You squat to pull weeds all morning, or sit with your legs crossed through a long meeting, and when you stand up the top of your foot tingles as if ants were crawling over it. A few steps later, the toe of your sandal scuffs the tiled floor. Usually it passes within a few minutes. Sometimes it does not: the next morning the numbness is still there, and you have to lift your knee higher than usual to get up a step without tripping.
In episodes like these, the place where the nerve is being pressed is often on the outer side of the knee, a whole shin’s length away from the numb patch of skin.
Where the peroneal nerve passes the knee
The common peroneal nerve branches off the sciatic nerve just above the back of the knee, then curves around to the outer side of the knee. The bony bump you can feel on the outer side, just below the knee joint, is the head of the fibula. The nerve runs just below this bump and then wraps around the neck of the fibula. Along this stretch it lies right under the skin, against the bone, with almost no padding, so the hard edge of a chair or the other knee resting on it is enough to compress it.
After wrapping around the neck of the fibula, the nerve divides into two branches. The deep branch controls the muscles that lift the foot and toes, and carries sensation from the web space between the big toe and the second toe. The superficial branch controls the muscles that tilt the foot outward, and carries sensation from most of the top of the foot and the outer side of the shin.
According to a review by Fortier and colleagues (2021), the peroneal nerve is the most commonly entrapped nerve in the lower limb, and the most common place for it to be pressed is where it passes the head of the fibula. Because the nerve lies so close to the surface, simply avoiding pressure on the outer side of the knee already lowers the risk.
Numbness on the top of the foot, and foot drop
When the superficial branch is affected, the top of the foot feels numb or tingly, and sometimes burns. When the deep branch weakens, the front of the foot cannot lift in time as you step, so the toes scuff the floor before the heel has even touched down. People unconsciously bend the knee higher to avoid tripping, and then the foot slaps down on the floor with a sound. This is foot drop, the most common sign of peroneal nerve damage (Masakado and colleagues, 2008). Older people whose toes keep catching are very likely to fall, and our article on preventing falls in older adults covers ways to stay safe at home.
Postures and situations that often press on the nerve
- Sitting cross-legged for a long time, with one knee resting on the outer side of the other, a habit our article on sitting correctly while working explains how to correct;
- Squatting for a long time while gardening, mopping the floor or preparing vegetables;
- Lying still for many hours, such as after surgery or during a serious illness, with the outer side of the knee pressing into the bed;
- A cast, knee brace or bandage that is too tight around the knee;
- An injury around the knee;
- Rapid weight loss.
The last item even has its own name in the medical literature: slimmer’s paralysis. Cucu and colleagues (2025) pooled 380 cases. About 96% affected only one side, and nerve conduction studies placed the damage around the head of the fibula.
Telling it apart from an L5 nerve root pinched in the back
The L5 nerve root in the lower back also supplies the muscles that lift the foot, so compression there causes exactly the same symptoms. Carolus and colleagues (2019) report that the L5 root and the peroneal nerve are the two most common causes of foot drop, and that one person can be compressed at several points in a row along the same nerve pathway.
Back pain with pain spreading from the buttock down the outer side of the shin points more toward the L5 root; see our article on pain spreading from the buttock down the leg. Another clue lies in muscles that the L5 root supplies but the peroneal nerve at the knee does not reach, such as the muscle that tilts the foot inward and the hip abductor muscle. If the foot drops while those two muscles are still strong, the doctor thinks more of the knee. Tapping lightly where the nerve wraps around the neck of the fibula and feeling tingling shoot down into the foot (Tinel’s sign) also suggests the knee. But in Cucu’s review only about 38% of patients had this sign, so tapping without tingling does not rule it out.
At the clinic, Dr. Dinh Ngoc Duc (MD, MSc in Traditional Medicine) uses muscle testing from Applied Kinesiology: the tibialis anterior (which lifts the foot), the peroneal muscles (which tilt the foot outward), then compares them with the tibialis posterior and the gluteus medius. Next, you place a fingertip on the head of the fibula on the outer side of the knee, and the next time on the lower back; each time, the doctor presses on the tibialis anterior once more to compare. If the muscle changes clearly when you touch the knee but changes little when you touch the back, the knee is more likely, and the reverse points to the back. Why the doctor uses this approach is explained in our article why doctors use muscle testing.
If the foot drop is already obvious, or has not improved after a period of watching, you need nerve conduction studies and electromyography (EMG) to find out where the nerve is damaged, how severe the damage is and what the outlook is (Masakado and colleagues, 2008).
Which kinds of foot drop need a hospital right away
Foot drop that comes on suddenly or weakness that gets quickly worse day by day, or leg weakness together with back pain spreading down the leg, numbness in the saddle area (between the legs and around the buttocks), being unable to pass urine, or losing control of your bladder, are reasons to go to the emergency department. Other warning signs with back pain are listed in our overview of back pain.
In the following situations, get checked early rather than waiting:
- Numbness, or difficulty lifting the front of the foot, after a cast, a brace or a knee injury: tell the place treating you right away;
- Numbness in both feet that gradually creeps upward like a pair of socks: you need to be checked for diabetes and for disease affecting many nerves (polyneuropathy);
- Weakness that spreads to muscles beyond the lower leg.
Examination and treatment at Tam Duc
The first step is to take the pressure off. Fortier and colleagues (2021) list removing outside compression as first-line treatment, and many cases recover on their own with monitoring and changes to daily habits. The doctor asks in detail how you sit, sleep and do housework, and how your weight has changed over the past few months.
Acupuncture often uses the Yanglingquan point, in the hollow in front of and below the head of the fibula, along with points down the outer side of the shin. In traditional medicine, numbness and tingling belong to the group of conditions called numbness (麻木, má mù), linked to qi and blood not reaching the skin and muscles to nourish them, so an herbal decoction is modified to fit each person’s pattern. If muscle testing shows that the pelvis or lower back is contributing, the doctor also makes adjustments there during the same session, then you lift the front of your foot against the doctor’s hand once more to compare the strength of the tibialis anterior. People who have just lost weight quickly have their meals reviewed. You are also shown how to practice lifting the front of your foot and how to walk safely while the nerve recovers.
Nerves recover slowly. In the review mentioned above, most people recovered well; if there is no improvement after about three months, decompression surgery is considered, and at that point the doctor will refer you to a specialist.
Worth keeping
- When you sit to work, keep both feet on the floor and drop the habit of resting one knee on the other;
- When you squat to do housework, stand up every so often and walk a few steps;
- If you are losing weight quickly and notice numbness on the top of your foot, tell your doctor early;
- Try standing on both heels and lifting the front of your feet; if one side cannot lift, get checked.
References
- Fortier LM, Markel M, Thomas BG, et al. An update on peroneal nerve entrapment and neuropathy. Orthop Rev (Pavia). 2021;13(2):24937. https://doi.org/10.52965/001c.24937
- Carolus AE, Becker M, Cuny J, et al. The interdisciplinary management of foot drop. Dtsch Arztebl Int. 2019;116(20):347-354. https://doi.org/10.3238/arztebl.2019.0347
- Masakado Y, Kawakami M, Suzuki K, et al. Clinical neurophysiology in the diagnosis of peroneal nerve palsy. Keio J Med. 2008;57(2):84-89. https://doi.org/10.2302/kjm.57.84
- Cucu LE, Popescu G, Maștaleru A, et al. Common peroneal nerve paralysis following rapid weight loss – a case report and literature review. Nutrients. 2025;17(11):1782. https://doi.org/10.3390/nu17111782
