Disc Degenerative Disease

Dimitris Papadopoulos MD Fellow Of Interventional Pain Practice (FIPP)

Updated 20 January, 2011

GENERAL

Disc Degenerative Disease (DDD)  is the distortion of the interior architecture of an intervertebral disc, not necessarily because of disc protrusion and with no clinical signs of nerve root compression. It is estimated that approximately 40% of patients suffering from chronic low back pain are due to intervertebral disc degeneration. (3,4)

ANATOMY

Intervertebral discs are located between vertebrae and serve as “cushions” absorbing vibrations generated by spine movements. Intervertebral discs and vertebrae form together the spinal canal, where the spinal cord and nerve roots are located. These nerve roots exit the spinal canal in order to innervate various parts of the body.  At the posterior part of the spine, intervertebral discs are supported by facet joints which limit the spine’s movements towards all directions, providing in this way further stability. (5)

Every disc is composed of the nucleus pulposus, annulus fibrosus and vertebral end-plates. The nucleus is the central gelatinous part of the disc and the annulus fibrosus is the outer ring. The healthy disc is normally avascular.

The intervertebral disc innervation is a complex mechanism. The sensory innervation pathway of the intervertebral disc follows branches of the sympathetic chain (consisting of sympathetic ganglia), travelling bilaterally down the sides of the spine to the coccygeal level and ending up to the last ganglion, i.e. ganglion IMPAR (ganglion of Walther). (6)

The posterior (dorsal) part of annulus fibrosus is innervated by branches of the recurrent meningeal nerve (sinuvertebral nerve), which is a branch of the ramus communicans connecting the spinal nerve with the sympathetic chain. The recurrent meningeal nerve (sinuvertebral nerve) courses ventrally along the nerve root and goes back into the spinal canal in order to create a network of smaller interconnected nerve branches which innervate the posterior longitudinal ligament and the anterior dura mater. The innervation of the vertebral body is provided by the same nerve network.

The anterior longitudinal ligament is innervated by a network of nerve fibers emerging from the sympathetic chain bilaterally. The anterior and lateral parts of the annulus fibrosus of the intervertebral disc are innervated by rami of the sympathetic chain: the ramus communicans and the network enclosed in the anterior longitudinal ligament.

Given that pain signals travel to the spinal cord through the sympathetic chain, many  researchers pioneered by NAKAMURA, believe that disc-induced pain signals are transmitted from every lumbar level of the spine to the dorsal root ganglion (DRG) of the 2nd lumbar spinal nerve and, through the spinal cord, finally reach the brain.

CLINICAL SIGNIFICANCE OF INTERVERTEBRAL DISC INNERVATION (6,9)

As mentioned above, nerve fibers innervating the posterior part of the disc and posterior longitudinal ligament create a nerve fibre network and are interconnected sidewards and upwards. This explains why patients with intervertebral disc degeneration very frequently complain about central pain in the spine radiating alternatively leftwards or rightwards.

The fact that pain signals coming from low back degenerated discs end up to DRG of the 2nd lumbar spinal nerve, explains why many patients complaining about chronic pain in the groin region (corresponding as to dermatome to L2 spinal root) suffer from IDD of the lower intervertebral discs of the lumbar spine.





MECHANISM OF DISCOGENIC PAIN (19-26)

The progressive intradiscal degeneration results in the nucleus dehydration and leads to circumferential or/and radial tears of  the annulus fibrosus (annular tears). When the degeneration advances, these annular tears extend up to the outer third of annulus fibrosus and the nucleus material stimulates neogenesis of a vascular network and of nociceptors outside and sometimes inside the disc.
The stimulation of these nociceptors through various mechanisms (involved in patients’ daily activities),  leads to chronic low back pain of discogenic aetiology.

DIAGNOSIS

SYMPTOMS

Patients often describe a recent attack of acute stabbing pain, which was induced by the acute rupture of the inner part of the intervertebral disc.

Patients with lumbar DDD  usually complain about a cenral pain in the low back, which aggravates with bending, getting up, prolonged standing and sitting, and subsides when lying down.

The pain may radiate down to the buttocks and lower limbs usually up to knee height, and only rarely does it have radicular nerve distribution that extends to the feet. In some rare cases the pain is distributed to the groin region and upper medial thigh or/and the lateral part of the scrotum.

