Anterior Spinal Fusion with the STALIF Cage

Rationale

When wear and tear changes affect one of the discs in the lower back this may cause symptoms of back pain. Pain may be coming from the damaged disc itself and this is often the major culprit, but problems may also arise from other structures such as the small joints at the back of the spine (the facet joints) which can become overloaded as the disc collapses and narrows. This narrowing of the disc, which occurs as the degenerative disease progresses, causes the vertebra above to sink down towards the one below putting extra pressure on the facet joints. The loss of disc height also reduces the size of the openings to either side where the nerves leave the spine, called neural foramen. This may pinch the nerve roots, adding leg pain, and sometimes other symptoms, to the problems experienced with a degenerative disc.

Anterior spinal fusion can address all these various problems. The disc generating pain is completely cleared away and in its place a special cage is inserted which restores the height of the disc, off-loading the facet joints and opening out the neural foramen on either side. The forward tilting of the vertebra which occurs as the disc collapses is also corrected. This forward tilting (kyphosis) can lead to overload of other levels of the spine.

Advantages

Compared to other fusion techniques, the particular advantages of a minimally invasive anterior spinal fusion are:

1. The damaged and painful disc can be removed and the cage inserted without the risks of operating through the spinal canal. These include the risk of serious nerve root injury, scarring affecting the nerve roots and even damage to the nerves controlling the bladder and bowel sphincters.
2. There is no damage to the very important muscles around the spine. Indeed, generally no muscles are damaged at all. This allows a quicker recuperation and eliminates one problem which can affect the long term outcome from surgery.
3. The risks associated with the use of pedicle screws are avoided.
4. A wider clearance of the painful disc can be achieved and a bigger cage with a larger bone graft contact area can be used.
5. A single surgical procedure for providing fixation and inserting cages in the disc space. This is an advantage when compared with the combined anterior and posterior technique, which requires two operation sites.
6. This is a good technique to use if the problem is a failure of a posterior fusion, either in stead of, or in addition to, a redo posterior fusion. It has the advantage of targeting the fusion process at fresh, healthy new bone.

Possible drawbacks

1. Spinal decompression can not be undertaken at the same time.
2. At L5/S1 (the lowest level of the spine) anterior surgery has a very small risk in male patients of causing retrograde ejaculation. If this problem occurred it could affect your ability to have children.
3. Although the facet joints are immobilized by anterior fusion, and this should prevent pain from these joints, the joints themselves are not excised and may still give some discomfort.
4. The fusion rates, which are an important factor in success, are good in both posterior and anterior fusion techniques, but the highest fusion rates are achieved with combined anterior and posterior surgery.

The STALIF cage

Mr Boeree was the principal developer of the STALIF cage which is now used widely around the world. The design allows the cage to be fixed in place with screws and provides immediate stability and an ideal environment for fusion to develop. The STALIF cage has many advantages and safety features when compared to alternatives.

In the past, anterior spinal fusion required large chunks of pelvis bone to be used. This was needed to provide the structural support between the vertebrae after removal of the disc but caused many problems for the patient. The STALIF cage now provides this structural support. The cage has two large spaces which can be packed with granular bone graft (sometimes called bone graft shavings) or with alternatives to bone graft such as BMP (bone morphogenic protein). If granular bone graft is used this is much less destructive and does not cause the significant long term problems that were seen with large structural pieces of graft.

The STALIF cage keeps the graft firmly in place. In the past there was a risk that the graft would be extruded. Of course, if any movement takes place between the vertebrae and the graft this will disrupt the fusion process. This is a real potential problem unless there is some form of fixation to hold the vertebrae still. In view of this it was often best, with other anterior cages, to undertake an additional operation from the back to provide fixation with screws. The STALIF cage makes this unnecessary since strong fixation is provided with screws which pass through the cage into the vertebral bodies. This gives the cage its name - the STand Alone Lumbar Interbody Fusion cage.

What is the cage made from?

The cage is made from PEEK, a strong biocompatible material which is similar in its “springiness” to bone. This reduces stress loading of the vertebra. Equally importantly, the material is invisible on x-ray examination. There are markers which allow us to see where the cage is placed but because the cage itself is transparent we are able to assess the progress of your fusion. The screws are made from titanium, which is MRI compatible.

How are the cages adapted to an individual?

The cages are available in a range of heights and widths and this allows the best size of cage to be selected for an individual. It is important to restore the original height of the disc and to recreate the proper orientation of the vertebrae. This assists with trunk balance and helps to protect other levels in the spine. When the disc wears out and collapses the space narrows and the angulation (or lordosis) between the vertebrae reduces significantly. All of these factors are addressed by selecting the correct size of cage. The cages all have the correct lordosis angle built in.

 

 

 

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