CORRECTING FOOT DROP
Depending on the cause, foot drop can be corrected with various bracing techniques
By Marlene A. Prost
What do people with stroke have in common with those with diabetes, knee injuries, and workers who pick strawberries?
They are all at risk of developing drop foot, a shuffling gait caused by weakness in the ankle and foot muscles. This weakness is due to an impairment of nerve conduction to the anterior muscles of the lower leg, causing weakness or paralysis and interfering with normal dorsiflexion of the foot.
The name drop foot (or foot drop) is self-explanatory. "When we walk, we pick the front part of our foot up, so we don't drag our toes. People with drop foot can't pick their foot up. When they swing their foot through, it drags on the ground," said Cheryl Trudeau, MA, PT, clinic coordinator of neurorehabilitation at Rehab East, a satellite clinic of The Rehabilitation Institute of Michigan in Flint.
Drop foot can result from a wide range of conditions. One major cause is an upper motor neuron lesion as a result of a cerebral vascular accident or brain injury. In the case of a stroke, the foot affected depends on the side of the brain involved. Drop foot is also a common symptom in multiple sclerosis that involves the lower legs.
"Anything that affects the motor cortex of the brain affects motor output," said Brian Litofsky, MS, PT, of Litofsky, Brager and O'Brien/Matrix Rehabilitation, Baltimore. Patients with damage to the cortex often have a problem moving the whole limb in gait because of high muscle tone. "The patient has lost some control of the motor impulses that control limb movement without the inhibitory components necessary to adjust the motor output," said Litofsky. "In many cases, the ankle has to be braced; however, there are neuromuscular techniques that are effective in reducing muscular tone."
For example, total contact casting can gradually break up the tone. "The cast is put on with the foot in as much dorsiflexion as can be tolerated. After several days, the cast is removed, the muscle is stretched, and a new cast is put on to gradually improve the range of motion at the ankle and reduce the plantar flexion tone."
Patients with peripheral neuropathy related to diabetes mellitus or Charcot-Marie-Tooth disease are also at risk of localized nerve damage resulting in drop foot. In both cases of CVA and peripheral neuropathy, the drop foot is usually not isolated and is associated with other problems with tone.
Yet another cause of drop foot is localized compression of the nerves to the anterior muscles of the leg that allow for dorsiflexion, or the ability to pull up the toes. This is usually a compression of the deep peroneal nerve against the lateral aspect of the fibular neck below the knee, causing "peroneal nerve palsy."
Localized swelling from a muscle injury, cellulitis or compartment syndrome can press against the nerve. Patients positioned on their side during surgery can develop drop foot if the bony side of the knee is pressed against the table for a very long period of time. A cast put on incorrectly for a broken bone can also compress the peroneal nerve.
"Strawberry pickers syndrome" is an occupational hazard for workers who constantly press on their knees, creating a tautness that compresses the nerve and causes the foot to drop," said Lit-ofsky. The prognosis in these cases depends on the duration of the compression. "The nerve can regenerate about 1 millimeter a month. That's very small. The nerve can heal, but very slowly. But [in the meantime] you can get atrophy of the muscles," he said. To treat this atrophy, electrical stimulation can be used to maximize the ability to contract the muscle.
Depending on the cause, some people with drop foot can regain flexibility through exercise and re-education. "If it's a flexibility problem and just the muscles in the ankle are tight, we work on stretching so they have the capability of lifting the foot, said Trudeau. "When they have a problem with decreased strength in the ankle or a decrease in muscle function ... Sometimes you can do exercises to teach the muscle (to function properly)." AFOs and Related Braces
Other patients, however, are not going to regain flexibility or strengthen the muscles. For them, a range of ankle-foot orthoses and braces are available to help keep the foot raised and create a fluid gait. The AFO, ankle foot orthosis, is a brace, usually plastic or polyprophylene, that is worn on the lower leg and foot to support the ankle. "It helps to keep the foot up. Some just maintain the position of the foot in neutral alignment. Others are a brace on the ankle that have a joint and a spring and goes up the back of the leg and fits in the shoe," said Trudeau. When the patient takes his weight off the spring, the toe comes up.
"For simple drop foot from cast pressure or a disk problem, you would just use a simple MAFO (molded AFO)," said James McGuire, DPM, PT, CPed, an assistant professor at Pennsylvania College of Podiatric Medicine in Philadelphia.
Over-the-counter or custom-fitted, the basic MAFO fits inside the shoe. It can be modified with hinges or ankle joints. For example, the posterior adjustable stop (PAS) is a device set at an angle that allows the foot to dorsiflex. For drop foot secondary to CVA, the orthosis may be fitted with a posterior spring assist (PSA), which is a spring-loaded dorsiflexion assist. Another device, the VAPC, is a posterior clasp brace that clips on the back of the shoe.
A more elaborate and expensive orthosis involves electrical stimulation of the foot. Some orthoses come equipped with foot plates that trigger electrical stimulation from a unit carried often in a hip-pack. "You step on a foot switch that activates an electrical current that contracts the anterior tibialis muscle and dorsiflexors, preventing foot slap," said McGuire.
In the meantime, gait training should include activities for the trunk, hip and knee, added Litofsky. The patient with drop foot has learned to compensate by "hiking the hip," and exercises should work on ensuring adequate mobility and strength of the trunk and entire lower extremity.
Marlene Prost is a freelance writer from Audubon, PA, and a regular contributor to ADVANCE.