Superficial peroneal nerve entrapment

What is superficial peroneal nerve entrapment?

The superficial peroneal nerve, also called the superficial fibular nerve, is a branch of the peroneal nerve. It travels down the outer side of the lower leg, passes through a layer of tough tissue called fascia a few inches above the ankle, and then runs just under the skin over the front of the ankle and the top of the foot. It gives feeling to the outer lower leg and the top of the foot, except for the small web space between the big toe and second toe, which is served by a different nerve. It also helps turn the foot outward.^[1]

“Entrapment” means the nerve is being compressed or tethered. For this nerve, the most common spot is where it exits the fascia of the lower leg. It is an uncommon cause of foot symptoms, so it is easy to miss.^[3,2]

Symptoms

• burning, tingling, aching or numbness on the top of the foot, the front of the ankle, or the outer lower leg
• symptoms that build with walking, running or standing, and ease with rest
• a tender spot on the outer leg, a few inches above the ankle, where tapping may send tingling into the foot
• discomfort from shoes or boots that press on the front of the ankle

The pattern of numbness can vary from person to person, because the way this nerve supplies the top of the foot varies.^[2]

What causes it?

The nerve can be squeezed where it leaves the fascia, stretched when the ankle rolls inward, or irritated by pressure from footwear.

• Ankle injury. Persistent symptoms after an inversion (rolling) sprain are common, and the nerve is one possible reason. In a report of children with severe ankle sprains, a few developed scarring around this nerve at the ankle.^[4]
• Pressure from outside, such as tight laces, boots, a brace or a cast.
• Swelling or tightness in the lower leg that crowds the nerve as it exits the fascia.
• An unstable ankle, which can repeatedly stretch the nerve.^[3]
• No clear cause. In many people, the cause is never pinned down.

How it’s evaluated

Several other problems cause similar symptoms: a pinched nerve in the lower back, peripheral neuropathy, tendon problems, a stress injury, and other nerves in the foot. The diagnosis rests mainly on a careful history and examination.

• Examination: mapping the numb area, tapping along the nerve, checking strength and reflexes, looking at ankle stability, footwear, alignment and circulation, and checking the back, knee and hip.
• Tests: an examination, nerve-conduction studies and imaging can all help establish the diagnosis.^[2] Ultrasound or MRI can show what is pressing on the nerve and where.^[5] Nerve studies are performed by another specialist, and we coordinate them and review the results with you. See nerve testing for foot pain.

Treatment options

Non-surgical care

First-line care removes what is causing pressure, gives support to any unstable joint and calms inflammation.^[3]

• Footwear: changing lacing, using a softer tongue or padding, or wearing shoes that don’t press on the front of the ankle.
• Activity changes, with a temporary break from the activity that provokes symptoms.
• Support for an unstable ankle, with bracing or therapy.
• Physical therapy and gentle nerve-gliding exercises.
• Medicine for nerve pain, coordinated with your other clinicians.

Many peroneal nerve entrapments improve with observation and activity changes.^[3]

Surgery

If symptoms persist despite well-tried non-surgical care, surgery to release the nerve may be discussed. The operation opens the fascia where the nerve exits, frees the nerve, and addresses any cause of pressure. Newer approaches, including microsurgical release and nerve stimulation, have been reported, but large studies of their results are lacking.^[3] Learn more about nerve decompression surgery. When an ankle injury has left the nerve scarred, the ankle itself may also need attention.^[4]

Recovery and outlook

Non-surgical care usually takes weeks to months to show its effect. After surgery, nerve symptoms generally improve over months, and some numbness may remain. Results depend on how long the nerve has been irritated and on the underlying cause. Bringing any earlier scans or nerve-study results to your visit helps us plan.

When to seek care

Consider an evaluation if burning, tingling or numbness on the top of your foot or outer lower leg lasts more than a few weeks, or keeps coming back after an ankle sprain.