COMMENTARY

When Is Foot Drop Recoverable?

Justin M. Brown, MD

Disclosures

August 23, 2011

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This is Dr. Justin Brown from the Division of Neurosurgery at the University of California at San Diego. My specialty is spine and peripheral nerve disorders. Today, I will be discussing foot drop. Foot drop, as we know, results from a number of etiologies: stroke and spinal cord injuries and, more commonly, injury to the lumbar nerve root or to the peroneal nerve distally.

Patients can develop foot drop immediately following a trauma or they can develop it spontaneously, in a painless situation. There can be a number of presentations, but when a patient comes to your office and cannot dorsiflex the foot, it's very important to be able to determine the source of this and whether it's recoverable.

As we know, the L5 nerve root contributes to the dorsiflexion of the foot as does the peroneal nerve. Thus, a skilled electrodiagnostician is an important part of the team for determining the source of the foot drop. The muscles [innervated by] the peroneal nerve and the L5 myotome do overlap, but there are differences, and EMG [electromyography] can help us determine whether the source is the back or the leg. But sometimes this is more difficult to discern.

When the spine is the source and patients have no accompanying pain, they are often told to wait and this will recover. But we have found that if, in serial examinations, we are not seeing improved motor units, then decompressing the nerve at the level of the spine can recover function for a large number of patients with foot drop who might not otherwise have recovered.

When the source is the leg, a peroneal nerve compression operation is a very simple procedure much like a carpal tunnel release but at the knee. Patients who have diabetes, swollen legs, or a poor outcome after knee replacement surgery often will recover almost instantaneously after an operation like this.

This outcome is related to the types of nerve injuries that are involved. Nerve injuries necessarily progress, from a neurapraxia, where the nerve is intact but not conducting, to axon loss, which over time becomes irrecoverable. But we have found that for many patients who present as long as a year or more after the development of the foot drop, if we can stimulate the nerve distal to the point of injury and we see those muscles contract, we know this injury is accounted for in part by a neurapraxia, and therefore, if it's decompressed, it will recover fully.

In the more advanced forms of nerve injury, sometimes a graft is required. If this is at the level of the leg, this can be successful. If it is at the level of the spine, it is much more difficult to obtain a good recovery. In this case, we can consider what's called nerve transfers, in which branches of the tibial nerve, which push the foot down and curl the toes, can be moved over and plugged into the peroneal nerve to bring the foot up. This requires a substantial retraining on the patients' part, but it can be a successful approach.

Lastly, if patients come years after with no function whatsoever in that nerve distribution and the muscles cannot be stimulated, and if it seems clear that the muscle is irretrievable, we refer them to our orthopaedic colleagues to undertake tendon transfer operations. A tendon transfer involves moving the tendons that push the foot down or curl the toes, to the front of the foot to pull it up. I've seen a number of cases in which this has been a very successful approach.

To summarize, foot drop is related to several etiologies and will respond to a number of potential interventions. It is important to get these patients to a treating physician as soon as possible after their injury.

I am Justin Brown at the University of California in San Diego. Thank you.

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