Radiologic Anatomy of the Lumbar Interlaminar Window and Surgical Considerations for Lumbar Interlaminar Endoscopic and Microsurgical Disc Surgery

Objective The interlaminar window is the most important corridor during both interlaminar approaches to intervertebral discs. The aim of this study was to measure radiologic parameters related to endoscopic and microsurgical interlaminar discectomy. Methods Measured parameters included lateral recess line (LRL) width, distance between LRL and endplates of upper intervertebral disc, superior and lateral angles of interlaminar window, interlaminar height, and interpedicular distance via optimized coronal oblique projection computed tomography images. Measurements were performed at L2, L3, L4, and L5 levels. Results LRL was found to be 16.3 ± 3.4 mm, 17.3 ± 3.3 mm, 21.7 ± 3.4 mm, and 27.7 ± 4.0 mm at L2, L3, L4, and L5. The distances between LRL and both upper endplates decreased from L2 to L5. Distance between LRL and upper endplate of same vertebra and between LRL and lower endplate of upper vertebra was measured. Interlaminar window height decreased from L2 to L5 levels (from 14.0 ± 4.1 mm to 11.1 ± 2.4 mm). Conclusions This study showed that width of LRL increases in lower lumbar segments, and height of interlaminar window increases in upper lumbar segments. This study also revealed that intervertebral disc is located cranial to LRL at L2-3, L3-4, and L4-5 levels and is located caudal to LRL at L5-S1 level. The results of this study may help surgical planning in both endoscopic and microscopic interlaminar surgery.