Radiographic Positioning of the Zygomatic Arch
Fractures of the zygoma region can occur with head trauma. In fact, the zygomatic arch is one of the most commonly fractured facial bones, typically following altercations in which the patient is punched in the face. Radiographic confirmation of zygomatic arch fractures allows early stabilization with better anatomic function and cosmetic results.
The skull is made of several bones that are held together at sutures by connective tissue called sutural ligaments. The bones of the skull can be categorized into the cranium and the face. The cranium consists of:
- Frontal bone
- A pair of parietal bones
- Occipital bone
- A pair of temporal bones
- Sphenoid bone
- Ethmoid bone
The facial bones include:
- A pair of zygomatic bones
- A pair of maxillae
- A pair of nasal bones
- A pair of lacrimal bones
- A pair of palatine bones
- A pair of inferior conchae
The facial bones form the structure of the face. The zygomatic bones (also referred to as the malar bones) are a pair of quadrilateral-shaped bones responsible for the prominence of the cheeks. The term “zygomatic” comes from the Greek word “zygoma” which means “yoke.” The zygomatic bone on each side is located below and lateral to the eye socket. It borders the frontal bone lateral to the orbit and the sphenoid and maxilla medially.
Anatomical Structure of the Zygomatic Bone
The zygomatic bone has four projections, which give it the characteristic quadrilateral (diamond) shape. The superior projection connects with the frontal bone. Medially, it forms the lateral portion of the infraorbital rim. Posteriorly, it forms the anterior portion of the zygomatic arch. Inferiorly, it connects to the alveolus of the maxilla.
The zygomatic bone is responsible for the malar prominence, an important aesthetic landmark in facial architecture. The zygomatic arch provides width to a person’s face and figures prominently in the oblique facial profile. Besides its aesthetic significance, the zygomatic-maxillary region plays an important functional role. It provides stability and support to the midface and protection to the orbit.
Surfaces of the Zygomatic Bone
The malar surface is convex and is perforated by a small central aperture called the zygomaticofacial foramen. This foramen allows the zygomaticofacial nerve and vessels to pass. A slight elevation just inferior to this foramen is the site of origin of the zygomaticus muscle.
The temporal surface is concave with a rough triangular area medially for articulation with the maxilla and a smooth concave surface laterally that forms the anterior boundary of the temporal fossa and the lower part of the infratemporal fossa. The zygomaticotemporal foramen is present centrally on this surface for transmission of the zygomaticotemporal nerve.
With its orbital surface, the zygomatic bone constitutes the lateral and inferior margin of the orbit. Traversing the zygomatic-orbital foramen on this surface is the zygomatic nerve. A small protuberance called the orbital tubercle is the site of attachment of the lateral palpebral ligament.
Processes of the Zygomatic Bone
The zygomatic bone on each side is diamond-shaped with three processes that articulate with the frontal, temporal, and maxillary bones. Each process forms an important structural component of the skull.
The frontal process of the zygomatic bone with its orbital surface constitutes the anterolateral orbital wall. There are a pair of small zygomaticofacial foramen opening on the lateral surface. The temporal process of the zygomatic bone forms the zygomatic arch along with the zygomatic process of the temporal bone. There are a pair of zygomaticotemporal foramen present on the medial deep surface of the bone. The maxillary process of the zygomatic bone on its orbital surface forms part of the infraorbital rim and also a small part of the anterior lateral orbital wall.
Borders of the Zygomatic Bone
The anterosuperior or orbital border is smooth and concave and forms a substantial portion of the circumference of the orbit.
The anteroinferior or maxillary border is rough and beveled at its inner table to articulate with the maxilla. The site of origin of the quadratus labii superioris muscle is near the orbital margin.
The posterosuperior or temporal border is curved in the shape of an italic letter f. It is continuous superiorly with the temporal line and inferiorly with the superior margin of the zygomatic arch with temporal fascia attachment.
The posteroinferior or zygomatic border provides attachment on its rough edge to the masseter muscle.
Articulations of the Zygomatic Bone
The zygomatic bone articulates with four bones – the frontal, temporal, sphenoid (greater wing), and maxilla.
Development of the Zygomatic Bone
The zygomatic bones ossify from three points, two in orbital area and one in the malar area. These ossification points appear at about the eighth week of gestation and fuse at around the fifth month. After birth, the zygomatic bone may sometimes be divided horizontally by a suture into a larger upper portion and a smaller lower portion.
Facial Bone Trauma
Fractures of the skull are common in adults, but occur less often in young children. The skull bones of an infant are more resilient compared to an adult because they are separated by fibrous sutural ligaments. In the adult skull, the bones are brittle due to their composition and structure. In addition, sutural ligaments become ossified as a person ages.
