Foot drop, also called drop foot, is a condition in which the muscles in the leg cannot raise the foot at the ankle effectively, causing difficulty when walking. The affected person must lift his or her foot high to allow the toes to clear the ground. When this condition is caused by pressure on the nerves that control the muscles in the leg or a knee injury, it can be temporary. Damage to the nerves, as well as a number of medical disorders, can cause this condition to be permanent, however.
The most obvious sign of foot drop are toes that point away from the body when the foot is relaxed. The person may have difficulty walking, scuffing his or her toes and tripping over the affected foot frequently. In an attempt to overcome this, he or she may lift the knees higher so there is less chance of stumbling over the toes; this distinctive movement is known as steppage gait. As the person walks, he or she may also slap the foot down with each step.
Some people experience tingling or numbness in the foot and ankle. This may be caused by the particular way of walking, or could be linked to the underlying cause of the condition. The feet and legs may also feel weak. Foot drop can affect both feet, but it is more common to experience it in only one.
The most common cause is an injury to the peroneal nerve at the top of the calf behind the knee. This nerve provides sensation and movement to the front and side of the leg, as well as the top of the foot. If it becomes compressed, a condition called peroneal nerve palsy, it may no longer be able to support the tibialis anterior, the muscle which lifts the foot. Damage to the nerve can also be caused by surgery on the knee.
Back problems can also affect the nerves in the legs. Compression of the lower bundle of nerves in the spinal cord, called the cauda equine, can cause this condition, as can damage to the discs that separate the bones of the spine. Because the nerves from the spinal cord pass through the hips and thighs on their way to the feet, damage to those body parts can also cause foot drop. In a small percent of cases, hip replacement surgery may cause temporary or permanent damage to the nerves that serve the legs and feet. Prolonged pressure on the nerves in the legs, which happens to some patients confined to a wheelchair or bed, can also cause problems.
Foot drop can also be caused by disorders that affect the brain and spine, like multiple sclerosis, cerebral palsy, and amyotrophic lateral sclerosis (ALS) or Lou Gehrig's disease. These disorders often cause problems with movement as well as muscle weakness. Peripheral nerve disorders, like Charcot-Marie Tooth disease, usually involve damage to the nerves in the extremeties — particularly the feet — and can cause numbness, muscle weakness, and balance issues, as well as foot drop. Muscle disorders, such as muscular dystrophy, can cause progressive weakness, including difficulty walking.
To diagnose foot drop, a health care professional will take a complete medical history, including information about parents or other family members who may have also experienced foot problems. He or she will evaluate the patient's symptoms, including any numbness and tingling in the leg or foot. Magnetic resonance imaging (MRI) and other x-ray tests may be used to see if there are any physical abnormalities that may be pressing on the peroneal nerve or the spinal cord. An electromyogram (EMG) may also be conducted to measure nerve activity to pinpoint the exact area of the damage. If a neuromuscular disorder is suspected, a muscle biopsy and/or MRI of the brain may also be performed.
There are a few factors that can increase the chances of someone developing foot drop. People who cross their legs at the knee are more likely to have this problem, as are those with an orthopedic cast on the lower leg that stops just below the knee; in both cases, extra pressure is put on the peroneal nerve, which could cause it to become inflamed or compressed. Nerve damage is also a possibility with any surgery on the hip or knee joints.
Neuromuscular disorders are often genetic. If a person has a family member with foot drop that is caused by another disorder, he or she is more likely to develop it as well. The cause of some diseases, like multiple sclerosis, that can cause this condition is not completely understood.
Special shoes and straps can be used to mimic the natural ankle motion for patients who have either temporary or permanent foot drop. An ankle-foot orthosis (AFO) is a brace that supports the ankle and holds it and the foot in the correct position. Patients can also benefit from physical therapy; certain exercises, including stretching, help strengthen the leg muscles, prevent stiffness in the heel, and improve gait by preserving the range of motion.
In cases where the foot drop is caused by a problem with the brain or spinal cord, electrical stimulation of the nerve may also help. Special devices can be worn below the knee that sense when the person is taking a step and stimulates the muscle in the leg and foot to lift the toes appropriately. This device does not work for people who have problems with the nerves in the feet.
If the peroneal nerve is injured, patients should seek treatment right away to improve the chances of recovery. When the nerve is compressed, surgery may be possible to relieve the pressure. In some cases, it may even be possible to transfer or graft a nerve from another part of the body to repair the area and allow for better feeling and movement.
It is also possible for a surgeon to fuse the bones in the ankle or foot together so that it is easier for the patient to walk. This typically limits how far the ankle can move, but many patients are able to compensate for this and walk more normally.