Dimensional Characterization of the Human Lumbar Interlaminar Space as a Guide for Safe Application of Minimally Invasive Dilators

Background: The risk of interlaminar passage of a dilator into the lumbar spinal canal in minimally invasive approaches is currently unknown. Among anthropometric data reported in the medical literature, there is no cadaveric report of the interlaminar dimensions of the lumbar spine.

Objective: To report the lumbar interlaminar dimensions in neutral, flexion, and extension postures.

Methods: A total of 8 spines were sectioned into lumbar segments. Digitized coordinate data defining the locations and movements of chosen anatomic points on the laminar edges at a given spinal level were used to measure changes in the opening dimensions during static neutral posture and flexion-extension movements. Interlaminar dimensions were averaged and categorized for each vertebral level and spinal posture.

Results: The mean interlaminar distance increased from neutral posture to flexion across all vertebral levels. The mean interlaminar distances in the neutral posture ranged from 12.21 mm (L5-S1) to 14.88 mm (L1-L2). In flexion, the range was from 17.15 mm (L5-S1) to 18.50 mm (L4-L5). These measurements are greater than the first several diameters of dilators in all minimally invasive dilator sets.

Conclusion: The precise measurements of the lumbar interlaminar space are valuable to minimally invasive spine surgeons for the dilatation phase of the operation. The risk of interlaminar passage of a minimally invasive dilator is greatest in flexion with dilators that have a diameter of 16 mm or less. There is considerably less risk of interlaminar passage in patients positioned on an extended Jackson table.