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It is very important to know the structure
and functions of the spine before we begin to understand
the cause of pain and what actually happens during
manipulation. We must be familiar with the preventive
methods and precautions we should take after the pain has
gone so that we may not suffer from it again.
Understanding and becoming familiar with the anatomy or
the structure of the human body is imperative to
understand pathology or the disease process. Then only
can we think of a remedy or treatment. Let us examine
what our aim in manipulation is, and how these measures
help to keep us healthy. Somebody has compared the human
spine to a sitar and an osteopath to the maestro who
plays the sitar. To learn the sitar, to master it, to
produce new ragas, calls for a deep understanding and
years of devoted practice. Appreciating the light and
almost imperceptible touch and, at other times, the deep
pressure applied on the strings, is what differentiates a
maestro from an ordinary player. So it is with the skill
of an osteopath. To manipulate the spine requires an
equal amount of devotion and understanding added to years
of an uninterrupted practice. The osteopath becomes a
master of his job only after a devoted practice of at
least five years after his graduation, during which he
learns the basic knowledge only. It is also true that he
never stops learning.
Man is a vertebrate. This means that he has a backbone
called the spine, extending from the neck to the tail
bone. The spine consists of a series of small irregular
bones called vertebrae placed in such a way that they
carry on different movements and support the weight of
the trunk, thus making weight bearing easier for the
lower limb. These small bones called vertebrae are
thirty-three in number. There are 7 vertebrae in the neck
which comprise the cervical spine, 12 in the upper back
comprising the dorsal spine, 5 in the loins called the
lumbar spine. Five sacral bones fuse together in the tail
bone region to form the sacrum, and below that is the
coccyx formed by four rudimentary coccygeal bones.
The part of the vertebra situated in the front mainly
helps to support the body weight. The posterior part
called the neural arch,, encloses the neural canal
through which passes the spinal chord. The neural arch
consists of:
- The pedicle or foot
of the vertebra
- A pair of transverse
process or projections
- Superior articular
process or surfaces.
- Inferior articular
process or surfaces.
- Spinous process
- Laminae or lining
covering the body of the vertebrae
The Cervical spine has
three peculiarities:
- First, the transverse
process of the cervical vertebrae is perforated
by an opening through which pass the vertebral
artery and the vein which supplies blood to the
brain.
- Second, the first
cervical vertebra named Atlas supports the globe
of the head and has no body.
- Third, the second
cervical vertebra called Axis provides the pivot
upon which the atlas, the first vertebra, and the
skull rotate.
Curves
of the Spine
The spine is not
straight. If it is viewed from a side, four curves can be
seen:
- The cervical curve
which is convex forward.
- The thoracic curve
which is convex forward. The upper part may have
a slight lateral curvature directed towards the
right side in a right-handed person and the left
side in a left-handed person.
- The lumbar curve is
convex forward. It is more pronounced in females
than males. It extends from the lower thoracic
vertebra to the lumbo-sacral angle.It is larger
than the upper two.
- The pelvic curve
extends from the lumbo-scaral joint to the apex
of the coccyx. Its concavity faces downwards and
forwards.
The vertebrae are held
together and perform their functions of protection,
movement and support. The spine with the help of its
inter-vertebral joints tries to perform the functions of
movement and support in the best possible way.
Intervertebral
Joints
Intervertebral
joints are the joints between two adjacent vertebrae.
They comprise the anterior joint-containing discs, the
posterior joints constituted by facet or surface joints,
A connecting ligament system, muscles, intervertebral
foramen, and nerves.
Intervertebral
Discs
The discs are
interposed between the adjacent surfaces of the bodies of
the vertebrae and form the chief bond of connection
between them. Their shape correspond with those of the
bodies of the vertebrae between which they are lodged.
Their thickness varies in different regions of the column
and in different parts of the same disc. They are thicker
in front on the cervical and lumbar region, thus
constituting the anterior convexity of these curves. They
are uniform in size in the thoracic region, and the
anterior concavity of this column is due to the shape of
the vertebral bodies, which are thinnest in the upper
thoracic area and thickest in the lumbar region.
The disc absorbs the pressure transmitted to it by the
central core, and, at the same time, keeps the vertebrae
together. It buffers the action of compression upon
bones. It is the chief shock absorber of the body. It
constitutes one-fourth (quarter) of the entire length of
the spine. The shock absorption is based more on the
hydraulic system, also akin to the elastic properties of
rubber. The disc consists of 3 parts: the end plate, the
peripheral portion called the annulus fibrosus, and the
central portion called the nucleus pulposus.
