OBJECTIVE: Few studies have concentrated on the sagittal alignment of lumbar disc herniation (LDH), especially the parameters of the pelvis, and controversy exists about whether pelvic morphology is involved in the pathogenesis of LDH. The present study analyzed the characteristics of the sagittal alignment in young Chinese LDH patients and explored the impact of pelvic morphology on the pathogenesis of LDH. METHODS: A retrospective analysis was conducted on 100 young patients with LDH (69 men and 31 women, aged 18-35 years), and the clinical and imaging findings met the criteria for the diagnosis of LDH. The control group included 100 asymptomatic volunteers with matching age and gender. Coronal and sagittal parameters were measured on the anteroposterior and lateral radiographs of the whole spine, including lumbar lordosis (LL), pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), thoracic kyphosis (TK), and sagittal balance (SVA). The cases were classified into four types by the apex position of lumbar lordosis (type I, L5 or the L4-5 intervertebral space; type II, bottom or middle of L4 ; type III, upper part of L4 or the intervertebral space between L3 and L4 ; type IV, L3 or more high level), and divided into three groups by PI; namely, a low PI group (PI < 40°), a medium PI group (40° ≤ PI < 50°), and a high PI group (PI ≥ 50°). The sagittal parameters, especially PI, were compared between the LDH group and the control group. Correlations between the parameters in the LDH group were analyzed. RESULTS: The PI value of the LDH group was not different from that of the control group (46.1° ± 10.0° vs 47.2° ± 8.8°, P > 0.05). The LDH group showed lower average LL, SS, and TK (P < 0.01), as well as higher PT and SVA compared with the control group (P < 0.01). The LL (34.4° ± 15.3° vs 50.8° ± 10.2°) and SVA (21.6 ± 53.6 mm vs - 18.4 ± 32.8 mm) showed a significant difference (P < 0.01); LL was correlated with PI, SS, PT, TK and SVA (P < 0.01); and SVA was also correlated with the parameters above (P < 0.01) except PI (P > 0.05), and the lordosis apex tended to be higher. The distributions of PI groups between the LDH group and the control group were not different. Pairwise correlations were found among LL, PI, SS, and PT. In addition, TK and SVA were correlated with LL, SS, and PT. CONCLUSIONS: There is no difference in PI between young Chinese patients with lumbar disc herniation and the normal population. Young LDH patients may present flat lumbar and thoracic curves, as well as lower sacral slope. The anteversion sagittal imbalance is regulated by both the spine and the pelvis.
OBJECTIVE: Few studies have concentrated on the sagittal alignment of lumbar disc herniation (LDH), especially the parameters of the pelvis, and controversy exists about whether pelvic morphology is involved in the pathogenesis of LDH. The present study analyzed the characteristics of the sagittal alignment in young Chinese LDH patients and explored the impact of pelvic morphology on the pathogenesis of LDH. METHODS: A retrospective analysis was conducted on 100 young patients with LDH (69 men and 31 women, aged 18-35 years), and the clinical and imaging findings met the criteria for the diagnosis of LDH. The control group included 100 asymptomatic volunteers with matching age and gender. Coronal and sagittal parameters were measured on the anteroposterior and lateral radiographs of the whole spine, including lumbar lordosis (LL), pelvic incidence (PI), sacral slope (SS), pelvic tilt (PT), thoracic kyphosis (TK), and sagittal balance (SVA). The cases were classified into four types by the apex position of lumbar lordosis (type I, L5 or the L4-5 intervertebral space; type II, bottom or middle of L4 ; type III, upper part of L4 or the intervertebral space between L3 and L4 ; type IV, L3 or more high level), and divided into three groups by PI; namely, a low PI group (PI < 40°), a medium PI group (40° ≤ PI < 50°), and a high PI group (PI ≥ 50°). The sagittal parameters, especially PI, were compared between the LDH group and the control group. Correlations between the parameters in the LDH group were analyzed. RESULTS: The PI value of the LDH group was not different from that of the control group (46.1° ± 10.0° vs 47.2° ± 8.8°, P > 0.05). The LDH group showed lower average LL, SS, and TK (P < 0.01), as well as higher PT and SVA compared with the control group (P < 0.01). The LL (34.4° ± 15.3° vs 50.8° ± 10.2°) and SVA (21.6 ± 53.6 mm vs - 18.4 ± 32.8 mm) showed a significant difference (P < 0.01); LL was correlated with PI, SS, PT, TK and SVA (P < 0.01); and SVA was also correlated with the parameters above (P < 0.01) except PI (P > 0.05), and the lordosis apex tended to be higher. The distributions of PI groups between the LDH group and the control group were not different. Pairwise correlations were found among LL, PI, SS, and PT. In addition, TK and SVA were correlated with LL, SS, and PT. CONCLUSIONS: There is no difference in PI between young Chinese patients with lumbar disc herniation and the normal population. Young LDH patients may present flat lumbar and thoracic curves, as well as lower sacral slope. The anteversion sagittal imbalance is regulated by both the spine and the pelvis.