Circumferential Spinal Fusion

Posterior means from the back of the body. Posterior spinal fusion actually encompasses several different techniques but in all of them the operation takes place purely from the back, usually with pedicle screws being inserted into the sacrum and/or each of the vertebrae being fused together. These screws will be linked by rigid rods.

If the intervertebral disc is to be cleared away, which is very often the case, this will also be done entirely from the back, through the spinal canal. After clearing away the disc material special cages are inserted into the space left by the removed disc. This is called posterior interbody fusion and various possible techniques for positioning the cages and the bone graft can be used.

The cages and the rods help to maintain the proper alignment and spacing between the vertebrae and also stop all movement, allowing the bones to fuse together. The cages are filled with and surrounded by bone graft and additional bone graft will also be placed over the back of the vertebrae. It is this bone graft that forms the mass of fusion bone which joins the vertebrae together.

Rationale

Pedicle screws and rods provide a very strong and rigid form of fixation. Pedicle screws have to be put in from the back and this is why spinal fusion is most commonly done from the back. Although the prospect of inserting screws into the vertebrae of the spine sounds quite frightening it is now very routine in spinal surgery. The screws and rods allow the position of the vertebrae to be altered and controlled as well as held in place.

Another good reason for a posterior fusion is that the problems that have to be dealt with in the lower spine often need some work to be done inside the spinal canal, for example a decompression or removal of protruding disc material. These procedures can easily be undertaken at the same time. If they are needed it is a strong reason for choosing a posterior procedure.

Finally, it is quite common for the facet joints to be contributing to back pain problems since these joints can become quite worn. These joints form part of the back of the spine and a posterior spinal fusion will involve removing the facet joint surfaces and overlaying the joints with bone graft to encourage them to fuse. This should stop any pain coming from these joints.

Advantages

Compared to other fusion techniques, the particular advantages of a posterior spinal fusion are:

1. 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.
2. Spinal decompression can easily be undertaken at the same time.
3. At L5/S1 (the lowest level of the spine) anterior surgery (an operation from the front) has a very small risk in male patients of causing retrograde ejaculation. If this problem occurred it could affect your ability to have children. The risk is avoided with posterior surgery.

Possible drawbacks

1. Posterior surgery does cause some damage to the functionally important muscles of the back. This can have a negative effect on the outcome from surgery. At The Spine Clinic this problem is dramatically reduced through the use of minimally invasive image guided pedicle screw techniques, but these can not be applied in all situations.
2. Clearing out the disc and inserting cages through the spinal canal does require that the nerve roots are moved well out of the way. They can be damaged by this or during the cage insertion. This can cause long term sciatic pain or loss of feeling and weakness in certain parts of one leg. This risk is largely avoided with other fusion techniques.
3. Although a good proportion of the disc can be cleared away, more complete clearance is obtained, and more importantly a bigger cage with more bone graft inserted, with anterior surgery.
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.
5. The use of pedicle screws does have some specific risks, such as the very small risk of injuring a nerve root

 

 

 

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