In spinal stenosis, part of the spine narrows, putting pressure on your
spinal cord or nerve roots. Knowing more about the spine's anatomy makes
it easier to understand where and how this narrowing occurs. The main
parts of your spine include:
Your spine is made up of 24 bones stacked on top of one another,
plus the sacrum and tailbone (coccyx). Most adults have seven
vertebrae in the neck (cervical vertebrae), 12 at the back wall of
the chest (thoracic vertebrae) and five vertebrae at the inward
curve of the lower back (lumbar vertebrae). The sacrum consists of
five fused vertebrae between the hip bones. The tailbone is composed
of three to five fused bones at the very end of the spine.
These tough, elastic bands of tissue help keep the vertebrae in
place when you move.
These elastic pads of cartilage separate the vertebrae. They keep
your spine flexible and act as shock absorbers to cushion the
vertebrae when you move. Each disk consists of a ring of tough
fibrous tissue (annulus fibrosis) surrounding a jelly-like center
Between each vertebra is an elastic pad of cartilage called an
intervertebral disk. The disks consist of a tough, fibrous outer
covering (annulus fibrosus) and a jelly-like center (nucleus pulposus)....Your
back is composed of 24 vertebrae plus your sacrum and tailbone (coccyx),
31 pairs of nerves, 40 muscles, and a number of connecting tendons and
ligaments. Between your vertebrae are fibrous,
Located on the sides, top and bottom of each vertebra, these joints
connect the vertebrae to one another and stabilize the spine while
still allowing flexibility. The joints are coated with a lubricant
so that they slide smoothly.
This long bundle of nerves extends from the brain stem at the base
of your skull to the second lumbar vertebra in your lower back. When
the spinal cord ends, another group of nerves (cauda equina)
continues down the spinal canal. The nerves within the spinal cord
(upper motor neurons) carry messages between your brain and the
nerves that go to all the parts of your body below your head. Two
spinal nerves one leading to the right side of your body and one
to the left side extend out from the spinal cord between each
vertebra. The nerves exit through openings on either side of the
vertebrae (intervertebral foramina). In all, there are 31 pairs of
spinal nerves in your neck and back. Some transmit information from
your body to your brain. Others convey messages from your brain to
your muscles, skin and other organs.
This is a channel in the spine through which the spinal cord passes.
Normally, the channel is spacious enough to accommodate the spinal
cord, but degenerative changes in the spine can narrow the canal.
How spinal stenosis develops
Doctors categorize stenosis as either primary or acquired. Primary
stenosis, which is relatively uncommon, results from disorders that are
present at birth. Acquired spinal stenosis, on the other hand, develops
later in life, usually as a result of degenerative changes in the spine
that occur with aging. Most cases of spinal stenosis are caused by these
The main cause of spinal degeneration is osteoarthritis, an arthritic
condition that affects the cartilage that cushions the ends of bones in
your joints. With time, the cartilage begins to deteriorate and its
smooth surface becomes rough. If it wears down completely, bone may rub
painfully on bone. In an attempt to repair the damage, your body may
produce bony growths called bone spurs. When these form on the facet
joints in the spine, they narrow the spinal canal.
Osteoarthritis can also affect the disks in your spine. By the time
you're 30, your disks may start to show signs of deterioration. They
begin to lose their water content, becoming flatter and more brittle.
Eventually, the tough, fibrous outer covering of the disk may develop
tiny tears, causing the jelly-like substance in the disk's center to
seep out (herniation or rupture). The herniated disk presses on the
surrounding nerves, causing pain which sometimes may be excruciating
in your back, leg or both. Sometimes you may also have numbness,
tingling or weakness in the buttock, leg or foot on the affected side.
The ligaments in your back may also undergo degenerative changes,
becoming stiff and thick over time. This loss of elasticity may shorten
the spine, narrowing the spinal canal and compressing the nerve roots.
Sometimes wear and tear on the disks and ligaments causes one lumbar
vertebra to slip over another a condition called spondylolisthesis.
This often compresses the spinal nerves, leading to numbness, tingling
and weakness in your legs, especially when you stand for long periods or
when you walk.
Not all spinal stenosis is age-related. Other causes of narrowing in the
A tumor is a mass of abnormal cells. In the spine, these growths may
occur inside the spinal cord, within the membranes (meninges) that
cover the spinal cord, or in the space between the spinal cord and
the vertebrae the most common site. Tumors may also spread
(metastasize) to the spine or the spinal cord from other parts of
the body. Primary or metastastic tumors can occur anywhere along the
spine, including the sacrum and thoracic spine, where osteoarthritis
Growing tumors may
compress the spinal cord and nerve roots. This can cause severe back
pain that may extend to your hips, legs or feet; muscle weakness and
a loss of sensation especially in your legs; difficulty walking or
even paralysis; and sometimes loss of bladder or bowel function.
Car accidents and other trauma can profoundly affect the spine and
spinal cord. Sometimes the spine or spinal canal may be dislocated,
putting pressure on the cord and lower motor neurons. In other
cases, fragments of bone from a spinal fracture may penetrate the
spinal canal. Swelling of tissue after back surgery can also put
pressure on the spinal cord or nerves.
Bone is living tissue engaged in a continuous process of renewal.
During this remodeling process, old bone is removed and replaced by
new bone. In Paget's disease, your body generates new bone at a
faster-than-normal rate. This produces soft, weak bones that are
prone to fractures. It can also create bones that are deformed or
abnormally large. When unusually large bones develop in the spine,
they compress the spinal cord or the nerves exiting your brain and
spinal cord. The resulting pain is often severe and may radiate from
your lower back into your legs. You also may experience numbness,
tingling or weakness in the legs or, in some cases, double vision.
This genetic disorder slows the rate at which bone forms during
fetal development and in early childhood. As a result, people with
achondroplasia are of short stature often no more than four feet
tall when fully grown. They often have small hands and fingers and
unusually short upper arms and thighs. They also have a small spinal
canal, which puts pressure on the spinal cord. This can cause severe
back and leg pain and may even lead to paralysis of the legs. In
some cases, babies or children with achondroplasia die suddenly
often in their sleep when compression of the upper end of the
spinal cord interferes with their breathing.
In fact, age is the main
known risk factor for the disorder.
Also at risk are people with skeletal fluorosis, a sometimes crippling
bone disease caused by high levels of fluoride in the body. Although the
disease is rare, the World Health Organization
estimates that nearly three million people worldwide have the most
severe form of the disorder. Fluorosis causes the spine to become nearly
immobile and joints throughout the body to stiffen, making movement of
any kind painful and difficult.
When to seek medical advice
Unfortunately, many people ignore the symptoms of spinal stenosis,
believing that the pain and stiffness they experience are a normal part
of aging. But discomfort, especially if it interferes with your
mobility, is never normal. Seek medical advice if you have pain,
stiffness, numbness or weakness in your back, legs, neck or shoulders
that's not related to exercise or overexertion. Spinal stenosis is
especially likely if you have leg pain that gets worse when you walk and
improves when you sit or bend forward. Get immediate care if you
suddenly have trouble controlling your bowels or bladder.
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