Lumbar disc herniation - Definitions and its clinical presentation

Updated: December 10, 2022.

The enigma of a 'disc herniation'

If we're not in pain - having a herniated disc is seldom a problem, and this isn't unusual. In a landmark study in the early 1990's Scott Boden and colleagues discovered that in a sample of 67 people who were assessed by neurologists and radiologists for lumbar spine disc lesions, that 24 of them were asymptomatic, they had no pain.[1]

While this is great for those who aren't in pain, it can be extremely uncomfortable for those who have a lumbar disc herniation and associated lower back pain and/or radiating leg pain. This brings me to the defining of a lumbar disc herniation and a basis for this article. What is a disc herniation? To start with, it's often got multiple names that leads to plenty of confusion in those who don't deal with the spine on a regular basis in either research or practice, so I aim to answer this question and clear up some confusion first, then I'll discuss a bit about what to expect in a clinical setting.

Appearance and Definitions

Think of the intervertebral disc that sits between two spinal vertebral bones as a custard filled donut. The middle (called the nucleus pulposus) is jelly-like and the crusty relatively firm dough (the annulus fibrosus) that holds the custard in is enmeshed and takes on circular ring formations. [Fig 1]

In the case of a true disc herniation, the jelly-like nucleus pulposus typically starts to protrude (or herniate) through a weakening of the internal part of the annulus fibrosus (or the 'doughy part' of the donut).

If enough pressure builds and the herniation reaches the outer 1/3 of the annulus (which just so happens to have nociceptive pain fibres) then some people can experience local lower back pain.[2]

We can also get a nice idea of a definition of a disc herniation if we think of it going through stages of degenerative change. [Fig 2] A note to keep in mind though is that degeneration is a normal process of ageing and so it may or may not be accompanied with pain.[5]

1. There is some initial disc degeneration that leads to something of a fault in the structure of the annulus fibrosus (the 'doughy part'). This could come about by repeated bouts of physical or mechanical trauma (or underlying disc disease like systemic bacterial infection such as tuberculosis).[3] This initial degeneration impacting on the biochemical architecture of the disc's integrity slackens the disc and the nucleus can shift without herniation outwards.
2. Following this, the jelly-like nucleus can prolapse and alter the structure of the discs outer fibres which changes the nice symmetrical shape of our donut. At this point, the prolapse or herniation is a true one because it can bulge backwards into the spinal canal and impinge upon a nerve root (it may not impinge on the nerve but still protrude backwards too).
3. The next stage - if it gets that far, and the jelly doesn't dry up in the process and resolve - leads to an extrusion of the nucleus pulposus (think of the jelly as now sitting visibly outside of the donut but staying put in line with the outer doughy part) yet it still sits within the disc's area.
4. Last we have might get a disc sequestration whereby the jelly-like nucleus breaks through the outer annulus and lies beyond the area of the disc. In some cases, the jelly can break off and 'float' around the spinal canal.

You'll note that I've bolded each name of the stage based on how the disc itself is mostly behaving. In the case of a true herniation, they're described in different forms from stages 2-4. The stage 1 degeneration is not actually a herniation but it precedes what might become a herniation.

Now that we've got those tricky definitions out of the way, lets touch upon the typical clinical presentation. That is, when someone actually has pain or other symptoms due to a disc herniation.

Clinical Presentation

I say this lightly, but the person presenting with a problem with their intervertebral disc will have a 'typical' set of symptoms that often accompanies it. As we noted earlier there can be no pain or symptoms in some people and there are also 'atypical' cases which - as the name suggests - are not typical of what a textbook presentation is. An example of an atypical disc case might be the phenomenon of referred pain.[6] In this instance, people can present with pain arising solely from the medial knee or other part of the leg due to the convergence of nociceptive afferents in the dorsal horn of the spinal cord.

Demographic

Strictly speaking a disc herniation is more common in people (and men more than women) aged between 20-45 because they still have a higher relative water content compared to older adults. The nucleus pulposus of the disc is jelly-like because it is well hydrated and this explains why younger rather than older people present with them.

The individual may be de-conditioned and have poor muscle mass or strength, or they might have underlying congenital anomalies that predispose them to a higher likelihood of having a disc herniation (eg. an excessive curvature of the spine such as scoliosis or hyper-lordosis). [4]

A thorough history will also help elucidate the onset of a disc herniation beyond classic demographic information, and whether it actually is one. Remember that the patient is entitled to more than one condition and the pain generator may be coming from the disc itself or it might be something completely unrelated and the history and examination will aid in telling us this.

You might want to ask if there was there a traumatic onset? Did it come on insidiously and without a known event or wake them suddenly their sleep? Were they playing sports involving bending and rotating? Have they recently gained a lot of weight (or lost a lot of weight without planning, indicative of something more serious)?

Potential Mechanisms

The disc herniation likely comes about through a chronic loading over time with a repeated pattern that puts strain or stress on the posterior aspects of the annulus fibrosus through bending forces and compressive forces. It might also be an abrupt trauma or incident where we twist and lift something heavy that leads to tearing or damage that creates a sharp pain.

Keep in mind that the spine is designed to be resilient for this sort of tolerance, hence loading and moving it is a good thing. If there's pain though - we often need to consider how to modify things indefinitely to calm the area down.

In addition, being inactive, smoking, eating poorly and having otherwise poor general health (including higher amounts of body fat and poor core and total body strength) may also increase the risk of developing a disc herniation.

There is also consideration of the disc level and nerve root levels themselves which have a pattern presentation depending on where the disc herniation is.

