- Zygomatic Bone: Anatomy, Function, and Treatment
- The Temporal Bone
- Anatomical Structure
- Zygomatic Process
- Styloid Process
- Muscular Attachments
- Clinical Relevance: Mastoiditis
- Clinical Relevance: Temporal Bone Fractures
- Clinical Relevance: Fractures of the Pterion
- Zygoma | Radiology Reference Article
- Gross anatomy
Zygomatic Bone: Anatomy, Function, and Treatment
The zygomatic bones are more commonly known as the cheekbones. These bones are located just below each eye and extend upward to the outer side of each eye. The zygomatic bones join with several other bones of the face, including the nose, jaw, portions of the eye, and bones just in front of the ears.
The zygomatic bone consists of cartilage when a fetus is in utero, with bone-forming immediately after birth. Due to its size and function in joining many facial bones together, underdeveloped zygomatic bones cause significant issues related to the construction of the face. The most significant condition associated with the zygomatic bones is a fracture.
The zygomatic bone is somewhat rectangular with portions that extend out near the eye sockets and downward near the jaw. The front portion of the bone is thick and jagged to allow for its joining with other bones of the face.
This thickness also allows the bone to remain strong and sturdy to protect the more delicate features of the face. Other portions of the zygomatic bone include joints near the jaw, near the ears, and near the forehead and skull.
Near the skull, the articulations (where two bones come together) are not as thick. This allows for the structure of the skull to take over as the main protector of the brain and other underlying structures. There is also a tunnel within the zygomatic bone called the zygomaticofacial foramen which allows for the passage of integral veins and arteries through the face.
Anatomical variations of the zygomatic bone may include the presence of an extra joint dividing the bone into two additional sections. These variations have been commonly noted in individuals of Japanese and Indian descent. Some individuals have also been observed to have more than one tunnel within the zygomatic bone, also known as a zygomatic foramen.
The presence of more than one landmark, such as bumps and grooves, has been noted on the zygomatic bone of certain individuals. Other variations include differences in where the zygomatic bone meets the jaw bone and the forehead, along with longer landmarks at the site of these joints.
Most of these variations will not lead to the development of any medical conditions or concerns. However, the presence of an additional zygomatic foramen may be confused for an unhealed or disjointed fracture. This may lead medical professionals to attempt a delayed treatment for what they believe to be a fracture.
The zygomatic bone functions as a structure which joins the bones of the face while protecting the arteries, nerves, veins, and organs which lie below the surface. The arches of the zygomatic bone provide a person’s cheeks with the structure to fill out the face.
The zygomatic bone itself has no ability to move, as it is a stationary bone which allows it to function mainly for protection. However, the lower portion of the zygomatic bone which joins with the jaw bone assists in providing movement to the jaw bone.
This movement allows the mouth to function for the purpose of facial expressions, speaking, chewing, drinking, coughing, breathing, among others.
The stability the zygomatic bone provides also allows for motion associated with other bones connected to the zygomatic bone.
Additionally, the grooves and indentations of the upper zygomatic bone provide space for muscles to insert in the forehead and upper portion of the skull. This allows the zygomatic bone and other facial bones to connect with the upper portion of the skull.
The most common condition associated with the zygomatic bone is a fracture. A fracture to the orbital floor, the portion of the zygomatic bone which is attached to the eye, also has an impact on the function of the zygomatic bone.
This type of fracture is called a blowout and can cause a fracture to the zygomatic bone, displace the upper portion of the zygomatic bone which articulates with the skull, and can cause a deeper fracture to the eye socket.
Jaw fractures can also impact the lower portion of the zygomatic bone, causing difficulty chewing, speaking, and other functions associated with the mouth.
Vision problems may be associated with orbital fractures, along with muscle spasms to the nearby facial muscles. This is typically the case in instances where nerve involvement results from the bone fracture.
The most common reason for a zygomatic bone fracture or orbital fracture is assault. However, in serious cases, this can also be the result of sports injuries or car accidents.
Fractures to the zygomatic bone are diagnosed through an X-ray. Patients are instructed not to blow their nose or perform any large facial movements which may cause pain or further disturb the fracture. Depending on the severity of the fracture, the zygomatic bone may be monitored through home health and treated with antibiotics to prevent or treat infection.
More serious zygomatic fractures may result in inward displacement of the eyeball, persistent double vision, or cosmetic changes. These instances require surgery to apply fixators to the bones and minimize complications.
The absence of cosmetic changes following a facial injury in children can result in a delayed diagnosis. White-eyed blowouts are orbital fractures which occur in children and result in a presentation similar to that of a concussion. This may include nausea, vomiting, and cognitive changes.
Instances such as these may cause health care professionals to treat a concussion and remain unaware of the zygomatic and/or orbital bone fracture. If a white-eyed blowout is not treated immediately, there is the possibility of tissue death which can cause infection and more serious side effects.
The Temporal Bone
The temporal bone contributes to the lower lateral walls of the skull. It contains the middle and inner portions of the ear, and is crossed by the majority of the cranial nerves. The lower portion of the bone articulates with the mandible, forming the temporomandibular joint of the jaw.
