🎧 Listen to this guideAudio version coming soon. Mr Sadek will read this guide for you.
Key points
- This operation relieves lumbar spinal stenosis by removing bone and thickened ligament through a small tube placed on one side of the spine.
- The surgeon angles across underneath the midline to clear both sides, leaving the central bone and ligaments in place.
- Relief of leg symptoms and disability appears similar to traditional open laminectomy, although long-term comparisons are limited.
- Reviews report less blood loss, fewer wound infections and a shorter hospital stay with the tubular approach, though most of that evidence comes from non-randomised studies.
- Not every surgeon offers it, NHS availability varies, and it is not suitable for everyone.
What is the operation for?
In lumbar spinal stenosis, wear in the discs, joints and ligaments narrows the spinal canal in the lower back and squeezes the nerves. Typical symptoms include pain, heaviness or numbness in the legs on walking or standing that ease when you sit or bend forward. When symptoms limit daily life despite non-surgical treatment, decompression surgery may be offered to make more room for the nerves.
For many years the standard operation has been a laminectomy, which removes the spinous process (the bony ridge you can feel down the back), the lamina and the ligaments between them. Newer techniques try to do the same job while keeping these midline structures, to preserve the integrity of the spine and limit tissue damage.[1] Unilateral laminotomy for bilateral decompression, often shortened to ULBD or called an over-the-top decompression, is one of them.
How tubular over-the-top decompression works
In one randomised trial the tubular technique was described as follows. The surgeon makes a cut of about 3 cm just to one side of the midline, on the side with the worse leg symptoms. Rather than stripping the muscles off the bone, a series of tubes of increasing size gently parts the muscle fibres, and a final tubular retractor is fixed in place. Working through the tube with an operating microscope, the surgeon removes part of the lamina and thickened ligament on that side.[2] The tube is then tilted so the surgeon can reach across under the spinous process and clear the opposite side as well, hence the name over-the-top.
The same bony operation can be done through a conventional small open incision under magnification, which is how it was performed in the large Norwegian NORDSTEN trial.[3] Fully endoscopic versions also exist, using a camera instead of a microscope.[2][4]
Who may be suitable, and who may not
Much of the trial evidence comes from people without a slipped vertebra, and the Thai trial included only narrowing at a single level.[2] The NORDSTEN trial left out people with degenerative spondylolisthesis, where one vertebra has slipped forward on another,[3] so its results do not tell us how well over-the-top decompression works in that group. If you have a slip, a curvature or signs of instability, your surgeon may discuss other options, sometimes including spinal fusion.
Evidence for narrowing at several levels is thinner. A 2025 meta-analysis of multilevel stenosis found only four studies (618 patients). Minimally invasive decompression reduced blood loss, but complications, reoperations, back pain and hospital stay did not differ significantly from open laminectomy.[5]
Learning curve and availability
Reaching the far side of the canal through a narrow tube is technically demanding, and surgeons need time to become fluent. In a 2026 study of 200 endoscopic over-the-top operations, one surgeon reached proficiency after 37 cases. A second surgeon, who trained under the first with supervision, got there after 29.[6] Tubular and endoscopic techniques are not offered by every hospital or surgeon, and NHS availability varies. A well-performed open decompression remains a good operation, and you can ask your surgeon which technique they use most and why.
Before, on the day and recovery
You will have a pre-operative assessment, and your team will tell you which medicines, especially blood thinners, to stop beforehand. In the trials described here, the correct level was confirmed with X-ray during the operation,[3] and in the Thai trial all operations were done under general anaesthetic with the patient lying face down.[2] Your anaesthetist will discuss the anaesthetic with you.
Hospital stay is short, but it depends on the hospital and the patient. In NORDSTEN the average stay after unilateral laminotomy was just under three days.[3] In a small Thai trial, stays were significantly shorter after fully endoscopic surgery than after tubular surgery.[2] A 2025 meta-analysis found that the tubular approach shortened hospital stay by about 1.4 days compared with open laminectomy.[7] Your surgeon will advise on driving and returning to work, and physiotherapy can help you rebuild walking distance and confidence.
Risks and complications
The figures below come from the studies cited. They vary because studies differ in the patients included and how complications were recorded.
| Risk | Approximate frequency (published studies) |
|---|---|
| Tear in the lining around the nerves (dural tear) | About 6 in 100 after unilateral laminotomy in NORDSTEN (ref 3). Not significantly different between tubular and open surgery in a 2025 meta-analysis (ref 7) |
| Wound infection | None after unilateral laminotomy in NORDSTEN (ref 3). Significantly lower with tubular than open surgery in a 2025 meta-analysis (ref 7) |
| Blood clot around the nerves needing another operation | About 1 in 100 after unilateral laminotomy in NORDSTEN (ref 3) |
| Worse nerve symptoms after surgery | About 2 in 100 after unilateral laminotomy in NORDSTEN (ref 3) |
| Further spinal surgery | About 8 in 100 within 2 years after unilateral laminotomy in NORDSTEN (ref 3); rates similar across techniques at 5 years (ref 8). No significant difference between tubular and open surgery (ref 7) |
| Any complication, tubular approach | 6 of 30 patients (20%) in a small randomised trial, none of them major (ref 2). Lower overall complication rate than open surgery in a 2025 meta-analysis (ref 7) |
| Spine becoming unstable after surgery | Uncommon after any technique; numerically fewer cases after over-the-top decompression than laminectomy, based on low-quality evidence (ref 1) |
NORDSTEN tested unilateral laminotomy with crossover done through a small open incision under magnification, the same bony technique as the tubular operation. Risks also depend on your general health and the number of levels treated, so ask your surgeon for their own figures.
