms present with drop foot as well as weakness of other muscles that the common peroneal nerve supplies. An essential component of drop foot is paresthesias that accompany the distribution of the common peroneal nerve.
Radiculopathy at the L4/5 level is the most commonly recognized cause of drop foot. It is usually the result of a disc herniation or foraminal stenosis at that level compressing the L4 and/or L5 nerve roots.2

   After radiculopathy, the second most common cause of drop foot is a common fibular (peroneal) neuropathy. The common fibular nerve originates in the popliteal fossa as one of two terminal divisions of the sciatic nerve and then divides at the fibular neck into the deep and superficial peroneal nerves.

   The fibular nerve is most often injured as it traverses around the fibular neck. The most common cause of nerve injury is external compression, which can happen in hospitalized patients due to rapid weight loss and compression from the bed rails, from casting or pneumatic compression devices. In addition, individuals with habitual leg crossing are subject to external compression. Common or deep fibular nerve injury can occur during surgical procedures such as a total knee arthroplasty, in which the nerve may be injured due to traction or compression.

   Other causes of common fibular nerve injury include: trauma; traction of the common fibular nerve with an inversion and plantarflexion ankle injury; prolonged squatting (strawberry picker’s knee); compression by an intraneural or extraneural mass lesion; diabetic neuropathy; inflammatory neuropathy; and vascular pathology.1

   Direct trauma to the tibialis anterior muscle that causes rupture or compartment syndrome may also lead to drop foot. Drop foot can also be a complication of rapid weight loss for two reasons. A decreased fat pad surrounding the fibular nerve at the fibular head can subject the area to increased compression from external sources. Alternately, a patient may have micronutrient deficiencies (i.e. vitamin B12) after bariatric surgery.3

   Peripheral nerve injuries can also arise from lumbosacral plexopathy and injury of the common fibular division of the sciatic nerve. Upper motor neuron causes are rare but one must consider them. These causes include: cerebrovascular accident, motor neuron disease, amyotrophic lateral sclerosis, multiple sclerosis, brain tumor and spinal cord injury.2

   The lumbosacral spine origin of drop foot is more common than one would think. Podiatrists need to look above the foot and ankle, and listen to the patient. One should first ask the patient if he or she has any history of lumbosacral spine symptoms or origin in the past. Ask the patient if there is any other joint pain. This may help find or localize the origin and cause of symptoms.

Add new comment