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Foot drop
Classification and external resources
ICD-10 M21.3
ICD-9 736.79
eMedicine orthoped/389

Foot drop is an inability or difficulty in moving the ankle and toes upward (dorsiflexion). In walking, the leg must be lifted higher than usual to prevent the foot from dragging along the ground. Foot drop is usually caused by nerve damage, but may also be caused by muscle damage, abnormal anatomy, or a combination.

Foot drop is caused by diseases that damage the long nerves. The deep fibular/peroneal nerve innervates the front (anterior) compartment of the leg. Damage to this nerve will lead to the inability for the leg to dorsiflex the foot, therefore causing foot drop. The result is an abnormal gait.

Contents

Features

Foot drop is characterized by steppage gait. When the person with foot drop walks, the foot slaps down onto the floor. To accommodate the toe drop, the patient may use a characteristic tiptoe walk on the opposite leg, raising the thigh excessively, as if walking upstairs, while letting the toe drop. This serves to raise the foot high enough to prevent the toe from dragging and prevents the slapping. Other gaits such as a wide outward leg swing (to avoid lifting the thigh excessively or to turn corners in the opposite direction of the affected limb) may also indicate foot drop.[1]

Patients with painful disorders of sensation (dysesthesia) of the soles of the feet may have a similar gait but do not have foot drop. Because of the extreme pain evoked by even the slightest pressure on the feet, the patient walks as if walking barefoot on hot sand.

Diagnosis

Initial diagnosis often is made during routine physical examination: A person with foot drop will have difficulty walking on his heels only. This is a good diagnostic test. The nerve that communicates to the muscles that lift the foot is the peroneal nerve. The muscles that push the foot down are innervated by a different nerve and often develop tightness in the presence of foot drop. The muscles that keep the ankle from turning in, as when you might sprain your ankle, are also innervated by the peroneal nerve, and it is not uncommon to find weakness in this area too. Numbness and tingling in the lower leg, particularly on the top of the foot and ankle, also can accompany foot drop, although it is not always linked.

Pathophysiology

The causes of foot drop, as for all causes of neurological lesions, should be approached using a localization-focused approach before etiologies are considered. Most of the time, foot drop is the result of neurological disorder; only rarely is the muscle diseased or nonfunctional. The source for the neurological impairment can be central (spinal cord or brain) or peripheral (nerves located connecting from the spinal cord to an end-site muscle or sensory receptor). Foot drop is rarely the result of a pathology involving the muscles or bones that make up the lower leg. The muscle that is designed to pick up the foot is the anterior tibialis. It is innervated by the common peroneal nerve, which branches from the sciatic nerve. The sciatic nerve exits the lumbar plexus with its root arising from the fifth lumbar nerve space. The descending spinal cord nerve that leads to the sciatic nerve is found in the anterior horn of the spinal cord and communicates from the brain—specifically, the cerebral cortex. Occasionally, spasticity in the muscles opposite the anterior tibialis exists in the presence of foot drop, making the pathology much more complex than foot drop. Isolated foot drop is usually a flaccid condition. There are gradations of weakness that can be seen with foot drop, as follows: 0=complete paralysis, 1=flicker of contraction, 2=contraction with gravity eliminated alone, 3=contraction against gravity alone, 4=contraction against gravity and some resistance, and 5=contraction against powerful resistance (normal power). Foot drop is different from foot slap, which is the audible slapping of the foot to the floor with each step that occurs when the foot first hits the floor on each step, although they often are concurrent.

Treated systematically, possible lesion sites causing foot drop include (going from peripheral to central):

  1. Neuromuscular disease;
  2. Peroneal nerve (common, i.e., frequent)—chemical, mechanical, disease;
  3. Sciatic nerve—direct trauma, iatrogenic;
  4. Lumbosacral plexus;
  5. L5 nerve root (common, especially in association with pain in back radiating down leg);
  6. Spinal cord (rarely causes isolated foot drop)—poliomyelitis, tumor;
  7. Brain (uncommon, but often overlooked)—stroke, TIA, tumor;
  8. Genetic (as in Charcot-Marie-Tooth Disease and hereditary neuropathy with liability to pressure palsies);
  9. Nonorganic;

If the L5 nerve root is involved, the most common cause is a herniated disc. Other causes of foot drop are diabetes, trauma, motor neuron disease (MND), adverse reaction to a drug or alcohol, and multiple sclerosis.

Treatment

The underlying disorder must be treated. For example, if a spinal disc herniation in the low back is impinging on the nerve that goes to the leg and causing symptoms of foot drop, then the herniated disc should be treated. If the foot drop is the result of a peripheral nerve injury, a window for recovery of 18 months to 2 years is often advised. If it is apparent that no recovery of nerve function takes place, surgical intervention to repair or graft the nerve can be considered, although results from this type of intervention are mixed.

Ankles can be stabilized by lightweight orthoses, available in molded plastics as well as softer materials that use elastic properties to prevent foot drop. Additionally, shoes can be fitted with traditional spring-loaded braces to prevent foot drop while walking. Regular exercise is usually prescribed.

The latest treatments include stimulation of the peroneal nerve, which lifts the foot when you step. Many stroke and multiple sclerosis patients with foot drop have had success with it. Often, individuals with foot drop prefer to use a compensatory technique like steppage gait or hip hiking as opposed to a brace or splint.

Treatment for some can be as easy as a foot-up ankle support. A cuff is placed around the patient's ankle, and a hook is installed under the shoelaces. The hook connects to the ankle cuff and lifts the shoe up when the patient walks.

See also

External links

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