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DISC.TXT
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1992-12-04
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THE "SLIPPED" DISC
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It seems frightening and sinister. A "slipped disc" sounds like
what could be causing the nagging pain in your back. Somewhere
you've heard that a friend needed extensive back surgery or
manipulation to restore or reposition a slipped disc into proper
position. A tidy explanation. However, as with most matters of a
medical nature, a little science, history and anatomy often
reveal a more accurate mixture of facts.
In 1764 a malady named sciatica was described in the medical
literature of the time. It referred to a sharp pain radiating
downwards into the legs, frequently originating from the region
of the lower back. By 1864 the terms sciatica and lumbago were
associated in medical journals.
The intervertebral disc was described in detail by the German
pathologist Virchow in about 1855 who noted briefly a specimen
which displayed a "tumor" or "swelling" he had observed
protruding into the spinal canal from one of the intervertebral
discs. Later the German physician Ribbert demonstrated that
these protrusions were not tumors but were extrusions of the
intervertebral disc tissue itself.
By 1861 the French physician Sicard proposed a theory that
sciatica might be due to pressure upon the nerve roots in the
region now named the sciatic nerve. The Italian doctor Putti
advanced the theory further by suggesting that the pressure or
irritation might be due to intervertebral disc abnormalities or
malformations.
The chain of cause and effect was almost complete, but it was
not until 1933 that a single cause was attributed directly to
the afflictions of sciatica and lumbago. Doctors Mixter and
Barr, American physicians practicing at Massachusetts General
Hospital, finally drew the threads of information into a single
coherent strand by linking the protrusion of intervertebral disc
tissue with pressure on the sciatic nerve as the cause of the
intense pain of sciatica.
A word of caution. Not every manifestation of sciatica is caused
by protruding or damaged disc tissue. However this is the most
common source of severe back pain which radiates or "shoots"
into the legs.
Let's turn back a few pages and glance at the anatomy of the
disc.
The intervertebral disc is actually constructed of several
tissues. Roughly oval in shape, it is composed of 1) top and
bottom plates of gristle-like cartilage which are joined to the
bony vertebrae, 2) the sides of the disc which are rounded and
quite elastic. These layers of tissue are present in a radial
layered arrangement like the belts of a tire. This makes them
extremely tough. These layers comprise the annulus fibrous.
Inside this disc "containment wall" is 3) the inner core of the
disc, the nucleus pulposus, which is a white flexible gel-like
tissue. Its function is to act as a shock absorber and force
distribution mechanism. Technically only this pulpy core is the
disc.
If you hear that a disc has been removed during surgery, it is
normally the inner nucleus pulposus which is extracted. As an
aside, about 22% of the average height or length of the spinal
column is due to the discs which provide both support and
lateral side-to-side movement. Their design allows a fair degree
of movement, but remember that the disc can only stretch so far
before it ruptures. The outer walls of the disc are bonded
directly to the vertebra and restrict their movement beyond
certain limits.
To understand the nature of a disc rupture you need to
understand that the pulpy inner core of a disc acts like all
hydraulic fluids. It can move, change shape and absorb shock but
it CANNOT be compressed to occupy a smaller volume (at least at
pressures normally present in the human body.) If the pressure
becomes too great, the fluid will bulge outwards at a point
opposite the compression. If a weak spot has been created in the
outer containment of the disc, a rupture can take place.
Sometimes the wall of the annulus merely bulges without actual
escape of the nucleus pulposis. Other times the nucleus can also
rupture.
Once this happens the disc loses its value as a shock absorber
because the pulpy core is no longer contained. It is important
to note that the shock absorbing nature of the discs sometimes
causes the bones of the vertebra to fracture first in cases of
severe impact! Surprisingly some victims of car accidents or
falls have fractured vertebra and scarcely damaged their discs -
a testament to their excellent design and load bearing
characteristics!
A slipped disc, then, is not slipped at all but actually a
rupture of the inner pulp of the disc either outwards away from
the spinal canal or inwards into the spinal canal. In most cases
the deterioration of the protective capsule of the disc is a
gradual process which frequently begins at the rear portion of
the disc. This is due to the fact that the wall of the disc is
thinner there than the front of the capsule. A gradual softening
or wearing down takes place in this outer disc wall.
Then perhaps a sudden twist of the spine, a load improperly
lifted or a fall causes a rupture to take place. This can
produce the classic protruded disc. Frequently the bulge
enlarges through the posterior longitudinal ligament of the
spine and begins to press on either the spinal cord or the nerve
roots which descend from it. Usually the protrusion will be
slightly to the left or right side of the midline of the spinal
canal which causes painful symptoms on only one side of the
body. This single-sidedness of the pain is sometimes a
diagnostic clue in cases of disc damage.
