Back or foot? Finding the source of foot nerve pain

One nerve pathway, many places for trouble

The nerves that supply your foot start in the lower spine. The nerve roots there join to form the sciatic nerve, which runs down the back of the thigh and divides near the knee into the tibial nerve and the peroneal nerve. These branches continue down the leg and split into the small nerves of the foot.^[4]

That means a problem at any point along the way, in the spine, the buttock, the knee, the ankle or the foot, can produce symptoms in the foot. The brain reads the signal as coming from the foot, whichever spot is irritated.

Sciatica is pain that follows the path of the sciatic nerve or one of its roots, usually from the buttock down the back or side of the leg, sometimes into the foot. It is most often caused by a pinched nerve root in the lower back, for example from a herniated disc.^[1,2] Foot nerve entrapment happens when a nerve is compressed further down, such as in the tarsal tunnel or between the toes in Morton’s neuroma.

Clues that point to the back or to the foot

These are tendencies, not rules, and they can overlap.

Symptoms in both feet, starting at the toes, point to a third possibility: peripheral neuropathy, a body-wide nerve condition. It can also occur together with either of the others.^[5]

When both are involved

Sometimes a nerve is affected in two places at once, for example at the spine and again in the leg or foot. This is called double crush syndrome. The idea is debated, and some specialists question it. Still, a body-wide neuropathy or a second pinch point can coexist with the first problem, which may help explain less satisfying results after treatment at only one site.^[3]

A recent case series described people with a pinched L5 nerve root and a compressed peroneal nerve at the knee. Some had both at the start. Others still had symptoms after their back was treated, and the peroneal nerve was found to be involved too. Releasing the peroneal nerve helped most of them, though the series was small and from a single center.^[6]

The practical lesson is simple: when symptoms persist after treatment at one site, it is reasonable to look at the whole pathway again.

How the source is found

• History: where symptoms start, what provokes and relieves them, back or leg pain, injuries, surgery, and other health conditions.
• Examination of the whole leg, not just the foot: the back, hip and knee, movements that stretch the sciatic nerve, strength and reflexes, sensation, tapping along nerves, foot alignment and circulation.
• Nerve studies and EMG, which can show whether the trouble is at the nerve root, along the nerve in the leg, or in the foot.^[7,8] These are performed by another specialist, and we coordinate them and review the results with you. See nerve testing for foot pain.
• Imaging such as an MRI of the lower back, or an ultrasound or MRI of a nerve or the foot. Scans are read together with the examination, because changes can appear on scans in people who have no symptoms.

What happens next

If the evidence points to the back, we’ll say so and help you reach the right care, such as your primary care physician, a spine specialist or a physical therapist. If it points to the foot, we’ll build a plan for the foot, starting with non-surgical care whenever it’s appropriate. If both are involved, we work with your other clinicians so that treating one doesn’t leave the other unaddressed.

When to seek care

Consider an evaluation if you have had foot pain, numbness or tingling for more than a few weeks and can’t tell whether your back or your foot is responsible, or if you’ve had treatment for your back or foot and still have symptoms.