What Is Spinal Stenosis?
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.
Who Gets Spinal Stenosis?
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.
What Structures of the Spine Are
Involved?
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). 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).
-
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.
What Causes Spinal Stenosis?
The normal vertebral canal (see
fig. 3) 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) 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 of (distance across) the spinal canal.
Acquired conditions that can cause spinal stenosis are
explained in more detail in the sections that follow.
Degenerative (Aging) Conditions, Including
Osteoarthritis
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). 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.
¹The National Institute of Arthritis
and Musculoskeletal and Skin Diseases Information Clearinghouse has
separate information packages on osteoarthritis and rheumatoid
arthritis. Single copies are free.
Rheumatoid Arthritis
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.
Nonarthritic Acquired Spinal Stenosis
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.
What Are the Symptoms of Spinal
Stenosis?
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.
How Is Spinal Stenosis
Diagnosed?
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 two-dimensional 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.
Who Treats Spinal Stenosis?
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.
What Are Some Nonsurgical
Treatments for Spinal Stenosis?
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.
²Brand names included in this fact
sheet are provided as examples only. Their inclusion does not mean that
these products are endorsed by the National Institutes of Health or
another Government agency. Also, if a particular brand name is not
mentioned, this does not mean or imply that the product is
unsatisfactory.
When Should Surgery Be
Considered and What Is Involved?
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.
What Are the Major Risks of
Surgery?
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.
What Are the Long-Term Outcomes
of Surgical Treatment for Spinal Stenosis?
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.
What Research on Spinal Stenosis
Is Being Supported by the NIAMS?
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
NIAMS-funded 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.
Keeping on Top of Your Condition
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