Acute Disc Prolapse

This is a controversial subject. Many spine surgeons, thirds-party insurers, WorkCover doctors and patients will disagree with the contents of this page!

It is very important that you also read The Spine - Basic Anatomy and Mechanics page and Causes of Back and Neck Pain page.

A great deal of confusion is generated when talking about disc prolapse, disc herniation and disc bulge. In my opinion they are terms best avoided. As we have discussed in other areas of this site the intervertebral discs start to dry out at an early age as part of the normal ageing process. About the age of 20! Sad but true. From this moment on, every step we take, every jump, game of soccer, swing of the gold club or moment of irrational intimacy causes some burden on the spine which is irreversible. During the course of daily living, every now and then, an incident will occur which causes a more significant, permanent, effect on a disc or discs which may be enough to raise the situation to a clinically evident condition – i.e. cause pain or symptoms. Often this event is one which is the "straw that breaks the camel's back" so to speak and causes the disc to undergo final catastrophic collapse. The disc can bulge into the spinal cord at the back either in a contained fashion – i.e. still contained by the PLL and other structures or in an extruded or sequestered fashion – i.e. a completely separated free-floating fragment. Sometimes even the cartilaginous endplate can be pushed out which is extremely inflammatory. The other side of the coin is the young adult, whose discs are too young to have undergone any significant degeneration who has a massive trauma to a disc – usually the result of a significant fall, motor vehicle accident or sporting injury – who reaches the stage of catastrophic failure in one fell swoop.

Forgetting about these young patients with sudden catastrophic failure for the moment, many patients will talk about a 'disc injury' as if the injury itself has caused the 'disc bulge' and liken the process in their mind to breaking a bone for example, and usually make some assumptions. The first assumption (which is wrong!) is that the disc was always perfect until an 'injury' occurred and then they are left with a 'bulging disc' or 'herniated disc'. If the patient has past their mid 20's in age then the disc most certainly would not be perfect at the time of their 'injury' – it would have already started to dry out, lose pressure in the nucleus and be degenerate – no matter how mild and no matter that it caused no prior symptoms. The second assumption (also wrong!) is that shaving off the disc bulge or herniation with surgery fixes the problem. What is left behind is now not just a disc which has been degenerating for a while, but now a degenerate disc which has had the insult of decompressive surgery attached to it.

The MRI scan shown in Figure 1 is a representation of what I see on a daily basis in my clinic. It is a sagittal slice through the lower 3 discs of the lumbar spine, and you can see a cascade of degeneration from the L3/4 disc down to the L5/S1 disc. On an MRI scan such as this, any fluid or water shows up as white. You can see that the disc at L3/4 has a nice white nucleus in the middle which is a good sign (blue arrow) – high water content and so hopefully high hydrostatic pressure. Conspicuous by its absence is the water content of the discs at L4/5 and L5/S1. Refer to The Spine – Basic Anatomy and Mechanics and Causes of Back and Neck Pain if the following sounds all foreign to you but at L5/S1 there is collapse of the motion segment, dehydration of the disc, and a large disc prolapse protruding out the back into the spinal cord (cauda equina at this level) – red arrow. Look at the L4/5 disc – it is not hard to see that this disc is suffering a similar demise to the disc at L5/S1 – green arrow. Overall look at how little lordosis is present over the whole segment. Discs take decades to look this bad, but this disc prolapse at L5/S1 has not been there that long – only a few weeks – it is an acute prolapse – it represents the final 'giving-up' of the whole disc on a background of many years of slow degeneration. There is also a disc prolapse at the L4/5 disc – less dramatic than the one at L5/S1 and the disc overall has managed to maintain more height. You don't have to be medically qualified to see the difference between the disc at L3/4 and these two discs. You also don't have to be medically qualified to understand that in the right context a patient such as this is much better off having these two segments reconstructed than having a portion of their discs removed, or having their spine decompressed – see the Lumbar Spine Reconstruction page.

Figure 2 shows a schematic of what the disc at L4/5 probably looks like when sliced across. The nuclear material has torn through the back of the annulus but is still contained by the posterior longitudinal ligament (PLL) – blue on the schematic.

Figure 3 is a schematic of what the disc at L5/S1 probably looks like when sliced across. The PLL has ruptured and the nuclear material, whilst still attached by a stem to its main body, is now in direct contact with the cauda equina. On the MRI scan above you can see the PLL still intact behind the disc prolapse at L4/5 – it is the dark band of tissue running from above the prolapse to below it. From the MRI scan and these schematics, you can see how this can only happen in the presence of a very degenerate disc. Nothing can reverse the presence of degeneration so unlike the scenario of the broken bone which is mechanically sound until the instance it is broken, and which can regain its mechanical integrity with solid bony healing, the disc is doomed.