The type of skull bone fracture largely depends on the location and intensity of the trauma as well as the age of the patient. The adult skull can be compared to an eggshell with limited strength and resilience beyond which it breaks. In a young child, the skull can be compared to a table tennis ball where a blow creates a depression without causing a break in the bone.
The developing facial bones of a child are more pliant than that of adults. Therefore, most facial bone fractures in children are greenstick or incomplete. In adults, however, most facial fractures are open fractures with a risk of infection and need for antibiotic therapy.
Falls, fist fights, and motor vehicle accidents are the most common causes of facial fractures. Signs of fracture of the facial bones include deformity, ocular/orbital displacement, abnormal movements accompanied by cracking or rattling sounds, and malocclusion of the teeth. The most common facial fractures involve the nasal bones, followed by the zygomatic bones, and then the mandible.
Fractures of the zygoma can occur with a blow to the lateral face. This type of trauma can result in an isolated fracture, such as from the impact of a clenched fist. However, it can also occur in conjunction with other fractures of the face, usually as a result of MVAs or other high-impact injuries. Moderate force can cause slightly displaced or non-displaced fractures at the suture lines. More forceful trauma usually results in displacement of the zygoma inferiorly, medially, or posteriorly.
Top: Schematic Structure of the Zygomatic Area. Bottom: Areas of the Zygomatic Bone that are Commonly Fractured (© Osborne Head & Neck Institute).
Zygomatic Bone Fractures
Simple Fracture: Simple zygomatic arch (orbitozygomatic) fractures are usually the result of a blow to the lateral face, for example, during a fist fight or from an object such as a baseball. They may also occur as a result of car crashes. They are less frequent than tripod fractures.
Tripod Fracture: A tripod fracture is a combination of three fractures that classically involve the zygomatic arch and the frontozygomatic and maxillozygomatic sutures. This type of triple fracture results in a free-floating zygomatic bone. This type of comminuted fracture that results in separation at the suture lines usually occurs during high-impact motor vehicle accidents or explosions.
Le Fort III Fracture: This is a transverse fracture of the midface. It is also called craniofacial dissociation. It involves the pterygoid plate and zygomatic arch.
Radiography of the Zygomatic Bone
Patients with suspected facial trauma and/or zygomatic fractures are evaluated primarily with craniofacial X-rays or CT scans. Several different radiographic views are useful to observe specific parts of the skull. The most common views that enable visualization of the zygomatic area are:
- Occipitomental (OM) or Water’s View
- Submentovertex (SMV) View
- Facial or Caldwell’s View
Occipitomental (OM) or Water’s View: This is an angled PA radiograph of the skull taken with the patient erect and facing an upright IR. The head is tilted back slightly so that the patient is gazing upwards. The chin is raised until the mentomandibular line is perpendicular to the IR and the orbitomeatal line is at an angle of 37 degrees to the IR. The central ray of the X-ray beam exits at the acanthion. This projection displays the orbital rim, floor of the orbit, maxillary sinuses, nasal septum, nasal bones, and zygomatic bones.
Submentovertex (SMV) View: This is a radiograph taken with the patient’s chin raised and neck fully extended. Cervical spine injuries and fractures must be ruled out prior to attempting this projection in trauma patients. The midsagittal plane of the body is at a right angle to the IR. The infraorbitomeatal line is parallel to the IR. The X-ray beam passes through the underside of the chin and exits are the vertex of the skull. The beam is directed perpendicular to the acanthomeatal line. This projection is used in combination with other views to maximize visualization of skull structures.
Caldwell’s View: Also called the occipitofrontal projection, this is an angled radiograph of the skull in which the plate is angled at 20 degrees to the orbitomeatal line. The patient is seated in front of a vertical detector with the forehead and nose pressed against the IR. The orbitomeatal line is at a right angle to the IR. The structures visualized on this projection include the paranasal sinuses (frontal and ethmoidal), orbits, orbital rims, medial orbital walls, zygomatic bones, nasal bones, nasal septum, and mandible.
In patients with suspected facial fractures, a basic facial series imaging workup is usually requested, consisting of three or four films. Of the various projections, Water’s view is preferred because it demonstrates all major facial structures more clearly than other views.
With advancements in medical technology, high-resolution computerized tomography (CT) scans have, for the most part, become the imaging modality of choice in patients with facial trauma. Compared to plain film radiography, CT scans more clearly demonstrate the complex bony anatomy of the face and the intricacy of injuries resulting from facial trauma.