Summary
A drop foot is the inability to bring the ankle up to a neutral position. It is usually caused by dysfunction of the muscles at the front of the leg (anterior compartment muscles). This may occur secondary to a nerve injury (ex. at the level of the knee) or a compartment syndrome. Patients with a drop foot will walk with a “high steppage gait” (similar to the way a horse walks). This gait pattern occurs because patients with a foot drop need to lift their leg substantially higher in order for the foot (which is in a downward resting position) to “clear” the ground.
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:
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Daily calf stretching to maintain ankle motion
With loss of the muscle function in the anterior compartment there is a tendency for the calf muscle to steadily pull the ankle into an equinus position (pointing down). This can be difficult to prevent over time because of the natural muscle imbalance. However, a regular program of daily calf stretching can be very helpful. 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.
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Ankle Foot Orthoses (AFO) bracing
AFO bracing is commonly used 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. 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 (ankle pointing downwards). Patients with a foot drop will often be able to walk with a much more normal gait pattern when they are wearing an AFO.
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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). The most commonly procedure is to transfer the posterior tibial tendon (assuming this muscle is functioning normally) through the space between the tibia and the fibula (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 lift the ankle upwards (dorsiflex the ankle).
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Peroneal Nerve Repair or Nerve Graft
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 led 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.
Edited August 16th, 2009
