Last Updated on October 31, 2023
Discogenic back pain is a common cause of axial low back pain [the pain is in the back as compared to radicular that that occurs in limbs as referred pain] without radicular symptoms. The condition is caused by damage to one or more discs.
Relevant Anatomy
The spine consists of stacked vertebrae that are connected by intervertebral discs anteriorly and facet joints posteriorly.
The discs are fibrocartilaginous pad-like structures that contribute to about one-third of the height of the spinal column.
These act as shock absorbers and help in the transmission of mechanical loading of the spine.
Each disc consists of
- Nucleus pulposus
- Central, gel-like substance
- Formed by water and proteoglycan
- Held together by elastin and type II collagen fibers.
- The annulus fibrosis
- A firm outer ring that surrounds the nucleus pulposus
- Composed of bundles of type I collagen arranged in multiple oblique layers called lamellae.
- A healthy lumbar disc has approximately 20 layers of lamellae.
The interverbal discs are supplied by the sinuvertebral nerve. The intervertebral discs are relatively avascular and have poor healing power.
Causes of Discogenic Back Pain- Pathophysiology
Degenerative disc Cascade was introduced by William Kirkaldy-Willis and describes the 3 general stages of disc degeneration
- Dysfunction
- Small circumferential tears within the outer layer
- Grow inward causing reduced mobility.
- Relative Instability
- Disc material protrudes outward through the tears
- Causes a decrease in the disc height
- Restabilization
- Osteophyte formation along disc margins
- Causes fixation of discs and vertebral segment restabilization.
Structural damage to the disc is characterized by endplate fracture, radial fissuring, and herniation.
Disc degeneration is accelerated by
- Familial predisposition
- Occupations involving sitting positions and vibratory forces
- Physically strenuous activities and repetitive motion
However, not all damaged or degenerated discs cause pain. Disc abnormalities are commonly seen on MRI in asymptomatic individuals.
Typically, the mechanism of injuries to the lower back is due to
- cumulative trauma such as bending
- sustained loads, such as sitting
The pain in the disc is due to the ingrowth of nerve fibers within annular fissures. In a healthy disc, neural penetration through the annulus is about 3 mm but degenerative discs have shown deeper penetration of the annulus fibrosus. These also have a higher density density of nerve fibers within the endplates as compared to healthy endplates
There are a number of inflammatory markers involved in stimulation leading to pain.
Clinical Presentation- Symptoms of Discogenic back pain
The duration of symptoms can be acute (less than 6 weeks) or chronic (more than 12 weeks). between 6-12 weeks, the symptoms are called subacute.
The main symptoms are
- Pain in the midline or paraspinal region
- Stiffness may be present
- Occasional radiation to buttocks or flanks may be present
- Pain is worsened by
- Forward bending
- Lifting
- Axial loading
- Coughing/sneezing
- Sitting especially for longer times (> 60 minutes)
There could be a history of a profession that entails heavy manual handling that involves bending and lifting.
On examination, the patient may carry himself normally as the pain is within limits of tolerance.
When pain is greater, the patient would be more comfortable standing than sitting as sitting loads the spine more.
Tenderness may be noted in the paraspinal region. The motion of the lumbar spine may be restricted in all the planes.
Neural examination for motor and sensory functions [strength, sensation, reflexes] is apparently normal.
Tests for neural involvement are negative though the maneuvers may lead to an increase in back/buttock pain.
(Compare disc herniation with radiculopathy)
Imaging
Radiographs
X-rays are the first line of imaging though they do not offer much information and that too until late. The X-rays may reveal
- Narrowing of the disc space
- Endplate sclerosis
- Vacuum vacuum disc phenomenon (Gas accumulation in the disc visible on x-ray0
- Osteophyte formation
Flexion and extension radiographs may be done to rule out instability.
CT
CT allows better visualization of the many elements such as a bone spur. CT is much more sensitive than X-rays and catches these changes early.
MRI
MRI provides the most detailed and comprehensive picture of the spine, spinal cord, and disc. MRI findings can identify the disc as a pain generator in a substantial number of cases clinical correlation is very necessary as with age, there are many degenerated discs that are asymptomatic.
A hyperintense signal within the posterior annulus indicates damage on MRI also termed as high-intensity zone, it is quite specific and has a predictive value of the disc being symptomatic with an annular tear as well.
MRI may also show modic changes which are degenerative changes in the vertebral endplates and bone marrow. There are 3 types of modic changes. Type modic changes are highly associated with disc degeneration and pain.
MRI is done usually after 6 weeks have passed without improvement. In case of neural deficit or suspicion of some other ailment, it can be done earlier. or there is some.
