Effect of surgical devices on the biomechanical characteristics of multi-segment implants in anterior cervical...

Anterior cervical discectomy and fusion (ACDF) is an established surgical method for restoring neurological function and reconstructing cervical curvature. However, a limited number of studies have investigated the biomechanical changes after ACDF involving multiple surgical segments. Therefore, this study aimed to investigate the effect of surgical devices, number of surgical segments and motions on the strain and stress distribution of the implants. A validated finite element cervical spine model (C2-C7) was used to develop four postoperative models involving zero-profile (ZP) devices or cage and plate (CP) constructs across two- and three-segment ACDF. We analyzed postoperative range of motion (ROM) and implant strain-stress characteristics. ZP devices yielded higher ROM values on fused segments compared to CP devices. The ZP group exhibited higher maximum strain values and predicted effective strain area (Pesa) on bone graft surfaces compared to the CP group. Similarly, maximum and average stress values were greater in the ZP group, with minimal influence from the number of surgical segments on strain and stress distributions. Two-way ANOVA showed that the type of surgical device significantly affected stress values across multiple moment sizes during extension and flexion, while the number of surgical segments was significant only under specific conditions, such as extension at 1.0 Nm and 1.5 Nm and flexion at 1.5 Nm. Our study found that increasing the number of surgical segments had little impact on implant biomechanics. ZP devices significantly increased strain and stress values on bone grafts, with higher stress and larger Pesa area at the graft-endplate interface, promoting bone growth in fused segments. In contrast, CP devices showed lower stress and strain values, warranting caution in multi-segment surgeries.