Spinemathema podcast · Episode 7 · About 7 minutes · October 2026

Episodes are narrated using an AI model of Mr Sadek’s own voice, from scripts he has written and approved.

Read the full article with references: Laminectomy With or Without Fusion for a Slipped Vertebra? The SLIP Trial

Transcript

Hello and welcome to the Spinemathema podcast. I’m Ahmed Sadek, a neurosurgeon. Today I want to talk about the SLIP trial, an American study that looked at whether people with a slipped vertebra in the lower back do better if a fusion is added to their operation.

First, a quick explanation of the condition. Degenerative spondylolisthesis is when one vertebra slips forward on the one below, usually because the joints and discs have worn over time. That slip often narrows the spinal canal, and the nerves to the legs get squeezed. The result is lumbar spinal stenosis: aching, heaviness or tingling in the legs when you walk, often with back pain as well.

When surgery is needed, the surgeon removes bone and ligament from the back of the spine to free up the nerves. That’s called a laminectomy, or a decompression. Many surgeons also add a spinal fusion, fixing the slipped vertebra to the one below with screws and rods, so that the slip can’t progress. But when the SLIP trial was set up, nobody really knew whether adding the fusion led to better results for people with a mild slip.

So, how did the trial work? SLIP stands for the Greenwich Lumbar Stenosis SLIP Study, and it ran at several centres in the United States. It recruited people aged fifty to eighty who had symptoms of spinal stenosis and a stable, mild slip, known as grade one, which here meant a slip of between three and fourteen millimetres. People were excluded if the slip moved more than three millimetres on bending X-rays, if they’d had previous surgery at that level, if the slip came from a stress fracture in the bone, or if they had serious medical illness.

Sixty six people took part. Their average age was sixty seven, and eighty percent were women. Each was randomly assigned to one of two operations. One group had a laminectomy alone. The other had the same laminectomy plus a fusion, with screws placed into the vertebrae and connected with titanium alloy rods.

The main measure was a little different from many spine trials. Instead of a back pain questionnaire, the researchers chose the physical part of a general health survey called the S F thirty six. That’s a widely used questionnaire about physical health and day to day functioning, where higher scores mean better health. They looked at how much it had improved two years after surgery. They also measured the Oswestry Disability Index, which is a back specific questionnaire, and they followed people for four years.

What did they find? At two years, the physical health score had improved by an average of fifteen point two points in the fusion group, and nine point five points in the laminectomy alone group. That’s a difference of five point seven points in favour of fusion. It was statistically significant, but only just, and the range of likely values was wide. The authors described it as a slightly greater but clinically meaningful improvement. The advantage for fusion was still there at three and four years.

On the back specific disability questionnaire, both groups improved. The scores fell by about twenty six points after fusion and about eighteen points after laminectomy alone. That difference was not statistically significant.

The fusion operation did involve more blood loss and a longer stay in hospital. But here’s a finding that caught a lot of attention. Over the follow-up period, fourteen percent of the fusion group needed another operation, compared with thirty four percent of the laminectomy alone group. That’s quite a big gap, although again it sat right on the edge of statistical significance.

Now, here’s what makes this trial especially interesting. It was published in April two thousand and sixteen in the New England Journal of Medicine, in the very same issue as a Swedish trial asking almost the same question. The Swedish Spinal Stenosis Study was much larger, with two hundred and forty seven people, and about half of them had a slip. That trial found no benefit from adding fusion, either at two years or later at five years, and similar rates of further surgery in both groups.

So two good trials, in the same journal on the same day, seemed to give different answers. Why might that be? The trials measured different main outcomes. SLIP used a general physical health score, while the Swedish trial used the disability questionnaire. Interestingly, on the disability questionnaire, which both trials used, neither found a statistically significant difference at two years. The trials also included different patients, and they were very different in size.

Let’s be honest about the limitations of SLIP. With only sixty six patients, the main result only just reached significance, so the true size of the benefit is uncertain. By four years, only sixty eight percent of patients were still being followed up, which makes the longer term results less certain. The trial registration lists no blinding, so patients knew which operation they’d had. And the trial only included people with a stable, mild slip, so it doesn’t tell us about larger or unstable slips. Surgical techniques have also continued to develop since then.

So what does this mean for you? If you have a mild degenerative slip and stenosis, the evidence doesn’t point firmly in one direction. SLIP suggests a fusion may give a modest extra gain in physical health and fewer repeat operations. The Swedish study suggests a decompression alone gives similar results with a smaller operation and a shorter hospital stay. In practice, your own symptoms, the features of your slip, your general health and what matters most to you all come into the decision.

Useful questions to ask your surgeon might include: is my slip stable on standing or bending X-rays? Is my main problem leg pain, back pain, or both? What would recovery look like after each operation? And what are the chances I’d need another operation with each approach?

And please remember: if you develop numbness around your bottom or genitals, new trouble passing urine or controlling your bowels, or rapidly worsening weakness in your legs, seek urgent medical help, because these can be signs of cauda equina syndrome.

This podcast is general information only and isn’t a substitute for advice about your own situation, so please speak to your own doctor. The full article, with diagrams, a side by side comparison of the two trials and all the references, is at spinemathema dot com. And if you found this helpful, please subscribe to our channel on YouTube. Thanks for listening.

This podcast is general information and is not a substitute for advice about your own situation. Please speak to your GP or specialist.