ILED — Interlaminar Endoscopic Discectomy

The interlaminar approach reaches the 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 saline irrigation and magnified vision. Because it comes from behind, it is a familiar direction to surgeons trained in traditional surgery, delivered here through a portal a few millimetres wide.

The choice of corridor is a judgement I make for each patient, and it is largely about anatomy. The interlaminar route comes into its own where the from-the-side transforaminal approach is difficult — most often at the lowest level of the spine, L5/S1, where the pelvis can physically block a side approach but the interlaminar window is usually generous. It is also the natural choice when a fragment sits in a position best reached from behind, or has migrated a short distance up or down where the endoscope can be angled to follow it. Rather than forcing every disc through a single route, having both techniques fully at my disposal lets me match the approach to the individual — which I regard as one of the real benefits of subspecialising in endoscopic surgery.

Under x-ray guidance, the interlaminar window is identified and the working channel docked at its edge. 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, the endoscope is angled to follow it. Decompression is confirmed when the nerve lies free and the dural sac pulses normally. Throughout, the muscles and the bulk of the bone are preserved.

The skill in the interlaminar approach lies in working safely right beside the nerve and its covering — the dura — through a very small window, retracting the nerve only as much as is needed and no more, and judging how much ligament and, occasionally, bone to remove to see the fragment while keeping the nerve protected. These are matters of training and experience. Being fluent in both the interlaminar and transforaminal techniques, and knowing which suits a given disc, is exactly the kind of subspecialty judgement I have concentrated my practice on.

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 two 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 — which is precisely the reasoning I apply.

Recovery is generally quick because the muscles and most of the bone 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 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: 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)