Occasionally my leg goes dead particularly if I’ve been kneeling down or have been sitting awkwardly. Typically after my leg falls asleep, I then get a sensation of pins and needles in my foot and lower leg, after which my leg returns to normal. Why does this happen?
Pressure on the peroneal nerve, which passes close to the surface of the skin on the outer, lower part of the knee or on the sciatic nerve, can cause something known as a temporary neuropathy. The pressure interferes with the blood supply to the nerve that then causes the nerve to produce abnormal signals.
These abnormal signals cause the sensation of pins and needles; this is called a parasthesia. By relieving the pressure on the nerve, the blood supply returns to normal and the parasthesia stops. Trauma or injury to the knee, fracture of the fibula and a too tight plaster cast may also cause the condition.
Can this type of pressure cause a dropped foot? I have a friend who has got a dropped foot. His doctor seems to think it’s the result of being in bed for prolonged periods. He uses a wheelchair and finds it difficult to change his position.
More severe pressure on the peroneal nerve can result in a condition called nerve palsy. This disorder can affect the muscles that lift the foot, so that the foot cannot be flexed upward. This is what is known as a foot drop. This type of foot drop is most common among thin people who are confined to bed, people who are incorrectly strapped into a wheelchair, or in those who habitually cross their legs for long periods of time.
The diagnosis is usually made based on symptoms and on the results of a physical examination. If a more serious cause is suspected, electromyography or nerve conduction studies may be performed. These tests may also be used to determine where the nerve is damaged and to assess the severity of the disorder. In some cases, surgery may be performed to correct a foot drop.
However, where surgery is not appropriate, orthotics or foot splints may be fitted to help keep the foot from dropping down while walking. In cases where temporary pressure is the cause, symptoms may be relieved by frequent changes in position, avoiding pressure on the nerve and taking non-steroidal anti-inflammatory drugs to reduce any inflammation.