The End
Plate. This
consists of a narrow zone of hyaline cartilage covering
each surface of the vertebral body. The end plate, along
with the annulus, is perforated by thousands of small
holes through which the tissue fluid diffuses. The fluid
diffuses both into and out of the disc.
The
Annulus Fibrosus. The
annulus fibrosus comprises the narrow outer zone of
collagenous fibres and a wider inner zone of
fibro-cartilage. It is attached to the end plates. Fibres
of this layer run obliquely, thus giving great strength
to the rotational movements. The annulus fibrosus
surrounds the nucleus pulposus in the form of a number of
layers which can be compared to the layers of an onion.
Around its periphery the annulus inserts itself on the
vertebral body. The marginal fibres are particularly
tough. The weakest point is located at the posterior near
the intervertebral foramen.
The disc is nourished by synovial fluid and if a piece
flakes off, it remains alive inside the joint cavity. The
cartilage has no nerve or blood supply. It is nourished
by the bone of the body of the vertebrae. It is therefore
slow to react to a trauma, and also slow and often
incapable of complete repair. That is why there is no
immediate pain if the cartilage is damaged. The pain is
felt only when adjacent sensitive structures are also
affected.
Following the trauma to any tissue, there is swelling
owing to the liberation of histamine and other
substances. The cartilage swells after the forced
activity, but due to the lack of nerve supply, it does
not cause pain, and due to the absence of blood supply,
it swells up slowly. Two or more days following the
injury may pass before the cartilage swells up. However,
ligaments, if injured, swell up in 2-3 hours. The
swelling may stretch to adjacent ligaments or the
periosteum (outer layer of a bone), causing pain, or the
swelling may block the full range of movements. Adequate
rest required for the repair of the joint is usually not
given to it. Repair is therefore often incomplete and
consequently, degenerative changes in the annuals are
induced much earlier than desired. All the damage to the
annulus is permanent: a union and regeneration never take
place here.
A disc has the quality of a sponge and is able to absorb
fluid as well as diffuse its own fluid content. This is
why the consistency of the disc keeps on changing. This
can be demonstrated by measuring the height of a person
at the end of the day and early in the morning when he
gets up. The height of the person increases by ¼ to ¾
of an inch after a night’s sleep.This height
difference is not due to the straightening of the curves
of the spine but due to an increase in the thickness of
the discs.
The
Nucleus Pulposus.
This is a soft ,
gelatinous, mucoid material at birth. It lies almost in
the centre of the intervertebral joint. But as age
advances, the anterior part of the body of the vertebra
grows much faster than the posterior part. Hence it
ultimately lies strictly behind the centre. It forms a
cushion between the vertebrae. There is a resultant
compression which exerts evenly distributed hydrostatic
pressure. The pressure within the nucleus is
considerable.
The disc can be damaged by direct or indirect trauma. If
the disc is healthy, it would need to be hit by a
considerable force to be damaged. Even an impact enough
to damage the body of a vertebra is not sufficient to
damage a healthy disc. It has been calculated that a
normal adult disc can withstand a compression force of
545 kg per square inch before rupturing , while less than
450 kg of pressure is enough to damage the vertebral
body. In normal weight bearing, when a person is standing
or sitting, the compression force is 45 kg. But it is
estimated that it increases considerably, reaching upto
225 kg when a person is bending forward. In this position
when a load of 30 kg is lifted by using only the spine
while bending, the force increases upto about 450 kg,
which is dangerously near the breaking limit. A
weightlifter trained to lift with proper techniques can
lift as much as 272 kg without any apparent damage to the
disc. This is why it is very important to learn the
correct method of weightlifting. When the correct method
is employed the weight is lifted with the help of the arm
and leg leverage, and the weight is supported by the
spine only when the person is erect. When a person lifts
a weight, a small role is also played by the abdominal
muscles, and part of the force is absorbed by the
intra-abdominal structures. It is estimated that, while
lifting, upto 30 percent of the force is absorbed by
these structures. This is why it is very important to
have strong abdominal muscles in order to protect the
lumbo-sacral spine. Exercising the abdominal muscles to
make them strong is also important in case of
lumbo-sacral pain.
When the disc has undergone degenerative changes, smaller
weights may be sufficient to cause damage. So it is
important to understand the degenerative changes of the
disc to understand pain. It is also important to check or
minimise degenerative changes as preventive measures.