Disc degeneration between the 3rd and 4th vertebrae usually induces pain radiating to the anterior thigh.  Disc degeneration between the 4th and 5th vertebrae usually induces pain radiating to the lateral thigh and sometimes to the posterior thigh, and finally when the degenerated disc is between L5 and S1, the pain radiates to the posterior thigh.

DIAGNOSTIC EXAMINATIONS

MRI provides detailed information on anatomical abnormalities of the spine. In case of  DDD-induced pain, the morphological findings are considered to be just indications and not diagnostic evidence for the pain aetiology. Many patients with MRI disc degeneration findings do not complain about any pain.

The presence of a high intensity zone (HIZ) in the MRI has been correlated with the presence of discogenic pain at the same level. HIZ may be an indication of annular tear extending up to the outer third of the annulus fibrosus. HIZ may be due to the presence of inflammatory cytokines. Some investigators support that there is 80% correlation between HIZ and discogenic pain, while others believe that HIZ is normally present in asymptomatic patients  as well.

Thus, the golden standard for the diagnosis of discogenic pain still remains the  provocative discography. This is the only minimally invasive examination connecting the MRI morphological abnormal findings with the pain as reported by the patient. The degree of disc degeneration is evaluated with CT scan that is conducted immediately after the discography with contrast medium. Based on the contrast distribution within the disc, the degeneration is classified according to the Dallas Scale. (14,16,17,18)

Dallas Scale
Degree 0 =  contrast confined into nucleus pulposa (normal disc)
Degree 1 =  contrast extending to the inner third of annulus fibrosus
Degree 2 =  contrast extending to the mid third of annulus fibrosus
Degree 3 =  contrast extending to the outer third of annulus fibrosus
Degree 4 = contrast extending to the outer third of  annulus fibrosus and around its circumference

Degeneration of the 1st and 2nd degree are almost always painless. Degeneration of the 3rd degree induces pain during discography in 75% of patients  . Degeneration of the 4th degree is the most severe form of degeneration and almost always manifested with pain.

TREATMENT

CONSERVATIVE TREATMENT (38,39,40)

In general terms, anti-inflammatory drugs and mild opioids are recommended for a short period of time (up to three months). Systematic review has not revealed additional benefit compared to active theraupeutic exercises, rest and other conservative treatments, such as spinal traction, chiropractic therapy, hot packs and support belts.

INVASIVE PAIN TREATMENT

Should the conservative treatment fail and the patient keeps complaining about disturbing pain restricting him/her in daily activities,  s/he has to be treated with minimally invasive therapeutic techniques.

Α) Transforaminal Epidural Corticosteroid Injection. There is no evidence for the therapeutic result of epidural corticosteroid injection. There are reports about cases where pain was improved but the pain relief period was short. However, there are also reports of other cases where pain did not improve at all.

Β)Intradiscal Corticosteroid Injection There is no evidence for the therapeutic result of intravertebral corticosteroid injection. In case reports, there are controversial views about the success of the method. (41,43)

C) Ramus Communicans Nerve Block The block is conducted diagnostically with local anesthesia. Should the patient report more than 50% pain relief, then follows another session of radiofrequency neurolysis/ ablation of the ramus communicans.  Radiofrequency is applied at two levels, i.e. at the vertebrae located above and below the degenerated intervertebral disc. This specific technique is evidence-based and is positively recommended. (6,9,62,63,63)

D) Disc Biacuplasty (DB). This is a minimally invasive technique applied under radiological guidance and local anesthesia. Two electrodes are inserted into the affected intervertebral disc (with special needles) developing a high-frequency electrical field with cool circuit at the posterior part of the intervertebral disc. (52,53)

The radiofrequency application lasts 15 minutes and the temperature elevation achieved  deactivates the nociceptors developed in the annulus fibrosus of the posterior disc surface.

The therapeutic result of this specific therapeutic technique is apparent about 2 months later and in the meantime the patient follows a special exercise and activity program. This is a relatively new but well-promising technique. There are some observation studies and individual case reports showing great improvement, but the results of evidence-based studies are still to be expected.

MEDICAL INFORMATION SOURCES

1. PAIN PRACTICE JOURNAL

2. BONICA”S MANAGEMENT OF PAIN

3. PAIN PHYSICIAN JOURNAL

4. INTERVENTIONAL PAIN MANAGEMENT BOOK

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