Comparison of Applied Anatomy at L4-L5 and L5-S1 in Context of Tubular Decompression for Lumbar Canal Stenosis

Tubular over-the-top decompression is getting popular in the management of lumbar canal stenosis (LCS). While L4-L5 is the most common level affected and operated for LCS, it is not uncommon to encounter patients with stenosis at L5-S1. No previous study has described the technical challenges of tubular decompression at the L5-S1 level as compared to at the L4-L5 level.

This observational study was done on 40 consecutive patients older than 45 years who underwent magnetic resonance imaging (MRI) for back-related issues. The following radiological parameters: interlaminar angle, tube angle, laminar thickness ratio at the isthmus, and the laminar length ratio were evaluated at the L4-L5 level (group A) and the L5-S1 level (group B). The hypothesis behind the study was that if these patients were subjected to tubular decompression, then there will be technical differences between doing the surgery at the L4-L5 and L5-S1 levels.

The mean age of the patients was 56.8 years (46-72) and the male to female ratio was 3:2. The mean interlaminar angle in group A was 71° and in group B was 102°. The tube angle in group A and group B was 36.8° and 49.7°, respectively. The laminar thickness ratio (L4:L5) was 1.34:1 and the laminar length ratio (L4:L5) was 1:1.42 in group A and B, respectively.

Tubular decompression at the L5-S1 level has its own challenges because of the different anatomy of the L5 lamina compared to that of the L4 lamina. The wide interlaminar angle of L5 as compared to L4 dictates more oblique tube docking (tube angle) and more extensive table tilting to reach the contralateral lateral recess, thus making it challenging. The authors recommend that surgeons be conscious of this fact while performing tubular decompression at the L5-S1 level.

This article provides information regarding technical challenges of doing surgery at L5-S1 level as compared to L4-L5 level.

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