Abstract: BACKGROUND: One-hole split endoscope as a new type of endoscopic technique is suitable for the treatment of far lateral lumbar disc disease. However, there are few research data on L5/S1, which has a very low incidence of far lateral lumbar disc herniation at home and abroad, and there is no detailed image anatomical data describing the one-hole split endoscope treatment of L5/S1 far lateral lumbar disc herniation.
OBJECTIVE: Through the three-dimensional image reconstruction, the bony landmarks were determined to accurately locate the positional relationship between the L5 outlet nerve root, the L5/S1 intervertebral space and other structures. One-hole split endoscope via posterolateral approach was used to accurately, safely and effectively decompress the L5 outlet nerve root and treat the L5/S1 far lateral lumbar disc herniation.
METHODS: Twenty-nine patients with L5/S1 unilateral far lateral lumbar disc herniation who met the inclusion and exclusion criteria were selected, including 12 males and 17 females at the age of 48-74 years. The lumbar CT data of the patients were imported into Mimics 21.0 software to reconstruct the three-dimensional lumbar model. Measurement of L5/S1 related parameters: (1) Measurement on the sagittal plane at the intersection (H) of the lower edge of the transverse process and the lateral edge of the isthmus: The vertical distance between H and the upper and lower edges of L5 outlet nerve root (a1, a2); the vertical distance between H and the lower endplate of L5 and the upper endplate of S1 (b1, b2); vertical distance from the lower edge of the pedicle from H to L5 (c). (2) Horizontal distance between the left and right sides of the sagittal surface where the medial wall of the pedicle was located from H to L5 (d). (3) The horizontal distance from H to the left and right side of the sagittal plane where the lateral margin of the dura was located (e). (4) Horizontal distance (f) between the left and right sides of the sagittal plane at the outermost edge of the lower endplate from H to L5. (5) Measurements were made on the sagittal plane where the outermost edge of the lower endplate of L5: The vertical distance between the cross section of H and the upper and lower edges of L5 outlet nerve root (g1, g2); vertical distance (h1, h2) between the transverse section of H and the lower endplate of L5 and the upper endplate of S1, respectively; (6) anteroposterior horizontal distance from H to L5 in the coronal plane where the last edge of the nerve root exits (i); (7) anteroposterior horizontal distance from the highest point of the posterior margin of the sacral wing to the last margin of the inferior endplate of L5 in the coronal plane (j).
RESULTS AND CONCLUSION: (1) There was no significant difference in the relevant measurement parameters between men and women (P > 0.05). (2) a1, a2, b1, b2, c, d, e, f, h1, h2, g1, g2, i, and j on the affected side were not significantly different from the healthy side (P > 0.05). (3) There was no significant difference between a1 and c (P > 0.05), indicating that the lower edge of the pedicle was the upper edge of the L5 outlet nerve root; the L5 outlet nerve root was close to the lower edge of the pedicle and ran anterolateral behind the L5 vertebral body, and H was located above the L5 outlet nerve root. (4) With H as the bony marker point, it was not necessary to probe upward or to remove the isthmus, but only to grind part of the bone downward and laterally to reveal the L5 outlet nerve root and vertebral space, and to have enough safe distance to avoid damage to the dural membrane to complete exploration and decompression of the lateral recess and foraminal region. (5) The surgeon could operate in the sagittal plane where the most lateral edge of the L5 inferior endplate was located, and in the “rectangular area” formed by the L5 transverse process and the sacral wing. The closer to the medial and inferior area (Kambin triangle), the safer the operation was. (6) It is suggested that using H as the bony landmark point to locate the L5 outlet nerve root and intervertebral space through one-hole split endoscope via posterolateral approach can achieve accurate, safe and effective decompression of L5/S1 far lateral lumbar disc herniation.

中国组织工程研究杂志出版内容重点：人工关节；骨植入物；脊柱；骨折；内固定；数字化骨科；组织工程

Key words:  far lateral lumbar disc herniation, one-hole split endoscope, three-dimensional image reconstruction, bony landmark, digital software