1. Anatomy

The spine plays a central role in the motor system. It consists of seven cervical vertebrae, twelve thoracic vertebrae, five lumbar vertebrae and the sacral bone or sacrum. Between each pair of vertebrae there is an intervertebral disc, and these 23 discs increase the spine's elasticity and mobility. Although in theory any of the intervertebral discs can become herniated, in practice only the three lowest discs are of significance. The hernias of the cervical spine constitute a category apart which will not be discussed here.

The most frequent hernias occur between the 4th and the 5th lumbar vertebrae, and between the 5th lumbar vertebra and the sacrum. Ninety percent of all hernias occur in this area; the remaining 10% can be found further up. Intervertebral discs consist of an elastic core that is surrounded by a fibrous ring. The posterior portion of the vertebral canal is made up of the vertebral arches, which taper off into a thorn-like protuberance (the spinous process) and between which runs a sturdy band. The vertebral canal houses the spinal cord, which does not however extend further than the first lumbar vertebra. Below this level there are only nerve roots running through the vertebral canal, with one leaving the canal on either side between each set os two vertebrae.

Anatomy of the spine

2. Disc degeneration

Over the course of the years, the volume of the core of the intervertebral discs (the nucleus pulposus) reduces due to loss of moisture. Indeed, over time we become shorter due to this shrinkage.

This is clearly visible on a magnetic resonance image with enhanced sensitivity for moisture containing structures.


This image shows the lowest intervertebral disc - no longer grey but black, which means that the nucleus has lost its moisture and thus its shock absorbing capability and function. This does not however mean that lower back pain will ensue. This image is perfectly normal and coherent with a normal aging process. However, if the outermost band of the disc begins to show cracks, this can in fact cause lower back pain. Such cracks can also be seen on MRIs and are often the cause of sudden severe lower back pain (lumbago) with significant mobility impairment. The chronic pain these small cracks cause usually starts after we've been up for a while and then increases as we go about our daily activities. As a result of disc degeneration the height of the intervertebral discs decreases, causing the vertebrae to sag a little more on top of each other and excess load to be placed on the small joints (the facet joints) located to the rear in the back. In this case the entire mobile segment between two vertebrae experiences damage. This usually translates into chronic lower back pain which is particularly noticeable on getting up and after long periods sitting, lying down or standing. As soon as patients move around for a while, the pain improves. All these problems can cause pain, and for each of them there is a specific treatment. In extreme cases they even qualify for surgical correction. Elective surgery treatment is available for each of these conditions separately. However, it is important that doctors make the correct diagnosis in the first place. This is not always simple, and sometimes supplementary examinations such as discography, in which a contrast medium is used to determine the extent of damage suffered by a given intervertebral disc, are required.

3. Surgical treatment of

  • Damaged nucleus pulposus
    The nucleus pulposus in itself can be replaced with another of man-made material. The new nucleus can be introduced in different ways - either via the abdomen, or via the back, or via an incision in the lumbar region. The surgeon makes a small opening in the annulus fibrosus to remove the broken up remains of the original nucleus pulposus. Then the new nucleus, made of hydrogel in a polyethylene jacket and having the same shock absorbing qualities as the original nucleus, is put into place. This surgery can be used only for the lumbar vertebrae.
  • Damaged disc
    When both the nucleus pulposus and the annulus fibrosus are damaged to the extent that they cause pain, the entire disc can be replaced with a prosthesis, which tries to imitate the movements of a normal disc, but does not have the shock absorbing functionality of a healthy disc. This new disc can only be placed via the abdomen. This technique can be applied to both cervical and lumbar vertebrae.
  • Damaged segment (disc + facet joints)
    Currently the only possible procedure is arthrodesis. This means fusing the entire mobile segment. This could be compared to the immobilisation of a broken and painful arm or leg. The application of a small plate or of a plaster cast causes the pain to cease. This is effectively what we do with a worn and painful backbone segment: it is immobilised. Several different therapeutic options are available. In essence the goal is to ensure that no further movement will be possible in the pertinent segment (two vertebrae + the intervertebral disc + the facet joints), resulting in significantly less pain. This technique can be applied to the entire spine. In our clinic, we are constantly testing different techniques to see which would be most suitable for each individual patient.

