The zygomatic arch is the prominent, bony ridge that forms the lateral contour of the cheekbone on the side of the skull. This structure is a noticeable landmark in facial anatomy, creating the visual width of the face beneath the eyes and extending toward the ear. It acts as a bridge, connecting the main cheekbone area to the side of the head.
Anatomy and Composition
The zygomatic arch is not a single bone but a slender, curved projection formed by the fusion of two different bony processes. The anterior portion originates from the zygomatic bone, commonly known as the cheekbone, as its temporal process. This part of the arch contributes significantly to the prominence of the cheek.
The posterior section of the arch is formed by the zygomatic process of the temporal bone, which extends forward from the side of the skull, just above the ear opening. These two projections meet and unite at an oblique junction known as the zygomaticotemporal suture. This bridge-like formation creates a space deep to the arch, through which the temporalis muscle and related structures pass.
The arch is positioned horizontally on the side of the head, located in front of the external ear canal. Its slender composition makes it one of the more exposed and delicate structures of the skull.
Primary Functions
The zygomatic arch serves a dual role in supporting the face and enabling the powerful action of chewing. Structurally, it defines the lateral facial contour, giving the cheek its characteristic fullness and providing a degree of protection for the underlying soft tissues and blood vessels. This bony span contributes to facial symmetry.
Functionally, the arch is a crucial anchor point for the masseter muscle. The masseter originates from the lower edge of the arch and inserts into the lower jawbone, or mandible. Contraction of this powerful muscle elevates the mandible, enabling the crushing force required for chewing food.
The arch also protects the temporalis muscle tendon as it passes deep to the structure to attach to the coronoid process of the mandible. Therefore, the arch is directly responsible for transmitting the strong forces generated by the masseter muscle during biting.
Common Injuries and Associated Symptoms
Due to its exposed and relatively delicate structure, the zygomatic arch is frequently susceptible to injury, most commonly in the form of a fracture. These fractures usually result from blunt trauma to the side of the face, such as from a fall or a direct impact. The force of the blow often causes the arch to be depressed or displaced inward toward the skull.
One of the most common and noticeable symptoms of a zygomatic arch fracture is a visible flattening of the cheek. The injury typically causes localized pain and tenderness along the arch. A displaced fracture may also result in a palpable “step defect” or irregularity in the bone.
Posterior displacement of the fractured bone fragments can lead to a condition called trismus, which is the restricted ability to open the mouth. This occurs because the displaced arch can impinge upon the coronoid process of the mandible, interfering with the movement of the chewing muscles. Fractures may also cause sensory abnormalities, such as numbness or tingling in the cheek or upper lip, due to potential damage to nerves that run near the bone.