Spinal Stenosis
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Spinal stenosis is a narrowing of spaces in the spine (backbone) that results in
pressure on the spinal cord and/or nerve roots. This disorder usually involves
the narrowing of one or more of three areas of the spine: (1) the canal in the
center of the column of bones (vertebral or spinal column) through which the
spinal cord and nerve roots run, (2) the canals at the base or roots of nerves
branching out from the spinal cord, or (3) the openings between vertebrae
(bones of the spine) through which nerves leave the spine and go to other parts
of the body. The narrowing may involve a small or large area of the spine.
Pressure on the lower part of the spinal cord or on nerve roots branching out
from that area may give rise to pain or numbness in the legs. Pressure on the
upper part of the spinal cord (that is, the neck area) may produce similar
symptoms in the shoulders, or even the legs.
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This disorder 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 or
who suffer an injury to the spine.
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The spine is a column of 26 bones that extend in a line from the base of the
skull to the pelvis (see fig. 1 on page 3). Twenty-four of the bones are called
vertebrae. The bones of the spine include 7 cervical vertebrae in the neck;
12 thoracic vertebrae at the back wall of the chest; 5 lumbar vertebrae at the
inward curve (small) of the lower back; the sacrum, composed of 5 fused vertebrae
between the hip bones; and the coccyx, composed of 3 to 5 fused bones at the
lower tip of the vertebral column. The vertebrae link to each other and are
cushioned by shock-absorbing disks that lie between them.
The vertebral column provides the main support for the upper body, allowing
humans to stand upright or bend and twist, and it protects the spinal cord from
injury. Following are structures of the spine most involved in spinal stenosis.
- Intervertebral disks—pads of cartilage between vertebrae
that act as shock absorbers.
- Facet joints—joints located on both sides and on the
top and bottom of each vertebra. They connect the vertebrae to each other
and permit back motion.
- Intervertebral foramen (also called neural foramen)—an
opening between vertebrae through which nerves leave the spine and extend
to other parts of the body.
- Lamina—part of the vertebra at the upper portion of
the vertebral arch that forms the roof of the canal through which the spinal
cord and nerve roots pass.
- Ligaments—elastic bands of tissue that support the spine
by preventing the vertebrae from slipping out of line as the spine moves.
A large ligament often involved in spinal stenosis is the ligamentum flavum,
which runs as a continuous band from lamina to lamina in the spine.
- Pedicles—narrow stem-like structures on the vertebrae
that form the walls of the bottom part of the vertebral arch.
- Spinal cord/nerve roots—a major part of the central
nervous system that extends from the base of the brain down to the lower
back and that is encased by the vertebral column. It consists of nerve cells
and bundles of nerves. The cord connects the brain to all parts of the body
via 31 pairs of nerves that branch out from the cord and leave the spine
between vertebrae (see fig. 2 on page 4).
- Synovium—a thin membrane that produces fluid to lubricate
the facet joints, allowing them to move easily.
- Vertebral arch—a circle of bone around the canal through
which the spinal cord passes. It is composed of a floor at the back of the
vertebra, walls (the pedicles), and a ceiling where two laminae join.
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The normal vertebral canal (see fig. 3 on page 5) provides adequate room for
the spinal cord. Narrowing of the canal, which occurs in spinal stenosis, may
be inherited or acquired. Some people inherit a small spinal canal (see fig.
4 on page 5) or have a curvature of the spine (scoliosis) that produces pressure
on nerves and soft tissue and compresses or stretches ligaments. In an inherited
condition called achondroplasia, defective bone formation results in abnormally
short and thickened pedicles that reduce the diameter (distance across) of the
spinal canal.
Acquired conditions that can cause spinal stenosis are listed in the box below
and explained in more detail in the text that follows.
Spinal stenosis most
often results from a gradual, degenerative aging process. Either structural
changes or inflammation can begin the process. As people age, the ligaments
of the spine may thicken and calcify (harden from deposits of calcium salts).
Bones and joints may also enlarge, and osteophytes (bone spurs) may form. When
the health of one part of the spine fails, it usually places increased stress
on other parts of the spine. For example, a degenerative condition affecting
the facet joints may eventually cause secondary changes, such as a herniated
(bulging) disk that places pressure on the spinal cord or nerve root (see fig.
5 on page 5). When a segment of the spine becomes too mobile, the capsules (enclosing
membranes) of the facet joints thicken in an effort to stabilize the segment,
and bone spurs may occur. This decreases the space (neural foramen) available
for nerve roots leaving the spinal cord.
