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.