Relationship between lumbar disc herniation and Roussouly classification in the sagittal alignment of the spine and pelvis in young people

BACKGROUND: The sagittal plane of spine-pelvis morphology of adult patients with lumbar disc herniation (LDH) differs from that of normal people. There is a correlation between abnormal sagittal plane morphology and adult LDH. This study aimed to investigate the relationship between LDH in young people and the Roussouly classification in the sagittal alignment of the spine and pelvis. METHODS: A total of 126 patients with LDH hospitalized in our tertiary hospital between January 2020 and January 2021 who met the inclusion and exclusion criteria were retrospectively analyzed in a cross-sectional study. Participants were grouped according to the spinal level of disc herniation (L4/5 group, L5/S1 group, L3/4 group). Pelvic incidence (PI), pelvic tilt (PT), and sacral slope (SS) of all cases were measured using standing lateral spinal radiographs. Facet joint angles (FJA) were measured using lumbar computed tomography (CT) horizontal radiographs, and the height of the anterior, middle, and posterior margins of the herniated disc was measured using sagittal radiographs. The classification of Pfirrmann disc degeneration was determined via magnetic resonance imaging (MRI) film of the lumbar region. Roussouly classification was performed according to sagittal plane morphology, and data were analyzed among each group. RESULTS: In all, 126 patients aged from 18 to 40 years, with an average age of 31.04±5.886 years were included. There were 63 cases of L4/5 disc herniation, 59 cases of L5/S1 herniation, and 4 cases of L3/4 herniation. There were 35 cases of epiphyseal separation. The Roussouly classification included 21 cases of type 1, 56 cases of type 2, 32 cases of type 3, 4 cases of type 4, and 13 cases of type 3 + anteverted pelvis (type 3-AP). The L4/5 disc herniation group had significantly more types 2 and 3 than the other groups, and the L5/S1 disc herniation group had significantly more types 1 and 2 than the other groups. There were no significant differences in the Pfirrmann grade of intervertebral disc degeneration; epiphyseal separation; the height of anterior, middle, and posterior margins of the herniated disc; the difference between left and right facet angle and bilateral facet angle; and the thoracic kyphosis (TK) value among any of the groups (P>0.05). There were significant differences in PI, PT, SS, lumbar lordosis (LL), and height of the anterior and posterior margins of the intervertebral space among all groups (P<0.05). PI values were grouped at 50°; PT, SS, and LL were significantly different (P<0.05), whereas TK values were not significantly different between the 2 groups (P>0.05). SS values were grouped at 35°, and there were significant differences in PI, TK, and LL between the 2 groups (P<0.05). According to the disc herniation segment, the patients were divided into L4/5 and L5/S1 groups. There were significant differences in PI, PT, anterior edge height, anterior to posterior edge height, left facet angle, right facet angle, and bilateral facet angle (P<0.05). CONCLUSIONS: LDH is common in L4/5 and L5/S1 segments. The incidence of Roussouly type 1 and 2 LDH is significantly higher than other types, and type 4 is the lowest. Small PI and small SS are more obvious in the L5/S1 segment. L5/S1 disc herniation is more common in patients with Roussouly type 1 and 2 classifications, whereas L4/5 disc herniation is more frequent in patients with Roussouly type 2 and 3 classifications.