Drop Foot

(aka Foot Drop)

Summary

Foot drop is the inability to bend the ankle ‘up” to avoid tripping when walking. It is caused by weakness or poor function of the muscles in the front of the leg (anterior compartment muscles). It is caused by direct injury to the muscle/tendon or nerve to those same muscles. Without treatment, patients with a drop foot will walk with a “high steppage gait” (similar to the way a horse walks) or tripping. Most people with foot drop can be treated to return to a functional gait, although it is uncommon that the ankle can ever return to “perfectly normal.”

Treatment

Treatment of a foot drop initially depends on the underlying cause. In the case of significant loss of muscle function from a compartment syndrome, the muscle will usually not recover. However, if the foot drop is cause by an injury to the nerve supplying the anterior lower leg muscle compartment (the peroneal nerve), there is a chance that the nerve will recover (if it has only been “stunned” rather than cut or injured beyond repair). Treatment of a foot drop may include:

Daily calf stretching to maintain ankle motion. There is a tendency for the calf muscle to steadily pull the ankle into an equinus position (pointing down). However, a regular program of daily calf stretching will prevent this. The stretch can be done seated or standing as long as the “knee goes over the toe.” For this reason, daily calf stretching in an attempt to maintain ankle dorsiflexion is often recommended as a part of the treatment plan for patients who have a drop foot. Range of Motion must be restored before any other treatment can be effective.
Ankle Foot Orthoses (AFO) bracing. AFO bracing is the most common and simplest method to treat a foot drop. This brace keeps the ankle up in a neutral position, essentially partially replacing the function of the lost anterior muscle compartments. It is thin enough to fit into a shoe, and some types can “spring” the ankle up when the foot is not on the ground. An AFO also serves to keep the ankle under relatively constant stretch, and thereby may minimize the potential for the ankle to fall into an equinus position. Patients with a foot drop will often be able to walk with a much more normal gait pattern when they are wearing an AFO. In cases in which the nerve or muscle damage is temporary, the AFO brace can possibly be reduced or eliminated once sufficient muscle function returns. However, in some cases the brace will be needed permanently unless muscle tendon transfer surgery is performed and sometimes even then.
Posterior Tibial Tendon Transfer to the Dorsal Midfoot. Patients with a permanent foot drop may benefit from a tendon transfer procedure designed to allow active lifting upwards of the ankle joint (dorsiflexion of the ankle) by taking a working muscle and redirecting it to work in place of the weak or non-working muscle. The most common procedure is to transfer the posterior tibial tendon (assuming this muscle is functioning normally) through the space between the tibia and the fibula bones (interosseous membrane) to the top of the foot. When this tendon transfer has healed and adequate rehabilitation and retraining of the muscle has occurred, this procedure can serve to splint to ankle in an improved position and provide some (but not necessarily normal) active muscle function to dorsiflex the ankle.
Peroneal Nerve Release, Repair or Graft. A release can be performed if there is a constriction(choking) of the nerve is caused by tight fibers of scar. The constriction prevents the muscles from receiving the the signal to dorsiflex the foot. Releasing the scar (after total knee replacement or knee fractures) can allow the nerve to work normally, although this can take a long time. In some instances when the cause of the foot drop is an injury to the peroneal nerve (usually at the level of the knee), a direct nerve repair or nerve grafting may be indicated. This type of surgery needs to be performed by a surgeon with expertise in microsurgical nerve repairs. It is designed to provide a path for the nerve to “grow back”. This type of procedure may lead to some return of muscle function over time (the nerve generally grows back at a rate of about 0.5-1mm/day and often it needs to “grow” 100-150mm in total). However, unfortunately this type of repair rarely leads to a return of near normal muscle function and therefore this type of treatment often needs to be combined with AFO bracing and/or tendon transfers. The nerve injury/involvement can also be at the level of the hip (hip fractures or replacement) or in the spine. Often the nerve at these locations are “stunned” and respond to stretching and temporary AFO use.

Edited on January 10, 2017

Originally edited by Anthony Van Bergeyk, MD

mf/ 7.3.18