Is That Leg Pain the Result of a Spine or Nerve Injury?
The human nervous system has a tremendous capacity to constantly relay vital messages throughout the body. If this complex system is damaged, nerve signals can go awry, causing intense pain.
The spinal cord is the main transportation hub of the body's central nervous system, carrying signals from the brain to nerves throughout the body. Nerves coming from and leading to all parts of the body enter and exit the spinal cord along its entire length.
Thirty-one pairs of spinal nerves exit the spinal cord through openings between the vertebrae. The point at which a nerve exits the spinal cord is called a nerve root. The nerve root then branches out into many smaller peripheral nerves that control different parts of the body.
The spinal cord starts at the base of the brain, runs throughout the cervical and thoracic spine, and typically ends at the lower part of the thoracic spine.
The spinal cord does not run through the lumbar spine (lower back). After the spinal cord stops in the lower thoracic spine, the nerve roots from the lumbar and sacral levels come off the bottom of the cord like a "horse's tail" (named the cauda equina) and exit the spine.
Because the lumbar spine has no spinal cord and has a large amount of space for the nerve roots, even serious conditions—such as a large disc herniation—do not typically cause paraplegia (loss of motor function in the legs).
Damage to any part of the central nervous system or peripheral nerves can cause neuropathic pain.
The spinal cord can be divided into segments according to the nerve roots that branch off it. Nerves along the cord consists of:
8 cervical nerves
12 thoracic nerves
5 lumbar nerves
5 sacral nerves
1 coccygeal nerve
For most spinal segments, the nerve roots run through the bony canal, and at each level a pair of nerve roots exits from the spine.
Cervical spine nerve roots. In the neck, the nerve root is named for the lower segment that it runs between (e.g. C6 nerve root at C5-C6 segment).
Lumbar spine nerve roots. In the lower back, the nerve is named for the upper segment that it runs between (e.g. L4 nerve root at L4-L5 segment).
A nerve that exits the lower back has peripheral branches that extend all the way down to the toes. Peripheral nerves comprise the peripheral nervous system. The peripheral nerves include both motor nerves and sensory nerves:
Sensory nerves are nerves that receive sensory stimuli, telling us how something feels—whether it is hot, cold, or painful. These nerves are made up of nerve fibers, called sensory fibers (mechanoreceptor fibers sense body movement and pressure against the body, and nociceptor fibers sense tissue injury).
Motor nerves lead to the muscles and stimulate movement. They are made up of nerve fibers called motor fibers.
The nerve passing to the next level runs over a weak spot in the disc space, which is the reason discs tend to herniate right under the nerve root and can cause leg pain—often referred to as (lumbar radiculopathy or sciatica).
Cervical disc herniations (in the neck) tend to irritate the nerve exiting at a set level (e.g. C6 at C5-C6).
Lumbar disc herniations (in the low back) tend to irritate the nerve that lies across a particular level (e.g. L5 at L4-L5).
Thoracic disc herniations (in the upper back) are less common than in the neck or lower spine, but they do occur.
Sometimes, a herniated disc will cause only leg pain or arm pain and not lower back pain or neck pain and may initially be thought to be a problem with the patient's leg or arm.
Arm pain from a cervical disc herniation is usually accompanied by numbness/tingling and runs to the fingers.
Leg pain from a lumbar disc herniation will usually run below the knee, and possibly to the foot, and may be accompanied by numbness or other neurological symptoms
Leg pain can be intermittent or constant and can range from a dull ache to a searing, throbbing, or burning sensation. Numbness may be felt like a loss of sensation or a cold, icy feeling in one or more areas of the leg.
Leg pain may be the symptom of a variety of underlying causes or conditions related to the spine, and getting a correct diagnosis is essential to informing the most effective course of treatment.
Leg pain may be caused due to a problem in the lower back, the pelvis, or a problem that originates within the leg. Common causes of pain in one or both legs include:
Spinal nerve compression or irritation. Inflamed, irritated, or compressed nerve roots in the lumbar or sacral spine may cause radiculopathy or nerve pain, commonly called sciatica, in the leg and foot. Nerves may also be damaged along their path in the leg, causing peripheral neuropathy and leg pain.
Spinal cord compression. Narrowing of the spinal canal in the neck may apply pressure on the spinal cord, causing pain and numbness, typically in both legs.
Pelvic and hip problems. Joint problems in the pelvis and hip regions, such as sacroiliac joint dysfunction or hip osteoarthritis, may cause leg pain; an associated nerve irritation may cause numbness. Pelvic muscle spasm, such as in piriformis syndrome, may cause pain to travel down along the leg with associated numbness and/or weakness.
Infection. Bone and disc infection, such as osteomyelitis or spondylodiscitis are known to cause leg pain.
Cauda equina syndrome. Compression of the cauda equina (a group of spinal nerves that descend from the spinal cord in the lower back) may cause severe pain, numbness, and weakness in both legs.
Tumors and cysts. The presence of growths and masses in the lower back or pelvis may compress blood vessels and/or nerves and lead to leg pain and numbness.
A consultation with a spine care specialist can help to determine if your leg (or arm) pain is indicative of a spine injury, a nerve injury or both.