Lumbar Spinal Stenosis

Spinal stenosis that occurs in the lower back is referred to as lumbar spinal stenosis. This type of spinal stenosis is the most common because this area of the spine is very mobile and is the site of much of the wear and tear on the spinal discs and other tissues. The thoracic spine (the middle regions of the spine) is much less mobile and so experiences much less wear and tear, making thoracic spinal stenosis quite uncommon. Cervical spinal stenosis (i.e. spinal narrowing in the neck) is the second most common type of spinal stenosis diagnosis as this area of the body is also very mobile.

Spine Anatomy

Understanding spinal anatomy can help us appreciate how spinal stenosis is acquired. A closer look at the structures of the spine reveals that each region of the spine is made up of four basic elements:

    • Vertebrae
    • Intervertebral discs
Click to Enlarge
  • Spinal cord
  • Spinal nerves

Lumbar Spine Anatomy

The lumbar spine region contains five vertebrae, referred to as L1, L2, L3, L4, and L5. The L denotes Lumbar and the number denotes level or position in the spine.

Between the vertebra are the shock-absorbing intervertebral discs. These help to maintain the height of the vertebral space and cushion the jolts and bumps to the spine to prevent the bones grinding against each other. The separation of the vertebra allow for the safe passage of spinal nerves out of the spinal column.

Vertebrae (in the lumbar spine and in the thoracic and cervical spinal segments) comprise facet joints which link vertebrae together and enable spinal mobility and stability. Intervertebral discs are named by the vertebrae that they separate, meaning that a disc that sits between the L4 and L5 vertebrae is known as L4/L5 disc, a thoracic T1/T2 (T=Thoracic) disc would be located between T1 and T2, and so forth.

Finally, each level of the spine houses nerves which have a particular function for the body. The nerve map below delineates which nerves control which function. Knowing these can help isolate the site of spinal stenosis by tracing symptoms back to the compressed or compromised nerve.

Treating Lumbar Spinal Stenosis

Treatment for lumbar spinal stenosis depends largely on the severity of the narrowing in the lower back. Typically spinal stenosis progresses over a long period of time, meaning that it is usually treated conservatively with an understanding that therapy needs to address both the immediate health issues and the potential for the condition to progress. As such, lumbar spinal stenosis severity, the health of patient and their quality of life will be taken into account before determining the best type of treatment.

Please review spinal stenosis treatment for more information.

Animation depicting L5/S1 Disc Protrusion

This two minute animation gives an overview of the anatomy of the spine and portrays what a disc protrusion might look like as it contributes to lumbar spinal stenosis.

Spinal Nerve Map Table

The table below outlines spinal nerves with their associated function(s).

Segmental spinal Cord
level and Function
Level Function
Cl-C6 Neck flexors
Cl-T1 Neck extensors
C3, C4, C5 Supply diaphragm
C5, C6 Shoulder movement, raise arm (deltoid); flexion of elbow
(biceps); C6
externally rotates the arm (supinates)
C6, C7, C8 Extends elbow and wrist (triceps and wrist extensors);
pronates wrist
C7, C8, Tl Flexes wrist
C8, Tl Supply small muscles of the hand
Tl -T6 lntercostals and trunk above the waist
T7-Ll Abdominal muscles
Ll, L2, L3, L4 Thigh flexion
L2, L3, L4 Thigh adduction
L4, L5, S1 Thigh abduction
L5, S1 S2 Extension of leg at the hip (gluteus maximus)
L2, L3, L4 Extension of leg at the knee (quadriceps femoris)
L4, L5, S1, S2 Flexion of leg at the knee (hamstrings)
L4, L5, S1 Dorsiflexion of foot (tibialis anterior)
L4, L5, S1 Extension of toes
L5, S1, S2 Plantar flexion of foot
L5, S1, S2 Nexion of toes