4. Hernias


Wearing down or degeneration of an intervertebral disc is a normal process that takes place in each of us to a greater or lesser extent. Back complaints and herniated discs are often frequent occurrences in certain families. Heavy work with much bending and lifting can indeed cause more back pain, but it does not cause herniated discs. Herniated discs occur just as frequently in people who perform light tasks as in those who do heavy work. It is however remarkable that smokers require back operations much more frequently than non-smokers, and that the outcome is worse in smokers. With degeneration the intervertebral disc can bulge out, but there can also be a crack in the fibrous ring or annulus fibrosus. Pieces of the core can be pressed forward and outward through this crack towards the vertebral canal. The ring usually tears at the weakest spot, which is precisely where the nerve root exits the vertebral canal. Anybody can get a herniated disc, but it is not known why it happens to some people and not to others. It is true, however, that herniated discs are sometimes frequent occurrences in certain families.

Usually back pain will precede the actual hernia. Many patients have had an attack of lumbago at some point. However, hernia symptoms include pain radiating into the leg, sometimes coupled with a numb or tingling sensation. This pain occurs in the area served by the nerve on which the pressure is exercised. Pressure on the nerve can bring about a loss of function in that nerve.

A nerve has a dual function: it serves the muscles, but also the skin. Each nerve has its "own" muscle and skin area "allocated" to it. Potentially resulting disorders can include paralysis of one or more muscles, or tingling or, alternatively, numbness. Because coughing, sneezing and straining cause both the pressure in the vertebral canal and therefore also on the nerve root to rise, the flash of pain can become more intense. By means of the description of the way in which the pain radiates and the functional deficiencies, if any, revealed in the examination, the doctor can usually tell directly which nerve is involved.

5. he diagnosis

To demonstrate that the pain in the leg is really caused by a herniated disc, further examination is necessary.

Three types of examination can be used:

  • CT-scan
    If the diagnosis is clear and the patient is not significantly overweight, this examination can provide sufficient anatomical information.
  • A contrast examination of the vertebral canal (caudography), sometimes supplemented with a CT scan. Given the current state of the art and equipment availability, this examination is the most accurate and provides the greatest amount of information.
  • MRI
    This examination is becoming very popular and will probably entirely replace caudography over time. At the moment there is still not enough equipment available and the quality of the results cannot always be compared to that of a contrast examination.

6. Surgery

Not every herniated disk requires surgery. With rest and physiotherapy, 70 to 80% of all hernias heal spontaneously. Thus one should not rush into surgery, but, on the other hand, the longer one waits, the longer recovery after surgery can take. As a rule, it is recommended not to operate before 6 weeks after the occurrence of the hernia (unless there is an urgency indication), but certainly within 6 months if the complaints persist.

There are two types of indications that speak for surgery:

  • Absolute
    When the nerve dysfunction is so significant that it causes paralysis symptoms, for example. Secondly, sphincter muscle dysfunction is almost always a reason to recommend surgery.
  • Relative
    When the pain is such that the patient is unable to function normally. The subjective complaint pattern thus plays a determining role in this case, so that the patient must actually decide for him/herself whether an operation is necessary, always provided that there is an indication for surgery. The surgery is carried out under general anaesthesia, with the patient in the knee-elbow position (resting on his or her knees and elbows) or lying on his or her abdomen. An incision of 8 to 12 cm is made into the skin above the area concerned, and then the long back muscles are drawn back on both sides of the vertebral arches. Then the band or ligament between the vertebral arches is cut and partially removed. In this way the surgeon exposes the nerve roots that exit the canal to the right and to the left a little below the intervertebral disk. As a rule, the herniated disc can be seen under the nerve, and sometimes part of it is also exposed in the vertebral canal. This is removed, and then the entire space between the vertebrae is evacuated. If this is not done, the hernia could occur again (recur) in the future. After the operation, scarring takes place between the two vertebrae, so that the vertebrae will not actually end up resting upon each other.

