Anatomy of Spinal Stenosis

Spinal Canal, Vertebrae, Facet Joints, and Foramen: How They're Affected by Spinal Stenosis

Spinal stenosis usually affects the cervical (neck) and lumbar (low back) spinal regions. Occurrence in the thoracic (upper/mid back) spine is rare. The purpose of this article is to help you understand the basic anatomy associated with spinal stenosis, a condition known to cause narrowing of the spinal canal and/or nerve passageways that leads to nerve and/or spinal cord compression.
spinal column structures labeledDifferent anatomical structures of the cervical, thoracic and lumbar spine.

Cervical, Thoracic and Lumbar Spine Anatomy Overview

Three primary components of the spine are the bones (and facet joints), neural structures (spinal cord, nerves or nerve roots), and ligaments.

  • The spinal canal is a ring of bones that houses and protects the spinal cord and spinal nerves. Much like a house, the canal has a floor (vertebral bodies), walls (lamina) and a roof (spinous process).
  • The spinal cord is a conduit for communication between the brain and body. The spinal cord ends near the first lumbar vertebral body and becomes the cauda equina, a series of nerves hanging off the end of the spinal cord like a horse’s tail.
  • The nerves that branch off the spinal cord (nerve roots) exit the spinal canal in pairs through naturally created passageways called neural foramen. These nerves branch out further to form the peripheral (outer) nervous system.
  • Nerves have both sensory (ability to feel, sense) and motor (enable movement) functions.
  • Ligaments are strong connective tissues that help connect the adjacent bones, stabilize the spine and restrict movement outside of the normal range.

spinal cord, nerves and ligaments, axial viewThe spinal cord, nerves, and ligaments are illustrated and named.

Cervical Spine Anatomy

The cervical spine supports the weight of the head and enables a wide range of movement. There are 7 bones in the cervical spine abbreviated C1 through C7 top to bottom. Eight pairs of nerves, similarly abbreviated C1 through C8, branch off the spinal cord and exit the neck’s spinal column through the neural foramen (sometimes called neuroforamen).

When spinal stenosis develops it can compress the spinal cord and/or nerve roots at one or more levels. This compression may cause symptoms in the neck as well as areas of the body served by the compressed nerve structures.

Below are areas of the body served by the most commonly affected cervical spinal nerves:

  • C5: Deltoids
  • C6: Biceps
  • C7: Triceps
  • C8: Small muscles of the hands

Spinal stenosis can affect the neural foramen (called foraminal or lateral stenosis). Causes include degenerative conditions (eg, herniated disc, osteophytes, spondylosis), or injury leading to compression of the spine’s neural structures. When these nerves are compressed, cervical radiculopathy may develop—pain, weakness, numbness, and tingling that can radiate from the neck down through the shoulders and down into the arms and/or hands.
spinal nerve compression in the cervical spineExamples of spinal nerve compression in the cervical spine.Additionally, a condition that causes significant nerve-related dysfunction throughout the body is compression of the spinal cord, called cervical myelopathy. Patients with cervical myelopathy can experience weakness of the arms and legs, difficulty with fine motor tasks, such as buttoning shirts or using keys. In severe cases, paralysis or incontinence can develop.

Lumbar Spine Anatomy

The lumbar spine supports the body’s weight and distributes forces. There are 5 vertebral bodies in the low back abbreviated L1 through L5 top to bottom and 5 pairs of lumbar spinal nerves. The spinal cord ends in the lumbar spine, usually between L1 and L2. At the base of the lumbar spine sits the sacrum, often referred to as S1. The sacrum is the foundation of the spine and is joined to the pelvis.

The lumbar nerves enable feeling (sensations, such as pain) and power the lower body’s musculature and movement (eg, flexion, extension) of the hips, knees, legs, ankles and feet.

Like its cervical counterpart, lumbar spinal stenosis is often caused by aging, wear and tear that affects the intervertebral discs and facet joints. Degenerative disc disease is an age-related disorder detrimental to the flexibility, strength, size and shape of one or more discs. Discs may flatten, bulge or herniate. These changes can trap, impinge and compress nerves leading to inflammation and pain.

Degenerative arthritis (eg, spondylosis) in the low back may trigger the formation of bone spurs and ligament thickening that can narrow the spinal canal and neuroforamen.
Overhead view of a lumbar vertebral segment Overhead view of a lumbar vertebral segment illustrates types of spinal stenosis (ie, central canal, lateral recess, and foraminal stenosis).

Why Leaning Forward May Ease Low Back Spinal Stenosis Symptoms

The ligamentum flavum is a dynamic structure, which means that it adapts its shape as the body is at rest or moves. When sitting down and leaning forward, the ligamentum flavum stretches and allows space to open up between structures relieving some compression on nerves. However, when standing up and/or leaning back, the ligamentum flavum shortens and thickens; that means there's less room for the spinal nerves.

This dynamic capability helps explain why people with low back spinal stenosis find sitting down feels better than standing or walking. It also explains why people with lumbar spinal stenosis tend to stand with the body bent forward. Patients with spinal stenosis often like to lean on the grocery cart at the store. We call this the “shopping cart” sign!

Knowing Your Spinal Anatomy Leads to Better Understanding of Spinal Stenosis

Understanding the spine’s anatomy as it relates to spinal stenosis is the first step in truly knowing your condition. When you have a strong grasp on your diagnosis, you can feel more confident in discussing care plans with your doctor. That confidence can translate to better adherence and response to your treatment, which bodes well for your long-term outlook.

Updated on: 03/08/18
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Pain, numbness, and tingling are common spinal stenosis symptoms that can affect the neck and low back and radiate into the arms or legs.
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