Foot drop after surgery: what it means and what to do next

You wake up from an operation, or start walking afterward, and your toes catch on the floor. Your foot slaps down with each step, or you can’t lift it at all. It is frightening, and it is natural to wonder whether it will come back. Here is what is known, and what to do next.

What foot drop feels like

Foot drop is weakness in the muscles that raise the front of the foot and the toes. Your toes may drag, your foot may slap down after the heel hits the floor, or you may lift the knee higher than usual to clear the ground. Some people also have numbness on the top of the foot or the outer part of the lower leg.^[1,5]

How common is it?

Foot drop after surgery is not common, but it is a recognized complication:

• Knee replacement. A systematic review of 47,585 knee replacements found 203 with a common peroneal nerve palsy, a cumulative incidence of 0.4%.^[3] A single-center registry study found a similar rate of 0.32%. Epidural anesthesia, a knee that was significantly knock-kneed (valgus) before surgery, and female sex were associated with higher risk.^[4]
• Hip replacement. Among 10,047 hip replacements, sciatic or peroneal nerve palsy occurred in 0.05% with the direct anterior approach and 0.46% with the posterior approach.^[6]

These are averages from specific studies, and they can’t tell you your own risk. Your surgeon can.

Why it happens

The signal that lifts your foot travels a long way: from the brain, down the spinal cord, out of the lower spine as the L4 and L5 nerve roots, into the sciatic nerve, and on as the peroneal nerve. A problem at any point can cause foot drop, so finding where is the key step.^[1,7]

After surgery, the usual suspects are:

• The peroneal nerve at the knee. It wraps around the outer side of the knee just under the skin, which is the most common site of compression. A tight cast, splint or brace can squeeze it.^[5,7]
• The sciatic nerve. Higher-up injury or pressure can weaken the same muscles.^[2]
• The L5 nerve root in the back. This is one of the two most common causes of foot drop overall, and it may be involved after or alongside spine problems.^[1]

Sometimes more than one site is involved. See sciatica or a foot nerve problem? for how those can overlap.

What to do right away

1. Tell your surgeon or surgical team the same day. Don’t wait for your next scheduled visit.
2. Ask whether anything is pressing on the nerve. A tight cast, dressing, brace or wrap that is getting more numb or painful is an emergency, so call at once.
3. Protect yourself from falls. A light ankle-foot orthosis (AFO), a brace that holds the foot up, is a helpful device that lets people with a severe foot drop walk better and more safely.^[2]
4. Ask for a proper evaluation. A careful examination can often show which nerve is affected. Nerve studies, arranged with another specialist, help locate the problem, measure how much nerve damage there is and estimate how well it may recover.^[2,5]

What recovery looks like

Recovery depends on how severe the weakness is at the start. In the knee replacement review, 39% of people with a complete palsy had complete recovery, compared with 66% of those with an incomplete palsy, at an average follow-up of 3.6 years.^[3] In the single-center study, about two-thirds of complete palsies and four-fifths of partial palsies recovered completely.^[4] After hip replacement, full motor recovery occurred in about 58% of sciatic or peroneal palsies.^[6]

Those figures are hopeful, but they also show that many people are left with some weakness. Nerves regrow slowly, about a millimeter a day, so recovery is measured in months, not weeks.^[8]

If the nerve isn’t recovering

Options depend on the cause and on whether the nerve has a realistic chance to recover. Many people do well with a brace and therapy. Surgery is considered when a nerve can recover, when something is pressing on it, or when it has been cut.^[5,1]

• Releasing the nerve at the knee. In a pooled analysis of 368 people who had the peroneal nerve released, ankle-lifting strength improved and serious complications were uncommon. About half (54%) reached full strength.^[9] In a smaller series, those who had surgery within 12 months of symptom onset fared significantly better.^[10]
• Nerve or tendon transfers. When a nerve is unlikely to recover, or a release didn’t work, working nerves or tendons can be used to restore the lifting movement.^[5,11]

Timing matters, so don’t wait many months to ask for a second opinion if there is no improvement. Read more in foot drop, common peroneal nerve compression, nerve decompression and nerve transfer.

When to see a specialist

Have foot drop checked promptly, even if it seems mild. Get an evaluation soon if your toes catch when you walk, you have started to trip, or your foot feels weak or numb after a knee or hip operation, a fall or a long stretch in a cast.