7. Treatment of a herniated disc

Ultimately, the surgeon and the patient will decide together what the best back problem treatment options will be. The surgeon will propose a specific surgical technique adapted to help resolve the patient's back problems. There follows a discussion of some of these techniques with, in each case, a short description of the diagnosis, an X-ray image and a short description of the surgical technique, sometimes supplemented by an animation or a compilation of actual surgical images. The type of surgical technique selected depends on the purpose and goal of the procedure.

What is the goal of the procedure?

  • Freeing the nerve
  • Percutane nucleolyse
    • Microendoscopic discectomy
  • Freeing the nerve + repairing the nucleus pulposus
    • Prosthetic Disc Nucleus (PDN)
    • Injectable Disc Nucleus (IDN)
  • Freeing the nerve + repairing the entire disc
    • Arthrodesis (Trabecular Metal)
    • Disc prosthesis (Maverick)

7.1. Freeing the nerve

7.1.1. Percutaneous nucleolysis

As already mentioned in the section on "neurosurgical clinical pictures", the nerve can be crushed by a hernia. If however the annulus fibrosus itself is not yet severed, the surgeon can choose to break down a portion of the nucleus pulposus in order partially to suction it off. This then ensures lower pressure in the disc itself, which may enable the annulus to resume its original shape.

This technique is performed under local anaesthesia and involves a stay of a few hours in a day clinic. The surgeon places a fairly large needle into the intervertebral disc. The entire treatment is administered by means of this needle.

The major advantage of this technique is avoiding surgery proper.

The disadvantage is that the chance of complete recovery is not as significant as with an MED (Micro-Endoscopic Discectomy) and that this treatment (the special needle) is not reimbursed by the Belgian mandatory health insurance (€ 1000).

7.1.2. Micro-Endoscopic Discectomy, or MED

If the annulus is truly severed, or if there is little chance that the patient will get better with percutaneous nucleolysis, your surgeon will suggest an MED.

This technique implies a 24 hour hospital stay (that is, overnight admission), unless the operation takes place under local anaesthesia.

This is a real operation involving a 16 mm incision into the back. Then a retractor tube (working tunnel) is introduced, onto which the surgeon mounts a camera. The neurosurgeon follows the procedure on a TV monitor. Arriving at the pinched nerve and freeing it by removing the hernia takes approximately 30 minutes.

Micro-Endoscopische Discectomie of MED

This drawing shows the vertebra, the torn annulus fibrosus with the herniating nucleus, and then the MED technique with the retractor tube and camera, by means of which the surgeon can repair the hernia.

The disadvantage of this technique is that it is real surgery. The advantage is that the hospitalisation period is very short and that the results are very good (95% patient satisfaction rate after one year).

7.2. Freeing the nerve + repairing the nucleus pulposus

7.2.1. Prosthetic disc nucleus (PDN)

Prosthetic disc nucleus (PDN) - 1 Prosthetic disc nucleus (PDN) - 1 Prosthetic disc nucleus (PDN) - 1 Prosthetic disc nucleus (PDN) - 1

When a herniated disc pinches a nerve and in addition the nucleus pulposus is damaged to the extent that there is almost nothing left, the neurosurgeon may propose removing the hernia and implanting a new nucleus pulposus at the same time. This will mostly be the case with younger people with a sudden large disc hernia. The nucleus pulposus in itself can be replaced with another of man-made material. The new nucleus can be introduced in different ways, either via the abdomen, or via the back, or via an incision in the lumbar region. The surgeon makes a small opening in the annulus fibrosus to remove the broken up remains of the original nucleus pulposus. Then the new nucleus, made of hydrogel in a polyethylene jacket and having the same shock absorbing qualities as the original nucleus, is put into place. This surgery can be used only for the lumbar vertebrae.

