Biomechanical evaluation of zygomatic-orbital-maxillary complex fractures following internal fixation

The aim of this study is to develop effective treatment strategies for zygomatic-orbital-maxillary complex (ZOMC) fractures using finite element analysis (FEA) and investigate the mechanical properties and stress distribution of different internal fixators.

A three-dimensional (3D) model was created from CT images of a patient with a unilateral ZOMC fracture, and the preinjury craniofacial structure was reconstructed. A cylindrical impactor was used to simulate facial impact. Biomechanical analysis was performed to assess the stability of internal fixation of the fracture lines at the frontal process of the zygomatic bone (FPZB), inferior orbital rim (IOR), and upper and lower parts of the zygomaticomaxillary suture (ZMS). The impact of different fixation methods on the anterior-inferior wall of the maxillary sinus (AIWMS) was also assessed in this study. A 120 N load was used to simulate physiological muscle force, and the maximum von Mises stress and maximum displacement for the fracture ends were assessed.

The stress distribution on the impact model was similar to that on the patient's fracture lines, with all internal fixation devices experiencing maximum stress below the yield stress. The model exhibiting the largest displacement of the zygomatic body, IOR, and FPZB had not undergone internal fixation of the FPZB. The greatest maximum displacement value was recorded for the maxilla, at the non-fixed lower ZMS. The maximum displacement value was lower for 2 fixators placed at the AIWMS than for a single fixator placed at the fracture midline.

The placement of 2 internal fixators along the zygomaticomaxillary (NMB) and nasomaxillary buttresses (NMB) provides greater stability than the placement of a single device does. Moreover, stabilizing the fracture lines in the FPZB is essential, as doing so reduces the extent of displacement of free fracture ends by counteracting the masseter muscle force.