What is foot drop?

Foot drop refers to difficulty in lifting the front part of the foot, due to weakness of the ankle and toe. The lower limb is highly muscular and the movements of these muscles are carefully coordinated by the brain via nerves. Foot drop occurs when the muscles, nerves or parts of the brain coordinating the movement of the foot is damaged or diseased. This may result in dragging the front of the foot on the ground while walking. Patients with foot drop attempt to compensate by altering the way they walk appearing as a characteristic pattern that is seen in the condition.

Foot Drop Walk

Foot drop may lead to an abnormal gait called steppage gait.

In steppage gait, the hip and knee are thrown outwards during swinging of leg. This prevents the toes from catching on the ground.

Also, the foot may slap the ground due to raising the lower leg higher in an attempt to prevent dragging.

Who gets foot drop?

Foot drop results from the most common nerve-related condition of the lower leg, called peroneal neuropathy. In this condition,the peroneal nerve is pinched along its route around a part of one of the long bones of the leg, called the fibular head. Peroneal neuropathy can affect people of all ages. Males are affected three times more frequently than females.

Foot drop is seen in 10% patients undergoing surgical procedure called proximal tibial osteotomy. In this surgery, tibial bone of leg is cut to bend the leg. The surgery may damage the peroneal nerve, which may also lead to foot drop. Apart from these situations, foot drop also occurs in people with diseases that affect the nerves and muscles of the body, or brain centers that control the leg movement.

Reasons for Foot Drop

The dorsiflexor muscles, which are the front (anterior) muscles of the lower leg, are affected in foot drop. The foot and ankle dorsiflexor muscles control two movements while walking :

  • clearing the foot during leg swing, and
  • controlling the foot on heel striking

If these muscles are weak or injured, it can result in abnormalities of gait seen as foot drop. Less commonly, it is the tendons of these muscles that are compromised thereby leading to foot drop.

However, it is not always the muscles itself that may be affected. Often the nerves controlling these muscles are the root of the problem in foot drop. Nerve damage, tear, or crushing of a nerve can hamper its control of the muscles and lead to foot drop.Sometimes, a pre-existing problem in the nerve that may not be causing muscle weakness may, however, make the nerve more susceptible to further injury. Such an event is called a double-crush phenomenon.

Signs and Symptoms

Symptoms of foot drop may include the following:

  • Difficulty lifting the front part of the foot
  • Dragging of foot on the floor while walking
  • Slapping the foot down onto the floor
  • Symptoms usually in one leg only
  • Standing with the foot outward
  • Pain in lower leg, calf muscles, and ankles
  • Pain in flexing the toes
  • Weakness in toes
  • Numbness in toes
  • Pain on exercising
  • Back pain
  • Bony block at the ankle joint

Foot Drop Causes

Various conditions can lead to foot drop. Injuries to dorsiflexor muscles (front muscles of the lower leg) or peripheral nerves, nerve compression, drug toxicities, or conditions like stroke or diabetes can cause foot drop.

Nerves

Nerve injury is the most common cause of foot drop. Compression of the peroneal nerve affects the control on the muscles involved in lifting the foot. The nerve may get compressed at the knee or in the lower spine. Knee or hip replacement surgeries of other nerve injuries may also damage the nerve. Diabetes is also associated with long-term nerve damage (diabetic neuropathy) and the peroneal nerve may be affected.

Muscles

Injury to the dorsiflexor muscles can also lead to foot drop. Rarely, rupture of a tendon called the tibialis anterior tendon may also be a cause. Muscle diseases like muscular dystrophy lead to progressive muscle weakness and loss of muscle tissue. Other diseases like Charcot-Marie-Tooth disease or polio may also cause foot drop. Compartment syndrome where excessive swelling in one of the muscle compartments of the lower leg can damage the muscles and nerves thereby leading to foot drop.

Brain and Spinal Cord

Diseases that affect the spinal cord or brain may result in foot drop. This includes :

  • amyotrophic lateral sclerosis (ALS)
  • multiple sclerosis (MS)
  • any nerve dysfunction (neuropathy)
  • stroke

Foot Drop Risk Factors

Activities that compress the peroneal nerve increase the risk of foot drop. Crossing the legs, squatting or kneeling for long periods, and wearing a leg cast or plasters that enclose the ankle may put pressure on the peroneal nerve. Hip replacement surgery increases the risk of developing foot drop. Diabetics and patients with any neuromuscular or neurodegenerative condition are also at risk.

Tests and Diagnosis

A foot drop is clearly evident and even very mild cases can be easily spotted by a medical professional. Presence of symptoms like changes in gait, weakness in leg muscles, and numbness on the top of the foot and toes and on the shin help in diagnosing foot drop. The following tests may be performed to diagnose foot drop:

  • Imaging tests: These tests can detect a bone overgrowth or a tumor, which might be pressing the peroneal nerve.
    - An x-ray or preferable a CT scan can detect a bone injury, outgrowth or defect.
    - An ultrasound can detect the presence of cysts, bleeding or tumors, which might be compressing the nerve.
    - A magnetic resonance imaging (MRI) scan can detect soft tissue lesions, which may place pressure on the peroneal nerve.
  • Electromyography (EMG) can detect abnormalities in the activity of muscles that control the movement of the foot.
  • A nerve conduction velocity (NCV) study can measure the speed of impulses in the peroneal nerve. In case of a damaged or injured nerve, the impulse will differ in comparison to the unaffected leg.
  • Lab tests can be performed to detect metabolic causes like diabetes, exposure to toxins, and alcohol abuse. The levels of hemoglobin, blood sugar, creatinine, and vitamin B12 are measured along with other biochemical markers.

Treatment for Foot Drop

Treatment for foot drop focuses on treating the underlying cause where possible and the condition may ease significantly or resolve completely. However, many of the causes of foot drop are permanent and therefore irreversible. Various measures are therefore necessary to assist with living with the condition and preventing it from worsening.

Devices

Wearing a splint into the shoe, a brace on the ankle and foot, or using an ankle-foot orthosis (mechanical apparatus) may help hold the foot in a normal position while walking.

Physical therapy

Exercises may be recommended to strengthen the leg muscles. Stretching exercises help maintain the range of motion in the knee and ankle. This improves the gait and prevents stiffness.

Medication

The medical treatment for foot drop primarily eases pain and helps speed up healing. Other medication may be used to treat and manage underlying conditions.

  • Tricyclic antidepressants and anticonvulsants may be used for pain.
  • Application of diclofenac or capsaicin can also ease the pain.
  • Narcotics like morphine are prescribed only in severe cases.
  • Erythropoietin treatment speeds up the recovery after nerve injury.

Surgery

There are various surgical procedures that may be of use for foot drop. The procedure of choice depends on the underlying cause. Where surgery is ineffective in restoring normal gait, some procedures may be able to help with symptomatic treatment. This includes changing the position of a tendon, relieving pressure on a nerve and other related procedures.

Electrical stimulation

Stimulation of the peroneal nerve may improve foot drop in some patients. Small bursts of electricity stimulate the nerves that lift the foot.

References :

http://www.ninds.nih.gov/disorders/foot_drop/foot_drop.htm

http://emedicine.medscape.com/article/1234607-overview

http://www.mayoclinic.com/health/foot-drop/DS01031


Article reviewed by Dr. Greg. Last updated on August 22, 2012