Two separate types of pain are frequently reported by patients
suffering from disc damage. If sensory nerves of the skin are
irritated by the pressure of the ruptured or protruding disc,
then the patient may report burning or tingling of the skin. If
motor nerves supplying muscles are pressed by the protruding
disc, muscles of the leg or back may go into uncontrollable
painful spasm - classic sciatica.
It is important to note that for all practical purposes the disc
does not "slip" back into place and only rarely heals itself.
The damage is permanent and does not heal completely. Eventually
tissue scarring will begin to take place in the area of the
protrusion which may further inflame nerve roots. If the
pressure of the protruding disc becomes too great, nerves of the
bladder and bowel may also be affected which almost always
indicates surgical intervention.
Lumbago is a different type of pain in which the back "suddenly
seizes up." The muscles of the lumbar region go into rigid spasm
and refuse to relax. The spasm may fade in a few hours or days.
By lying perfectly still, the pain may be minimized and finally
disappear as quickly as it began.
Disc related pain may also produce another manifestation. Lack
of activity of a disc-damaged back may cause recurring stiffness
unless the back is kept supple with motion and exercise. The
pain seems to be worse with inactivity and will diminish when
the person moves around a bit. This may also reflect both true
arthritis as well as a form of arthritis caused directly by long
term disc degeneration.
Treatment for mild disc protrusion is relatively specific.
Initially some physicians may prescribe bed rest, since standing
increases the pressure on the damaged disc. Pelvic traction may
be initiated while a patient lies in bed. The function of the
traction is not to pull or stretch the spine, but to tilt the
pelvis and reduce the curve of the spine which relieves some
pressure and produces comfort. Pain medications and some muscle
relaxants might be prescribed by a physician. X rays would be
taken along with some blood tests. After one or more weeks of
bed rest or traction some standing might be permitted with no
sitting allowed. Back strengthening exercises would gradually be
added to build muscle tone. This course assumes surgical
intervention is not attempted.
In more severe cases, a myelogram or NMR scan would be done to
confirm substantial disc protrusion and probable need for
surgery to remove the inner core of the disc. After surgery the
space within the disc gradually fills with scar tissue. In time,
and with some patients, the space between the two vertebrae may
gradually grow together in a type of spontaneous bone to bone
fusion which lessons mobility and further damage at that area of
the spine. After disc surgery, rehabilitative exercises are
prescribed to build up the muscles of the back so that proper
support is maintained.
The topic of surgical fusion, the deliberate joining of two or
more vertebrae after disc surgery, is controversial. Some
physicians routinely fuse vertebrae after a disc operation,
others fuse on a more selective basis. Usually small pieces of
bone from the hip or other area of the body are grafted directly
between vertebral bodies to limit their motion and provide
support. This technique is generally the most severe course of
action and is usually reserved for the extreme cases of disc
degeneration. It also performed for other diseases such as
spinal bifida, a birth defect.
So far we have discussed problems usually seen in the lower
lumbar region of the back. However, the cervical discs of the
neck region can occasionally be affected. Arthritis is a common
culprit here. Symptoms can involve radiating pain into the
shoulders, arms and hands. In severe cases of cervical disc
rupture or degeneration weakness of the arm and hand muscles
will be seen and "tingling" or even complete loss of sensation
in the skin of the hands and arms. Again this is caused by
pressure on sensory or motor nerves in the area of the cervical
region of the spine. Cervical disc problems are more frequently
seen in older people since these complains are more commonly
arthritic in origin. Cervical disc protrusion can be more
serious than lumbar disc problems since a large section (more
nerves) of the spinal cord is present at this level of the
spine. Bed rest, traction and neck braces or cervical collars
are usually attempted in milder forms of this disc problem.
The bottom line, however, in dealing with disc disease is that a
weak back is unstable and prone to disc disease and injury.
Proper exercise and posture can go a long way to preventing disc
disease in the first place and minimizing its impacts.
This tutorial is merely a starting point! For further
information on back care and back pain, be sure to register this
software ($25.00) which brings by prompt postal delivery a
printed, illustrated guide to back pain written by a physician
plus two software disks. From the main menu select "Print
Registration Form." Or from the DOS prompt type the command
ORDER. Mail to Seattle Scientific Photography (Dept. BRN), PO
Box 1506, Mercer Island, WA 98040. If you cannot print the order
form, send $25.00 to the above address and a short letter
requesting these materials. End of chapter.