Analysis of spino-pelvic sagittal parameters in patients with highly downward-migrated lumbar disc herniation

To investigate the characteristics of spino-pelvic sagittal alignment in patients with highly downward-migrated lumbar disc herniation (HDM-LDH).

A retrospective analysis was conducted on 149 hospitalized patients diagnosed with HDM-LDH, and 138 asymptomatic adults undergoing physical examination were enrolled as the control group. Sagittal alignment parameters including thoracic kyphosis (TK), thoracolumbar kyphosis (TLK), lumbar lordosis (LL), sacral slope (SS), pelvic tilt (PT), pelvic incidence (PI), PI-LL, and sagittal vertical axis (SVA) were measured on standing full-spine lateral radiographs. The differences in these parameters between the two groups were analyzed.

Compared to the control group, the HDM-LDH group exhibited significantly lower LL and SS, whereas PT, SVA, and PI-LL were significantly higher (P < 0.05). No significant differences were found in PI, TLK, or TK between the groups. In spinal parameters, LL was moderately correlated with PT and SS, and weakly correlated with PI and TK. Regarding pelvic parameters, PI was moderately correlated with SS and PT, while PT showed a weak correlation with SS; all were statistically significant. SVA was weakly correlated with LL. The predominant lumbar lordosis subtype in the HDM-LDH group was Roussouly type II (SS < 35°, reduced LL, apex at L4). The proportions of types I, II, and IV were higher in the HDM-LDH group, while type III was less prevalent compared to the control group (P < 0.05).

Patients with HDM-LDH exhibit distinct spino-pelvic sagittal characteristics compared to asymptomatic individuals, characterized by loss of lumbar lordosis, pelvic retroversion, and a nearly straight spinal alignment with horizontally oriented intervertebral discs. These morphological features alter the biomechanical structure of the spine and may underlie the pathogenesis of downward-migrated disc herniation.