Cauda equina
horse's tail · horse's-tail nerves
The cauda equina is a bundle of nerve strands that extends downward from where the spinal cord ends in the upper part of the lower back. It gets its name from its resemblance to a horse's tail. Nerves traveling to the legs, pelvis, bladder, and bowel pass through this area, so it often comes up in discussions of lumbar disc herniation and the spinal canal. It is useful to know about because compression of the bundle as a whole can lead to an emergency.
Where is it, and what does it do?
The spinal cord is a thick column of nerve tissue that extends from the brain and runs down a passage inside the vertebrae called the spinal canal. However, it does not extend the full length of the spine. In adults, the spinal cord usually tapers to an end at the level of the first and second lumbar vertebrae. This is because, although the spinal cord reaches the end of the spine during fetal development, the spine grows longer than the spinal cord as the body grows.
Even below the end of the spinal cord, nerves are still needed to reach the legs and pelvis. These nerve roots branch off from the end of the spinal cord and descend a long way; this bundle is the cauda equina. It contains multiple pairs of nerve roots that emerge at the lower lumbar, sacral, and coccygeal levels. A thin cord that anchors the end of the spinal cord toward the coccyx—the filum terminale—runs through its center. The way the individual strands spread out and descend gives it the name “horse's tail.”
The nerves in the cauda equina have several roles.
- Leg movement and sensation — They allow the thighs, calves, and feet to generate force and perceive sensation.
- Bladder and anal control — Nerves responsible for holding and passing urine and controlling bowel movements pass through this area.
- Sensation around the pelvis — The bundle also includes sensory nerves serving the groin and inner buttocks, as well as those involved in sexual function.
The individual nerve strands of the cauda equina float in a space filled with cerebrospinal fluid. When a needle enters, the nerves can move aside, often avoiding contact with it. This is why a lumbar puncture to collect cerebrospinal fluid is performed below the level where the spinal cord ends.
How might it affect everyday life?
You will rarely feel the cauda equina itself. However, narrowing of the spinal canal in the lower back or a protruding disc in lumbar disc herniation can compress these nerve roots. If a nerve root on just one side is compressed, you may experience pain or numbness and tingling extending from the buttock into the leg, or weakness in the toes. These situations are discussed in more detail in lumbar radiculopathy.
If you notice a pattern in which leaning backward while standing brings on numbness and tingling in your legs, while sitting or bending forward brings relief, it may be related to narrowing of the spinal canal, so it is worth having it checked at a hospital.
How does Integrative Manual Therapy view it?
Integrative Manual Therapy (IMT) views the spinal cord and the nerve structures extending below it as moving together with the surrounding tissues. A condition in which the end of the spinal cord is pulled downward is covered separately under tethered cord syndrome. The approach is based on the view that nerves need to glide well relative to their surroundings for comfortable movement. Methods for examining nerve movement are also covered in neurodynamics and neural mobilization.
Ways to look after it
There is no way to directly release the cauda equina, but everyday habits that maintain adequate space along the nerves' pathways can help.
- Avoid sitting for long periods. Get up and walk at least once an hour to vary the spaces between the lumbar vertebrae.
- Bend your knees when lifting something heavy. Holding the object close to your body reduces pressure on the lumbar discs.
- Strengthen your abdominal and buttock muscles. When the muscles support the spine well, they reduce the load on the lumbar vertebrae.
- Walk regularly. Even if your lower back is uncomfortable, walking on level ground is generally a low-strain form of exercise.
When to get checked
If any of the following apply, do not delay even a day—get checked in an emergency department. It could be an emergency condition called cauda equina syndrome.
- Sensation is reduced or absent in the areas that touch a saddle when you sit on it: the groin, around the anus, and the inner buttocks.
- You cannot pass urine, or conversely, urine leaks without your awareness.
- You have difficulty controlling bowel movements.
- You have weakness in both legs, or numbness and tingling in both legs rapidly worsen.
These may be signs that the cauda equina is being compressed as a whole, and a shorter duration of compression is more favorable for recovery. Do not try to resolve this with stretching or hands-on treatment—hospital care comes first.