Lumbar Fusion Without a Cage: A Less Invasive Option, and Who It Suits

If you have been told you may need lumbar fusion surgery, it is natural to worry about how big an operation it is, especially if you are older or concerned about complications. The good news is that fusion is not a single, fixed procedure. There is a less invasive approach that suits some patients better, and choosing the right one comes down to you, not just your scan.

Here I explain a procedure called minimal access posterior lateral fusion, how it differs from a standard fusion with a cage, and who it is most suitable for.

What is lumbar fusion, and why is a cage usually used?

Fusion means joining two bones of the spine, the vertebrae, together. We do this when a segment is unstable and that instability is causing nerve compression.

A standard fusion uses a construct of screws placed in the bones, connected by rods, to lock the vertebrae together, realign them, and help decompress the nerves. In many cases it also involves placing a device between the bones, called a cage. The cage sits in the disc space and acts as the medium through which the two bones fuse together.

A common reason for lumbar fusion is spondylolisthesis, where one bone has slipped forward relative to the bone beneath it. Sometimes a neighbouring bone slips backwards as well, narrowing the central canal and compressing the nerves, a condition called stenosis. This causes back pain along with pain radiating down the legs, particularly on standing and walking.

What is minimal access posterior lateral fusion?

This is a fusion that does not use a cage, which reduces both the invasiveness of the operation and the time spent in surgery.

We place a construct of just screws and rods at the back of the spine, through very small incisions in the skin, using image guidance to position the screws accurately. The rods are then used to realign the segments. The disc space is left alone, and no cage is placed.

Realigning the bones in this way generates some decompression of the nerves on its own. Then, through a further small incision under the microscope, any thickened tissue pressing on the nerves can be removed, and the nerves themselves can be seen directly to confirm they are free.

Why is a cage often used, and what are the trade-offs?

The cage is popular for a good reason. By working in the disc space beneath the two vertebral bodies, there is far more surface area of bone available to achieve a solid fusion. X-ray studies confirm that an interbody cage does help achieve a better fusion.

The trade-off is what it takes to get there. Reaching that disc space means removing the facet joint and carrying out a lot of dissection close to the nerves, all of which adds considerable operative time.

The posterior lateral approach has its own challenge: it can be harder to achieve a fusion by joining the bones at the back of the spine. To encourage it, we use a drill to create a channel between the bones at the back and lay down bone graft, allowing them to fuse over time.

What does the latest research say?

A 2026 study compared patients undergoing lumbar fusion with and without a cage. Those who had a cage inserted showed a slightly higher complication rate in the peri-operative period.

Importantly, the overall outcomes between the two groups, in terms of pain and general quality of life, were the same. In other words, the cage helped the fusion on the X-ray, but it did not produce a better result for the patient overall.

How I decide: my protocol for choosing the approach

This is where treating the patient matters most. My approach depends on your individual circumstances.

If you need a lumbar fusion for a spondylolisthesis and you are relatively young, or fit and healthy without significant medical conditions that raise your surgical risk, I carry out a standard lumbar interbody fusion, still through a minimally invasive approach. Placing the cage gives better alignment of the spine and maintains the disc height between the two bones, which provides a longer-lasting construct.

If you are in your 70s or 80s, where the risks of surgery do rise slightly, I do not rule out a cage completely. I check things with my anaesthetist and any other physicians involved in your care, and I then consider the posterior lateral fusion, placing just the screws, realigning the bones, and carrying out a decompression. This saves time and can still achieve a very good result.

The goal is never a picture-perfect X-ray afterwards. The goal is a good outcome: an improvement in your symptoms and your quality of life. As I always say, we treat the patient, not the scan.

A promising idea for the future

I want to finish with a hypothesis that is currently being researched.

The theory is that if we place only the screws, without an interbody cage, and allow fusion to take place at the back of the spine using bone graft, the construct may behave differently. Bone has a degree of elasticity. It is slightly bendable, which allows a small amount of motion between the bones.

That tiny amount of motion may help protect the segments above and below the fusion from wear and tear, a problem we sometimes see develop next to rigid constructs. This is still being studied, but it is a promising idea. If we can improve the posterior lateral fusion in this way, we may one day be able to remove the need for an interbody cage altogether.

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