What the evidence shows
A Cochrane review published in 2015 is still the main summary comparing midline-sparing techniques with laminectomy. It included 10 randomised trials and 733 people, of whom 173 were in trials of over-the-top decompression. Disability and leg pain were similar after the newer techniques and laminectomy, and there was no clear difference in complications or hospital stay. The quality of evidence was low or very low, and long-term results were lacking.[1]
Since then, the NORDSTEN trial has added strong evidence. It randomised 437 patients in 16 Norwegian hospitals to three midline-sparing operations, including unilateral laminotomy with crossover. Disability improved by similar amounts in all three groups at two years,[3] and the picture was unchanged at five years, with similar rates of further surgery.[8] NORDSTEN did not include a laminectomy group, so it compares the newer techniques with each other rather than with the older operation.
The 2025 meta-analysis comparing tubular decompression directly with open laminectomy pooled nine studies and 2,860 patients. Tubular surgery was linked with fewer overall complications, fewer wound infections, about 47 ml less blood loss and a shorter stay. Patient-reported outcomes, dural tears and reoperations were similar. The authors cautioned that most included studies were retrospective and differed from one another.[7]
Endoscopic versions are being compared with tubular and microscopic ones. A small randomised trial found fully endoscopic and tubular decompression gave similar disability scores at two years. The endoscopic group had less back pain, less blood loss and a shorter stay.[2] A 2026 meta-analysis of five studies (349 patients) found that endoscopic over-the-top decompression gave similar leg pain relief to the microscopic version, with a shorter stay, less blood loss and fewer complications.[4] These are early results from small numbers of patients.
Seek urgent medical help (A&E or 999) if you have:
- Numbness around the back passage, genitals or inner thighs, or new difficulty passing or controlling urine or stools (possible cauda equina syndrome)
- New or rapidly worsening weakness in one or both legs
- A fever, or a wound that becomes red, hot, swollen or starts to leak
- Clear fluid leaking from the wound with a severe headache
- A painful, swollen calf, or sudden chest pain or breathlessness
References
- Overdevest GM, Jacobs W, Vleggeert-Lankamp C, et al. Effectiveness of posterior decompression techniques compared with conventional laminectomy for lumbar stenosis. Cochrane Database Syst Rev. 2015;(3):CD010036. Link
- Kotheeranurak V, Tangdamrongtham T, Lin GX, et al. Comparison of full-endoscopic and tubular-based microscopic decompression in patients with lumbar spinal stenosis: a randomized controlled trial. Eur Spine J. 2023;32(8):2736-2747. Link
- Hermansen E, Austevoll IM, Hellum C, et al. Comparison of 3 different minimally invasive surgical techniques for lumbar spinal stenosis: a randomized clinical trial. JAMA Netw Open. 2022;5(3):e224291. Link
- Feng R, Pang C, Ji D, et al. Uniportal endoscopic versus microscopic unilateral laminotomy for bilateral decompression in the treatment of lumbar spinal stenosis: a meta-analysis. Neurol India. 2026;74(2):206-214. Link
- Sharma E, da Silva Lobo KE, Ayesha A, et al. Minimally invasive decompression versus open laminectomy in multilevel lumbar stenosis: a systematic review and meta-analysis. World Neurosurg. 2025;198:124031. Link
- Liu S, Yao S, Zhang Y, et al. Impact of mentorship on the learning curve of unilateral biportal endoscopic unilateral laminotomy for bilateral decompression in lumbar spinal stenosis: a cumulative sum analysis across 2 generations of surgeons. Wideochir Inne Tech Maloinwazyjne. 2026;21(2):197-205. Link
- Kartal A, Manalil NF, Hamad MK, et al. Minimally invasive tubular decompression versus traditional open surgery for lumbar spinal stenosis: a systematic review and meta-analysis. Sci Rep. 2025;16(1):176. Link
- Hermansen E, Indrekvam K, Franssen E, et al. ISSLS Prize in Clinical Science 2025: a randomized trial on three different minimally invasive decompression techniques for lumbar spinal stenosis. Five years follow-up from the NORDSTEN-SST. Eur Spine J. 2025;34(5):1590-1599. Link
This guide is general information and is not a substitute for advice about your own situation. Please discuss the benefits and risks of any procedure with your surgeon.
Leave a comment