A spondylodesis is a fusion: two or more vertebrae are connected in such a way that they grow together as bone and no longer move against one another. There are two building blocks for this, used singly or in combination — screws and rods that hold the vertebrae from behind, and a cage, a spacer made of plastic or titanium that maintains the height in place of the removed disc and grows in with bone. At the cervical spine we insert cages from the front and from behind, at the lumbar spine screw-and-rod systems with or without a cage; stabilisation of the facet joints and screw fixation of the sacroiliac joint are also among the procedures we perform.
A fusion is the answer to instability — not to wear on an image and not to back pain alone. The more clearly the instability has been proven, the clearer the benefit.
Who is spinal fusion suitable for?
The procedure is the exception, not the rule. Most spinal symptoms need no fusion, and most operations on the spine manage without one. It is considered in clearly defined situations:
- Spondylolisthesis with instability — when a vertebra demonstrably travels relative to the one below it, nerves are constricted and treatment without an operation is not enough. More on this on the page spondylolisthesis.
- Cervical spine — in a herniated disc or a narrowing with compression of a root or of the spinal cord, when the disc has to be removed from the front; the cage then fills the space. In myelopathy the point is to relieve the spinal cord and to keep the cervical spine stable.
- Highly unstable vertebral bodies — for instance after a fracture that has destroyed the load-bearing structure.
- Facet joints and sacroiliac joint — only where the joint has been secured as the source of pain by targeted anaesthetic injections and everything else has been exhausted. What has to apply for this is on the pages facet joint osteoarthritis and sacroiliac joint pain.
Fusion is not suitable as a treatment for back pain from “disc wear” without instability. IQWiG reviewed three studies with a good 450 participants: they showed no advantage of a fusion operation over a multimodal pain treatment. In spinal stenosis without spondylolisthesis, too, fusion as an addition to decompression is not indicated.
What happens exactly?
All the procedures take place under general anaesthetic; the position of the implants is checked with X-ray during the operation. Which approach fits depends on the site and the cause of the instability.
- Lumbar spine: screws and rodsThrough several small incisions in the back, screws are placed into the two vertebrae involved and connected with rods. The constricted nerves are relieved in the process under the microscope. If the segment is particularly unstable, the disc is additionally removed and a cage with bone material is placed in the intervening space, so that the vertebrae also grow together at the front.
- Cervical spine from the front: cageA short skin incision on the front of the neck; the approach runs between the carotid artery and the oesophagus, without cutting through muscle. The disc is removed, the nerve root and the spinal cord are relieved under the microscope, and the cage is inserted into the disc space, secured with a small plate where needed. The skin is closed with narrow adhesive strips.
- Cervical spine from behind: small cages in the jointsThrough a short incision at the back of the neck, the facet joints are exposed and small cages are placed on both sides, spreading the segment open and immobilising it.
- Facet joints of the lumbar spineThrough a small incision, the joints on both sides are exposed and stabilised with wedge-shaped implants (wedges).
- Sacroiliac jointThrough a small incision at the side of the pelvis, two to three screws are placed through the joint under X-ray control.
The implants hold the vertebrae until the bone connects them. That takes months and is checked with X-rays. Where findings are suitable, screws can also be placed through small incisions at the side; whether that has advantages in the individual case depends on the finding.
What spinal fusion can achieve — and what it cannot
The most important question in stenosis and spondylolisthesis is: is decompression enough, or is a fusion needed as well? Three large randomised trials have examined it, with not entirely consistent answers. In the Swedish study of 247 patients — with and without spondylolisthesis — the limitation in everyday life was the same after two years (27 against 24 points on a scale of 0 to 100), and likewise after five years; within an average of six and a half years, about one in five in both groups had a further operation. The Norwegian study of a good 260 patients with spondylolisthesis found decompression alone to be equivalent: 71 out of 100 against 73 out of 100 achieved an improvement of at least 30 per cent; 12.5 against 9.1 out of 100 had a repeat operation. A smaller American study with 66 participants, by contrast, saw an advantage of fusion in physical quality of life and markedly fewer repeat operations — 14 against 34 out of 100 — but more blood loss and longer stays.
The sum of it: in stable spondylolisthesis, decompression is usually enough; fusion is the reserve for proven instability and for the cases in which decompression alone did not hold. Compared with treatment without an operation, the SPORT study in degenerative spondylolisthesis showed markedly better values for pain and function over two years in the as-treated analysis — with the reservation that many of those assigned had changed groups. At the cervical spine, removal of the disc from the front with a cage has for decades been the standard method when the root or the spinal cord has to be relieved.
What fusion does not achieve: it does not pull a vertebra that has travelled all the way back to its old place — that is usually neither necessary nor sensible — it does not remove every back pain, and it does not protect the neighbouring levels; on the contrary.