The gelatinous properties of the nucleus depend upon its
mucosaccarides which tend to break down with age.
Imbibation of fluid diminishes, making the nucleus more
rigid. The distance between the vertebral bodies
diminishes; the annulus fibrosus bulges, growing weak at
certain points. Under some circumstances and especially
with trauma, the internal hydrostatic pressure rises, and
the weakened annulus gives way. The disc herniates or
prolapses through the weakened annulus, which may, in
turn, pass through the end plate. Symptomatology depends
upon the location of the prolapse. The most susceptible
area of the spine is the lower lumbar spine. It is here
that spondylosis is most common. The intensity of the
pain depends upon the sensitivity of the site of
protrusion. Sometimes a fragment of the cartilage,
generally in a degenerated disc, can break off and move
inside the intervertebral joint, lodging against a
sensitive area and causing pain. This pain may have a
sudden onset. The broken fragments may consist of
fibro-cartilage or nuclear tissue. The lumbar spine,
however, is not the only part subjected to such
pressures. For example, take the cervical spine. Here in
spite of the smallness of the vertebrae, their bodies and
facet joins support a large ball weighing approximately 5
kg – that is the man’s head. The head is
balanced over two small facets, small as nails, yet
mobile in all directions. Some people can even carry a
weight of upto 54 kg on their heads, entirely supported
by the joints of the two upper cervical vertebrae.
After 20 years of age, degenerative changes start
occurring, which may result in necrosis or breakage of
the nucleus pulposus, and the softening and weakening of
the nucleus fibrosus. Under these circumstances even a
minor strain can cause internal derangement in the joint
as the nucleus is displaced and the nucleus fibrosus is
weakened, making the nucleus pulposus bulge out. Unequal
tension within the joint causes disc-prolapse, resulting
in a sudden onset of acute lumbago. Prolapsed nucleus
material can cause irritation in the adjacent nerve root.
This may cause pain known as sciatica in the leg. This
generally occurs in the lower lumbar or lumbo-sacral
joint or lower cervical joints.
During middle age, when degenerative changes start,
bulging of the disc material may take place in any
direction, producing a pull on the ligaments during
weightbearing. A ligamentous pull lifts the periosteum
from the margin of the body of the vertebrae. New bone
formation takes place under this periosteal lift and in
due course, osteophytes appear. The osteophytes, when
viewed through an X-ray, called osteoarthritic changes.
They limit mobility. Ligaments also become hard by this
age. Generally the osteophytes are thought to be
responsible for pain, but in most cases they are not.
This can be proved just by looking at a number of X-rays
taken to reveal kidney stones in patients belonging to a
middle or higher age group. Most of the time, the
patients insist that they have never had a backache in
their life.
The
Posterior Joints
From a strictly
anatomical point of view the posterior joints of the
spine are the true joints of the spine. The extent and
the variety of movements depends on the shape and
direction of the facet joints. They determine the extent
of movement and direction of a particular segment. These
facet joints are covered by a dense articular capsule
which is quite elastic. thin and loose. They are attached
just beyond the margins of the articular facets, and are
larger and looser in the cervical than in the thoracic
and lumbar spine.
The facet joints are supplied by a nerve which runs to
the two adjacent joints. Each joint therefore derives its
nerve supply from two segments. Each vertebra has a pair
of superior and a pair of inferior facet joints. These
play an extremely important role in the minor traumatic
pathology of the spine, as they have a central area of
rich blood and nerve supply. They are the most richly
innervated structures of the entire spinal column. This
innervation helps the spine to adapt to the variation of
tensions to which the capsule of facet joints is exposed.
Derangement of these joints can be extremely painful.
In the cervical region the superior facet joints are
inclined upwards at forty-five degrees. This helps in
free flexion and extension of the neck. At this level
usually, extension can be done more easily than flexion.
Lateral bending and rotation are always combined. In the
thoracic region, the facet joints are more oblique, say,
at an approximately sixty degree inclination. In the
upper part of the thoracic spine, movements are greatly
restricted due to the direction of the facet joints and
attachment of the ribs to the body of vertebrae. Rotation
at this level is of a greater range than flexion and
extension. Lateral bending is restricted due to the ribs
and the sternum. Extension (backward bending) is freer in
the lumbar spine. A considerable amount of side bending
and a small amount of rotation can occur at this level.
Ligaments
The spine consists
of a series of joints which are united from the second
cervical to the first sacral by a number of ligaments.
