Causes of Cervical spinal stenosis

The bony spinal canal normally has more than enough room for the spinal cord. Typically, the canal is 17 to 18 millimeters around, slightly less than the size of a penny. Spinal stenosis occurs when the canal narrows to 13 millimeters or less. When the size drops to 10 millimeters, severe symptoms of myelopathy occur. Myelopathy is a term for any condition that affects the spinal cord. The symptoms of myelopathy result from pressure against the spinal cord and reduced blood supply in the spinal cord as a result of the pressure.

Spinal stenosis may develop for any number of reasons. Some of the more common causes of spinal stenosis include

• congenital stenosis
• degeneration
• spinal instability
• disc herniation
• constriction of the blood supply to the spinal cord

Congenital Stenosis

Some people are born with a spinal canal that is narrower than normal. This is called congenital stenosis. They may not feel problems early in life, but having a narrow canal to begin with places them at risk for stenosis. Even a minor neck injury can set them up to have pressure against the spinal cord. People born with a narrow spinal canal often have problems later in life, because the canal tends to become narrower due to the affects of aging. These degenerative changes often involve the formation of bone spurs (small bony projections) that point into the spinal canal and put pressure on the spinal cord.

Degeneration

Degeneration is the most common cause of spinal stenosis. Wear and tear on the spine from aging and from repeated stress and strain can cause many problems in the cervical spine. The intervertebral disc can begin to collapse, shrinking the space between vertebrae. Bone spurs may form that protrude into the spinal canal and reduce the space available to the spinal cord. The ligaments that hold the vertebrae together may become thicker and can also push into the spinal canal. All of these conditions narrow the spinal canal.

Spinal instability

Spinal instability can cause spinal stenosis. Spinal instability means there is extra movement among the bones of the spine. Instability in the cervical spine can happen if the supporting ligaments have been stretched or torn from a severe injury to the head or neck. People with diseases that loosen their connective tissues may also have spinal instability. For example, rheumatoid arthritis can cause the ligaments in the upper bones of the neck to loosen, allowing the topmost neck bones to shift and close off the spinal canal. Whatever the cause, extra movement in the bones of the spine can lead to spinal stenosis and myelopathy.

Disc herniation

Spinal stenosis can occur when a disc in the neck herniates. Normally, the shock-absorbing disc is able to handle the downward pressure of gravity and the strain from daily activities. However, if the pressure on the disc is too strong, such as from a blow to the head or neck, the nucleus inside the disc may rupture through the outer annulus and squeeze out of the disc. This is called a disc herniation. If an intervertebral disc herniates straight backward, it can press against the spinal cord and cause symptoms of spinal stenosis.

Constriction of the blood supply to the spinal cord

The changes that happen with degeneration and disc herniation can choke off the blood supply that goes to the spinal cord. The sections of the spinal cord that don't get blood have less oxygen and don't function normally, leading to symptoms of myelopathy.