Aging with secondary changes is the most common cause of spinal stenosis. Two
forms of arthritis that may affect the spine are osteoarthritis and rheumatoid
arthritis.1 Osteoarthritis is the most common form of arthritis and is more
likely to occur in middle-aged and older people. It is a chronic, degenerative
process that may involve multiple joints of the body. It wears away the surface
cartilage layer of joints, and is often accompanied by overgrowth of bone, formation
of bone spurs, and impaired function. If the degenerative change affects the
facet joint(s) and the disk, the condition is sometimes referred to as spondylosis.
This condition may be accompanied by disk degeneration, and an enlargement or
overgrowth of bone that narrows the central and root canals.
Spondylolysthesis, a condition in which one vertebra slips forward on another,
may result from a degenerative condition or an accident, or may be acquired
at birth. Poor alignment of the spinal column when a vertebra slips forward
onto the one below it can place pressure on the spinal cord or nerve roots at
that place.
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 vertebral column with the greatest mobility (for example,
the neck area) are often the ones most affected in people with rheumatoid arthritis.
The following conditions that are not related to arthritis or degenerative disease are causes
of acquired spinal stenosis:
- Tumors of the spine are abnormal growths of soft tissue that may affect
the spinal canal directly by inflammation or by growth of tissue into the
canal. Tissue growth may lead to bone resorption (bone loss due to overactivity
of certain bone cells) or displacement of bone and the eventual collapse
of the supporting framework of the vertebral column.
- Trauma (accidents) may either dislocate the spine and the spinal canal
or cause burst fractures that produce fragments of bone that penetrate the
canal.
- Although surgery that involves fusion (union) of vertebrae may be skillfully
performed, tissue swelling after surgery may place pressure on the spinal
cord.
- Paget’s disease of bone is a chronic (long-term) disorder that typically
results in enlarged and deformed bones. Excessive bone breakdown and formation
cause thick and fragile bone. As a result, bone pain, arthritis, noticeable
deformities, and fractures can occur. The disease can affect any bone of
the body, but is often found in the spine. The blood supply that feeds healthy
nerve tissue may be diverted to the area of involved bone. Also, structural
deformities of the involved vertebrae can cause narrowing of the spinal
canal, producing a variety of neurological symptoms.
- Fluorosis is an excessive level of fluoride in the body. It may result
from 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 or softened bones and to degenerative conditions
like spinal stenosis.
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Spaces within the spine can narrow without producing any symptoms. However,
if narrowing places pressure on the spinal cord or nerve roots, there may be
a slow onset and progression of symptoms. The back itself may or may not hurt.
More often, people experience numbness, weakness, cramping, or general pain
in the legs that occurs during flexing the lower back while sitting. (The flex
position “opens up” the spinal column, enlarging the spaces between vertebrae
at the back of the spine.) If a disk between vertebrae is compressed, people
may feel pain radiating down the leg (sciatica).
People with more severe stenosis may experience abnormal bowel and bladder
function and foot disorders. For example, cauda equina syndrome is a partial
or complete loss of control of the bowel or bladder and sometimes sexual function;
it is due to compression of the collection of spinal roots that descend from
the lower part of the spinal cord and occupy the vertebral canal below the cord.
In very rare instances, compression above the area where the lumbar vertebrae
and sacrum meet results in partial or complete paralysis of the legs.
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The doctor may use a variety of approaches to diagnose spinal stenosis and rule out other
conditions.
- Medical history—the patient tells the doctor details about symptoms and
about any injury, condition, or general health problem that might be causing
the symptoms.
- Physical examination—the doctor (1) examines the patient to determine
the extent of limitation of movement; (2) checks for pain or symptoms when
the patient hyperextends the spine (bends backwards); and ( 3) looks for
the loss of extremity reflexes, which may be related to numbness or weakness
in the arms or legs.
- X ray—an x-ray beam is passed through the back to produce a twodimensional
picture. An x ray may be done before other tests to look for signs of an
injury, tumor, or inherited abnormality. This test can show the structure
of the vertebrae and the outlines of joints, and can detect calcification.
- MRI (magnetic resonance imaging)—energy from a powerful magnet (rather
than x rays) produces signals that are detected by a scanner and analyzed
by computer. This produces a series of cross-sectional images (“slices”)
and/or a three-dimensional view of parts of the back. An MRI is particularly
sensitive for detecting damage or disease of soft tissues, such as the disks
between vertebrae or ligaments. It shows the spinal cord, nerve roots, and
surrounding spaces, as well as enlargement, degeneration, or tumors.
- Computerized axial tomography (CAT)—X rays are passed through the back
at different angles, detected by a scanner, and analyzed by a computer.
This produces a series of cross-sectional images and/or three-dimensional
views of the parts of the back. The scan shows the shape and size of the
spinal canal, its contents, and structures surrounding it.
