A woman in her forties comes in after losing 45 pounds in eight months. She started catching her right toes on the subway stairs a few weeks ago, and now her foot slaps on the sidewalk. The top of the foot is numb. She has no back pain. She works at a desk with her right leg crossed over the left most of the day, and she was told to get a lumbar MRI. When Dr. Alex Movshis taps just below the outer side of her knee, the tingle runs down the outer shin. She can still turn the foot inward and hold her hip steady on one leg. That pattern points to the common peroneal nerve at the fibular neck, not her back.
What peroneal nerve entrapment is
The common peroneal nerve, also called the common fibular nerve, branches off the sciatic nerve above the back of the knee. It then wraps around the neck of the fibula, the thin outer bone of the leg, just below the knee. For a short stretch it sits right under the skin against bone, with almost no padding. It then passes through a tight opening under the peroneus longus muscle and splits in two:
- The deep peroneal nerve lifts the foot and the toes and carries feeling from the web between the big toe and the second toe.
- The superficial peroneal nerve turns the foot outward and carries feeling from the outer shin and most of the top of the foot.
Pressure at the fibular neck usually hits both branches, which gives the classic picture: the foot drops, and the top of the foot goes numb. It is the most common single-nerve problem in the leg (Marciniak 2013).
Why the nerve gets pinched at the knee
Most cases have an identifiable cause. In an Italian multicenter study of 69 patients, it was prolonged posture in 23 percent, surgery in 20 percent, no clear cause in 16 percent, weight loss in 15 percent, injury in 12 percent, being bedridden in 7 percent, pressure from a cast in 6 percent, and a cyst near the fibula in 1 percent. Men outnumbered women about four to one (Aprile 2005a). In everyday terms:
- Leg crossing, especially for hours at a desk or on long flights.
- Long squats or kneeling, in gardening, tiling, flooring and some yoga positions.
- Pressure from outside: a cast, a knee brace, knee-high boots, a bed rail, or lying in one position through a long illness or hospital stay.
- Surgery. Not only around the knee. Peroneal palsy has followed hip, chest and abdominal operations as well (Aprile 2000, Aprile 2005a).
- Knee injury, including ligament tears and fractures of the upper fibula.
- A ganglion cyst that tracks along a small joint branch of the nerve and swells inside or next to it.
Fast weight loss and the peroneal nerve
Fat at the outer knee cushions the nerve against the bone. Lose it quickly and the nerve loses its padding. Weight loss caused 15 percent of cases in the Italian study (Aprile 2005a). After bariatric surgery it is well described. In one series of five patients, foot weakness appeared an average of 7.2 months after the operation, following a mean loss of 36.6 percent of body weight (Gunduz 2026).
We have not seen a published series after GLP-1 medications such as semaglutide or tirzepatide yet. The mechanism, losing the fat that protects the nerve, is the same, so anyone losing weight quickly who starts catching a toe should be examined and should stop crossing their legs. The same geometry change is linked to meralgia paresthetica, the outer-thigh nerve at the hip.
Symptoms of peroneal nerve entrapment
- Foot drop. The toes catch on curbs and stairs, the foot slaps down after the heel lands, and some people lift the knee higher than usual to clear the foot.
- Weak turning of the foot outward, which makes the ankle feel unstable on uneven ground.
- Numbness or tingling on the top of the foot and the outer shin. The sole stays normal, because a different nerve supplies it.
- Often little or no pain. In the Italian study nearly every patient had weakness and most had sensory symptoms, but only about one in five had pain (Aprile 2005b).
- A tender spot just below the outer knee, where tapping sends a tingle down the shin.
When only a branch is pinched
Lower in the leg, either branch can be pinched on its own. The superficial peroneal nerve comes through the fascia of the outer shin about a hand’s width above the ankle, and a tight boot top, an old ankle sprain or a fascial defect can irritate it there. The result is burning or tingling on the top of the foot and the outer lower shin, with normal strength. The deep peroneal nerve can be squeezed on the top of the foot under tight laces or a ski boot, where it gives numbness in the first web space. These are pain-and-tingling problems more than weakness problems, and they respond to lacing and footwear changes and to a targeted injection.
Foot drop: the knee, the back, or something else?
Foot drop is a finding, not a diagnosis. Sciatic nerve injury, the nerves of the pelvis, motor neuron disease, generalized neuropathy and an L5 root in the back all have to be told apart from a peroneal palsy (Masakado 2008). The exam narrows it quickly:
- An L5 root in the lower back. Usually there is back or buttock pain running down the outer leg. The giveaway is weakness outside the peroneal nerve’s reach: turning the foot inward (tibialis posterior, a tibial-nerve muscle) and holding the hip level on one leg (gluteus medius, the superior gluteal nerve) both get weak with an L5 root and stay strong with a peroneal palsy. See radiculopathy and sciatica.
