The spinal canal is the space behind the vertebral bodies, formed by the overlapping neural arches of each vertebra. This tunnel serves as protection for the spinal cord and spinal nerves that travel through it.
If there is a pre-existing and acquired tightness within the canal, these nerve tissues can become compressed and injured. This tightness is called spinal canal stenosis.
Symptoms of Spinal Canal Stenosis
Spinal canal stenosis pain feels like:
- An ache in the back
- Sharp catches
- One- or two-sided sciatica
- and feet.
- Numbness, tingling, cramping, or weakness in the legs
- Limited tolerance of standing and walking
- Relative relief with sitting
- If severe — cauda equina syndrome
- Loss of control of bladder or bowel
- Urinary retention
- Severe Constipation
- Soiling self
- Loss of sexual ability
- In men
- Erectile dysfunction, especially of sudden onset
- Men and women
- Inability to orgasm
- Altered genital sensation
- In men
Spinal canal stenosis can also be symptom-free.
Causes of Spinal Canal Stenosis
There are three main categories of spinal canal stenosis.
The first category is primary. Primary stenosis is spinal canal stenosis that is:
- Congenital — present at birth
- Developmental — emerging in early life after birth from abnormal growth
The second category is secondary. Secondary stenosis occurs in a developmentally normal spine that has developed an acquired condition:
- Degenerative (“spondylotic change”)
- Disc height loss
- Bone spur growth (osteophytes)
- Facet bone overgrowth
- Ligamentum flavum thickening
- Degenerative spondylolisthesis
- Vertebral body fractures
- Physical trauma
- Fragility fracture in osteoporosis
The third category is a combination of the other two categories, termed a combined stenosis. In a combined stenosis there is a congenital or developmental problem that makes the spinal canal smaller than normal but not so small as to cause symptoms. Due to the pre-existing tightness, even a mild secondary problem, such as a modestly sized disc bulge, can cause out-sized symptoms.
There just wasn’t much room to begin…
Most cases of spinal canal stenosis arise from secondary or mixed causes.
How Large Should the Spinal Canal Be?
In an adult, the front-to-back (anteroposterior) length should be 15 to 25 millimeters. The stenotic anteroposterior length is 5 to 10 millimeters.
The lateral recess at the sides of the central canal should be 3 to 5 millimeters wide in a normal spine and is reduced to 1 to 2 millimeters in a stenotic spine.
Here is this same information in a table:
How is lumbar spinal stenosis diagnosed?
Diagnosis of spinal canal stenosis depends upon:
- Clinical assessment
- Medical interview
- Physical examination
- MRI of the lumbar spine
The clinical assessment determines whether your symptoms are consistent with a spinal canal stenosis.
A lumbar spinal stenosis diagnosis depends upon the presence of MRI findings. This type of problem is virtually always observable on the MRI. Point is, if there is no lumbar spinal stenosis on your MRI, then you don’t have this diagnosis.
How is lumbar spinal stenosis treated?
- Postural correction: The typical posture that is relieving for most cases of spinal stenosis involves a mild amount of flexion. The reason is flexion postures increase the amount of space in the spinal central canal and neural foraminal. This phenomenon explains why you might feel good when you sit in a chair with “bad” posture or feel comfortable pushing a grocery cart around. Standing with military posture causes your spine to arch into extension, which compresses your nerves.
- Movement quality: Learning how to move stresses to your hips (rather than the spine) will take load off your back.
- Exercises: The focus of rehabilitative exercise should include movement quality and lumbar stabilization. In select cases, nerve exercises—known as nerve flossing—may help reduce sciatica symptoms.
- Surgery: You need immediate medical attention if you have symptoms of cauda equina syndrome. This medical condition, involving dangerous compression of the spinal nerves, can cause lifelong loss of bladder, bowel, or sexual function. Timely decompression surgery, ideally within 24 to 48-hours of these red flag symptoms, provides the best chance of a positive outcome.
Surgery may be indicated in some cases of spinal canal stenosis without cauda equina syndrome. A positive surgical outcome is more likely if you have: (Binder)
- severe compression of the spinal nerves within the spinal canal
- Severe leg symptoms
- Moderate or no significant weakness
- Little or no back pain
Surgery is less likely to be helpful or even contraindicated in the following circumstances:
- Mild amount of compression around the thecal sac without compression of the spinal nerves
- Leg symptoms are vague and inconstant
- Main symptom is neurogenic claudication—pain, tingling, cramping, and weakness in legs—and you can walk a quarter mile (400 meters) or more
- Nerve symptoms don’t correspond to the level of nerve-root compression seen on the MRI.
McGill, Stuart. Low back disorders: evidence-based prevention and rehabilitation. Human Kinetics, 2015.
Jim, Lysander. Specific Spine: A Doctor’s Guide to a Healthy Back. M.D. Muse Media, 2023.
Binder, Devin, K, et al. “Lumbar Spinal Stenosis.” Seminars in Neurology, 2002.
Postacchini, Franco. “Management of lumbar spinal stenosis.” The Journal of Bone and Joint Surgery. British volume 78.1 (1996): 154-164.