Abstract: BACKGROUND: One-hole split endoscope technique has been widely used in the treatment of lumbar degenerative diseases, but there is no relevant literature on the safety analysis of this technique in the treatment of upper lumbar disc herniation.
OBJECTIVE: To observe the position relationship of nerve roots, intervertebral space and bone landmarks in the upper lumbar spine by three-dimensional lumbar CT reconstruction technology, and to provide a basis for the clinical operation of one-hole split endoscope surgery.
METHODS: Twenty-six patients with upper lumbar disc herniation underwent a lumbar CT scan. Mimics 17.0 software was imported to measure the related imaging parameters of L1/2 to L3/4 segments: (1) Measurement of vertical distance: In coronal view, the distance (a) from the intersection point of the medial facet of the superior articular process and the superior endplate (N) to the apex of the articular process (S); in the coronal view, the distance (b) from the sagittal intersection (M) of N and the inferior endplate to the apex of the inferior articular process (X). (2) Measured horizontal distance: the distance (c) between the cross-section of N and the lower edge of the outlet nerve root (N2); distance (d) between the cross-section of N and the intersection point of neural tissue (N1); N1 to N2 distance (e); distance (f) between the cross-section of M and the lateral edge of the nerve tissue (M1); M to M cross-section and exit nerve root intersection (M2) distance (g); distance (h) from M1 to M2; distance (i) from M2 to N1; distance (j) from the posterior edge of the articular surface (R) to M2 in sagittal view of the superior articular process. 
RESULTS AND CONCLUSION: (1) With the decrease of the segment, the distances a and b gradually increased, and the distance j gradually decreased. There was no significant difference between L1/2 and L2/3 segments (P > 0.05). (2) With the decrease of the segment, distance d first decreased and then increased; distance f gradually decreased; distances c, e, g, h and i gradually increased; and there was no significant difference between L2/3 and L3/4 segments (P > 0.05). (3) Distance i was the shortest distance without pulling nerve roots in the natural state, and the area of the safety zone was between four points M1, M2, N1, and N2. The bone was removed to the upper and lower endplates by biting the bone downward and upward through S and X, respectively, to expose the intervertebral space, and the window of distance g to M2 could be opened outward to avoid injury of the outlet nerve roots. (4) In conclusion, the upper lumbar vertebrae have unique anatomical characteristics. Based on the relevant measurements of nerve roots, spinal dura and intervertebral space, the parameters of the one-hole split endoscope technique are more accurate and safe during operation. 

Key words: one-hole split endoscope, upper lumbar spine, lumbar disc herniation, three-dimensional reconstruction, imaging anatomy