- The sciatic nerve higher up. After hip surgery, a deep buttock injection or a hip fracture, the peroneal part of the sciatic nerve can be hurt and mimic a knee problem. The nerve study places the level.
- The brain or spinal cord. Sudden weakness with other signs, such as a drooping face or a weak arm, is a stroke until proven otherwise. Call 911.
- Generalized neuropathy. Both feet, numb from the toes up, often with diabetes.
- Slowly spreading weakness in more than one limb, with muscle twitching and no numbness, needs a neurologist.
How peroneal nerve entrapment is diagnosed
The exam
Dr. Movshis tests each muscle that lifts the foot and toes, turns it out and turns it in, checks hip strength on one leg and the ankle reflex, and maps the numb skin. He taps the nerve at the fibular neck and asks about leg crossing, squatting, weight change, recent surgery and anything that has pressed on the outer knee.
When we do a nerve conduction study and EMG
An EMG and nerve conduction study answers the two questions that decide the plan: where the nerve is injured, and what kind of injury it is (Masakado 2008, Marciniak 2013). It is done in our office. A certified technologist performs the nerve conduction portion, and Dr. Movshis performs the needle EMG and reads the study.
The kind of injury predicts recovery. A conduction block, where the nerve is squeezed but its fibers survive, usually recovers well once the pressure is gone. Loss of nerve fibers takes longer and recovers less completely. In the Italian study, a conduction block was found in about 50 to 70 percent of cases caused by posture or weight loss, while about 60 percent of cases after injury showed only fiber loss (Aprile 2005a). The needle part of the study shows fiber loss most clearly a few weeks after the weakness begins, so the timing of the test is planned around when the foot dropped. A repeat study can show early regrowth before strength returns.
Ultrasound, and when MRI helps
Ultrasound of the nerve at the fibular neck is done at the first visit when the exam calls for it. It shows swelling of the nerve at the pinch point and, most importantly, a ganglion cyst, which needs a surgeon rather than waiting. MRI is ordered when a cyst or other mass needs to be mapped, or when foot drop has no obvious cause.
Peroneal nerve treatment, step by step
Step 1: Take the pressure off the nerve
- Stop crossing your legs, and keep it stopped for months, not days.
- Avoid long squats and kneeling with weight on the outer knee.
- Recheck anything that presses on the outer knee: a cast, a knee brace, tall boots, the bed rail or the side of a chair.
- After fast weight loss, slow down if you can, and have your nutrition checked as part of the workup.
Step 2: Walk safely while the nerve recovers
An ankle-foot orthosis, usually a light plastic brace that fits inside the shoe, holds the foot up so the toes clear the ground. It prevents trips and falls, and it does not weaken anything. Our in-house physical therapy team keeps the calf from tightening, so the ankle can still bend up when strength returns, and works on balance and the muscles that are recovering.
What recovery usually looks like
When pressure is the cause, the outlook is good. In a series of 36 patients followed long term, 13 had a good recovery and 12 more improved (Aprile 2000). Recovery runs over weeks to months. Strength in the foot lift usually returns before the numbness on top of the foot fully clears.
Injections, when pain is the problem
Most peroneal palsies are painless weakness, and an injection does nothing for a foot that will not lift. Some patients, though, mostly have pain: an ache at the outer knee with tingling down the shin and a tender nerve at the fibular neck, or burning on the top of the foot from a pinched branch. For them, Dr. Movshis can place a small amount of local anesthetic, with or without a corticosteroid, around the nerve at the tender point under ultrasound. The local anesthetic tests whether that spot is the source of the pain. The steroid can calm the irritated nerve for a while. No trial has tested either for this nerve, so it is used for pain, alongside the steps above, not instead of them. Our nerve blocks page describes how these injections are done.
Referral for peroneal nerve decompression
Surgery comes up when a ganglion cyst or other mass is pressing on the nerve, when strength is not coming back after a few months with the pressure off, or when the EMG shows fiber loss without signs of regrowth. A laceration or a knee dislocation that injures the nerve needs a surgeon’s opinion right away.
Decompression frees the nerve at the fibular neck and through the opening under the peroneus longus. In a meta-analysis of 368 patients, most with severe weakness, the strength of the foot lift went from a median of 1 out of 5 before surgery to 5 out of 5 after, and 54 percent reached full strength. Infection, wound and bleeding complications each ran under 1 percent, and one death from sepsis was reported (Chow 2021). The average time from onset to surgery in those studies was about ten months, and the authors called for higher-quality studies. After bariatric surgery, four of five patients had full strength six months after decompression in one series (Gunduz 2026).
