Abstract: BACKGROUND: A novel one-hole split endoscope technique has been used in the treatment of lumbar spondylolisthesis, but there is no literature on the safety, feasibility and effectiveness of this technique.
OBJECTIVE: The relationship between bone markers and L4, L5 nerves and intervertebral space position is observed by lumbar CT three-dimensional reconstruction to evaluate the safety of intervertebral fusion with one-hole split endoscopic L4/5 spondylolisthesis. 
METHODS:  Totally 26 patients with grade I L4/5 spondylolisthesis (spondylolisthesis group) and 26 volunteers (normal group) underwent lumbar CT scanning. Data were input into Mimics 17.0 software to measure the following parameters: (1) vertical distance. a, b: The intersection of the medial edge of the articular surface at the coronal position of the upper endplate of L5 and the upper articular process of L5 (N) to the highest point of the posterior edge of the mastoid process (R) and the tip of the superior articular process of L5 (S); c: point of intersection between L4 inferior articular process tip (X) and N on sagittal plane and L4 inferior endplate (M). (2) Horizontal distance. d: intersection point between R and N and lower edge of  L4 outlet nerve root (N1); e: intersection point of transverse section from R to M with lower edge of L4 outlet nerve root (M1); f: intersection point of N to N cross section and lateral edge of nerve tissue (N2); g: N1 to N2; h: M1 to M2; i: N2 to M1; j: Posterior edge of articular surface (R1) in sagittal position of superior articular process from M1 to L5. (3) Nine patients underwent a one-hole split splinterbody endoscopic interbody fusion with bone grafting. The outcomes were evaluated by visual analogue scale for lumbar and leg pain, Japanese Orthopaedic Association Evaluation score, Oswestry Disability Index, and 36-item Short-Form scale.
RESULTS AND CONCLUSION: (1) There was no significant difference between b and c in the spondylolission group (P > 0.05), indicating that only equal amounts of upper and lower articular processes and/or laminae were removed to expose the L4/5 disc. (2) There were statistically significant differences in d and e between the two groups (P < 0.05), so surgery should be planned according to pathological changes. (3) There were no significant differences in f, g and i between the two groups (P > 0.05), indicating that the degenerative spondylolisthesis did not change the position relationship between walking and outlet nerve, and it was safe to implant the fusion device in the constant transverse workspace of both groups. (4) Visual analogue scale score, Japanese Orthopaedic Association Evaluation score, Oswestry Disability Index and 36-item Short-Form scale score of nine patients with lumbar spondylolisthesis were significantly improved at the last follow-up compared with the data before operation and 6 months after operation (P < 0.05). (5) Safe fenestrating range: S down (11.78±2.34) mm to N, X up to L4 lower endplate to expose the upper and lower margins of the intervertebral disc. Opening the window outward to M1 would not damage L4 nerve; decompress inwards to prevent damage to N and its adjacent L5 nerves. Understanding the technical features of the novel one-hole split endoscope technique can help improve surgical safety and efficacy.

Key words: lumbar spondylolisthesis, one-hole split endoscope, interbody bone graft fusion, mimics, lumbar CT three-dimensional reconstruction