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

Abstract

The risk of interlaminar passage of a dilator into the cervical spinal canal in minimally invasive approaches is currently unknown. Among the various anthropometric data reported in the literature, there is no report of the interlaminar dimensions in the cervical spine. To report the cervical interlaminar dimensions in neutral, flexion, and extension. A total of 8 spines were sectioned into cervical (C2-T1) 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 compute the dimensions during a static neutral posture, flexion, and extension positions to mimic the positions during surgery. Interlaminar dimensions were averaged and categorized for each vertebral level and spinal posture. Based on the reported measurements, the smallest diameter dilator in commonly used dilator sets has the potential to traverse the interlaminar space at all levels in flexion. In a neutral posture, the average interlaminar distance at C2-3, C6-7, and C7-T1 was still greater than 2.0 mm, the smallest diameter of the initial dilator. The largest interlaminar distance was at C6-7 in flexion (7.68±1.60 mm). Because dilators pass directly onto the cervical lamina without visualization of the midline structures, the interlaminar distances have increased relevance in the minimally invasive cervical approaches of foraminotomy and laminectomy. The data in this report demonstrate the theoretical risk of interlaminar passage with small diameter dilators in posterior minimally invasive approaches to the cervical spine.