Decompression of the leg nerves is also offered elsewhere as a treatment for diabetic neuropathy in both feet. A Cochrane review found no controlled evidence that it works for that (Chaudhry 2008), and Aetna classes it as experimental for diabetic neuropathy itself, while still covering release of a true entrapment in someone who also has diabetes (Aetna CPB 0729).
Modal does not perform the operation. Dr. Movshis refers to peripheral nerve surgeons once the level and the type of injury are confirmed.
When foot drop needs urgent care
- Foot drop with new back pain and numbness between the legs, or new trouble controlling the bladder or bowels. These are signs of nerve root compression in the spine. Call 911 or go to the nearest emergency room.
- Sudden weakness or numbness on one side of the body, a drooping face or trouble speaking. These are signs of a stroke. Call 911.
- Severe, rising pain in the lower leg with a tight, swollen calf, after an injury or inside a cast. This can be compartment syndrome. Call 911 or go to the nearest emergency room.
- Foot drop right after a knee injury or dislocation. This needs to be seen the same day.
- Weakness that is spreading or getting worse week by week. Not an emergency, but book promptly.
Peroneal nerve care with Dr. Movshis in Midtown
The first visit covers the history, a full strength and sensation exam of both legs and the back, and an ultrasound of the nerve at the outer knee when the exam calls for it. The nerve study is done in the office, timed to when the weakness started. Most people start with taking the pressure off, a brace and physical therapy, and are rechecked as strength returns. A cyst, a mass or a foot that is not recovering moves the plan to imaging and a surgical referral.
What we document before you see a surgeon
If you are headed for surgery, Dr. Movshis sends the surgeon your exam, ultrasound and nerve testing results, along with dated records of the care you have tried. Each surgeon and each insurance plan asks for slightly different things, so we fill in whatever they request.
Most commercial PPO plans cover the evaluation, ultrasound, nerve testing and injections. Check your insurance before your first visit, at no cost.
Same-week appointments are available. Book online or call (646) 290-6660.
References
- Aetna. Diabetic Neuropathy: Selected Treatments. Clinical Policy Bulletin 0729. Reviewed 2026-10-21. aetna.com
- Aprile I, Padua L, Padua R, et al. Peroneal mononeuropathy: predisposing factors, and clinical and neurophysiological relationships. Neurol Sci. 2000;21(6):367–71. doi:10.1007/s100720070052 · PubMed
- Aprile I, Caliandro P, La Torre G, et al. Multicenter study of peroneal mononeuropathy: clinical, neurophysiologic, and quality of life assessment. J Peripher Nerv Syst. 2005;10(3):259–68. (Aprile 2005a) doi:10.1111/j.1085-9489.2005.10304.x · PubMed
- Aprile I, Caliandro P, Giannini F, et al. Italian multicentre study of peroneal mononeuropathy at the fibular head: study design and preliminary results. Acta Neurochir Suppl. 2005;92:63–8. (Aprile 2005b) doi:10.1007/3-211-27458-8_14 · PubMed
- Chaudhry V, Russell J, Belzberg A. Decompressive surgery of lower limbs for symmetrical diabetic peripheral neuropathy. Cochrane Database Syst Rev. 2008;(3):CD006152. doi:10.1002/14651858.CD006152.pub2 · PubMed
- Chow AL, Levidy MF, Luthringer M, et al. Clinical Outcomes After Neurolysis for the Treatment of Peroneal Nerve Palsy: A Systematic Review and Meta-Analysis. Ann Plast Surg. 2021;87(3):316–323. doi:10.1097/SAP.0000000000002833 · PubMed
- Gunduz HB, Aydin I, Kara B, et al. Peroneal neuropathy with foot drop after bariatric surgery: A neurosurgical perspective. Dusunen Adam. 2026;39(3):205–211. doi:10.14744/DAJPNS.2026.00337 · PubMed
- Marciniak C. Fibular (peroneal) neuropathy: electrodiagnostic features and clinical correlates. Phys Med Rehabil Clin N Am. 2013;24(1):121–37. doi:10.1016/j.pmr.2012.08.016 · PubMed
- Masakado Y, Kawakami M, Suzuki K, et al. Clinical neurophysiology in the diagnosis of peroneal nerve palsy. Keio J Med. 2008;57(2):84–9. doi:10.2302/kjm.57.84 · PubMed