Before getting started, I have to repeat that I am not offering any medical advice, simply illustrating some of the engineering aspects of the body. A doctor should always be consulted first. However, this and the following posts may provide some help in understanding the possible causes of pain in certain cases.
When we look at a human skeleton from the side, we are immediately struck by one important fact??.the skeleton is not straight, it has curves in it. In fact, it has four curves in it:
One is in the neck, called the ?CERVICAL? curve, one is in the upper back called the ?THORACIC? curve, one is in the lower back called the ?LUMBAR? curve, and the final one is down by your tailbone, called the sacral curve.
Figure 5 below shows some typical curves ( these vary from person to person ). As with all the weblinks, I am using them simply because they have good diagrams, and do not have any connection to the people involved:
Why is the skeleton not simply a straight line ? In other words, no curves at all, and just a bunch of vertical bones ?
Imagine that you took a piece of straight wire and managed to stand it on it?s end on a table. Now, you apply a vertical force straight down on the piece of wire. I think that we can pretty much see that it wouldn?t take long for the wire to buckle and collapse.
Now, imagine that we take that same piece of wire and make a spring out of it. Now, we repeat the same experiment.
This time, when the spring has pressure applied to it, the spring deforms and becomes shorter in height. Provided we do not apply a ?massive? force to it, when the force is removed, the spring restores itself to it?s correct height.
The curves in our spines act a little bit like that.
Our spines are made up of little bones that interlock with each other ( an extremely important fact that can be one of the main issues in neck and arm pain ). These bones are called VERTEBRAE and they interlock with each other via small hinges called FACET JOINTS.
So far we have only spoken of bones and not of anything else. For a spine to act like a spring, there must be something ?flexible? somewhere, otherwise, a bunch of bones are simply not going to be flexible. The missing element is what is known as an ?INTERVERTEBRAL DISC OR DISK ?. The term ?intervertebral? simply means that the disk is in between two vertebrae.
Disks are nature?s shock absorbers. They are what turn our spines into ?springs?.
What are disks made up of ?
They have two parts. The first part ( in a healthy disk ) is called the ?NUCLEUS? PULPOSUS. From ancient languages ( Greek and Latin ) we get most of the terms used in reference to the spine. The term ?nucleus? refers to the center of something, like an atom. So, the nucleus pulposus is at the center of the disk. The term ?pulposus? means ?pulp like?. In other words, a jelly. We will see later that this is not always the case.
We now come to the second part of the disk, known as the ?ANNULUS FIBROSIS?. Imagine that we take an onion and chop off the top and bottom. We then cut out the center of the onion and throw it away. Now we are left with a series of concentric onion rings. In a fresh onion, we can apply some force vertically down on the onion, and it will ?bounce back? again when we remove the force. Now imagine that we leave the onion out for a couple of weeks. It becomes dry and brittle. Now, if we apply a vertical force, the onion rings start to split and crack. This is exactly what can and does happen to the disks of our spines if the curves in our spines are not what they should be. What can cause this will be discussed later. The term ?annulus? means a ring ( like our onion ring ), and the term ?fibrosis? means fiber like. Thus, we have a series of concentric fibrous rings, with a hollow center. The nucleus pulposus or jelly lays in the middle.
In a healthy disk, there is plenty of mosture in the disk, both in the jelly like center and in the rings. These disks lay in between the bones of the vertrebrae. When a vertical force is applied to the spine, the jelly like center distorts and transfers the force to the side. We call this a lateral distribution of force. It?s a bit more complex than that, but for our purposes, it will suffice.
The disks act like shock absorbers in our spines and when healthy, will restore themselves back to their original size.
When we are young, we have a blood supply to the disks. As we get older, that supply gradually reduces. Blood brings nutrients and fluids to the disks. It also removes waste products. As we get older, and this supply begins to die off, we need another mechanism to bring fluids in and waste out. A pumping action is needed. That pumping action is brought about by simply walking for example. When we walk, an incredibly complex sequence of events occurs. One of these events involves the disks being compressed and decompressed with every step. This pumping action invokes an osmotic type reaction which causes a transfer of fluids. Our bodies were made for walking ( hunting animals, fetching water, walking long distances to cut crops and fetch fruits and berries etc ). Our bodies need this motion in order to keep our disks healthy. Going on the treadmill or running doesn?t always quite cut it, for a variety of reasons that I won?t go into here. Right off the bat, we can see that sitting at a computer all day can certainly cause at least one problem. Our bodies were in no manner whatsover designed to sit at a desk all day.
When our spines move away from their correct positions ( either the curve becomes too small or too large ), forces applied to the spine change dramatically in their effect on the disks. The increased pressure causes mositure removal from the disks. This means that the disks become drier, and the annulus fibrosis becomes dry and brittle, just like the onion that lay out too long .
Several things can now happen.
Firstly, the disk can bulge. When this happens, the jelly like center is pushed against the onion rings of the annulus fibrosis. The annulus fibrosis, in turn becomes deformed and one part of the ?onion? will deform and push outwards. Big deal you might think. Unfortunately, there is another aspect of the spine for which this is very important. Our nerves pass from our brain down our spinal chord. Like the electrical wiring in our home junction box, the nerves leave the spinal column at certain exit points down the spine and head off to our arms, legs, hearts, kidneys etc.
So what are these exit points ? We spoke earlier about how one vertebra or spinal bone connects to another vertebra or spinal bone directly above it. Little pieces of bone on the top vertebra link to little pieces of bone in the bottom vertebra. They form what is called a ?FACET JOINT?. This little joint should be able to operate smoothly, and has lubricating fluid inside it. Think of it as a little hinge. Imagine the hinge on your car door. It normally operates nice and smoothly. Imagine that you have an accident and the door gets bent. Now, the hinge parts are not perfectly parallel to each other. The door does not open or close easily, and noises are heard. Exactly the same thing can happen with your neck. If the hinges parts are not aligned, pressure can cause them to ?stick together?.
If we now have a bulging disk and the bulge happens to ?line up? at the point where the nerves are exiting the spine through a little hole formed from the upper and lower vertbrae called the ?INTERVERTERBRAL FORAMEN?, pain can be caused. ?Intervertrebral? simply means ?Between the vertebrae?, while ?foramen? is just a fancy word for a hole.
The height of the hole depends on the thickness or height of the disk. The height of the disk depends on the amount of fluid in it. The amount of fluid depends on a number of factors, but the most important is how much pressure is applied. Ignoring falls and other accidents, the pressure applied depends largely on the shape of the curve of the spine. Too shallow or too deep in terms of curvature, causes an increase in pressure. This causes fluid to be squeezed from the disk and it?s height decreases. When the height decreases, the hole ( or foramen ) becomes smaller. This now means that the hole through which the spinal nerves pass becomes narrower. Remember that we don?t just have forces applied up and down, we also have them left to right and in a rotational manner etc, as we turn and twist during our daily activities.
Now we can get hit with a ?double whammy?. The human body does some incredible things. One thing that it does ( and we still don?t understand all the details ) is that when the body detects excessive pressure, it will often lay down a protective coating of extra calcium in what is known as a bone spur ( or ?OSTEOPHYTE? ). Literally, the body will try to ( and can, in some cases ) fuse the upper and lower vertebrae together.
Before this happens, the spurs grow around the foramen holes. Even without anything else happening, they can push against the spinal nerves leading from the foramen and cause pain.
I?ll break this portion into two parts, as there is quite a lot to cover.
The best video that I have found showing some of the issues covered here, are shown in the following. I have no connection to the people who make the device, neither have I used it. It just happens to be the best video that I have found: