Radiographic positioning of Zygomatic Arch

The skull is made up of a number of separate bones joined at fixed points called sutures. These bones are joined by connective tissue called sutural ligaments. The bones that make up the structure of the skull can be categorized into two: those that make up the cranium, and those that are part of the face. The cranium consists of the following: 1 frontal bone, 2 parietal bones, 1 occipital bone, 2 temporal bones, 1 sphenoid bone, and 1 ethmoid bone. The facial bones include: 2 zygomatic bones, 2 maxillae, 2 nasal bones, 2 lacrimal bones, 1 vomer, 2 palatine bones, 2 inferior conchae, and 1 mandible.

The facial bones are not part of the cranial cavity, but they aid in the formation of the structure of the face. The zygomatic bones (sometimes referred to as the malar bones) are a pair of quadrilateral-shaped bones that is responsible for the prominence of the cheeks. It is found below and lateral to the eye socket. It borders the frontal bone on the outside of the orbit and the sphenoid and maxilla inside the orbit. The zygomatic bones are formed without a cartilaginous antecedent and are ossified during birth.

The term “zygomatic” comes from the Greek word “zygoma”, which means “yoke”.

Anatomical Structure

The zygomatic bone has four projections, which gives it its quadrilateral (diamond-like) shape. It projects superiorly connecting with the frontal bone, medially and creates the lateral portion of the infraorbital rim, posteriorly forming the anterior portion of the zygomatic arch, and inferiorly to the alveolus of the maxilla.

The zygomatic bone creates the malar prominence, an important aesthetic facial landmark. Also, the zygomatic arch establishes the width of a person’s face and figures quite prominently in the oblique facial profile.

In addition to its aesthetic significance, the zygomatic-maxillary region provides stability and support to midface, at the same time protection to the orbit.

Surfaces

The malar surface is convex and perforated near its center by a small aperture, the zygomaticofacial foramen, for the passage of the zygomaticofacial nerve and vessels; below this foramen is a slight elevation, which gives origin to the zygomaticus.

The temporal surface, directed posteriorly and medially, is concave, presenting medially a rough, triangular area, for articulation with the maxilla (articular surface), and laterally a smooth, concave surface, the upper part of which forms the anterior boundary of the temporal fossa, the lower a part of the infratemporal fossa. Near the center of this surface is the zygomaticotemporal foramen for the transmission of the zygomaticotemporal nerve.

The orbital surface forms the lateral part and some of the inferior part of the bony orbit. The zygomatic nerve passes through the zygomatic-orbital foramen on this surface. The lateral palpebral ligament attaches to a small protuberance called the orbital tubercle.

Processes

Each zygomatic bone is diamond-shaped and composed of three processes with similarly named associated bony articulations: frontal, temporal, and maxillary. Each process of the zygomatic bone forms important structures of the skull.

The orbital surface of the frontal process of the zygomatic bone forms the anterior lateral orbital wall, with usually a small paired foramen, the zygomaticofacial foramen opening on its lateral surface. The temporal process of the zygomatic bone forms the zygomatic arch along with the zygomatic process of the temporal bone, with a paired zygomaticotemporal foramen present on the medial deep surface of the bone. The orbital surface of the maxillary process of the zygomatic bone forms a part of the infraorbital rim and a small part of the anterior part of the lateral orbital wall.

Borders

The antero-superior or orbital border is smooth, concave, and forms a considerable part of the circumference of the orbit.

The antero-inferior or maxillary border is rough, and beveled at the expense of its inner table, to articulate with the maxilla; near the orbital margin it gives origin to the quadratus labii superioris.

The postero-superior or temporal border, curved like an italic letter f, is continuous above with the commencement of the temporal line, and below with the upper border of the zygomatic arch; the temporal fascia is attached to it.

The postero-inferior or zygomatic border affords attachment by its rough edge to the masseter.

Articulation

The zygomatic bone is joined to four bones: the frontal, temporal, sphenoid (greater wing), and maxilla.

Development

The zygomatic bones are generally said to ossify from three points—two from the orbital sections and one from the malar area. These are said to appear at the eighth week and fuse on the fifth month of fetal maturity. After birth, the zygomatic bone is sometimes divided horizontally by a suture into a larger upper portion and a smaller lower portion.