Surgery that addresses only the disc prolapse (i.e. by performing a 'laminectomy' – which is an open discectomy – or a 'microdiscectomy' -through a microscope) does not address the cause of the disc prolapse, or the back pain from the DDD.

A 'laminectomy for discectomy' or 'microdiscectomy' is an operation performed with the patient face down with an incision on the back. Part of the lamina on the side of the disc prolapse is removed and the cauda equina and nerve roots pushed to one side to remove the fragment of disc. The surgery takes about 30-40 minutes and an overnight stay or two is required in hospital.

This surgery is incredibly effective in addressing the radicular symptoms of leg pain and is used frequently in this context. If this surgery is expertly performed, then very little extra trauma or instability is created by the surgery and most spine surgeons describe these patients as their most grateful clients. In some patients the disc prolapse has completely separated from the nucleus and is lying free in the vertebral canal (this is called a 'sequestered fragment'). In a strange paradox these patients often fare very well without surgery because the completely separated fragment often resorbs by itself with good resolution of the radicular symptoms over about 8-10 weeks. Patients who have a disc extrusion (i.e. still attached to the nucleus but ruptured through the PLL – see diagram above) often undergo some resolution of their symptoms as the fragments undergoes a lesser amount of resorption but less reliably so than the patient's whose fragments have truly separated. There are some patients however, that reliably do very badly with simple discectomy surgery, and we will discuss them next.

In 2003 Professor Carragee (orthopaedic spine surgeon) studied 187 patients who underwent discectomy for radicular symptoms and correlated the results against what the disc degeneration looked like pre-operatively. Essentially this study found 4 types of disc protrusion, 2 did well from discectomy and 2 did very badly. The two that did very well had one thing in common – the tear in the annulus from the nucleus to the protruded fragment was a small one. It didn't matter too much if the PLL had ruptured in association with this but provided the pathway from the nucleus to the protruded disc i.e. the annular tear was a small one then patients did very well with a simple discectomy. However, 2 groups did very badly. One of these groups had annular tears which were large – 27% of these patients re-herniated following surgery with most of these undergoing further surgery. The other group which did very badly had just a diffusely degenerate and deflated disc with no real fragment to remove. These patients did the worst of all in terms of resolution of their pain. You might be bewildered into thinking “why did someone need to perform scientific research to work this out, it sounds just intuitive to me” – I agree. Basically, the 'meat and two veg' of this study is that if you have a very degenerate disc or just a diffusely bulging disc then discectomy shouldn't be performed. It is possible to work out pre-operatively if you fit into one of these latter groups by performing discography or looking close and hard at the MRI scan. This study was published in the American edition of the Journal of Bone and Joint Surgery in 2003 Volume 85, pages 102-108 if you are interested in reading the whole thing.

Another very good study made by an orthopaedic spine surgeon and published in the same journal but in the British edition (85:pages 871-874) looked only at patients with confirmed disc protrusions on the MRI scan. The study specifically excluded patients with diffusely deflated discs – i.e. the group that did very badly in Carragee's study. This was a large study of over 500 patients. Overall the success rate in alleviating leg pain was very good with an 8% surgical failure rate (which is better than average). Interestingly though 80% of the patients who did fail and had to undergo further surgery came from the group were the PLL was still intact – indicating another group which possibly should not undergo discectomy.

Reading the scientific literature and trying to work out what to do and how to treat your patients is called working with evidence-based medicine. Evidence based medicine is not perfect but is the best method physicians and surgeons have of communicating with each other with regards to the most correct ways of treating our patients. Some evidence is terrible and some excellent. The evidence in the literature regarding whether or not to perform open or micro-discectomies on our patients would tell us that only patients with completely extruded (i.e. ruptured through the PLL) disc fragments should have this procedure and probably not if the disc is very degenerate to begin with. The 'protruded' patient group have a not inconsiderable failure rate, and the 'sequestered' patient group often get spontaneous resolution. What this tells me, if you want to follow evidence-based medicine, is that only a very select few patients are likely to do well with a laminectomy for discectomy – or microdiscectomy. In my clinical practice this surgery is restricted to that young patient, with very little in the way of pre-existing degeneration, with a sudden, catastrophic failure of a disc. Caveats to this, of course, are when a severe neurological threat exists to the nerve and when something has to be done quickly, or when pain is incapacitating and there are other time-barriers to definitive reconstructive surgery such as pregnancy, and when something relatively simple needs to be performed to get a patient out of trouble prior to considering definitive reconstructive surgery.