Anatomical Importance of Inner Ligamentum Flavum Parameters for Successful Endoscopic Lumbar Decompression Surgery

Objective Predicting the gross anatomy of the inner ligament flavum and surrounding interlaminar window is essential for sufficient neural decompression because endoscopic spine surgery is performed in a limited, narrow surgical corridor. This article aims to analyze the anatomical data of inner LF and interlaminar window on the 3D lumbar computed tomography (CT) for easy application to the endoscopic decompression surgery. Methods We measured nine parameters indicating the contour of inner LF and interlaminar window on 3D CT from 100 patients who were diagnosed with lumbar spinal stenosis or disc herniation. Inner LF angle, inner LF distance, inner LF volume, and inner foraminal ligament distance for inner LF contour; height, width, and lateral corner angle of interlaminar window contour were measured in five age groups consisted of twenty individuals from the 30s to the 70s. We then compared two age groups(ages 30–49 years, n=40; ages 60–79 years, n=40). Results In the old age group, the interlaminar window was changed to a smaller triangle shape representing decreased width and height and increased lateral corner angle. Inner LF volume, inner LF angle, inner LF distance were also reduced in the old age group. But these parameters have variations in levels with a significant difference. Uniportal endoscopic docking point has moved according to changed interlaminar window features more caudal and lateral direction. Inner LF angle could have used to decide the approach angle for endoscopic contralateral foraminotomy. Conclusion We found the changing features of these structures correlated with age and levels to help with endoscopic decompression surgery has a limited surgical corridor. The present study results may help the endoscopic surgeons decide the endoscopic docking site, the extent of bone drilling at the medial facet joint part, and the approach angle for contralateral lumbar foraminotomy.