tissue sites of pain origin

lower Back pain syndrome

tissue sites of pain origin

TISSUE SITES OF PAIN ORIGIN

The intervertebral disc itself is a non-pain-sensitive tissue. The total

disc is an inert tissue and the nucleus has been found completely free of

any sensory type of nerve endings. Nerve endings have been found in

the annulus, but neurophysiologic studies have failed to discover pain

sensory transmission from these nerves. The discs, therefore, both

annulus and nucleus, must be considered insensitive to pain sensations,

2.3.4

If the absence of sensory nerves emanating from the disc be accepted

it must be assumed that it is not possible to consider the disc a painproducing

unit. The commonplace disc-pain must, therefore, originate

from contiguous tissues, with the disc itself in some manner participating

in the instigation of disc-pain by its action on these surrounding

tissues.

-If the internal pressure within a normal disc is experimentally in

FIGURE 20. Pain-sensitive tissues of the functional unit. The tissues labeled + are

pain-sensitive in that they contain sensory nerve endings that are capable of causing pain

when irritated. Tissues labeled - are devoid of sensory nerve endings

(IVF= intervertebral foramen containing nerve root (NR

LF = ligamentum navum

PLL = posterior longitudinal ligament

ALL = anterior longitudinal ligament

IVD = annulus fibrosus of intervertebral disc

FA = facet articular cartilage

ISL= interspinous ligamen

creased by injecting saline solution into the disc the mere increase of

such pressure does not cause pain. In a disc, however, that has previously

been degenerated, which degeneration can be considered fragmentation

of the annulus with a dehydrated nucleus, increase in the

interdiscal pressure causes an ache in the region of the low back.'

If the same method of increasing pressure within a disc of known

degeneration is used no pain sensation occurs when the posterior

longitudinal ligament is anesthetized by procaine. It can be assumed

then that the irritation of the posterior longitudinal ligament by increase

in internal pressure within a degenerated disc is the mechanism

of pain production, and the posterior longitudinal ligament is the painsensitive

tissue. The posterior longitudinal ligament therefore must

contain sensory nerve endings

It is apparent that a normal disc has sufficient elasticity and resiliency

to withstand significant increases in internal pressure which will prevent

a bulging irritation of contiguous tissues. Degeneration of a disc

due to annular fragmentation decreases its resiliency and resistance to

increase in internal pressure, permitting encroachment on surrounding

tissues.

-The ligamentum flavum and the interspinous ligaments are nonsen
sitive .Similarly, stimulation or movement of the dura mater elicits no

sensation of pain. These tissues, therefore, must be classified as insensitive

to pain

The synovial lining of the facets and the articular capsule of these

joints are richly supplied by sensory as well as vasomotor nerves. The

synovial tissues of these joint spaces respond to stimuli and inflammations

as do all other synovial joint tissues elsewhere in the body.

Inflammatory responses of these tissues result in swelling and engorgement

of the synovial linings, increase viscosity of the synovial

fluid, causing periarticular muscle spasm that results in progressive

limitation of movement. The part becomes "frozen" or at least significantly

immobilized. Inflammation of synovial joints produces dull to

severe pain depending on the severity and extent of the inflammation

The concomitant muscle spasm that accompanies spine dysfunction

is in itself capahle of eliciting pain. In animal experiments, painful

irritation of the lumbosacral joints and ligaments causes reflex spasm of

the erector spinae and hamstring muscles. This spasm in a human being

undoubtedly is painful. In addition to pain resulting from the joint and

ligamentous irritation, there can arise irritation from the sustained

muscle spasm, compression of the interposed intervertebral disc by the

spasm of the muscle, which will result in pain if any disc degeneration

exists. In the presence of any disc degeneration the spasm can constitute

a significant compressive force. Multiple factors, such as these, can

be seen to contribute to the production of pain at the functional unit

.level

Another factor is the sciatic nerve root which emerges through the

intervertebral foramen. It is a combined motor-sensory nerve and thus

is a pain-sensitive nerve. irritation of this nerve evokes pain localized

to the dermatome distribution of the specific rootlet irritated.

Pain elicited from irritation of the nerve root, felt either locally or

distally, is considered as resulting from dural irritation. The dura is

(innervated by the recurrent nerve of Luschka (Fig. 21

As the nerve roots descend the spinal canal, they cross the disc

immediately above the foramen. The roots enter the foramina beneath



                     


FICURE 21. Innervation of the recurrent nerve of Luschka

PPD - posterior primary division

APD - anterior primary division

eeL - sympathetic ganglion

INN - internuncial neurons

VSN - ventral sensory nerve sse - sensory sympathetic ganglion

RN - recurrent nerve of Luschka

D - to dura

PLL - posterior longitudinal ligament

,the pedicle. After they leave the foramina, they incline downward

outward, and forward. In the lower disc levels the nerves enter the

origin of the psoas muscle (Fig. 22). By virtue of their vertical entry into

the foramen, they are located in the superior aspect of that foramen

.(Fig. 23)

At their entry into the foramen on their extravertebral course, they

invaginate the dura and the arachnoid and carry a sheath of each into

the foramen. The arachnoid continues along the nerve root as far as the

ganglion (Fig. 24). The dura continues along the combined nerve (sensory

and motor portion) until it fuses with the arachnoid, forming the

,distal end of the sleeve. The dura then continues along the distal nerve

.forming the outer fibrous sheath of the nerve, the perineureum

-The posterior (sensory) nerve root is twice the thickness of the an


                                                 

FIGURE 22. Relationship of nerve roots t o vertebral levels


                               

FICURE 24. Dural and arachnoid sheaths of the nerve root complex. The arachnoid

follows the sensory and motor nerve roots to the beginning of the intervertebral foramen

and follows the sensory root to the beginning of the ganglion. The dura follows the nerve

roots until they become the combined sensory and motor nerve outside the foramen and

continues as the perineurium and epineurium. Neither the dura nor the arachnoid

attaches to the intervertebral foramen