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BASIC ANATOMY PART TWO
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Everyone has head the term ligament. We think of football or
basketball players who have "torn a ligament." Likewise most of
us have head the term tendon.
A ligament is a tough, dense strand of gristle-like tissue which
attaches one bone to another while a tendon attaches muscle to
bone. The two are thus different.
Ligaments pass between two bones and have some flexibility so
that motion can occur, but their elasticity is low. They can
usually be stretched only a short length before a tear occurs.
Once torn, a ligament does not normally heal itself and is
repaired surgically. If left unrepaired, the unrestrained
movement of the joint can cause additional pain, damage and loss
of joint function.
Many ligaments connect the spinal vertebrae, sacrum and pelvis
into a single structure. 1) Interspinous ligaments connect the
bony transverse spinous processes together and limit motion
which can happen between two vertebrae. 2) Intertransverse
ligaments pass between the transverse processes on each side of
the vertebra. They are largest at the lower lumbar region of the
spine and prevent you from bending too far from side to side. 3)
The ligamentum flavum secures the rear section of vertebrae and
forms the upper encasement of the spinal canal. It protects and
covers the spinal cord and is a bit more elastic than most
ligaments of the spine. 4) The annullus fibrosus connects each
vertebra to its neighbor via a circular band. It contains the
gel-like pulp of the disc. Curiously, its fibers are oriented in
a radial ply orientation much like radial ply cords of an
automobile tire. While it contains the pulp of the disc, its
primary function is to hold the disc in alignment with its
vertebral neighbors. 5) The anterior and posterior longitudinal
ligaments which extend between the top and a bottom of the
vertebrae in a longitudinal path.
The muscles of our spine are for the most part under our
conscious control unlike muscles of the internal organs such as
the intestine or stomach. This is an important distinction since
certain exercises which we can perform consciously can help
alleviate back pain. It is also important to understand that the
muscles within your back are only PART of the entire story.
Other muscles outside the back region strongly affect the shape
and structure of the back, notably the abdominal and buttock
muscles.
Four general groups of muscles support and affect your back. 1)
The all important abdominal muscles which provide frontal
support and keep internal organs such as the stomach in correct
alignment. 2) Extensor muscles of the spine which hold the
rearmost portion of the torso in an upright position 3) Lateral
muscles which provide side to side support 4) Hip muscles which
affect the spine by virtue of their attachment to the pelvis.
Each of these groups of muscles works in concert with the other.
One or several groups may contract while the others
cooperatively relax. Just like the young tree with guy wires to
hold it erect in the wind, several groups of muscles function
together to add stability to a less than ideal spinal design.
The abdominal muscles consist of 1) The rectus abdominus 2)
internal oblique 3) external oblique 4) transverse abdominus. In
addition to support for internal organs, when contracted and in
proper tone, these muscles control bending movements of the
spine and affect proper posture. Some backaches can be relieved
by strengthening this group of muscles.
The extensor muscles lie along the length of the spine. They are
positioned in layered bands and have detailed names which are
not necessary within this brief discussion. Some of the layers
are long, usually those lying close to the skin. Other extensor
muscle layers are short, and are those which are much deeper
below the skin. The attachment points of this set of muscles is
complex, with segments connecting to spine, pelvis, ribs and the
head. They are most frequently used when you arch your back,
pull a heavy weight or tense your spine rigidly.
The lateral muscles, are layered into the side regions of the
spine. Two major groups are apparent: 1) The quadratus lumborum
and 2) The psoas major. The quadratus helps in bending and is
used in dancing and gymnastics. The psoas is quite large and
attaches to the top of the thigh after running along the side
the spine.
In addition, four muscle groups of the hips, although not
directly connected to the spine, can intimately affect its shape
and performance. These hip group muscles are 1) the hip flexors
2) hip abductors 3) hip adductors 4) hip extensors. Groups or
combinations of these muscles can affect the tilt of the pelvis
and the all important lumbar lordosis or curve of the lower
back. The hip muscles dramatically control posture and exercise.
Proper tension and tone of these muscle groups can affect back
pain.
The final stop on our anatomical tour of the back is the nervous
system. Although the bones, muscles, ligaments and tendons form
the mechanical structure of the back, it is the nerves which
transmit sensations of pain.
The tolerance for pain varies from individual to individual. A
laborer or professional football player can endure one level of
pain. An office worker or student perhaps a different level. The
fact the back pain is often more nagging, virulent and
unrelenting does not necessarily make it different - just more
noticeable in our modern society.
