Human Lumbar Ligamentum Flavum Anatomy for Epidural Anesthesia: Reviewing a 3D MR-Based Interactive Model and Postmortem Samples

The ligamentum flavum (LF) forms the anatomic basis for the loss-of-resistance technique essential to the performance of epidural anesthesia. However, the LF presents considerable interindividual variability, including the possibility of midline gaps, which may influence the performance of epidural anesthesia. We devise a method to reconstruct the anatomy of the digitally LF based on magnetic resonance images to clarify the exact limits and edges of LF and its different thickness, depending on the area examined, while avoiding destructive methods, as well as the dissection processes. Anatomic cadaveric cross sections enabled us to visually check the definition of the edges along the entire LF and compare them using 3D image reconstruction methods. Reconstruction was performed in images obtained from 7 patients. Images from 1 patient were used as a basis for the 3D spinal anatomy tool. In parallel, axial cuts, 2 to 3 cm thick, were performed in lumbar spines of 4 frozen cadavers. This technique allowed us to identify the entire ligament and its exact limits, while avoiding alterations resulting from cutting processes or from preparation methods. The LF extended between the laminas of adjacent vertebrae at all vertebral levels of the patients examined, but midline gaps are regularly encountered. These anatomical variants were reproduced in a 3D portable document format. The major anatomical features of the LF were reproduced in the 3D model. Details of its structure and variations of thickness in successive sagittal and axial slides could be visualized. Gaps within LF previously studied in cadavers have been identified in our interactive 3D model, which may help to understand their nature, as well as possible implications for epidural techniques.

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