Finite element analysis of two-level discontinuous cervical hybrid revision surgery strategy to reduce biomechanical responses of adjacent segments.

Background: Hybrid surgery (HS) combined cervical disc arthroplasty (CDA) with anterior cervical discectomy and fusion (ACDF) is emerging, but its biomechanical effects as a revision surgery (RS) on adjacent segments were unclear.

Objectives: This finite element (FE) study aimed to investigate the biomechanical characteristics of HS to treat two-level discontinuous ASD in ACDF RS.

Methods: A C2-T1 intact FE model was established and modified to a primary C5/6 ACDF model and five RS models. These RS models' segments C4/5 and C6/7 were revised using cage plus plate (C), zero-profile devices (P), and Bryan disc (D), respectively, generating C-C-C, P-C-P, D-C-P, P-C-D, and D-C-D models. In the intact and C5/6 ACDF models, a 1.0 Nm moment was used to produce the range of motion (ROM). A displacement load was applied to all RS models, to achieve a total ROM match that of the primary C5/6 ACDF model.

Results: In the P-C-P model, biomechanical responses including ROM, Intradiscal pressure (IDP), Facet joint force (FJF), and Maximum von Mises stresses of discs at segments C3/4 and C7/T1 were slightly lower than the C-C-C model. The biomechanical response parameters at segments C3/4 and C7/T1 of P-C-D, D-C-P, and D-C-D were smaller than those in C-C-C and P-C-P models. D-C-D had the most significant effect on reducing all biomechanical responses among all RS models in segments C3/4 and C7/T1. Moreover, the disc stress cloud maps showed that the maximum von Mises stress of the C3/4 disc was higher than that of C7/T1.

Conclusions: D-C-D, P-C-D, and D-C-P are good RS choices for reducing the biomechanical responses, and D-C-D was the best choice. P-C-P can be the best recommendation when it does not meet the CDA indications. This study provided a biomechanical reference for hybrid surgical decision-making in the ACDF RS for preventing ASD recurrence.