It seems most folks might be able to limp through the day with a
toothache or muscle ache from playing weekend baseball. But back
pain SEEMS different. It can lay you low and make you want to
curl up in bed for days on end. The fact the few treatments SEEM
to alleviate back pain makes it seems a special breed of pain.
More unrelenting, debilitating and immune from the treatments of
modern medicine.
To understand backaches you need to glance at the anatomy of the
nervous system. In man and most vertebrates the nerves are
composed of thin fibers of tissue. The largest cluster of these
fibers are obviously in the brain. The second largest
concentration is in the spinal cord. Two separate structures
distinguish the nervous system. 1) The autonomic nervous system
and 2) the somatic nervous system.
The autonomic portion of the system controls involuntary actions
and senses. Functions such as vascular pressure, nutrition,
heartbeat and digestion fall in this area. The somatic portion
of the system governs voluntary actions and senses which we can
consciously control like bending, looking, opening our mouths
and so forth. At each level of the spinal chord are groups of
nerves which receive impulses from transmission points like the
skin and muscles. These are afferent nerves. Other groups of
nerves transmit impulses from the brain and spinal cord back to
the skin, muscle or site of origin. These are efferent nerves or
motor nerves.
Approximately 30 pairs of mixed spinal nerves emerge from
openings in the vertebrae along the length of the spinal cord.
The small holes which permit passage of nerve tissues through
the vertebrae are known as foramens. The central spinal canal
within each vertebra of course houses the spinal cord itself.
Curiously the main spinal cord is housed in ONLY the upper two
thirds of the spinal column. The spinal cord terminates and does
not travel within the spinal canal lower than the first lumbar
vertebra. In an infant the spinal cord does run the length of
the bony spinal structure, but differential growth allows the
spine to become longer while the growth of the spinal cord lags
behind and thus occupies less than the full spinal column length
in a mature individual.
The nerves of the spinal cord continue their downward trip
towards the legs and lower pelvis OUTSIDE the bony spinal
structure once they have reached the level of the first lumbar
vertebra. However the lumbar nerve roots do extend downward and
emerge on the sides of the lower 5 vertebrae and sacrum. These
lower lumbar nerve roots are extremely important in the
production of pain from the classic "slipped disc" which we will
discuss in a later chapter.
From a practical standpoint what does this discussion of the
nervous structure have to do with back pain? In simplest terms,
this vast collection of nerves MONITORS a variety of locations
which can cause pain: weak muscles, torn ligaments, torn discs,
fractured bones and so forth. In some cases, efferent nerves can
cause a specific muscle group to become overly tense and
contract into painful spasm. This may be due to a torn disc,
simple fatigue or poor posture. However this secondary muscle
contraction in response to an initial pain can make a bad pain
seem worse.
We have looked at muscles, bones, tendons and nerves, but until
this point we have not tied them together with a key word:
SHAPE.
Held together by the overlapping forces of various muscles, the
spinal column assumes a precise S shape when viewed from the
side. The reason why the spine is not normally straight is that
varying forces and demands are present along its length. The S
shape acts as an elegant "counterbalance" to these opposing
forces. In fact, it has been calculated that the spine is 15
times stronger due to its natural S curvature than if it were
straight!
This S-shaped curve is formed from four separate curves. Two
curves bend towards the front of the body and two curves arch
toward the back. The rearward bends are produced by the precise
wedging of the vertebrae and are called primary spinal curves
while the forward arches are produced by the wedging of the
intervertebral discs and are called secondary spinal curves.
The primary curves probably arose as a mechanical strengthening
design during our existence as four legged quadrupeds. The two
primary curves are in a sense genetically "ancient." They have
been with us and all four legged quadrupeds for a long time.
The secondary curves of the spine arose much later during
evolution and were necessary when our upright posture was
assumed. In a sense, nature had to counteract the primary curves
when we began to walk in an erect position. And the only way to
do this was to add rearward secondary curves.
Only man has these unique secondary curves which are located in
the cervical region, near the top of the spine, and the
troublesome and pain-prone lumbar region in the lower spine. As
we age, the lumbar curve tends to deteriorate and actually begin
to reverse its curvature. In women the lumbar curve is also more
acute or pronounced. The curvature becomes still more pronounced
with pregnancy to offset the protruding abdomen. This effect can
also occur in people of either sex who are overweight. We will
talk more about this in a later chapter, but it is sufficient to
understand that these curves are unique to man, crucial to
proper balance of the spinal structure and somewhat adjustable
depending on age, weight and sex.
This ends our brief anatomical tour of the back. Obviously both
structure and function have been simplified, but understanding
even this basic level of anatomy sets the stage for that which
comes next: what are the causes of pain and ultimately how do
you treat them?
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.