Provocative Discography
It is a fluoroscopically guided diagnostic procedure performed in cases of discogenic back pain to confirm whether a particular disc is the source of pain or not.
The procedure involves the administration of contrast into the nucleus pulposus of the suspected painful disc. This leads to an increase in intradiscal pressure and mimics the loading and pain caused if the particular disc is responsible.
However, the use of provocative discography in discogenic back pain is not extensive because of
- Technique is invasive
- Risk of accelerating the degeneration
- High false positives
Differential Diagnosis
- Lumbosacral Facet Syndrome
- Spondylolisthesis
Treatment of Discogenic Back Pain
Non Operative Treatment
Most of the patients with discogenic back pain are treated by nonoperative means. Operative/invasive treatments are considered only for those who have not responded to nonoperative measures.
Physical therapy and home exercise is typically the first step in the treatment. Pain relief drugs like NSAIDs are used for pain control.
Other measures that help are
- Cognitive therapy
- Lifestyle modifications
Nonoperative treatments are quite effective in discogenic back pain but may take longer to provide relief when compared with surgery. However, studies have shown that there is no significant difference in short-term or long-term in patients treated with exercise and drugs than the patients treated by surgical procedures like discectomy with or without fusion.
Minimally Invasive Procedures
Earlier the discectomy was the standard surgical procedure for disc-related issues. However, many minimally invasive procedures have developed with their own sets of indications. Though the procedures require a greater number of studies these are worth mentioning.
These procedures are together termed as minimally invasive procedures and are more interventional procedures than surgical ones. These have been used in discogenic back pain with mixed results.
- Epidural steroid injection – Has been observed to have fair efficacy in discogenic back pain. The exact mechanism is not clear but antiinflammatory action has been thought to be responsible for it.
- Minimally Invasive Procedures
- Nucleoplasty – Heat is used to denaturation of nucleus pulposus which is drained to cause decompression
- Intradiscal electrothermal therapy and Biacuplasty
- A heat probe is used to destroy sensory fibers innervating the disc
- Done under fluoroscopy
- The level of evidence varies from good to fair
- Intradiscal PRP injection
- Uses platelet-rich plasma (PRP) injections
- PRP is made from autologous blood and contains growth factors and cytokines
- An emerging treatment option for discogenic back pain
Surgery
Surgery is indicated in patients with discogenic back pain who have not improved with conservative treatment
The various surgical options are
- Removal of the disc
- Spinal fusion
- Artificial disc replacement
It must be emphasized that short-term and long-term results of discectomy in discogenic back pain are comparable with non-operative measures. However, surgery results in earlier pain relief.
Spinal fusion is done in case of instability of the spine and is not routinely done with disc removal. One of the complications of blocking motion by fusion is that there is an exaggerated motion of adjacent segments leading to hastened wear and tear of adjacent vertebrae, termed as adjacent segment disease.
[Read more about Spinal fusion]
Discectomy
Discectomy can be done in selected cases of discogenic pain using an open method or using endoscopy. The aim is to remove the diseased disc that is impinging on the neural structures.
Though clear indications are not defined yet for discogenic pain, a lack of response to conservative measures may lead to the consideration of a disc removal procedure.
Total Disc Arthroplasty
The most common indication of total disc arthroplasty is a single-level disease without facet joint involvement.
The procedure preserves the disc height and segmental motion and prevents the development of adjacent segment disease.
The instability of the prosthesis is a known complication. This may result in back pain and necessitate posterior stabilization.
Sometimes revision of the arthroplasty may be needed. Fusion may be considered in other cases.
Artificial replacement of the disc is more relevant in the cervical spine where mobility is needed. For lumbar spine, it is still in the trial phase.
Complications
- The disability might range from mild to severe. Most of this is temporary
- Stress
- Depression
- Loss of work hours
- Complications due to surgical procedures
References
• Ohtori S, Inoue G, Miyagi M, Takahashi K. Pathomechanisms of discogenic back pain in humans and animal models. Spine J. 2015;15(6):1347–55. [Link]
• Adams MA, Roughley PJ. What is intervertebral disc degeneration, and what causes it? Spine (Phila Pa 1976). 2006 Aug 15;31(18):2151-61. [Link]
• Aoki Y et al. Increase of nerve growth factor levels in the human herniated intervertebral disc: can annular rupture trigger discogenic back pain? Arthritis Res Ther. 2014 Jul 28;16(4):R159. [Link]
• Fujii K, et al. Discogenic Back Pain: Literature Review of Definition, Diagnosis, and Treatment. JBMR Plus. 2019 May;3(5):e10180. [Link]
