Back Pain – A Mechanical, but Often Multifactorial Problem

Back pain can have many causes. Most cases are mechanical in nature, involving the spinal joints, intervertebral discs, or the vertebrae themselves. However, pain can also arise from non-spinal structures such as the kidneys, uterus, bladder, or blood vessels, which can sometimes mimic spinal pain (Henschke et al., 2009). Increasingly, research has shown that back pain isn’t always purely structural. In some cases, central sensitisation where the nervous system becomes hypersensitive, leading to pain that persists even after tissues have healed (Nijs et al., 2021). Psychosomatic influences, emotional stress, and lifestyle factors are also now recognised contributors.

Modern understanding has therefore shifted towards a biopsychosocial model, recognising that back pain is influenced by a combination of physical, psychological, and social factors rather than being explained by a single anatomical problem (Hartvigsen et al., 2018). This broader approach explains why two people with similar imaging findings can have very different pain experiences. This is why a thorough assessment is essential not only to identify the physical source of pain but also to consider the wider context.

Patients often describe discomfort in the centre of the lower back or localised to one side, and it is also common for pain to radiate into the buttocks. This happens because many spinal structures are capable of referring pain into nearby regions (Bogduk, 2009). Even everyday activities such as lifting, sneezing, twisting, or sleeping awkwardly can trigger an episode. In more acute cases, people may find themselves bent forward and unable to straighten up.

Here, we’re going to look more closely at some of the main mechanical reasons for lower back pain—focusing on the facet joints, intervertebral discs, and vertebral endplates (Modic changes), Please see the separate Tabs below to better understand why they are such frequent sources of Pain.

References

Bogduk, N. (2009) On the definitions and physiology of back pain, referred pain, and radicular pain. Pain, 147(1–3), pp.17–19.

Hartvigsen, J., Hancock, M.J., Kongsted, A., Louw, Q., Ferreira, M.L., Genevay, S., Hoy, D., Karppinen, J., Pransky, G., Sieper, J. and Smeets, R.J. (2018) ‘What low back pain is and why we need to pay attention’, The Lancet, 391(10137), pp.2356–2367.

Henschke, N., Maher, C.G., Refshauge, K.M., Herbert, R.D., Cumming, R.G., Bleasel, J., York, J., Das, A., McAuley, J.H. (2009) ‘Prevalence of and screening for serious spinal pathology in patients presenting to primary care settings with acute low back pain’, Arthritis & Rheumatism, 60(10), pp.3072–3080.

Nijs, J., George, S.Z., Clauw, D.J., Fernández-de-Las-Peñas, C., Kosek, E., Ickmans, K., Fernández-Carnero, J., Polli, A. and Malfliet, A. (2021) ‘Central sensitisation in chronic pain conditions: latest discoveries and their potential for precision medicine’, The Lancet Rheumatology, 3(5), pp.e383–e392.

Discogenic Pain
Each spinal disc has a tough outer ring (the annulus fibrosus) and a jelly-like centre (the nucleus pulposus) that acts not only as a shock absorber but also as a piece of scaffolding, keeping the vertebra above from compressing directly onto the one below. When this outer ring becomes overstretched or torn, often through lifting, twisting, or trauma, it can cause pain and protective muscle spasm. In some cases, the inner material bulges out and presses on nearby nerves. This can lead to symptoms such as sciatica, where pain radiates from the lower back down the leg, or in the case of the neck, radiates into the arm (Freemont, 2009).

As we age, spinal discs naturally begin to dehydrate and lose height—a process similar to a sponge drying out. This age-related change, often referred to as spondylosis, is frequently symptom-free in many people. However, in others, this reduction in disc volume can cause the vertebrae to sit closer together, leading to joint compression, instability, or nerve irritation (Brinjikji et al., 2015).

A helpful way to visualise this is to think of your spinal discs like the suspension system of a car. When the suspension is healthy, the ride is smooth, absorbing every bump in the road. But when it wears out or loses tension, the ride can become unstable and uncomfortable.

In a similar way, degenerated or worn discs can reduce your spine’s ability to absorb shock, resulting in discomfort, stiffness and pain, this would be classed as “discogenic pain.” If the disc has a slight bulge, compression of a local nerve may occur, potentially leading to sciatica (Jensen et al., 2019). If the disc completely fails to absorb forces, increased stress occurs in the adjacent vertebral bone, leading to inflammation known as Modic Type I bone oedema (Herlin et al., 2018).

References

• Brinjikji, W., Luetmer, P.H., Comstock, B., Bresnahan, B.W., Chen, L.E., Deyo, R.A., Halabi, S., Turner, J.A., Avins, A.L., James, K. and Wald, J.T., 2015. Systematic literature review of imaging features of spinal degeneration in asymptomatic populations. AJNR American Journal of Neuroradiology, 36(4), pp.811-816.

• Freemont, A.J., 2009. The cellular pathobiology of the degenerate intervertebral disc and discogenic back pain. Rheumatology, 48(1), pp.5-10.

• Herlin, C., Kjaer, P., Espeland, A., Skouen, J.S., Leboeuf-Yde, C. and Karppinen, J., 2018. Modic changes—Their associations with low back pain and activity limitation: A systematic literature review and meta-analysis. PLoS One, 13(8), p.e0200677.

• Jensen, R.K., Leboeuf-Yde, C., Wedderkopp, N. and Sorensen, J.S., 2019. Is the presence of a lumbar disc herniation associated with low back pain in adolescents? A prospective cohort study. BMC Musculoskeletal Disorders, 20(1), p.110.

