The word ‘Stenosis‘ is derived from an ancient Greek phrase meaning narrowing, so when we pair it with ‘spinal‘ it simply means ‘narrowing of the spine’. So where and why does this happen. Well its easiest explained along side some basic anatomy.
We have 24 moveable vertebrae in our spines. Each of these has a large vertebral body at the front and a bony complex a the rear. The latter changes in both size and shape as you move up the spine towards the head, with the largest and most rhobust of these being at the base. This is simply a reflection of the pressures applied through this area by external forces and muscles (We will use the lumbar spine in our explanation). Between these two anatomical features sits a hole, this is the spinal canal and houses the spinal cord.
When we place two vertebra on top of each other we create a pair of weight bearing joints called the facet joints. These allow, but also control the movement available within the spine. Sitting between the anterior bodies is an intervertebral disc that, acting like a shock absorbing spacer, maintains a healthy gap ensuring the joints can move freely.
The two primary areas of interest with regards to spinal stenosis are the spinal canal and the neural foramina (foramen). These are both highlighted on the diagram below and enable you to see them on a spinal model in context. To enable you to orientate your self, this picture is taken from the ‘rear right’ side.
Neural Foramina
The Neural Foramina are a pair of anatomical ‘holes‘ located on opposite sides of the vertebra, created by the joining of two neighbouring bony complexes. Through this bony opening travels the nerve roots or branches from the spinal cord that go on to serve all of the nerve related functions throughout the body. Foraminal stenosis here is normally a consequence of either bony growth or a shift of one of the vertebra on the other (Spondylolithesis or Retrolithesis). The latter is a condition with a dedicated section so for more information please locate the link in the left hand menu.
Bony Growth or ‘Osteophytic spurs’ occur mainly in response to increased mechanial load and are seen around many of the weight bearing joints in the body. This build up of bone is in stark contrast to the common belief that ‘wear and tear’ is only the wearing down of the joints. In spinal stenosis the facets are the commonly affected joints normally caused by changes in the spinal biomechanics. This may be due to any number of reasons however disc degenration appears to be a very common contributor. The side effect of disc degeneration includes a loss of disc height and shock absorptive properties, with the knock on effect of overloading the facets. This loss of height will also cause a direct reduction in the size of the foramen. These effects are shown in the picture below.
The end result of any of these changes is the risk of nerve irritation. It is vital however to appreciate that these changes are extremely common and there variable nature means that although present, many of us will never actually get any sympoms arising from here.
Spinal Canal
As mentioned above, the spinal canal is a continuous protective channel that runs the length of the spine and houses your spinal cord. This is shown below with the spine being depicted from the front, i.e through your tummy. The important bit of anatomy to note is the ‘ligamentous Flavum’ in the picture to the right, that sits between the back of the vertebra and covers the anatomical bony gap that would otherwise be there (see original diagram at top). This ligament through overload, chronic injury or age related changes can become thickend with the possiblilty of subsequent encroachment into the spinal canal. Over time this can begin to compress and/or irriate the spinal cord and give pain and/or associated neurological symptoms such as leg pain, pins and needles, numbness and weakness.
We can also get cord compression from disc prolaspes (’slips‘) however these are detailed in their own right such is their commonality. For further information regarding disc prolapse please find the lick in the left hand column.
What does it feel like?
This is actually quite difficult to answer specifically due to the varying origins of the stenosis. Commonly seen symptoms are pain and cramping through the legs that is worse with walking but eases with sitting or forward bending. This is simply because in walking we will normally compress the spine excacerbating any narrowing but open them when we adopt a more flexed position. Symptoms can occur in one leg ( unilateral) or both ( bilateral) depending of the site and degree of stenosis and in rare cases can cause bladder or bowel dysfunction (Cauda Equina). If the latter is ever seen immediate medical attention should be sought. Local back pain is generally seen but with a lesser degree of intesity than that in the associated limbs.
Self diagnosing back pain, especially if neurological symptoms are present is extremely difficult, and you should always seek professional advice if you are unsure, your neurological symptoms are severe or, if the symptoms persist. For more information regarding spinal stenosis, its symptoms and applied anantomy try some of the following links:
