Foot drop is usually caused by malfunction of a nerve in the lower leg due to problems affecting it either low down in the leg, or higher up in the spine where its fibers originate.
This nerve is called the common peroneal nerve. However, it is also sometimes called the common fibular nerve, the external popliteal nerve or the lateral popliteal nerve. It’s a small nerve that comes down off 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.
The most common causes are:
- Injury to the common peroneal nerve.
- Lower back damage (including a slipped 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. These include:
- 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.
- Transient ischaemic attack (TIA).
- Multiple sclerosis.
- 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.