Lower Back pain


lower Back pain syndrome

lower Back pain  syndrome

functional unit in anterior portion


The vertebral column is an aggregate of articulated, superimposed

segments, each of which is a functional unit. The function of the
vertebral column is to support a two-legged animal, man, in an upright
position, mechanically balanced to conform to the stress of gravity,
permitting locomotion and assisting in purposeful movements.
The functional unit is structurally and functionally capable of permitting
all these functions through the decades of man's existence.
Natural attritional changes of aging, recovery from repeated minor
trauma and stresses, impairment from disease or major trauma, and
dysfunction from misuse and abuse-all may lead to disability and
pain. Its resiliency is a tribute to its structural perfection.
The functional unit is composed of two segments: the anterior segment
containing two adjacent vertebral bodies, one superincumbent
upon the other, separated by an intervertebral disc, and a posterior
neural segment. The anterior segment is essentially a supporting,
weight-bearing, shock-absorbing, flexible structure. The posterior
segment is a non-weight-bearing structure that contains and protects
the neural structures of the central nervous system as well as paired
joints that function to direct the movement of the unit
Fig. 1

The anterior portion of the functional unit is well constructed for its
weight-bearing, shock-absorbing function. The unit is comprised of
two cylindrical vertebral bodies with flattened cephalic and caudal
ends that, in their normal state, are adequate to sustain extremes of
compressive stresses. These two vertebral bodies are separated by a
hydraulic system called a disc.
At birth the vertebral bodies are bi-convex with the end plates being
cartilaginous. These cartilage plates gradually undergo ossification and

FICURE 2.Annulus fibrosus. AboveLayer concept of annulus fibrosusBelow: Circumferential annular fibers
about the centrally located pulpy nucleus
(nucleus pulposus).
posus, is thus confined within a fibrous resilient wall, the annulus, and
between a floor and ceiling composed of the end plates of the vertebrae

(Fig. 2). The annulus fibrils are attached around the entire circumference
of both the upper and inferior vertebral bodies and crisscross and
intertwine in oblique directions. The manner in which these semielastic
fibers intertwine permits movement of one vertebra upon the
other in a rocker-like movement and to a lesser degree permits movement
in a shearing direction.
The fluid contained within the confines of the encircling annulus is a
colloidal gel and by its self-contained fluidity has all the characteristics
of a hydraulic system. Because the nucleus is approximately 88 percent
fluid, it cannot itself be compressed, but since it exists in a closed
container, it conforms to the law of Pascal (Blaise Pascal, 1623-1662),
which states that: "Any external force exerted on a unit area of a
confined liquid is transmitted undiminished to every unit area of the
interior of the containing vessel
The self-contained fluid accepts the shock of a compression force."

FICURE 3. Hydraulic mechanism of the intervertebral disc. A. The nonnal resting disc
with the internal pressure indicated by the arrows exerted in all directions. The disc is
confined above and below by the vertebral plates and circumferentially by the annulus.
The annulus fibers are taut. 8. Compression of the disc is permitted by the noncompressible
fluid of the nu·deus annulus. C. Flexion of the spine is permitted by horizontal shift of the nuclear nuid which
maintains its cuhicoontent but causes expansion of the posterior annulus and contraction
oCthe anterior annulus. The intertwining of the annular fibers permits this change in the
capsule with no loss of turgor.
attempting to approximate the two vertebrae and maintains the separation
of the two vertebral bodies. Movement of one vertebra on the other
in a rocking-like manner is permitted by the ability of the fluid to shift
anteriorly or posteriorly within a semi elastic container (Fig. 3). The
constant internal disc pressure separates the two end plates and thus
keeps the fibroelastic mesh of the annulus taut (Fig. 4).
The elastic properties of the disc are considered to reside in the
elasticity of the annulus rather than in the fluid content of the nucleus.
In a "young" and undamaged disc the fibroelastic tissue of the annulus
is predominantly elastic. In the process of aging, or as a residual of
injury, there is a relative increase in the percentage offibrous elements.
As the relative increase of fibrous elements occurs, the disc loses its
elasticity, and its recoil hydraulic mechanism decreases. The "older"
annulus reveals a replacement of the highly elastic collagen fibrils by
large fibrotic bands of collagen tissue devoid of mucoid material. This
disc is, therefore, less elastic