- Myelogram—a liquid dye that x rays cannot penetrate is injected into
the spinal column. The dye circulates around the spinal cord and spinal
nerves, which appear as white objects against bone on an x-ray film. A myelogram
can show pressure on the spinal cord or nerves from herniated disks, bone
spurs, or tumors.
- Bone scan—an injected radioactive material attaches itself to bone, especially
in areas where bone is actively breaking down or being formed. The test
can detect fractures, tumors, infections, and arthritis, but may not tell
one disorder from another. Therefore, a bone scan is usually performed along
with other tests.
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Nonsurgical treatment of spinal stenosis may be provided by internists or general practitioners.
The disorder is also treated by specialists such as rheumatologists, who treat arthritis and
related disorders; and neurologists, who treat nerve diseases. Orthopaedic surgeons and
neurosurgeons also provide nonsurgical treatment and perform spinal surgery if it is required.
Allied health professionals such as physical therapists may also help treat patients.
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In the absence of severe or progressive nerve involvement, a doctor may prescribe one or more
of the following conservative treatments:
- Nonsteroidal anti-inflammatory drugs, such as aspirin, naproxen (Naprosyn)2
, ibuprofen (Motrin, Nuprin, Advil), or indomethacin (Indocin), to reduce
inflammation and relieve pain.
- Analgesics, such as acetaminophen (Tylenol), to relieve pain.
- Corticosteroid injections into the outermost of the membranes covering
the spinal cord and nerve roots to reduce inflammation and treat acute pain
that radiates to the hips or down a leg.
- Restricted activity (varies depending on extent of nerve involvement).
- Physical therapy and/or prescribed exercises to maintain motion of the
spine and build endurance, which help stabilize the spine.
- A lumbar brace or corset to provide some support and help the patient
regain mobility. This approach is sometimes used for patients with weak
abdominal muscles or older patients with degeneration at several levels
of the spine.
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In many cases, the conditions causing spinal stenosis cannot be permanently
altered by nonsurgical treatment, even though these measures may relieve pain
for a time. To determine the extent to which nonsurgical treatment will help,
a doctor seldom recommends surgery during the first 3 months of treatment. However,
surgery might be considered within the 3-month period if a patient experiences
numbness or weakness that interferes with walking, impaired bowel or bladder
function, or other neurological involvement.
The purpose of surgery is to relieve pressure on the spinal cord or nerves
and restore and maintain alignment and strength of the spine. This can be done
by removing, trimming, or adjusting diseased parts that are causing the pressure
or loss of alignment. The most common surgery is called decompressive laminectomy:
removal of the lamina (roof) of one or more vertebrae to create more space for
the nerves. A surgeon may perform a laminectomy with or without fusing vertebrae
or removing part of a disk. Various devices may be used to enhance fusion and
strengthen unstable segments of the spine following decompression surgery.
Patients with spinal stenosis caused by spinal trauma or achondroplasia may
need surgery at a young age. When surgery is required in patients with achondroplasia,
laminectomy (removal of the roof) without fusion is usually sufficient.
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All surgery, particularly that involving general anesthesia and older patients, carries risks.
The most common complications of surgery for spinal stenosis are a tear in the membrane
covering the spinal cord at the site of the operation, infection, or a blood clot that forms
in the veins. These conditions can be treated but may prolong recovery.
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Removal of the obstruction that has caused the symptoms usually gives patients some relief;
most patients have less leg pain and are able to walk better following surgery. However, if
nerves were badly damaged prior to surgery, there may be some remaining pain or numbness
or no improvement. Also, the degenerative process will likely continue, and pain or limitation
of activity may reappear 5 or more years after surgery.
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The National Institute of Arthritis and Musculoskeletal and Skin Diseases (NIAMS)
is supporting several research projects on spinal stenosis. For example, at
the Multipurpose Arthritis and Musculoskeletal Disease Center at the Hospital
for Special Surgery in New York City, doctors are comparing the effectiveness
of injecting a steroid (cortisone-like) medicine with that of injecting an analgesic
medicine into the epidura (outermost membrane covering the spinal cord) for
relief of pain and disability due to spinal stenosis. In another NIAMSfunded
study involving 11 different medical centers, researchers are comparing surgical
vs. nonsurgical treatment of spinal stenosis and two other conditions that cause
back pain.
Other researchers are exploring why spinal cord changes lead to a decreased
pain threshold or an increased sensitivity to pain, and how fractures of the
spine and their repair affect the spinal canal and intervertebral foramen.
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Arthritis Foundation
National Institute of Arthritis and Musculoskeletal
and Skin Diseases Information Clearinghouse
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Ankylosing Spondylitis
