Not all foot pain is due to problems in the feet. In fact, the origin of the problem may be due to an injured nerve in the lower back that then travels to the foot.
An irritated nerve in the low back can cause pain, altered sensation, or weakness in legs and feet. Some people may complain of a tingle in their foot, describing a feeling that their foot has gone ‘asleep’.
People with foot pain due to a ‘pinched nerve’ in the lower back will usually also have the same symptoms in the leg. It is very rare to have a pinched nerve in the low back causing foot pain and not have leg pain as well.
If the foot pain is caused by an irritated nerve, your spine specialist will often be able to identify which nerve is involved, based on where the pain or other symptoms are located.
The patient who complains of altered sensation in the front of their shin or top of their foot will be asked to walk about the room with only their heels touching the ground.
The nerve that controls the muscles that makes this movement possible also supplies sensation to the front of the shin and top of the foot.
Injury to this nerve can cause the inability to walk on the heels, and pain down the front of the shin to the top of the foot
Foot drop describes someone whose foot slaps the ground when walking, like a clown in oversized shoes. A nerve from the low back controls the muscle that allows a controlled placement of the foot on the ground. When the nerve is injured, foot drop may occur, as well as pain on the side of the calf and top of the foot to the big toe.
The main calf muscle, the gastrocnemius muscle, provides the pull on the foot so we can walk on our toes. A nerve from the low back also controls this muscle. Injury to this nerve can result in so much weakness in the calf that walking or driving may no longer be possible. Further, there may be pain experienced along the bottom of the foot.
All of these nerves together form the sciatic nerve. The sciatic nerve is the largest nerve in the body, and is about the thickness of a thumb!
The sciatic nerve is a conglomeration of five nerves from the lower spine that join together in the mid-buttock.
From the buttock, the sciatic nerve extends down the back of each leg all the way to each foot. Pain or altered sensation in the sciatic nerve is called sciatica.
It gets tricky
Here is the tricky bit: the roots of the sciatic nerve are in the low back, but the nerve itself isn’t formed until the mid-buttock. Therefore, it is possible to have an injury in the low back that pinches a nerve root, but is felt as leg or foot pain – not low back pain!
There are several different conditions that can cause this phenomenon.
When there is a prolapsed disc, a part of the inner softer part of the disc bulges out (herniates) through a weakness in the outer part of the disc (like a squeezed jelly donut).
A prolapsed disc is sometimes called a herniated disc. The bulging disc may press on a nerve coming from the spinal cord which then travels to the foot.
Lumbar spinal stenosis.
Lumbar spinal stenosis is caused by narrowing of the spinal canal so that the spinal cord is compressed. The spinal cord connects the brain to nerves of the body.
Stenosis of the spinal canal is most often caused by a combination of loss of disc space, bone spurs, and other arthritic changes.
Spondylolisthesis is the movement of one vertebrae on another, either forwards or backwards. The vertebrae are not supposed to move in these directions, but it can occur due to arthritis, instability or fracture. This improper placement of the vertebrae can pinch one of the nerves that eventually travel down the leg and into the foot.
The exact cause of foot pain can be tricky to determine. If you have foot pain with other leg symptoms, please see your spine specialist for an accurate diagnosis.