What Causes Spinal Stenosis?
What Causes Spinal Stenosis? The spinal canal is the opening in the vertebrae that facilitated the passage of the spinal cord. The opening through which the spinal cord passes is made up of the body, pedicles, and laminae of the vertebrae. The bone of these individual segments that make up the vertebral foramen (through which the spinal cord passes) may begin to thicken, narrowing the size of the opening. This narrowing this opening may begin to squeeze the spinal nerves and disrupt functioning. This thickening of the bone and constriction of the spinal nerves may lead to pain and disability, and possibly paralysis.
So far we have discussed what happens to the spinal canal when the bony segments that make up the vertebral arch thicken. But what causes the bone to thicken? That is the subject of this article.
Spinal stenosis has been known to affect adults of all ages, but it is much more prevalent after the 5th decade. Physical changes related to this condition begin after about the fifth decade, but patients begin experiencing symptoms around the age of 60. Many people with spinal stenosis don't experience any symptoms at all.
The two most common types of spinal stenosis include cervical spinal stenosis and lumbar spinal stenosis. Patients with lumbar spinal stenosis present in doctor's offices with symptoms such as leg pain and difficulty walking. Lumbar spinal stenosis may cause sciatica if it affects the nerves that give rise to the sciatic nerve (spinal nerves spinal nerves L4 through S3).
The bony elements of the spine and its vertebrae. The main building block of the spine that takes on the most weight and downward forces includes the vertebral body. This vertebral body is block shaped, and each vertebral body is separated from the one above and below it by the intervertebral discs. From the body, a ring of bone arches towards backwards and is known as the vertebral arch. The first two portions of the arch, leading away from the vertebral body, is known as the pedicles. The last two sections that complete the arch is known as the laminae. The opening within the arch is known as the vertebral foramen, and it is though this cavity that the spinal cord travels. Any pathology that thickens the bone will decrease the size of the vertebral foramen and cause spinal stenosis.
From this vertebral arch, two bony processes project upwards to connect to the vertebra above it, and two bony processes project downwards to connect to the vertebra below it. The processes that project upwards are known as the superior articular processes. The processes that project downwards are known as the inferior articular processes. The structure that connects the processes and holds them together are known as the facet joints.
The physical health or lack thereof of these facet joints, and of the processes themselves, may also affect the functioning of the spinal nerves. Between vertebral bodies and the locations where the processes meet are openings in the spine for the spinal nerves to exit. These openings are known as the intervertebral foramen. Inflammation of the facet joints or a thickening of the superior and inferior articular processes may begin to close the size of these openings and also contribute to the symptoms of spinal stenosis.
What are the major types of spinal stenosis? The three main types of spinal stenosis are foraminal stenosis, central stenosis, and lateral stenosis. These labels are associated with the parts of the vertebra that have undergone degenerative physical changes.
Foraminal stenosis: Bone spurs, also known as osteophytes, may develop due to arthritic changes in the joints such as the spinal discs (intervertebral foramen). When the discs fade in size, they may cause the vertebrae to contact one another. This contact between the bones may lead to the development of bone spurs. When bone spurs are oriented towards the lateral foramen, the cause foraminal stenosis.
Central stenosis: When the thickening of the bone that makes up the bony arch thickens, it may cause a condition called central spinal stenosis. When this central stenosis occurs around the level L1-L3 of the spine, it may cause a condition known as cauda equine syndrome.
Lateral stenosis may occur due to a herniated disc, bulging disc, or bone spur that affects the spinal nerve beyond the foramen.