Biomechanical effects of different lateral mass injury patterns on subaxial cervical fracture dislocations after anterior cervical surgery: a finite element study

Objective: The lateral mass joint plays an important role in maintaining the mechanical stability of the subaxial cervical spine. We first performed a three-dimensional finite element (FE) biomechanical study to evaluate the local mechanical stability of subaxial cervical fracture dislocations after anterior-only fixation for lateral mass injuries of varying severity.

Methods: A three-dimensional FE model of the subaxial cervical spine with simple anterior fixation for C5-6 fracture dislocation was reconstructed. According to their different morphological characteristics of unilateral lateral mass injuries, the lateral mass injury was divided into six types. The range of motion (ROM) of each part and the stress of the cage, each intervertebral disc, titanium plate, and screw stress were recorded.

Results: The ROM of C3-4, C4-5, C5-6, and C6-7 in type 4 was higher than that of the other five types. The maximum equivalent stress on C4-5 intervertebral discs, titanium plates, and screws in type 4 under various sports loads was higher than that produced by the other load types. In the stress cloud diagram of the front titanium plate and screws, the degree of stress was the highest in type 4. Stress placed on each part of the model, from high to low, was as follows: plate, screw, C6, C5, and C7.

Conclusion: Greater injury severity is associated with higher stress on the plate and screw with exercise loads. Type 4 lateral mass injuries, characterized by ipsilateral pedicle and lamina junction fractures, significantly affected biomechanical stability after simple anterior fixation.