Foot drop

What is foot drop?

Foot drop is a condition where it is difficult or impossible to lift up the toes and forefoot (front part of the foot).

Foot drop usually affects just one foot. However, it can affect both sides, either equally or to different degrees. It may be temporary or permanent.

There are several grades of foot drop. These are measured from 0 to 5 depending on the strength and movement in the muscles which lift the foot. 5 is normal strength and 0 is total paralysis.

This causes an abnormal walk (gait) which is caused by the front half of the foot dropping downwards during walking.

The gait in foot drop may involve:

• The affected foot (or feet) catching on the floor during walking.

• Lifting the leg high to avoid the foot catching whilst walking (high stepping gait). People who do this often tend to walk on tiptoe on the other side to equalise the sides.

• Swinging the affected leg out to the side to avoid it catching on the floor whilst walking.

What causes foot drop?

Foot drop is usually caused by malfunction of a nerve in the lower leg called the common peroneal nerve. This can be due to problems affecting it either in the leg itself or higher up in the spine where its nerve fibres originate.

The common peroneal nerve is also sometimes called the common fibular nerve, the external popliteal nerve or the lateral popliteal nerve. It's a small nerve that branches off from the sciatic nerve in the thigh.

It runs down the back of the knee and winds around the top of the fibula to go into the muscles of the lower leg. It is very near the surface at this point and can be easily bruised or compressed.

Common causes of foot drop

• Injury to the common peroneal nerve.

• Lower back damage (including a 'slipped' disc (prolapsed disc) affecting the nerves in the lower leg).

Foot drop can also be due to other causes of nerve damage. More rarely, it can be due to damage to the muscles of the lower leg or to poisonous substances or a tumour.

Other causes of foot drop

• Hip replacement.

• Knee surgery.

• Sciatic nerve damage.

• Cauda equina syndrome. (This is compression of the nerves in the tail of the spinal cord, usually caused by a 'slipped' disc or tumour.)

• Diabetes with peripheral neuropathy.

• Stroke.

• Transient ischaemic attack (TIA).

• Multiple sclerosis (MS).

• Cerebral palsy.

• Charcot-Marie-Tooth disease.

• Poliomyelitis (rarely causes isolated foot drop).

• Motor neurone disease.

• Friedreich's ataxia.

• Brain tumour.

• Adverse drug or alcohol reaction.

Patients with pain on the soles of the feet may also walk with a high stepping gait which looks similar. However, they do not have foot drop; they are lifting their feet for a different reason.

Which nerve causes foot drop?

The peroneal nerve controls the muscles that lift your foot. This nerve is quite exposed to trauma where it runs just under the skin on the outer side of the knee. Activities that compress this nerve can increase your risk of foot drop. Examples include:

• Crossing the legs. People who habitually cross their legs can compress the peroneal nerve on their uppermost leg, particularly if they are slim.

• Prolonged kneeling. Occupations that involve prolonged squatting or kneeling can result in temporary foot drop. Certain yoga positions can also cause nerve compression resulting in foot drop.

• Wearing a leg cast. Plaster casts that enclose the ankle and end just below the knee can exert pressure on the peroneal nerve and cause foot drop.

How does walking with foot drop differ from normal walking?

The cycle of action in normal walking is as follows:

• The foot moves forwards (swing phase).

• The foot touches the ground. Usually the heel touches the ground first (initial contact, sometimes called heel strike or foot strike) and then you move forwards on to the ball of the foot.

• The foot pushes off and leaves the ground again (terminal contact, or 'foot off').

The normal foot can flex upwards (dorsiflexion). It can also invert (turn so that the soles tend to face each other) or evert (the opposite of inversion). In foot drop these movements (which occur mainly in heel contact and in the swing phase, are absent. Therefore:

• The swing phase may involve bending the leg at the knee to lift the foot away, rather like climbing stairs.

• The initial contact is not with the heel but with the whole of the foot which 'slaps' or plants on to the floor at once

• The 'foot off' motion does not function properly at all and a walking stick or cane may be needed to help lift the foot.

How is foot drop diagnosed?

Foot drop is usually diagnosed on examination. A clinician will observe the gait and may check the leg muscles for weakness. They will also assess nerve function by checking reflexes and the sensation in the skin.

How is foot drop investigated?

Foot drop is a symptom rather than a diagnosis and it is important to understand what has caused it. Investigations for the cause of foot drop may include:

• X-rays. Plain X-rays may be used to look for a soft tissue growth or a bone abnormality that may be causing your symptoms.

• Ultrasound. This may be used to check for cysts or tumours that may be pressing on the nerve.

• Computerised tomography (CT) scan. This can be used to look for growths (masses) or other changes anywhere in the body.

• Magnetic resonance imaging (MRI). MRI is particularly useful in visualising soft tissue lesions that may be compressing a nerve, such as a 'slipped' disc (prolapsed disc) in the back. It can also examine the brain for the characteristic lesions of MS.

• Electromyography (EMG) and nerve conduction studies. These measure electrical activity in the muscles and nerves to look for the location of the damage along the affected nerve.

How do you treat foot drop?

If the underlying cause can be treated, foot drop may improve or disappear. If the underlying cause can't be treated, foot drop may be permanent. Some nerve damage can heal but full recovery can take up to two years.

In addition to treatment of the underlying problem, specific treatment may include:

• Braces or splints. These help hold the foot in a normal position.

• Ankle-foot orthoses (AFOs). These are specialised L-shaped ankle splints. They simply hold the foot at 90° to the lower leg so that it can't drop down.

• Physiotherapy. Exercises to strengthen leg muscles may improve walking problems associated with foot drop. Stretching exercises can prevent the development of stiffness in the heel. Learning to use a high stepping gait or swinging gait is an alternative approach that some people prefer.

• Specialised shoes. Shoes fitted with spring-loaded braces can help prevent the foot dropping whilst walking. One type uses a cuff around the ankle, a spring above and a hook in the shoelace area which connects to the spring and pulls the foot up during walking.

• Nerve stimulation. Sometimes stimulating the common peroneal nerve electrically improves foot drop. This type of treatment is usually used in people with disabilities and is sometimes called neuromuscular electrical stimulation or functional electrical stimulation. Many people with multiple sclerosis, or who have had a stroke, have had success with it.

• Surgery. Depending upon the cause, nerve surgery is occasionally helpful, aiming to repair or graft the nerve. If foot drop is long-standing, complex surgery that shifts working tendons to a different position is occasionally considered.

What can I do to help myself?

One of the problems related to foot drop is that it can increase the risk of tripping as the toe catches on the floor. It can be sensible to take precautions at home to reduce the risk of falls and injury:

• Keep all floors clear of clutter.

• Avoid loose rugs, electrical cords and other trip hazards.

• Make sure rooms and stairways are well lit.

• Stick fluorescent tape on the top and bottom steps of stairways to help prepare for them.

• Seek advice from a suitably qualified health professional (usually a physiotherapist or occupational therapist) on walking aids and exercises.

Dr Mary Lowth is an author or the original author of this leaflet.