Vertebral Oedema (Modic Type I Changes)
Less commonly discussed, but increasingly recognised, is vertebral oedema, also known as Modic Type I changes. These appear on MRI scans as inflammation within the vertebral bone and are strongly associated with degenerative disc disease. When a disc loses its ability to absorb load, excess stress is transferred to the adjacent vertebrae, triggering inflammation and bone marrow swelling. Over time, this persistent fluid disrupts the inner structure of the bone (Herlin et al., 2018).

To understand this better, it helps to visualise the inside of bone. It is not solid, it’s made up of fine, hair-like structures called trabeculae, which form a mesh-like scaffolding. If fluid or inflammation sits within this delicate network for weeks, months, or even years, it can soften and weaken the structure. The vertebra becomes less capable of handling normal stress, and pain may result from even minor movement or loading (Jensen et al., 2008).

A helpful analogy is to think of a crispy roasted potato fresh from the oven. If you place it in a cup and pour gravy over it, then leave it for an hour or two, the outer crispiness and inner potato soften, turning into mush and losing its form. The same can happen to the vertebrae, constant fluid exposure weakens the internal support, making it more sensitive and vulnerable to pain.

Although still under active research, Modic Type I changes are increasingly recognised as a distinct and treatable cause of chronic back pain (Kjaer et al., 2006; Herlin et al., 2018). Encouragingly, these changes can repair over time, often progressing to Modic Type II, characterised by fatty infiltration, and eventually to Modic Type III, where sclerosis of the vertebrae occurs (Bråten et al., 2019).

References

• Bråten, L.C.H., et al., 2019. Efficacy of antibiotic treatment in patients with chronic low back pain and Modic changes (the AIM study): double blind, randomised, placebo controlled, multicentre trial. BMJ, 367, l5654.

• Herlin, C., Kjaer, P., Espeland, A., Skouen, J.S., Leboeuf-Yde, C. and Karppinen, J., 2018. Modic changes—Their associations with low back pain and activity limitation: A systematic literature review and meta-analysis. PLoS One, 13(8), p.e0200677.

• Jensen, T.S., Karppinen, J., Sorensen, J.S., Niinimäki, J. and Leboeuf-Yde, C., 2008. Vertebral endplate signal changes (Modic change): a systematic literature review of prevalence and association with low back pain. European Spine Journal, 17(11), pp.1407-1422.

• Kjaer, P., Korsholm, L., Bendix, T., Sorensen, J.S., Leboeuf-Yde, C. and Leboeuf-Yde, C., 2006. Modic changes and their associations with clinical findings. European Spine Journal, 15(9), pp.1312-1319.

The facet joints are small stabilising synovial joints at the back of the spine, linking one vertebra to the next and guiding movement, particularly in bending and twisting. Over time, repetitive strain, poor posture, or trauma can cause these joints to enlarge, degenerate, or become inflamed. This can lead to stiffness and localised back pain, which may also radiate into the buttocks or thighs.

Think of the facet joints like the hinges on a door: when they’re well-aligned and lubricated, the door moves freely; when worn or irritated, they creak, stick, and put strain on the frame. Similarly, when facet joints become inflamed or overloaded, movements such as extension, rotation, or initiating flexion often become painful.

Facet joint–related pain is typically mechanical in nature. It often worsens after periods of inactivity or prolonged rest and can ease with gentle movement (StatPearls, 2025). It is also frequently seen in combination with disc degeneration, as both conditions often coexist in spinal osteoarthritis or age-related spondylosis (Cohen et al., 2020).

Research has shown that facet joints contribute to between 15% and 45% of chronic low back pain cases, making them a significant but sometimes overlooked cause of spinal pain (Friedly et al., 2019; Manchikanti et al., 2020). Despite this, diagnosis can be challenging, as symptoms and imaging findings alone are not always reliable. Instead, medial branch blocks or diagnostic nerve injections remain the gold standard for confirming facet-mediated pain (Falco et al., 2020).

Facet joint degeneration is strongly associated with age, particularly after 50, and is more common where disc degeneration is already present (Boateng et al., 2023). Understanding the interplay between discs, joints, and surrounding spinal structures is therefore essential for accurate diagnosis and effective treatment.

References

• Boateng, K.A., Ampomah, K., Baidoo, P.K., Osei, L.B. and Osei-Poku, F., 2023. Lumbar facet joint arthrosis on magnetic resonance imaging and its association with low back pain in a selected Ghanaian population. Journal of Neurosciences in Rural Practice, 14(4), pp.511–517.

• Cohen, S.P., Raja, S.N. and Lamer, T.J., 2020. Pathogenesis, diagnosis, and treatment of lumbar facet joint pain. Anesthesia & Pain Medicine, 15(3), pp.235–248.

• Falco, F.J.E., Manchikanti, L., Datta, S., Sehgal, N., Geffert, S. and Singh, V., 2020. Systematic review of diagnostic utility and therapeutic effectiveness of lumbar facet joint interventions. Pain Physician, 23(6), pp.E557–E590.

• Friedly, J.L., Comstock, B.A., Turner, J.A. and Heagerty, P.J., 2019. Long-term effects of repeated injections for lumbar facet joint pain. Annals of Internal Medicine, 171(7), pp.441–450.

• Manchikanti, L., Kaye, A.D., Soin, A., Albers, S.L., Beall, D.P., Latchaw, R.E. and Hirsch, J.A., 2020. Facet joint pain and its management: a review of current evidence. Pain Physician, 23(6), pp.E557–E590.

• StatPearls, 2025. Facet Joint Disease. [online] Available at: https://www.ncbi.nlm.nih.gov/books/NBK541049/[Accessed 28 August 2025].