This week alone we've had two patients present to clinic with a potential spondylolisthesis. So what is it? Is it dangerous, can it be seen or felt? You can't slip a disc like people will tell you, but you can slip a vertebral joint. Here's how. Spondylolisthesis refers to the forward slippage of a vertebral joint of the spine due to a fracture of something called the ‘pars interarticularis’. Spondylolysis is the stage preceding spondylolisthesis, where the pars has either weakened or has stress fractured, but no slippage has occurred. If this fracture is severe and unstable, the vertebral joint is able to slide forward as its no longer 'locked in' by the pars. Leading to the condition known as spondylolisthesis. You can see these three stages below. Look out for the pars in the diagram and how it would work to prevent the joint below it slipping outside of its normal range. It acts almost like a jigsaw puzzle, fitting nicely with the joint below. Most commonly, spondylolisthesis affects the lumbar spine (low back) due to the curvature of the spine and the fact that it's the most weight bearing region. However, it can be seen in the neck and thoracic spine.
It can be caused by traumatic injury, typically some sort of hyperextension injury of the low back e.g. gymnastics fall or car accident. However, more commonly it's caused through repetitive stress or degeneration of the pars described above. A spondylolisthesis is graded depending on the severity of the forward slippage. There are four grades as shown below. These gradings are important as it alters prognosis and instability within the spine.
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Natural selection acts solely by accumulating slight successive favourable variations, it can produce no great or sudden modification; it can act only by very short steps. - Charles Darwin Structure governs functionDuring my time at university, I was introduced to the principle "structure governs function". In anatomical terms, this means that our bodies developed in a way that serves a specific, necessary ability e.g. 4 fingers and a thumb which allow humans to grip, use tools and illustrate hand signals as communication. I use the word necessary intentionally. Darwin's theory of evolution by natural selection tells us the long term changes to anatomy and physiology only occur when they give an organism an advantage, therefore being deemed necessary. There was always debate amongst my peers and lecturers on whether this principle can be flipped around; "function governs structure". In the short term, yes. When a person permanently loses a sense, for instance hearing, it's common knowledge that the remaining senses often become heightened. A study published in the Journal of neuroscience in 2012 found that when the brains of congenitally deaf people were observed through fMRI (A fancy MRI scanner that allows activity of the brain to be monitored), the researchers found that rather than the area of the brain that is in charge of hearing (Heschl's gyrus) being missing or empty, it's role had been altered through the process of neuroplasticity to detect vision and touch.
However, this trait is not passed on through reproduction and the function of the parents advantageous vision and touch has not altered the structure of their child's Heschl's gyrus. The reason for this is summarised in the Darwin quote at the top of this page. Permanent changes to anatomy only occur over extremely long periods of time, in tiny incremental progressions. Therefore, it doesn't appear that function can govern structure, particularly in the short term in a way that will positively adapt a human being to a new day to day lifestyle. This, I believe is the underlying issue of modern societies battle with pain, stiffness and disease. It gives a reason as to why our bodies don't suddenly alter themselves to suit our office jobs, evenings slumped on the sofa, diets dense in processed foods and the 3-4 hours UK adults spend on average watching television every day. |
AuthorsNiall Walsh Archives
July 2023
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