Risks and side effects
As with every operation, infection, post-operative bleeding, thrombosis and the risks of the anaesthetic. Specific to the procedure at the lumbar spine: an injury to the dura with leakage of cerebrospinal fluid, rarely damage to a nerve root with altered sensation or weakness, a misplacement or later loosening of screws, a failure of the bony connection to form (pseudarthrosis) with persistent symptoms and the possibility of a further procedure. In the long term the neighbouring segment is loaded more heavily and can wear out faster. At the cervical spine with the approach from the front: difficulty swallowing and hoarseness, which usually pass, rarely a lasting weakness of a vocal cord; very rarely an injury to the oesophagus or to blood vessels; post-operative bleeding in the neck with shortness of breath, which has to be treated immediately; a displacement or a sinking-in of the cage; damage to a nerve root or to the spinal cord — very rare, but serious.
In figures: after a fusion for stenosis, according to the IQWiG review, 9 to 10 out of 100 of those operated on had to go into hospital because of a complication, and in 3 to 4 out of 100 it was life-threatening; after a fusion for disc wear, a complication occurred in 16 out of 100, and 6 to 8 out of 100 had a repeat operation within two years because of problems with the implants. In a Cochrane analysis, the operation with fusion took on average just under two hours longer and involved about half a litre more blood loss than decompression alone. After a fusion of the cervical spine from the front, in a long-term observation of 374 patients about 3 out of 100 developed new symptoms at a neighbouring level each year; after ten years about one in four was affected. Which of these is to the fore in your situation is something we discuss before the procedure.
Before and after
Before the procedure: besides the MRI and the examination, the decision often needs X-rays taken standing and in flexion and extension, which make an instability visible, and sometimes a computed tomography for planning the screws; the terms in your report are explained on the page on the MRI report. Where osteoporosis is suspected, a bone density measurement is worthwhile, because screws hold less well in soft bone. Smoking worsens bone healing; anyone who can stop should do so before the operation. Clarify beforehand who will support you in the first weeks, and whether follow-up rehabilitation will be applied for.
After the procedure: getting up on the day after the operation; walking is encouraged. In the Swedish study the stay after fusion averaged about seven days, and about four after decompression alone. For a few weeks no heavy lifting, no twisting under load, no deep bending; at the cervical spine no jerking head movements, and a rigid collar is usually not necessary. Physiotherapy begins after the wound has healed, at first with walking and posture training, later with strengthening. The bony union takes months and is checked with X-rays; until then loading remains measured. Follow-up rehabilitation is often worthwhile after a fusion of the lumbar spine. How long you are unfit for work depends on your occupation.
Alternatives
The first alternative is treatment without an operation — movement, physiotherapy, painkillers for a limited time, targeted injections — because a spondylolisthesis can also remain stable for years. The second is decompression without fusion, which is usually enough where the segment is stable and which we likewise offer. For pain lasting months without a clear cause, a multimodal pain treatment can come into consideration. A motion-preserving disc prosthesis instead of a cage can come into consideration where the finding is suitable; IQWiG reports that in the years after insertion 10 to 20 out of 100 have a repeat operation, and it is only suitable if the neighbouring structures are not worn. A fusion is one of the procedures for which people with statutory health insurance have an express entitlement to a second opinion.
Frequently asked questions
Will my back be stiff afterwards?
A single fused segment contributes only a small part of overall mobility; the remaining segments and the hips take over. Most people notice no difference in everyday life, except when bending deeply or twisting. The more segments are fused, the more noticeable it becomes.
Do screws and cage stay in the body for ever?
As a rule, yes. Once the bone has connected the vertebrae, the implants no longer carry any load, but neither do they cause trouble. They are removed only if they cause symptoms or have worked loose. You receive an implant passport.
When has the bone fused?
That takes months and varies from person to person. In the Norwegian study the bony connection was reliably demonstrable after two years in 86 out of 100. Smoking, osteoporosis and certain medicines delay healing. X-ray checks show how it is progressing.
Why is a cage almost always used at the cervical spine?
Because with the approach from the front the disc has to be removed completely in order to reach the root and the spinal cord. The cage maintains the height of the intervening space and with it the width of the nerve exit openings, until the vertebrae have grown together. Without it the segment would sink in.
Can I have an MRI with the implants?
Modern implants made of titanium are as a rule MRI-compatible; details are given in the implant passport, which you should take with you to every examination. Image quality in the immediate vicinity of the metal is limited.
What happens at the neighbouring levels?
They take over the movement of the fused segment and are loaded more heavily. Over the years, wear there can progress faster; some of those operated on need a further procedure later because of it. Strong trunk muscles and a back-friendly daily routine are the best protection.
If a fusion has been recommended to you elsewhere, you can obtain a second opinion from us. We look at your images, examine you and tell you frankly whether we consider the instability proven and the fusion indicated — or whether decompression alone or waiting is the better route. What you should bring is on the page Your first appointment.