Ultrasound Measurement of the Intervertebral Space in the Lateral Recumbent Versus Sitting Positions.

Background: Diagnostic lumbar puncture (LP) is an invasive procedure routinely performed within the emergency department (ED). LP is traditionally performed with the patient in either the lateral recumbent or sitting position. We investigated if the intervertebral space is larger in one of these positions. If one position is larger than the other, this would imply that one position offers a higher chance of a successful lumbar puncture than the other position.

Objective: We sought to determine if there is a significant size difference of the L4/L5 intervertebral space in the lateral recumbent compared with the sitting position.

Methods: Point-of-care ultrasound (POCUS) was performed to measure the size of each volunteer's L4/L5 intervertebral space in both the seated and lateral recumbent positions. All volunteers >18 years of age were eligible for the study. Thirty volunteers had measurements taken. Three measurements were taken by each investigator in both positions for each volunteer.

Results: The median L4/L5 intervertebral space distance was 1.7511 cm in the lateral recumbent position and 1.9511 cm in the seated position with a Wilcoxon signed rank p value <.0001. The interspinous space in the seated position was found to be significantly larger than in the lateral recumbent position.

Conclusion: The size of the interspinous space in the seated position on ultrasound was found to be larger than the lateral recumbent position, suggesting that LP may be more successful in the seated position.