The advantage is of a theoretical nature; the removed nucleus is replaced with a new one. We believe that this is a maximum restoration of the disc to ensure optimal function. To date there has been no scientific proof of this theory. The disadvantage is the introduction of a foreign body and the cost (€ 1000) which is not fully reimbursed by the Belgian mandatory health insurance.

7.2.2. Injectable Disc Nucleus (IDN)

Injectable disc nucleus (IDN) - 1

This technique follows the same reasoning as PDN (see above), but instead of implanting a man-made nucleus, now an injection is performed into the nucleus location. The substance used is a conglomerate of elastine and silk. It has the same elastic and biomechanical properties as a healthy nucleus and therefore makes a good replacement. Its use in practice is at present purely experimental. If your surgeon suggests this technique, he or she will also ask you for your consent to the conditions governing the study.

Illustration : The illustration shows how the product (IDN) is introduced through the annulus into the area formerly occupied by the nucleus.

This graph compares the elasticity of a normal ("native") nucleus, an IDN restored nucleus and a nucleus removed after a traditional herniated disc operation. It shows clearly that IDN restores the original elasticity.

Injectable disc nucleus (IDN) - 1

7.3. Freeing the nerve + repairing the entire disc

When both the nucleus pulposus and the annulus fibrosus are damaged to the extent that they cause pain, the entire disc can be replaced. The damaged disc is then removed. Either the two vertebrae will be fused to each other (this process is called arthrodesis) or the entire disc will be replaced with an actual prosthesis. Both techniques have their advantages and disadvantages. Your surgeon will discuss them with you and you will decide together which the best option is in your particular case.

7.3.1 Lumbar arthrodesis / spondylodesis Introduction
Electronen-microscopisch beeld van het Trabecular Metal Beeld van Trabecular Metal tussen de vijfde lenden-wervel en het heiligbeen

Spondylodesis means fixing vertebrae to each other so as to immobilise them. The following section examines only the fixing of vertebrae in the lower, or lumbar spine. This procedure has been done for many years, but has recently been significantly gaining in popularity because of the ever greater availability of modern materials that make it safer and more effective every day.

This technique can be applied to the entire spine. In our clinic, we are constantly testing different techniques to see which would be most suitable for each individual patient. Most of the time we use Trabecular Metal, a new product made of a rare metal called tantalum.

Illustration 1: Electron microscopy image of Trabecular Metal. This material is very strong, is not rejected by the body, and promotes fusion between two vertebrae. .

Illustration 2: Image of Trabecular Metal between the fifth lumbar vertebra and the sacrum. Indications

One undoubted indication is instability. This could be the result of, among other things, a fracture or a tumour. In fact what is under discussion is the necessity for spondylodesis with instability as a result of wear and tear or degenerative changes. These are actually signs of aging which appear sooner in some people than in others. They consist primarily of a loss of elasticity in the intervertebral disc, enlargement of the small joints between the vertebral arches (facet joints) and thickening of the ligament stretching between the arches. This causes a narrowing of the vertebral canal and also increased mobility of the vertebrae in relation to each other, and can lead to a slippage of vertebrae in relation to each other. This can clearly be seen on an X-ray image. Discussion is focusing on the question as to whether increased mobility without slippage should be considered to be instability, whether it is causing a health condition, and on whether anything should be done about it, and if so, what. Surgery requiring complete removal of the vertebral arches (laminectomy) to create room for the nerves to exit the vertebral canal automatically also cause instability. Over the short term, this is not really a problem. The patient's complaints are usually effectively resolved. However, problems can come about over the long term due to the instability thus created, so that currently it is often preferred to combine a more significant laminectomy with a fixation with a posterior approach. Today, the view that back complaints can be the result of wear and tear giving rise to instability is gaining ground. In this connection, it is necessary to realise that what is actually involved are "micromovements", with X-ray images not necessarily showing any distinct shift or slippage. This minimally increased mobility leads, on the one hand, to pain, and on the other to further progressive wear and tear, which is the start of a vicious circle. When the enlargement of the ligaments and facet joints does not leave enough room within the vertebral canal, this can result in pressure on one or more nerve roots. They converge in the lowest portion of the lumbar spine. The pressure can lead to pain or loss of function related to the nerve roots affected. While a herniated disc will usually affect only one nerve root, canal narrowing normally concerns several nerve roots. Pain is felt mostly while walking, because the exit paths for the nerve roots are so to speak flattened by the angle assumed by the pelvis and the increased curvature of the lumbar spine (the lordosis). This causes pain and potentially also loss of function in the nerve, as well as a loss of strength and/or a feeling of numbness. A psychological evaluation is often also part of the standard evaluation procedure. The evaluation helps doctors obtain an insight into the patient's attitude to his condition, his or her expectations in connection with surgery and how rehabilitation can best take place following surgery. Surgery