In more typical cases of paracentral or posterolateral disc herniations (circled in blue below) in the lumbar spine, the nerve root involved is usually one level below the corresponding vertebral body (eg. L5 nerve root with L4 vertebral body). If the disc herniation is located in a far lateral position (circled in red below), the same nerve root (eg. L4 nerve root with L4 vertebral body) is often effected.

In the cervical spine, disc herniations are more common in the lower part of the neck between C5-C7 (but less prevalent overall than the lumbar spine) and the orientation of the nerve roots are more horizontal on their way out to supply the arms. Clinically this usually leads to a C6 nerve root being impacted by the disc between C5 and C6 regardless of where the disc herniation is (whether it is far lateral or paracentral in location).[7]

Knowledge of these anatomical aspects is very important as neurological signs and symptoms can present differently if one nerve root is impacted over another in both the upper and lower limbs.

Symptoms and signs

The patient often presents with acute sharp or 'electrical-type' low back pain after a lifting and bending incident with or without leg pain down one side (typically on the side of the herniation, which abuts or comes into contact with the nerve root) which can be worse than the LBP. The L4-L5 and L5-S1 segments and their discs are the most common sites.

The increased pressure through the involved disc can accentuate the herniation and any associated inflammation. The outer third of the disc that receives impact from a nucleus containing different tissue material appears to respond with a neuro-immune inflammation and this is pure discogenic pain than can swell, distend and cause compression on exiting peripheral nerves. Any prolonged static positions (sitting or standing) or increasing the intra-abdominal pressure (a sneeze, a cough or laughing) and bending forward will usually increase the symptoms. They may walk with an altered or antalgic gait and are often sensitive to direct palpation at the level of the involved disc.

Muscles around the lower back may also undergo a reactive-type of splinting response to general joint stressors and once they realise the stimulus is relatively harmless, typically settle within a few days to a week in most cases (naturally and without any intervention necessary).

A neurological exam of the lower limb may show signs of LMN involvement including muscle weakness at the involved level, areflexia (or hyporeflexia) of the patella tendon or achilles tendon and diminished sensation over the involved nerve root dermatome of the skin. Visible muscle atrophy may be present if the disc herniation is more chronic, longstanding and been there for a while.

Neuro-orthopaedic tests that tension or traction the sciatic nerve pathway (the level of L4 nerve root and below in typical lumbar disc herniations) may be aggravated including a straight leg raise, with additions to Bowstring, Bragard's and Sicard's tests.

Finally, to confirm the presence of a disc herniation an MRI is the gold standard for it (and any soft tissue lesions suspected that may be the cause beyond a disc itself, such as a space occupying lesion in the spinal canal or intervertebral foramen). Plain film radiography typically won't reveal anything outside of potential loss of disc height and is not indicated.

Don't forget

While the above shows us a reasonably accurate way to consider the definitions and clinical aspects of a lumbar disc herniation, always remember that other more serious or sinister things may be occurring as a part of the differential diagnosis including cauda equina syndrome and osteolytic diseases such as primary bone cancer, metastasis or spinal/discal infection.

Some of the other less serious considerations to think about which may present similarly - and sometimes more often - to a lumbar disc herniation can include piriformis syndrome, facet joint syndrome or lateral canal stenosis.

Disclaimer: This is not intended as medical advice and is for use strictly as an educational resource.

References

[1] Baker AD. Abnormal magnetic-resonance scans of the lumbar spine in asymptomatic subjects. A prospective investigation. InClassic papers in orthopaedics 2014 (pp. 245-247). Springer, London.

[2] García-Cosamalón, J., del Valle, M. E., Calavia, M. G., García-Suárez, O., López-Mu?iz, A., Otero, J., & Vega, J. A. (2010). Intervertebral disc, sensory nerves and neurotrophins: who is who in discogenic pain?.?Journal of anatomy,?217(1), 1–15. https://doi.org/10.1111/j.1469-7580.2010.01227.x

[3] Garg, R. K., & Somvanshi, D. S. Spinal tuberculosis: a review.?The journal of spinal cord medicine. 2011?34(5), 440–454. https://doi.org/10.1179/2045772311Y.0000000023

[4] Chang HK, Chang HC, Wu JC, Tu TH, Fay LY, Chang PY, Wu CL, Huang WC, Cheng H. Scoliosis may increase the risk of recurrence of lumbar disc herniation after microdiscectomy. Journal of Neurosurgery: Spine. 2016 Apr 1;24(4):586-91.

[5] Carnes MA, Vizniak NA. Quick reference evidence-based conditions manual. Professional Health Systems Incorporated; 2011.

[6] Bogduk N. On the definitions and physiology of back pain, referred pain, and radicular pain. Pain. 2009 Dec 1;147(1):17-9.

[7] Yolas C, Ozdemir NG, Okay HO, Kanat A, Senol M, Atci IB, Yilmaz H, Coban MK, Yuksel MO, Kahraman U. Cervical disc hernia operations through posterior laminoforaminotomy. Journal of Craniovertebral Junction & Spine. 2016 Apr;7(2):91.

Figures

[1] Courtesy of NIH Medline Plus (https://medlineplus.gov/ency/imagepages/19469.htm)

[2] Courtesy of Spine Universe (https://www.spineuniverse.com/conditions/herniated-disc/chiropractic-care-back-pain-non-invasive-treatment-bulging-ruptured-or)

[3] Courtesy of Orthobullets (https://www.orthobullets.com/spine/2035/lumbar-disc-herniation)

[4] Courtesy of Orthobullets (https://www.orthobullets.com/spine/2030/cervical-radiculopathy)