Describing back injury concerning the discs of the spine has become confused over the years. In particular the term ‘slipped disk’ has led to the misconception that anytime someone has hurt their back, or has a disk problem, that it is because their disk has ‘slipped’.
There is no such thing as a ‘slipped disk’
By looking closely at the anatomy of a disk it is clear that a disk has very strong ligaments that attach to the vertebra above and below, and as such it cannot physically move. However there a very unique structural injuries that can occur to a disk, that can then cause problems and create a back injury.
The disc is made up of the vertebral end-plates, a hard outer fibrous shell (annulus fibrosis) and inside this is a semi fluid substance similar in consistency to toothpaste (nucleus pulposus). Only to the end-plates have blood supply, and the spinal disc itself has very few nerve endings and these are towards the outer third of the disc. So injuries occurring deeper within the disc present a challenge to identify and heal, and without a blood supply the disc lacks a way to repair itself.
Disc bulge and disc herniation
In order to visualise how a disk is affected during injury, comparison with the properties of a tomato serves as the best analogy. If we were to place a tomato on a bench and slowly lower a brick on top, the tomato will reduce in height and at the same time widen as it accommodates the weight of the brick. This is similar to what happens to a disk when it developed a disk bulge. So this bulging occurs when there is some loss in the integrity of the disk, and this can be caused by simple wear and tear through ageing, or through excessive load on the back over a long period of time. So in essence the disk is structurally intact but it is undergoing structural changes which compromise it’s ability to function well.
Now if we take another tomato and drop the brick on top instead, it is easy to imagine that the outer skin of the tomato will split as the material inside bursts through allowing what is inside to leak out. This is what happens in a disk herniation, where the disk is inherently weak on a posterolateral angle (a 45 degree position behind and to the side).
So if someone bends forward and attempts a heavy lift, this forces the nucleus pulposus to push against the back wall of the disk, and if the disc has been structurally weakened through the a load over a few years or if the force is sufficiently large enough, then the toothpaste like centre of the disk can burst through the discs’s outer fibre. Unfortunately the exact location where this burst has occurred is the same place where the nerve comes out of the spinal canal. As the nerve is held down in position by ligaments it is unable to move out of the way and thus the burst disk material places pressure on the nerve.
This object pushing on the nerve compromises the blood supply to that nerve, which then creates an irruption to the nerve sleeve causing nerve related symptoms. This can be pain radiating down the leg, pins and needles or numbness. So as the symptoms of this type of disc injury are more severe the recovery will be much slower.
Most people who consult a physiotherapist for a back injury tend to have a disk related problem. It is very rare to get muscle tears in the spine, you can have joint injuries but these are very specific and easily identified. So most of our lifestyle tends to effect the function of the disk.
If there is injury to the disc itself, without any nerve involvement, you can still have lower back pain or some referral of pain into the leg as well. However when the nerve is involved the pain tends to be very severe in the leg, quite disabling, with loss or altered sensation, pins and needles or numbness and you may get weakness of the muscles too. A physiotherapy consultation can identify the cause of these issues, so in this instant it is important that you consult your physiotherapist or GP as soon as possible. Sometimes this is the type of condition that responds well to surgery.
Avoiding disc related back injury
Of course the best thing for your discs is to avoid back injury in the first place. The main way that disks become injured is through bending related activities, as this increases internal disc pressure. If we were to start with standing, as a mark of 100% pressure on the disk, then bending at the back to pick something off the floor standing would place 50% more load through the lumbar discs, than if we squatted and kept the back straight. Over time, this bending of the back puts you at a much higher risk of developing an injury.
You would think sitting upright in a chair, takes pressure off the back, but in fact the load increases to 140%. Add a slouch to your sitting position and you can almost double the pressure on the disk, compared to standing upright. These figures clearly illustrate why incorrect lifting or posture commonly leads to disc overload and ultimately lower back pain.
Back injury occurs in two ways.
Firstly, very gradually over time, where load can be cumulative. In this instance, low levels of load on the back create very small structural tears, but not enough to reach the threshold of feeling pain. This is until one day, you do a simple move, such as bending over to pick up a pen from the floor, and your back will suddenly become sore. Often people describe this injury as ‘my back just went’.
Secondly you can also have injury to a disk from a sudden, large force. For example when you bend over to pick up something very heavy, and you have done so in a hurry, without bending the knees.
So a lot of these injuries we can minimise if we just develop some good habits throughout our daily activity. The best habit is that if you need to pick something up from the floor, is that you bend your knees and not your back. These good habits are demonstrated in this squatting technique video or alternatively you can use this golfer’s lift exercise.
The other important way to reduce the load on the disk, is to have an appropriate chair to sit in, that supports the curve of your spine. Other general practices that will improve the health of your spine include;
- use proper techniques when lifting
- use proper ergonomics when sitting
- taking regular breaks from sitting
- avoid bending or awkward postures
- stay active and work on general fitness
- maintain a healthy weight
- stay hydrated to help joint elasticity and fluidity
- pay attention to your body for warning signs
One last major factor for disc health is smoking, as this has been shown to reduce the blood circulation in the disc. Consequently if an operation is needed to repair the disc, the outcomes of surgery can then be quite poor for recovery.
Once you have hurt your back and have had a disc problem you can reduce the risk of it coming back by strengthening your core and by being conscious of how you sit, bend and stand. If you look at how a toddler picks things up from the floor, they naturally squat down. It becomes harder as we get older because we lose the flexibility in our knees and ankles. However the more we use the correct lifting technique, the easier it becomes.