The vertebral bodies are united by anterior and posterior
ligaments, and the posterior series of facet joints and
neural arches are united by the ligamentum flavum. The
function of these and other ligaments is to hold the bone
together and yet allow some calculated movements. The
ligaments are elastic structures with an elastic limit.
They remain healthy with intermittent stretching.
Ligaments can be torn in two ways: sudden force and
uninterrupted prolonged moderate stretching. This is why
intermitted traction is more physiological than
continuous sustained traction.
Anterior
Longitudinal Ligament
A long and strong
fibrous ligament runs on the anterior surface of the
vertebrae. It is attached firmly to the disc and margins
of the vertebral body, and loosely attached to the middle
part of the body. It is wider at the level of the disc
and narrower at the level of the body. A tear in any of
the ligament fibres leads to haemorrhage, oedema and
fibrin formation. If given sufficient time, the ligament
becomes as strong as before, but if stretched too soon,
it remains weak and repair is incomplete. The ligament
may get elongated, making the joint hypermobile. When
stretched continuously for prolonged periods, the
ligament starts aching and its elasticity gets
diminished.
Posterior
Longitudinal Ligament
The posterior
longitudinal ligament is attached to the posterior margin
of the vertebral body within the vertebral canal. It
forms a bridge over the body of the vertebrae and is
attached firmly to the intervertebral disc and to the
margins of the vertebral body. Thus it reinforces the
disc posteriorly. This ligament plays an important role
in disc protrusion. The resistance of the ligament helps
to push the protrusion back again. The constant
occurrance of lumbago in some persons may be caused
because the protrusion is enlarged and pushed to the area
of lesser resistance, thus producing unilateral sciatica
pain. It is due to the posterior longitudinal ligament
rupturing so completely, backwards and thus the cauda
equina (lowermost roots of the spinal chord) is subjected
to great pressure which may result in bilateral sciatica.
Muscles
There are quite a
few muscles which act on the spine and help in its
different movements. There are short muscles which act
directly and long muscles which act indirectly and aid in
the movements of the spine. They help to steady the
spine. They produce extension, lateral bending and
rotation.
Short muscles help to maintain the posture. They contract
intermittently, and during an upright posture, there are
slow spontaneous swaying movements. They help to initiate
flexion and assist the short muscles in further flexion
and control of it. It is surprising to know that in
incomplete flexion, the short muscles are inactive and
controlled by the spinal ligaments. Any imbalance and
weakness of these muscles produces a deformity of the
spine known as scoliosis.
Side bending is also helped by short muscles. They play a
great role in mechanical vertebral pathology. A sudden,
enexpected movement can produce a harmful distribution of
the forces on the intervertebral joints. If certain parts
are compressed or put into a traction beyond their
capacity., they can damage the joint to a varying degree,
depending on the force causing the painful muscle spasm.
Synchronisation of muscular activity is more important
than just increasing the strength of these muscles by
various spinal exercises. This is why manipulation is an
important therepeutic measure.
When the muscles are weak, the ligaments and joints are
more strained, thus becoming more vulnerable. Generalised
muscle weakness is also the cause of bad posture.
Excessive powerful muscle contraction can also damage the
bone: for instance, there can be a fracture of the
kneecap due to contraction of the high muscles.
Intervertebral
Foramen
The intervertebral
foramen is a short canal lodged between contiguous. It is
ellipsoid in form. Its form changes with the mobility of
the intervertebral joint. In the dorsal and lumbar spine
it is directed laterally to the right and left. In the
cervical spine it is directed slightly to the front, say
by fifteen degrees, as compared to the dorsal or lumbar
foramen. The canal is covered by a fibrous structure
which is connected to the intervertebral disc and capsule
of the posterior joints. Through it passes the spinal
nerve which consists of a ventral root and a dorsal root.
These appear to be united with each other in the canal,
but when seen microscopically they are found to be
seperated. The dorsal root contains the spinal
ganglion. Each spinal nerve, after coming out of the
intervertebral foramen, has an offshoot of a small
branach called a meningeal branch which re-enters the
vertebral canal through the intervertebral foramen and
ennervates the vertebral ligaments and blood vessels of
the spinal chord.
The compression or irritation of elements contained in
the intervertebral foramen may occur due to the
degeneration of the disc, osteoarthritis ofn the
intervertebral joints, posterior profusion of the disc,
or rupture of the disc with herniation of the nucleus
pulposus. This may cause pain, some muscular weakness,
lumbago, sciatica and a diminished feeling all over the
skin.
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