Stenosis means narrowing. The spinal canal is a space that runs the full length of the spine. It contains a tube filled with spinal fluid. The spinal cord extends from the brainstem to the lower end of the rib cage and floats in the spinal fluid within the spinal canal. The nerve roots leave the bottom of the spinal cord and extend down to the pelvis to provide movement and sensation in the legs and the bowel and bladder. This collection of nerve roots looks like a horses tail and is therefore called the cauda equina. The spinal canal is surrounded and protected by the spine. The spine consists of the bony vertebrae and discs in the front of the spinal canal. The back of the spinal canal is formed by the facet joints on either side, the lamina and the spinous processes which are the bumps that you feel if you run your finger down the back of your spine. There are ligaments between the spinous processes and lamina at the back of the spine. Spinal stenosis usually occurs due to a combination of degenerative changes that lead to a progressive narrowing of the spinal canal. The discs in the front of the spine have two components. The annulus is the outer part of the disc and is formed by layers of fibrous tissue like a tire. As we age the tissue in the annulus weakens resulting in bulging of the annulus backwards into the front of the spinal canal. The centre of the disc is called the nucleus, which has the consistency of crab meat. If there is a tear in the outer annulus of the disc then some of the nucleus material can pass through the annulus into the spinal canal. This is called a disc herniation. The facet joints are the small joints at the back of the spine that allow the spine to bend and twist. As we age these joints can develop osteoarthritis just like knees and hips. As a result, they become enlarged which encroaches on the back of the spinal canal on each side resulting in narrowing of the spinal canal. The most significant changes occur in the ligaments at the back of the spine between the spinous processes and lamina. Degeneration leads to thickening of the ligaments, which encroaches on the spinal canal from behind. This combination of changes leads to a progressive narrowing of the spinal canal called spinal stenosis which gradually puts pressure on the spinal cord and/or nerve roots resulting in the symptoms which can include leg pain, numbness, weakness, fatigue and bladder control problems.

Side view of the spine showing spinal stenosis between the 3rd and 4th (L3-4) and the 4th and 5th (L4-5) spinal vertebrae in the lower back in the image on the left. The image on the right shows a normal spine with no narrowing of the spinal canal.

In the lumbar spine, stenosis results in pressure on the nerve roots, which causes symptoms of pain, fatigue, weakness or numbness in the legs that is made worse with activity such as walking. With severe stenosis people can often walk less than a block before they have to stop and rest. Bending forward can often relieve the symptoms.

Cross sectional images of the spine show a normal spinal canal on the right which is the white area between the dist at the top and the arch of bone at the back of the spine. The image on the left depicts narrowing of the spinal canal, which is called spinal stenosis. The central white area, which contains the spinal cord or nerve roots is much smaller than in the image on the right.

As we age there are degenerative changes that occur in the spine that combine to result in narrowing of the spinal canal. This can result in pressure on the spinal cord or on the nerve roots of the cauda equina. This narrowing is called spinal stenosis. It is graded as mild, moderate and severe depending on the degree of narrowing. The symptoms that people experience depend on the degree of narrowing, in which location, and severity of the stenosis. In the cervical and thoracic spine, stenosis results in compression of the spinal cord, which can cause weakness or numbness in the arms and the legs, balance problems and sometimes urinary urgency. When you feel the urge to urinate, you need to go immediately, or you can lose control of your bladder. Compression of the spinal cord results in a myelopathy meaning that the spinal cord is not functioning properly because it is being compressed. In the lumbar spine, which is below the rib cage, spinal stenosis causes pressure on the nerve roots. This can lead to numbness or weakness in the legs. People often experience claudication, which means symptoms in their legs associated with activity such as walking. People can experience pain or a sense of fatigue in their legs when they walk. If they stop and rest the pain will go away and they can walk again until the symptoms recur. Bending forward or squatting down will often relieve the symptoms. When people go shopping, if they lean on a shopping cart they can walk further before they have to stop.

As the degree of stenosis gets worse the distance they can walk lessens considerably. People with severe spinal stenosis can usually walk less than a block before they need to stop and rest or bend forward to relieve the pain or fatigue sensation in their legs. In the most severe cases people can develop a condition called cauda equina syndrome where they can lose control of their bladder and bowel function due to weakness in their legs and numbness in their legs, genital area and buttocks. Unless the pinched nerves are dealt with quickly these symptoms can be permanent. It is therefore considered a medical emergency.

Treatment for spinal stenosis consists of surgery to relieve the pressure on the spinal cord or nerve roots. The most common operation is called a laminectomy, which is the removal of the spinous process, lamina and ligaments from behind the spinal canal to make more room for the nerve roots and spinal cord. Most people do not require a fusion unless they have instability in their spine. Removing the bone and relieving the pressure on the nerves usually results in relief from the symptoms. People often report that they feel taller because they can stand up straight without pain and they can walk again without getting the pain, fatigue or weakness in their legs. The most common place where people develop spinal stenosis is between the 4th and 5th vertebrae (L4-5) in the lower back. The operation involves removing the L4 and the L5 spinous process and lamina, and the ligaments between the 3rd and 4th, between the 4th and 5th, and between the 5th lumbar and 1st sacral vertebrae. This decompresses the spinal canal from L3 to S1. If the spinal stenosis is limited to one level, then just removing the ligaments and a small portion of the bone may be adequate. However stenosis is usually present at 2 or 3 levels to a variable degree. 

The images show that removal of the spinous process and lamina at the back of the spine enlarges the space for the nerve roots. The facet joints are not removed and the spine remains stable. The image on the left shows the spine from behind and the image on the right is a cross sectional picture.

The diagnosis of spinal stenosis can be made by taking a person’s history and performing an examination. Computed tomography (CT) scans and Magnetic Resonance Imaging (MRI) scans are the best studies to show the degree and location of the stenosis for planning treatment. Cortisone injections into the spinal canal called epidural blocks can sometimes relieve or improve the symptoms temporarily. However, it does not correct the structural problem and therefore will not relieve the symptoms forever. Surgery is the only way to relieve the pressure on the nerves and provide more permanent relief of the leg symptoms.

Spinal stenosis causes symptoms of pain, fatigue or weakness in the legs. It can also cause back pain that is made worse by standing or walking and relieved by sitting. Some people also experience their back and leg symptoms at night making it difficult to sleep.  Spinal stenosis is caused by degenerative changes in the spine.  It usually affects people over the age of 60 and is most common in people in their 70’s and 80’s. Spinal stenosis has an 80 to 90% success rate for relieving the leg symptoms and usually improves the back pain as well. The goal of surgery is to restore the person’s ability to walk without pain so that they can return to normal activities such as walking, hiking and golfing. Complications from surgery can include infection or nerve damage resulting in weakness or numbness that can be temporary or permanent. Complications occur in less than 5% of operations. It is important to talk to your healthcare provider to determine if you should have an MRI scan and whether you are a candidate for surgery.

Lumbar Spinal Stenosis