Comparison of Biomechanics at the Cervicothoracic Junction in C3-6, C3-7, and C2-T2 Constructs: A Parametric, Finite Element Analysis

Posterior Cervical Decompression and Fusion (PCDF) is a treatment for degenerative cervical spinal disorders; however, there remains uncertainty about the most effective instrumentation, particularly near the cervicothoracic junction. This study examines the biomechanics of C3-6, C3-7, and C2-T2 constructs using patient-specific finite element analysis.

A CT scan of the cervical spine was segmented and meshed. C3-6, C3-7, and C2-T2 constructs created in fusion and analyzed with FEBioStudio. Five bone density conditions were created by applying a global bone density modifier to the elastic modulus values of the bone materials for each construct. A pure compressive 100N follower load was applied and 1.5 Nm moment applied to the odontoid used to elicit flexion, extension, and lateral bending. Von Mises stress was extracted from the screw-rod construct and C7-T1 disc, and segmental motion was measured at the C7-T1 level.

75 total finite element solver runs were conducted on 15 models. Compared with the C2-T2 construct, the C3-7 and C3-6 constructs experienced lower rod stress and had greater segmental ROM. However, for C7-T1 disc stress, both the C3-6 and C3-7 constructs experienced higher stress. Bone density was not associated with differences in these outcomes. There were significant differences in rod stress, C7-T1 disc stress, and C7-T1 segmental ROM based on construct type, with C2-T2 constructs experiencing the highest rod stress, but the lowest C7-T1 disc stress and C7-T1 segmental motion.

C3-6 may represent a happy medium, given its low rod stress, middling C7-T1 disc stress, and C7-T1 segmental ROM.