Interlaminar Endoscopic Lumbar Discectomy (IELD)

The interlaminar approach reaches a herniated disc from the back of the spine, but through a small keyhole rather than an open incision. The endoscope is passed through the interlaminar window — the natural gap between the laminae, the bony plates that roof the spinal canal — and a small amount of the ligament is opened to enter the canal. The nerve is gently protected and moved aside just enough, and the herniated fragment is removed from beneath it under continuous magnified vision and irrigation. Because it comes from behind, it is a more familiar direction to surgeons trained in traditional surgery, delivered here through a keyhole with the tissue-sparing advantages of the endoscope.

The reason the interlaminar route matters is largely anatomical, and this is a judgement I make for each patient. At the very bottom of the spine, at the L5/S1 level, the pelvis rises up on either side — the iliac crest — and can physically block the from-the-side transforaminal corridor, especially in people with a high crest. The interlaminar window at this level, by contrast, is usually generous. So where the pelvis gets in the way of a side approach, coming from behind through the interlaminar window is often the cleaner, safer route to the disc. The choice between the transforaminal and interlaminar approaches is not about one being universally better; it is about matching the corridor to the individual's anatomy and the position of the herniation, and knowing both techniques well is what allows that choice to be made properly.

Under x-ray guidance, the interlaminar window is identified and the working channel is docked at the edge of it. A small opening is made in the ligamentum flavum to enter the canal. The travelling nerve root is identified and protected, and the herniated fragment beneath it is mobilised and removed with fine endoscopic instruments. Where a fragment has migrated a short distance up or down, the endoscope can be angled to follow it. Decompression is confirmed when the nerve lies free and the dural sac pulses normally. As with all these approaches, the operation is carried out through a portal a few millimetres wide, sparing the muscles and the bulk of the bone.

The skill in the interlaminar approach lies in working safely right next to the nerve and its covering — the dura — through a very small window, retracting the nerve only as much as is needed and no more. Judging how much ligament and, occasionally, bone to remove to see the fragment, while keeping the nerve protected, is where training and experience tell. Having both the transforaminal and interlaminar techniques fully at my disposal means I can select the approach that fits the anatomy in front of me rather than forcing every disc through a single route — and that flexibility is, I think, one of the real benefits of subspecialising in endoscopic surgery.

The interlaminar full-endoscopic technique was established alongside the transforaminal one in the landmark randomised trial by Ruetten and colleagues, which found full-endoscopic discectomy at least equal to open microdiscectomy with less tissue trauma. Since then, meta-analyses and randomised trials comparing the transforaminal and interlaminar approaches have found broadly similar clinical outcomes overall, while consistently identifying the interlaminar route as the more practical choice at L5/S1, particularly where a high iliac crest limits transforaminal access. This is precisely the anatomical reasoning I apply in selecting the approach, and it is well supported by the published evidence.

Recovery from interlaminar endoscopic discectomy is generally quick, because the muscles and most of the bone of the back are spared. Relief of the leg pain is often early, and most people go home the same day or the next, walking, with a small dressing. Because the approach works right beside the nerve, some temporary nerve sensitivity can occur early and usually settles; numbness and long-standing weakness may take longer to recover and do not always resolve fully. As with any disc surgery, care is taken with lifting and bending in the early weeks, and the spine is followed up over the longer term.

• —Ruetten S, et al. Full-endoscopic interlaminar and transforaminal versus microsurgical lumbar discectomy (RCT). (PMID 18427312)
• —Jitpakdee K, et al. Transforaminal versus interlaminar endoscopic discectomy for lumbar disc herniation: systematic review and meta-analysis. (PMID 35993298 / PMC9972290)
• —Percutaneous endoscopic lumbar discectomy for L5-S1 via interlaminar versus transforaminal approach (RCT). (PMID 27454540)
• —Transforaminal versus interlaminar percutaneous endoscopic discectomy: meta-analysis of randomised trials. (PMID 33592819)
• —Endoscopic L5/S1 interlaminar discectomy for high iliac crest with migrated disc. (PMID 33053537)
• —Gadjradj PS, et al. Full-endoscopic transforaminal versus open microdiscectomy: systematic review and meta-analysis. (PMID 35867477)