Abstract: BACKGROUND: Cervical disc herniation can cause pain in the neck and shoulder area, as well as radiating pain in the upper limbs. The incidence rate is increasing year by year and tends to affect younger individuals. Fully understanding the biomechanical characteristics of the cervical spine in adolescents is of great significance for preventing and delaying the onset of cervical disc herniation in this age group.
OBJECTIVE: To reconstruct cervical spine models for both healthy adolescents and adolescent patients with cervical disc herniation utilizing finite element analysis techniques, to analyze the motion range of the C1-T1 cervical vertebrae as well as the biomechanical characteristics of the annulus fibrosus, nucleus pulposus, endplates, and the cartilage of the small joints.
METHODS: A normal adolescent’s cervical spine and an adolescent patient with cervical disc herniation were selected in this study. The continuous scan cervical spine CT raw image data were imported into Mimics 21.0 in DICOM format. The C1-T1 vertebrae were reconstructed separately. Subsequently, the established models were imported into the 3-Matic software for disc reconstruction. The perfected models were then imported into Hypermesh software for meshing of the vertebrae, nucleus pulposus, annulus fibrosus, and ligaments, creating valid geometric models. After assigning material properties, the final models were imported into ABAQUS software to observe the joint motion range of the C1-C7 cervical vertebrae segments under different conditions, and to analyze the biomechanical characteristics of the annulus fibrosus, nucleus pulposus, endplates, and small joint cartilage of each cervical spine segment.
RESULTS AND CONCLUSION: (1) In six different conditions, the joint motion range of the C1 vertebra in the cervical spine models of both normal adolescent and adolescent patient with cervical disc herniation was higher than that of the other vertebrae. Additionally, the joint motion range of each cervical spine segment in normal adolescent was greater than that in adolescent patient with cervical disc herniation. (2) In the cervical spine model of normal adolescent, the maximum stress values in the annulus fibrosus and nucleus pulposus were found on the left side during C2-3 flexion conditions (0.43 MPa and 0.17 MPa, respectively). In the cervical spine model of adolescent patient with cervical disc herniation, the maximum stress values were found on the left side during C7-T1 flexion conditions (0.54 MPa and 0.18 MPa, respectively). (3) In the cervical spine model of normal adolescent, the maximum stress value on the endplate was found on the left side of the upper endplate of C3 during flexion conditions (1.46 MPa). In the model of adolescent patient with cervical disc herniation, the maximum stress value on the endplate was found on the left side of the lower endplate of C7 during flexion conditions (1.32 MPa). (4) In the cervical spine model of normal adolescent, the maximum stress value in the small joint cartilage was found in the C2-3 left rotation conditions (0.98 MPa). In adolescent patient with cervical disc herniation, the stress in the small joint cartilage significantly increased under different conditions, especially in C1-2, with the maximum stress found during left flexion (3.50 MPa). (5) It is concluded that compared to normal adolescent, adolescent patient with cervical disc herniation exhibits altered cervical curvature and a decrease in overall joint motion range in the cervical spine. In adolescent with cervical disc herniation, there is a significant increase in stress on the annulus fibrosus, nucleus pulposus, and endplates in the C7-T1 segment. The stress on the left articular cartilage of the C1-2 is notable. Abnormal cervical curvature may be the primary factor causing these stress changes.

Key words: adolescents, cervical disc herniation, cervical spine stress, finite element analysis, biomechanics