Zygomatic Arch Fracture

Excerpt

The zygomatic arch includes segments of the temporal bone (posteriorly) and the zygoma (anteriorly), contributing vital to the midface's structure and aesthetic appearance. As the primary determinant of the width of the cheeks, the zygomatic arch articulates with several bones of the craniofacial skeleton and supports critical muscles such as the masseter and zygomaticus major. The zygoma and its articulations with other facial bones comprise the zygomaticomaxillary complex (ZMC), also known as the zygomatico-orbito-maxillary complex. Fractures of the zygomatic arch or any of its bony articulations can cause significant functional and cosmetic morbidity. Managing zygomatic arch and ZMC fractures should be patient-specific but may range from simple observation to open reduction with internal fixation.

Anatomy

The zygomatic arch is the most lateral projection of the midface; this structure plays a key role because it absorbs and dissipates traumatic forces away from the cranial base. The zygoma also contributes significantly to the inferior and lateral orbital walls. Fractures of the zygoma necessitate evaluation for concomitant fractures of the orbit.

The zygoma has 4 articulations, referred to as the ZMC complex (see Images. Skull Anatomy Surface Markings and Frontal Skull and Zygomatic Bones and Left Zygomatic Bone in Situ):

1. Zygomaticotemporal suture: This is the temporal process of the zygoma, which articulates with the zygomatic process of the temporal bone to form the zygomatic arch.

2. Zygomaticomaxillary (ZM) suture: This suture line crosses the inferior orbital rim, resulting in the frequent coexistence of orbital floor fractures with ZMC fractures. The ZM suture is within the ZM buttress, a key vertical support structure within the midface. The other 2 vertical buttresses of the midface are the nasomaxillary and the pterygomaxillary buttresses.

3. Zygomaticofrontal (ZF) suture: This is lateral to the brow and is a small suture line easily accessed via a short lateral brow incision. Properly reducing a displaced ZF suture is critical to reestablishing correct facial height.

4. Zygomaticosphenoidal (ZS) suture: The alignment of this suture is critical when reducing a fracture to reestablish pre-traumatic orbital volume, even though this suture line is not typically fixated after reduction.

Fractures of the zygomaticomaxillary complex may be called "tripod fractures." The correct terminology is "tetrapod fracture," given the 4 bony articulations of the zygoma.

Neuroanatomy

Paresthesia of the face is a common sequela of ZMC fractures given the proximity of sensory nerves, such as the infraorbital nerve, the zygomaticofacial nerve, and the zygomaticotemporal nerve (all branches of cranial nerve V2) to the zygoma.

1. The infraorbital nerve exits the maxilla via the infraorbital foramen, medial to the articulation between the maxilla and the zygoma. The infraorbital nerve provides sensory input from the cheek, upper lip, nose, and anterior maxillary dentition.

2. The zygomaticofacial and zygomaticotemporal nerves transmit sensory input from the lateral cheek and anterior temporal area, respectively. They are branches of the zygomatic nerve that arise in the pterygopalatine fossa and enter the orbit via the inferior orbital fissure before traveling along the lateral orbital wall (See Image. Temporal Branch Course). The zygomaticofacial and zygomaticotemporal branches then exit via correspondingly named foramina in the zygoma.

Severe ZMC fractures may also result in ipsilateral facial palsy because the facial nerve is intimately associated with the zygomatic arch (see Image. Zygomatic Arch). The facial nerve's frontal branch emerges from the parotid gland deep into the superficial musculoaponeurotic system and crosses the zygomatic arch on its superficial surface. The frontal branch then transitions to the undersurface of the temporoparietal fascia, where it travels to innervate the frontalis muscle.

Muscular Anatomy

The temporalis muscle originates along the temporal line of the parietal and frontal bones and travels deep to the ZA to insert into the coronoid process of the mandible; it also has attachments to the zygoma. Depressed fractures of the zygomatic arch may impede movement of the temporalis muscle and cause trismus.

The masseter muscle originates on the inferior aspect of the zygoma and zygomatic arch and inserts on the angle of the mandible. This is a powerful muscle of mastication, and its contraction can displace unstable bone segments inferiorly in certain cases.

The zygomaticus major and minor are muscles of facial expression that originate on the zygoma and are inserted near the modiolus of the oral commissure to assist with corner-of-mouth elevation and lateralization during smiling.

Other Landmarks

The tubercle of Whitnall is the attachment site of the lateral canthal tendon, located on the medial surface of the frontal process of the zygoma.