The lumbar spine can be approached both from the front and from the back.

  • Vanuit de voorzijde From the front
    The procedure can be performed either "open", i.e. via an abdominal approach or an incision behind and along the abdominal cavity, or alternatively by means of endoscopy. It is used to remove the intervertebral disc, whereupon a "cage" is placed in the space thus freed up. Sometimes more than one disc is treated at the same time. There is no "best" method. The choice of method depends very much on the surgeon's preference and on the patient's situation. An anterior approach (from the front) makes it harder to reach the nerve roots, especially if they are pinched on the posterior (back) side. In such cases the purpose of the procedure is usually also to relieve back pain.
  • Vanuit de achterzijde invasief - 1 Vanuit de achterzijde invasief - 2 Invasively from the rear
    The approach is the same as for a standard hernia. After exposing the nerve roots by removing the arches and ligaments, if applicable in combination with removal of the disc, fixation can be performed with cages and/or screws and pins and plates. The fixation will stand up to exercise, which is one of the great advantages of this method. The screws and plates ensure that the segment remains immobile so that it can fuse. This takes approximately three months, so that after this period of time the fixation will in fact no longer be necessary. On the other hand, the screws are rarely if ever removed.
  • Vanuit de achterzijde minimuminvasief - 1 Vanuit de achterzijde minimuminvasief - 2 From the rear, minimally invasive procedure
    The site is approached by a number of small incisions. Risks

Generally, the risks are the same as for any other back surgery. In addition, there are the risks connected with the implantation of the prosthetic material and with the material itself. There is greater manipulation of the nerves, which can lead to deficiencies. The material itself can become loose, break or shift. Despite skilled techniques and a wealth of experience, such complications cannot completely be ruled out, but they are fortunately relatively rare.

7.3.2. Lumbar disc prostheses
Lumbale discus prothese - 1 Lumbale discus prothese - 2

They are designed to imitate the movements of a normal disc, but they do not have the shock absorbing properties of a healthy disc. This new disc can only be placed via the abdomen. This technique can be applied to both cervical and lumbar vertebrae.

Illustration: These images show the purpose of the procedure. A mobile prosthesis is placed at the location of the diseased disc between the fifth lumbar vertebra and the sacrum. The disc itself consists of two titanium plates linked by a central ball joint. These "artificial discs" are available in different sizes for different patients. The results of these studies are presented at international conferences and published in medical journals (see scientific contributions). The theoretical advantage of this technique is that a moving segment (a 'natural' joint) is replaced by another joint, even though man-made. Thus mobility remains optimal and the adjacent intervertebral discs are relieved from additional stress. The disadvantage is that there is still insufficient scientific evidence to enable doctors to consider this technique as being the unquestionably best option for treatment of a diseased intervertebral disc. Another disadvantage is the cost of the procedure (€ 2500), which is not reimbursed by Belgian mandatory health insurance.