Trauma

The most common type of trauma that the head or the skull gets is fractures. Fractures of the skull are somehow common to adults, but very much less so in young children. In the skull of an infant, the bones are more resilient compared to that of an adult because they are separated by fibrous sutural ligaments. In adult skulls, the bones are particularly brittle due to its composition and structure. Add to that the fact that the sutural ligaments become ossified as the person progresses in age.

The type of fracture that occurs on the bones of the skull largely depends on the location and intensity of the trauma, and the age of the patient. The adult skull may be compared to an eggshell wherein there is a certain limit to its strength and resilience beyond which it breaks. In a young child, the skull may be compared to a table-tennis ball wherein a blow creates a depression without breaking.

The still-developing facial bones of a child are more pliant than that of adults, thus, most of the fractures that they sustain are greenstick or incomplete ones. In adults, however, most facial fractures are thought as open fractures that are at risk for infections, thus requiring antibiotic therapy.

Falls, fist fights and vehicular accidents are the most common causes of facial fractures. Signs of fractures of the facial bones include facial deformity, ocular/orbital displacement, or abnormal facial movements accompanied by a cracking or rattling sound and maloclussion of the teeth. The most common facial fractures involve the nasal bones, followed by the zygomatic bones, then the mandible.

The zygoma or the zygomatic arch can be fractured by a blow to the side of the head or the face. Such trauma can occur as isolated fracture, such as a result from the impact of a clenched fist, however it can also be connected in conjunction to other fractures of the face, commonly as a result of vehicular accidents and other high-impact catastrophes. Moderate force may result in slightly or non-displaced fractures at the suture lines. More serious hits usually result in the displacement of the zygoma, whether it is inferior, medial or posterior.

Figure 2. 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. Simple zygomatic arch (orbitozygomatic) fractures are usually the result of a blow to the side of the face from a fist, and object (such as a baseball), or as a result of vehicular accidents. They are less frequent than tripod fractures.

Tripod. A tripod fracture is a combination of three fractures. The fractures are classically located at the zygomatic arch, the frontozygomatic and the maxillozygomatic sutures. This type of triple fracture results in having a free-floating zygomatic bone. These comminuted fractures that separate at the suture lines are usually the result of high-impact vehicular accidents or explosions.

Radiography

Patients with supposed facial trauma as zygomatic fractures needs to be primarily assessed using x-rays or complete craniofacial CT scans.

When taking the x-ray approach, several different views are useful to observe specific parts of the skull most favorably. Most common are the occipitomental (OM) or Water’s view, submentovertex (SMV) basal view, and Caldwell’s (facial) view.

Figure 3. Diagrams of Facial Imaging

The occipitomental (OM) or Water’s view is a PA radiograph of the skull taken with the patient’s head tilted back at an angle. In this view, the x-ray beam is angled either at 45° or 30° to the orbitomeatal lines. The rays then pass through the chin, to behind the skull, and perpendicular to the plate. This type of projection best displays the orbital rim, the floor of the orbit, the maxillary sinuses, the nasal septum, the nasal bones, and the zygomatic bones.

Figure 4. Water’s View Film
The submentovertex (SMV) view is a radiograph taken with the neck fully extended (thus cervical injuries must first be ruled out prior to employing this projection). The x-ray beam passes through the underside of the chin (close to the mental tubercle of the mandible) and exits are the vertex of the skull. The beams are directed perpendicular to the cantho-meatal line. This projection is used in combination with other views to maximize the visualization of the skull.

Figure 5. Submentovertex View Film

The Caldwell’s view (also known as the occipitofrontal projection) is a radiograph of the skull that features the x-ray plate angled at 20° to the orbitomeatal line. The rays then pass through from behind the head, perpendicular to the radiographic plates. Among the structures seen through this visualization are the frontal sinuses, the ethmoidal sinuses, the orbits, the orbital rims, the medial orbital walls, the zygomatic bones, the nasal bones, the nasal septum, and the mandible.

Figure 6. Caldwell’s View Film

In cases of facial fractures, a basic facial series imaging work-up is usually requested consisting of three to four films. Of the different views and projections, the most reliable is the Water’s view since it has a tendency to show all of the major facial structures better than the other radiographic imaging of the face.

With the advancement in medical technology, high-resolution computerized tomography (CT) scans are the imaging/visualization procedure of choice for facial trauma in most medical institutions. This is because the complex arrangement of the bone anatomy in the face, including the intricacy of the injuries resulting from facial trauma, is shown really well by CT scans.

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