Background and objectives The lumbar interlamina space height is an important determinant of successful spinal puncture. We aimed to evaluate the influence of age, laterality, patient position, and spinal level on the height of the interlamina window using ultrasonography.

Methods Ultrasonographic examination was performed in 20 adult patients aged under 40 years (group Y) and 20 patients aged over 60 years (group O). We set three primary outcomes: difference in the interlamina height of the ligamentum flavum-dura mater complex (LFD) according to (1) age, (2) laterality, and (3) position. For secondary outcomes, the degree of ultrasonography visualization (poor, intermediate, or good) and the depths from the skin to LFD and to anterior complex were also measured on right and left paramedian sagittal oblique view in both lateral and sitting positions at L3/4, L4/5, and L5/S1 levels. All variables were analyzed in association with age, laterality, patient position, and spinal level.

Results The interlamina height of LFD was higher, and the degree of visualization was better in group Y than in group O. It differed depending on laterality in paramedian sagittal oblique view images in the same patients at all spinal levels. The interlamina height of LFD was the largest at L5/S1 level in both groups. Position had little influence on the interlamina height of LFD.

Conclusions Scanning both sides and all spinal levels before selecting a puncture site for ultrasound-guided spinal anesthesia is recommended. The L5/S1 spinal level is a good option for spinal puncture in the elderly.

Trial registration number NCT03929874.