Recent evidence suggests that for many patients, a much smaller operation gives results just as good as fusion.
You may have a condition of the spine known as spondylolisthesis, where one vertebra has slipped forward relative to the one beneath it. It is usually caused by weakness or wear and tear of the supportive facet joints at the back of the spine.
Where non-surgical measures such as physiotherapy and pain management have failed, the common operation offered is some form of lumbar fusion: a construct of screws, rods and metalwork placed in the spine to realign it and hold it together.
But recent evidence suggests a less invasive operation can sometimes be the better option, and it is worth understanding why.
What happens in degenerative spondylolisthesis
In the degenerative form, the facet joints wear and weaken, allowing a vertebra, often L4, to slip forward over time.
This causes a secondary problem: stenosis, narrowing of the central canal through which all your nerves run. With the nerves slightly compressed, the result is usually leg pain in both legs, worsening the longer you stand and walk.
The question worth asking
I often say we treat the patient, not the scan.
So if your symptoms are predominantly leg pain on standing and walking, and back pain is not what is really bothering you, the question becomes: do we actually need to fuse the spine at all?
Or can we get away with simply taking pressure off the back of the spine and decompressing the nerves through a much smaller operation?
A word about “minimally invasive”
You may have heard the phrase minimally invasive fusion, or MIS-TLIF (minimally invasive transforaminal lumbar interbody fusion). It is an operation I carry out frequently.
But we should be careful with that phrase as surgeons.
It generally means getting the screws and rods into the spine through small skin incisions, which is why the term is used. Rather more goes on beneath the surface than the phrase suggests.
It is certainly far less invasive than the traditional method, which involved a large midline incision and dissecting through all the muscle. But it still involves a fair amount of dissection of the soft tissues around the back of the spine and the spinal joints, clearing out the whole disc space, and inserting the cage. That can cause a good deal of post-operative pain, albeit less than the older technique.
There is a further consideration. Fusing the segment immobilises it, placing additional stress on the segment above, which must move more to compensate. Over time this produces adjacent segment disease: accelerated wear and tear above or below the fusion.
The smaller operation
For stenosis without spondylolisthesis, we often carry out a minimally invasive posterior lumbar decompression.
This goes through a very small midline incision, usually no more than one and a half to two centimetres. A special soft-tissue retracting system is placed, so there is some dissection but genuinely very little. The excess tissue pinching the nerves is then removed under the microscope, with the image magnified so we can see the nerves are thoroughly decompressed by the end.
It is far less invasive than inserting metalwork, and recovery is quick.
But does it work with a slip?
The concern is reasonable. If we remove some of the supportive tissue at the back of the spine in someone whose vertebra has already slipped, are we going to destabilise things further and allow it to slip more?
The NORDSTEN-DS trial addresses this directly. This Norwegian randomised, multicentre, non-inferiority study followed two groups of patients, all with both spondylolisthesis and stenosis. One group had the fusion surgery described above; the other had decompression alone.
At five years, the results in both groups were fairly similar. Those who had decompression alone did not do any worse.
How we decide before operating
One useful test is a set of dynamic X-rays, taken standing: one leaning backwards into extension, one leaning forwards. What we are looking for is how much movement occurs between the segments.
A more recent study in Clinical Spine Research examined patients with spondylolisthesis who underwent those dynamic X-rays, showed up to 2 to 3 mm of movement, and then had the minimally invasive decompression. Overall the results were quite good.
A necessary caution
As clinicians we must be careful how we apply research to individual patients. These results do not mean the smaller operation suits everybody with spondylolisthesis and stenosis.
There are several factors to weigh:
- Is the leg pain worse than the back pain?
- How much back pain do you actually have?
- Is there significant instability on the dynamic X-rays?
- Can you perform the X-rays at all, with enough flexion to demonstrate any instability?
The key takeaway
If your dominant symptom is leg pain and the segment proves reasonably stable, decompression alone may serve you as well as a fusion, with a smaller operation and a faster recovery.
But that conclusion rests on a careful history, examination and assessment, which matter far more than any scan.
