Morphological characteristics of the nucleus pulposus and biomechanical finite element analysis in patients with adolescent lumbar disc herniation

English Keywords:Lumbar disc herniation  Adolescent  Nucleus pulposus  Morphological characteristics  Finite element analysis

English Abstract:

  【Abstract】 Objectives: To analyze the morphological characteristics of the nucleus pulposus in patients with adolescent lumbar disc herniation(ALDH) and to investigate the biomechanical changes via finite element models, thereby exploring potential risk factors for ALDH. Methods: From January 1, 2023, to March 1, 2025, 98 ALDH patients treated at the Affiliated Hospital of Xuzhou Medical University, were enrolled as the case group, including 60 males and 38 females, aged 13-21 years, with herniation at L4/5 level in 52 cases and at L5/S1 level in 46 cases. 42 adolescents who presented with low back pain during the same period but had negative lumbar MRI findings or only lumbar myofasciitis were selected as the control group. All subjects underwent lumbar MRI examination. The area ratio and centroid position of the nucleus pulposus at L2-S1 levels were measured using Mimics software. R software was used to compare the morphological parameters of the nucleus pulposus between the herniated levels and non-herniated levels in the case group and those in the control group. Based on clinical parameters, nine L4-5 level models(M0-M8) were established, with nucleus pulposus area ratios ranging from 20% to 60% and centroid position offsets from -2mm to +2mm. The equivalent stress distribution of the intervertebral disc under physiological loading was simulated to analyze the biomechanical effects of changes in morphological parameters. Additional L5-S1 level models were constructed under the same conditions to verify consistency across levels. Results: (1)The nucleus pulposus area ratio in herniated levels of the case group was significantly higher than that in the control group(P<0.05), and the centroid position was significantly more posterior(P<0.05). Except for the centroid position at L2-3, the nucleus pulposus area ratio and centroid position in other non-herniated levels of the case group also showed similar changes, with statistically significant differences(P<0.05). (2)Finite element analysis revealed consistent findings between the L4-5 and L5-S1 models: an increased nucleus pulposus area ratio raised the peak disc stress under extension, lateral bending, and rotation conditions. When the centroid shifted posteriorly, the peak disc stress decreased under flexion but increased under extension. Conclusions: ALDH patients exhibit morphological characteristics of a relatively larger nucleus pulposus area and a more posterior centroid position. An increased nucleus pulposus area ratio elevates the peak disc stress under extension, lateral bending, and rotation, while posterior displacement exacerbates stress concentration under extension. These morphological alterations may increase the risk of ALDH by altering the mechanical environment of the intervertebral disc.