Is disc narrowing a source of low back pain?
There is a misconception that disc narrowing is not a potential source of low back or neck pain. This may be partly due to studies that show some people with disc narrowing have no low back pain. Any structure with a nerve supply is a potential source of pain. In the vertebral disc complex the outer layer of the disc is innervated. The vertebral end plate also develops new blood vessels and nerves when disc narrowing occurs therefore is also a potential source of pain.
The skeleton is a series of bones with fluid washers often present between bones and vertebrae. Once the fluid washers deteriorate they often narrow and pressure falls on underlying bones. The best example is knee pain from osteoarthritis. Once the fluid washer thins pain is generated when walking or running but improves on sitting.
I have seen the expression “Mechanical” low back pain for over two decades now in letters from Orthopaedic surgeons. I suspect this means low back pain that is caused by loading of the vertebral/disc complex such as when lifting, bending, sitting for long periods and improves when unloading the disc such as when lying down. This pattern of symptoms is very common in people with low back pain and in deed people can be found lying down in the waiting room with severe low back pain at least once a month.
So we have damaged fluid washers and pressure combining to create the sensory component of pain. The other factor that determines an individual’s pain perception is their pain threshold. Migraine is the genetic predisposition to amplify pain as the electrical channels in the brain sensory pathways opens up quicker that in people without migraine. A large population study showed people with migraine have three times the risk of low back pain and over six times the risk of fibromyalgia. Another factor likely to reduce pain threshold is sympathetic nervous system and Hypothalamic-Pituitary-Adrenal activity, a topic I researched during my PhD.
The research shows that people with disc narrowing have an increased risk of low back pain compared to those without disc narrowing. The research shows people who have disc narrowing have an increased risk of low back pain. Torgersen and Dotter (1976) showed in 40 to 49 years olds that 6% of people without low back pain had disc narrowing and 48% of people with low back pain had disc narrowing. The research also shows in people with disc narrowing the risk of pain increased with occupations that loaded the lumbar spine discs. Luoma et al (2000) also concluded that low back pain is more likely in those with narrowed discs. Furthermore in those with disc changes on MRI scan there was an increased risk of pain with occupations that loaded the lumbar spine discs. Office worker 1.0, carpenter 2.9 and machine driver 4.7. Machine drivers experienced 4.7 times the low back pain for the same changes in the disc seen on MRI scan compared to office workers.
When taking all this into account, the risk of experiencing low back pain with disc narrowing, for someone with migraine, who performs a labouring job is likely to be markedly greater than for people who perform office work without migraine.
When considering whether disc narrowing causes low back pain modic changes are almost irrelevant. Factors such as how narrowed the discs are, the biomechanical forces applied to the disc and a persons pain threshold are infinitely more important. The person with the markedly narrowed discs in the above scan has performed a very heavy occupation for the past eight years and I suspect will never be able to return to her previous occupation without significant pain due to both the extent of narrowing and the heavy nature of her occupation. Optimism is a fairy tale in this patient.