The most common cause of foot drop is an injury to the peroneal or sciatic nerve. This results in denervation of the tibialis anterior muscle which is responsible for upward ankle movement; loss of that movement results in foot drop. This is a severe functional problem and inhibits normal walking and activity.
The nerve is often injured during hip replacement surgery when it becomes stretched. Another important cause is during severe knee injuries during athletic activity, when the nerve becomes stretched or torn. Knee replacement surgery is another cause of peroneal nerve trauma with resultant foot drop. Direct injury to the nerve by gunshot or stab wounds can cause significant injury as well.
The anatomy of nerves and muscles dictates treatment for foot drop. If a nerve to any muscle is injured, the muscle is paralyzed until the nerve either regenerates spontaneously or is repaired surgically. Following surgery, if nerve recovery takes longer than one and a half years, paralysis may be permanent. Because nerves grow back very slowly, one inch or so per month, nerve injuries farther than several inches from the muscle do not recover well. The nerve transfer surgery pioneered by Dr. Nath bypasses the area of nerve injury to provide healthy nerve to the paralyzed muscle close to the muscle itself. This has resulted in good return of function in cases that would otherwise be hopeless.