Abstract: BACKGROUND: Compared with the common segment of lumbar disc herniation, upper lumbar disc herniation is rare, but the structure of the high spinal canal is complex, so the clinical manifestations are often serious and varied. Analysis of related imaging parameters can provide a deep understanding of the disease characteristics, and provide ideas for early diagnosis and treatment and postoperative prevention of recurrence.  
OBJECTIVE: To analyze the characteristics of sagittal imaging parameters in patients with upper lumbar disc herniation, and to explore the possible influence of different parameters on the incidence of upper lumbar disc herniation.
METHODS: A total of 46 upper lumbar disc herniation patients hospitalized from January 2019 to January 2022 were collected as the observation group, including 9 cases of disc herniation at the L1-L2 level, 10 cases at the L2-L3 level, and 27 cases at the L3-L4 level. According to the 1∶1 ratio, 46 patients with L4-L5 lumbar disc herniation during the same period were selected as the control group. Sagittal imaging parameters of the two groups were measured on the anteroposterior and lateral lumbar X-ray films in standing position, including: pelvic tilt, pelvic incidence, sacral slope, lumbar lordosis, thoracolumbar kyphosis, and wedging angle of the vertebrae. Multivariate Logistic regression analysis was used to determine the correlation between the above parameters and the incidence of upper lumbar disc herniation, and receiver operating characteristic curve was used to analyze the influence of risk factors for meaningful results.  
RESULTS AND CONCLUSION: (1) Pelvic tilt, pelvic incidence, sacral slope, and lumbar lordosis of the observation group were significantly less than those in the control group (P < 0.05). Thoracolumbar kyphosis and wedging angle of the vertebrae in the observation group were larger than those in the control group (P < 0.05). (2) Multivariate Logistic regression analysis showed that high thoracolumbar kyphosis (OR=1.963, 95%CI:1.341-2.874, P=0.001) and high wedging angle of the vertebrae (OR=1.635, 95%CI:1.069-2.499, P=0.023) affected the incidence of upper lumbar disc herniation. Although the differences of pelvic tilt, pelvic incidence, sacral slope, lumbar lordosis and other indicators between the two groups were statistically significant, they could not be used as independent risk factors. (3) Receiver operating characteristic curve analysis showed that thoracolumbar kyphosis and wedging angle of the vertebrae had certain warning significance for the occurrence of upper lumbar disc herniation, and the cutoff values of thoracolumbar kyphosis and wedging angle of the vertebrae were 10.45° and 6.45°, respectively. (4) It is concluded that the anteroposterior and lateral lumbar radiography can better evaluate the sagittal related parameters in patients with upper lumbar disc herniation. The pelvic tilt, pelvic incidence, sacral slope, and lumbar lordosis of patients with upper lumbar disc herniation are significantly lower than those of patients with conventional lumbar disc herniation, and the physiological curvature of the lumbar spine decreases or disappears, presenting a relatively straight state as a whole. Thoracolumbar kyphosis and wedging angle of the vertebrae are relatively high, and thoracolumbar kyphosis > 10.45° and wedging angle of the vertebrae > 6.45° are the high-risk alert values of upper lumbar disc herniation.

Key words: upper lumbar disc herniation, sagittal parameter of spine and pelvis, wedge angle of vertebrae, imaging finding, anatomical risk factor, receiver operating characteristic curve