Abstract: BACKGROUND: There are few domestic and foreign literature reports on the treatment of thoracic disc herniation by percutaneous endoscopy, and the operative indications, technical points and technical limitations of this technique have not been thoroughly expounded.
OBJECTIVE: To guide the treatment of thoracic disc herniation by the percutaneous endoscopic posterolateral approach through three-dimensional CT imaging. 
METHODS: Thirteen patients with thoracic disc herniation admitted to the Affiliated Hospital of Binzhou Medical College from August 2017 to March 2020 were included. Thoracic computed tomography myelograhy examination was performed and three-dimensional CT images of thoracic vertebra were reconstructed. (1) Measuring articular process under the lower edge and articular process on the lateral margin of intersection point (Y) to the lateral edge of dura mater (a), medial margin of articular process (b), lower endplate of upper vertebra (c), and distance of upper endplate of lower vertebra (d), angle between lateral margin of dura mater to medial margin of vertebral arch root and vertebral body centerline (g), angle between the lateral edge of dura mater to posterior midline of the vertebral bodies and vertebral body centerline (h). At the level of the scapula (T1/2-T6/7), the angle between the medial edge of the vertebral arch root to the medial edge of the scapula and the midline of the vertebral body was measured in cross section (i). In the 3D view of the software, a 7.5-mm 3D cylindrical guide plate was created according to the working channel, and the osseous structure of the guide plate to the inner edge channel of the vertebral arch root was observed, and the range of facet joint defect (j) was measured. (2) All the 13 patients underwent thoracic discectomy via percutaneous endoscopic posterolateral approach. Visual analogue scale score, Japanese Orthopedic Association thoracic spinal function score, Oswestry disability index and modified MacNab were used to evaluate the clinical efficacy. The study was approved by the Ethics Committee of Binzhou Medical University Hospital.
RESULTS AND CONCLUSION: (1) There was no significant difference in the distance from Y point of T2/ 3-T10/11 vertebral body to the lateral edge of the dura mater (P > 0.05). There was no significant difference in the distance from Y point of the T1/2-T10/11 vertebral body to the medial edge of the facet joint (P > 0.05). (2) Y point on the sagittal plane of the T1/2 vertebral body was projected above the intervertebral space, while Y point on the sagittal plane of the other segments was projected at the level of intervertebral space. (3) T1/2 vertebral body h < i, guide plate abduction without scapula barrier; T2/3-T4/5 vertebral body h > i, the guide plate was blocked by the scapula during abduction. (4) Visual analogue scale, Japanese Orthopedic Association thoracospinal function scale and Oswestry disability index score of the 13 patients in the last follow-up were significantly improved compared with those before surgery (P < 0.05); the excellent and good rate after modified MacNab was 92%. (5) The posterior lateral approach of percutaneous endoscopy was applicable to paracentral soft thoracic disc herniation due to the deep location of T1/2-T4/5 segments, which were blocked by the shoulder blades and the work passage was limited in extension. In T5/6-T11/12 segments, this technique is applicable to various types and properties of thoracic disc herniation (except for giant type). (6) Results confirm that Y point can be used as a marker of bone localization under endoscope, and its constant projection on the sagittal surface is at the level of intervertebral space (except T1/2). The different bone structure of each thoracic vertebra segment should be removed to establish the bone channel. The treatment of thoracic disc herniation by percutaneous endoscopic posterolateral approach is effective, safe and feasible.

Key words: bone, disc herniation, three-dimensional CT, percutaneous spinal endoscopy, posterolateral approach, thoracic discectomy, osseous channel, clinical curative effect