The range of M-shaped zygomatic arch fractures: a retrospective study

The M-shaped zygomatic arch fracture consists of anterior and posterior segments, presenting an M-shaped configuration when viewed from the skull base. However, the extent of involvement of the anterior and posterior fracture segments has not been reported. This study aims to define the range of M-shaped zygomatic arch fractures. Forty-six patients were enrolled in this study. Clinical data along with CT images were collected from the patients. Landmarks were identified on coronal CT sections using the horizontal plane at the zygomatic arch root as the reference plane. The deepest point of the fracture depression was located at the zygomaticotemporal suture in 91.30% of cases. In 97.83% of patients, the posterior fracture line was situated anterior to the articular eminence of the temporomandibular joint. The superior extent of the anterior fracture line could reach the zygomaticofrontal suture, its inferior extent extended to the zygomaticoalveolar crest, and its anterior limit reached the lateral orbital wall. The anterior fracture line can be classified into five types. When the coronoid process was above the fracture's deepest point, mouth opening (1.58 ± 0.80 cm) was significantly less than when it was below (2.59 ± 0.99 cm) ( p < 0.001). In typical M-shaped zygomatic arch fractures, the location of the deepest depression point and the posterior fracture line remains relatively constant while the anterior fracture line varies in its course and position. The spatial relationship between the deepest point and the coronoid process determines the degree of mouth opening.