This study hypothesizes that the spinopelvic sagittal alignment can influence the development of lumbar disc herniation (LDH). To investigate this relationship, the spinopelvic data of surgical LDH patients was compared to that of a healthy historical control group.

The spinopelvic data of LDH patients aged 15–45 years, undergoing herniated disc surgery (L4-L5/L5-S1) from 2015 to 2019, was compared to that from healthy controls reported by Roussouly et al. Sacral slope (SS), pelvic incidence (PI), pelvic tilt (PT), and Roussouly classification (spinal curves type 1–4) were assessed with full body radiographs in a standing weight-bearing position (EOS® system) using KEOPS software. The prevalence of spine types (1–4) were evaluated in both groups, with subgroup analysis based on herniation level. Proportions were compared using Fisher’s exact tests, means by Student’s t-tests, and confidence intervals for odds ratios (OR) using the exact conditional tail interval (ECTI) method.

Spinopelvic data from 350 patients (190 LDH/160 healthy controls) showed that LDH patients had a significantly higher prevalence of Roussouly type 2 spines ("flat spine") (27.9% vs. 11.2%, OR 3.04, p = 0.001). The LDH group also exhibited lower mean PI (−3.0°, p = 0.009), significantly lower mean SS (−6.9°, p < 0.001), lower lumbar lordosis angle (−10.6°, p < 0.001), and higher thoracic kyphosis angle (+3.6°, p < 0.001). The ratio of OR (2.73, p = 0.01) indicated that type 2 spines pose a stronger risk for LDH surgery at L5-S1 compared to L4-L5.

Patients <45 years old undergoing surgery at L4-L5/L5-S1 showed a threefold higher prevalence of type 2 Roussouly spines, compared to a healthy control group, suggesting a potential role of "flat spine" and lower PI in the development of LDH.

III; case-control study.