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What Is Spinal Stenosis

What Is Spinal Stenosis?

 

Spinal stenosis refers to a narrowing of spaces within the spine. This narrowing sometimes results in pressure on the spinal cord and/or nerve roots. Spinal stenosis usually involves the narrowing of one or more of the following two areas of the spine: (1) the central spinal canal through which the spinal cord and nerve roots traverse, and/or (2) the openings between the vertebrae (bones of the spine) through which nerve roots traverse the spinal column to other parts of the body. The narrowing of critical spaces may involve one or more levels of the spine. Compression of the lower part of the spinal cord or on nerve roots branching out from the low back region may give rise to pain or numbness in the legs whereas pressure on the cervical (neck portion) of the spinal cord may produce similar symptoms in the shoulders, arms, hands and the legs.

 

Who Gets Spinal Stenosis?

Spinal stenosis is most common in people over 50 years of age. However, it may occur in younger people who are born with a narrowing of the spinal canal (congenital stenosis) or who suffer an injury to the spine.

 

Structures Involved in Spinal Stenosis

The most common cause of spinal stenosis is degeneration of one or more spinal segments. The degenerative changes often involve the intervertebral disc, spinal joints (facet joints), bone and the ligaments to varying degrees.

Causes of Spinal Stenosis

The normal central spinal canal provides adequate room for the spinal cord, the nerve roots, blood vessels and spinal fluid. Narrowing of the canal, which occurs in spinal stenosis, may be inherited or acquired. Some people have a developmentally (congenital) small spinal canal or may have a curvature of the spine (scoliosis) that alters the dimensions of the spinal canal and neuroforamen. In an inherited condition called achondroplasia, defective bone formation results in abnormally short and thickened pedicles (bony region of the spine) that reduce the diameter of (distance across) the central spinal canal.

 

Spinal stenosis usually occurs secondary to a chronic gradual degenerative process, which includes age related changes. Both structural and inflammatory changes occur. As part of the degenerative process spinal ligaments may thicken, calcify and buckle.  Marginal bony areas of the spine may also enlarge, and osteophytes (bone spurs) often develop. The intervertebral disc may bulge and/or herniate. This combined process contributes to the development of spinal stenosis.

When the health of one part of the spine (spinal motion segment) fails, it usually places increased physical stress upon other areas of the spine. For example, degeneration of an intervertebral disc eventually leads to a loss of vertical disc height contributing to increased physical stress upon spinal joints (facet joint) at the same spinal level thus promoting spinal joint arthritis with joint enlargement in susceptible individuals. Bulging or herniation of the intervertebral disc associated with degenerative changes may narrow the spinal canal and compress the spinal cord or nerve root. When a segment of the spine becomes too mobile, the membrane (joint capsule) surrounding the spinal joints may thicken in an effort to stabilize the segment, and bone spurs may occur. This decreases the space (neuroforamen) available for nerve roots leaving the spinal cord. Conversely, when a segment of the spine is surgically fused or becomes stiff it may lead to additional physical stresses upon adjacent spinal segments.

 

Two more common forms of arthritis, which afflict the spine and can cause spinal stenosis, are osteoarthritis and rheumatoid arthritis. Osteoarthritis remains the most common form of spinal arthritis. it occurs more frequently in middle-aged and older people. It is a chronic and degenerative process that typically involves multiple joints of the body, particularly larger weight bearing joints. The condition is characterized by a loss of normal cartilage integrity often accompanied by the overgrowth of bone, formation of bone spurs, and abnormal joint mobility. Degenerative changes affecting the vertebral body, spinal joints (facets) and the intervertebral disk at the same level is commonly referred to as spondylosis.

 

Another condition, which can lead to spinal stenosis, is spondylolithesis, a condition in which one vertebra slips forward with respect to the one below it. This may occur secondary to a degenerative condition. A traumatic injury to the region or may be acquired at birth (congenital). The vertebral malposition and associated disc changes can result in compromise of the adjacent spinal cord or nerve roots.

 

Rheumatoid arthritis usually affects people at an earlier age than osteoarthritis does and is associated with inflammation and enlargement of the soft tissues of the joints. Although not a common cause of spinal stenosis, damage to ligaments, bones, and joints that begins as synovitis (inflammation of the synovial membrane) has a severe and disrupting effect on joint function. The portions of the spine with the greatest mobility are often the areas most often afflicted in people with rheumatoid arthritis.

 

There are a number of conditions not related to arthritis, which can result in  acquired spinal stenosis. Non-arthritic causes include tumors of the spine referring to the development of abnormal growths of bone or soft tissue that may compromise the spinal canal or neuroforamen directly by growth into the regions. Abnormal tissue growth may lead to bone resorption (bone loss) or the displacement of bone either of which can cause collapse of the involved bone.

Trauma can result in spinal stenosis secondary to spinal dislocations or fractures, which encroach upon or penetrate the central spinal canal and/or neuroforamen. Enlarged and deformed bones occur with a chronic disorder called Paget’s, which can affect any bone in the body including the spine.  The disorder is characterized by excessive bone breakdown and development leading to a bony region with unusual areas of thick and fragile bone. The condition may be associated with bone pain, arthritis, bony deformities, and resultant fractures. Structural abnormalities of the involved vertebrae can cause narrowing of the spinal canal, producing a variety of neurological symptoms.

An uncommon cause of spinal stenosis is flourosis, which refers to an excessive level of fluoride in the body. This may occur secondary to chronic inhalation of industrial dusts or gases contaminated with fluorides, prolonged ingestion of water containing large amounts of fluorides, or accidental ingestion of fluoride-containing insecticides. The condition may lead to calcified spinal ligaments, softened bones and to degenerative conditions including spinal stenosis.

Symptoms of Spinal Stenosis

 

The central spinal canal and lateral neuroforamen can become narrowed without producing any symptoms. However, if the narrowing or spinal stenosis places pressure on the spinal cord or nerve roots, there may be gradual onset and progression of signs and symptoms. The initial presentation is often subtle an intermittent and can occur in the absence of back or neck pain. More common symptoms arising from spinal stenosis include extremity numbness, muscle weakness, muscle cramping, incoordination and clumsiness. Spinal stenosis with spinal cord compression may lead to difficulty with postural balance and altered gait due to extremity incoordination, weakness and muscle stiffness.

 

With lumbar (low back) stenosis lower extremity complaints are usually magnified with low back extension and temporarily improved with low back flexion.  Flexion or forward bending of the low back opens up the central spinal canal making it larger and more accommodating for the nerve roots.

 

Some individuals with severe spinal stenosis may experience abnormal bowel and bladder function along with extremity signs and symptoms.  For example, a cauda equina syndrome refers to partial or complete loss of control of the bowel or bladder and sometimes-sexual function secondary to compromise of a group of spinal nerve roots that descend from the lower part of the spinal cord and occupy the central spinal canal below the end of the spinal cord.

 

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