In this article, we shall look at the different parts of the temporal bone, their articulations, and any clinical correlations.Fig 1 – Lateral view of the skull. The temporal bone has been highlighted.
The temporal bone itself is comprised of five constituent parts. The squamous, tympanic and petromastoid parts make up the majority of the bone, with the zygomatic and styloid processes projecting outwards.Fig 1.1 – The constituent parts of the temporal bone.
We shall now examine the constituent parts of the temporal bone in more detail.
Also known as the squama temporalis, this is the largest part of the temporal bone. It is flat and plate-, located superiorly. The outer facing surface of the squamous bone is convex in shape, forming part of the temporal fossa.
The lower part of the squamous bone is the site of origin of the temporalis muscle
The bone articulates with the sphenoid bone anteriorly, and parietal bone laterally.
The zygomatic process arises from the lower part of the squama temporalis. It projects anteriorly, articulating with the temporal process of the zygomatic bone. These two structures form the zygomatic arch (palpable as 'cheek bones').
One of the zygomatic processes' attachments to the temporal bone forms the articular tubercle – the anterior boundary of the mandibular fossa, part of the temporomandibular joint
The masseter muscles attaches some fibres to the lateral surface of the zygomatic process.
The tympanic part of the temporal bone lies inferiorly to the squamous, and anteriorly to the petromastoid part.
It surrounds the external auditory opening, which leads into the external auditory meatus of the external ear.
The styloid process located immediately underneath the opening to the auditory meatus. It acts as an attachment point for muscles and ligaments, such as the stylomandibular ligament of the TMJ.
This portion of the temporal bone is located posteriorly. It can be split into a mastoid and petrous parts. On a lateral view of the temporal bone, such as figure 1.1 above, only the mastoid part is visible.
There are two items of note on the mastoid. The first is the mastoid process, an inferior projection of bone, palpable just behind the ear. It is a site of attachment for many muscles, such as the sternocleidomastoid.
Also of clinical importance are the mastoid air cells. These are hollowed out areas within the temporal bone. They act as a reservoir of air, equalising the pressure within the middle ear in the case of auditory tube dysfunction. The mastoid air cells can also become infected, known as mastoiditis.
Fig 1.2 – Coronal section of temporal bone, showing the mastoid air cells in more detail
The petrous part is pyramidal shaped, and lies at the base of temporal bone. It contains the inner ear.
The temporal bone serves as a point of attachment for many muscles. Due to the involvement of the temporal bone in forming the temporomandibular joint (i.e.
joint of the jaw) some fibres from muscles of mastication such as the temporalis and masseter muscles attach to the temporal bone. In addition to this the mastoid process of the temporal bone is a major site of muscle attachment.
Some key muscular attachments are outlined in the table below.
|Muscle||Site of Attachment||Description|
|Temporalis||Originates from the lower part of squamous||Muscle of mastication|
|Masseter||Lateral zygomatic surface||Muscle of mastication|
|Sternocleidomastoid||Mastoid process||Superficial muscle of the neck. Involved in rotation of head and flexion of neck. Important landmark for the anterior and posterior cervical triangles.|
|Posterior belly of digastric||Mastoid process||A suprahyoid muscle. Involved in processes such as swallowing.|
|Splenius capitis||Mastoid process||Strap- muscle in the back of the neck. Involved in movements such as shaking the head.|
A major articulation of the temporal bone is with the mandible (i.e. jaw bone) to form the temporomandibular joint which is covered in detail here.
The squamous part of the temporal bone also articulates with the sphenoid bone anteriorly and the parietal bone laterally.
The zygomatic process of the temporal bone also articulates with the zygomatic bone to form the zygomatic arch (i.e. cheekbones).
Clinical Relevance: Mastoiditis
Middle ear infections (otitis media) can spread to the mastoid air cells. Due to their porous nature, they are a suitable site for pathogenic replication.
The mastoid process itself can get infected, and this can spread to the middle cranial fossa, and into the brain, causing meningitis.
If mastoiditis is suspected, the pus must be drained from the air cells. When doing so, care must be taken not the damage the nearby facial nerve.
Clinical Relevance: Temporal Bone Fractures
The temporal bone is relatively strong, and thus it is usually only fractured as a result of blunt trauma to the skull.
It has a varied presentation. Ear-related disorders are commonly seen, such as vertigo or hearing loss. As the facial nerve travels through the temporal bone, it can be damaged, with paralysis resulting. Other symptoms include bleeding from the ear and bruising around the mastoid process.
Clinical Relevance: Fractures of the Pterion
Where the temporal, parietal, frontal and sphenoid bones meet, the skull is at its weakest, and susceptible to fracture. This point is known as the pterion.
The middle meningeal artery (MMA) supplies the skull and the dura mater (the outer membranous layer covering the brain). It travels underneath the pterion, thus a fracture of the skull at the pterion can injure or completely lacerate the MMA.
Blood will then collect in between the dura mater and the skull, causing a dangerous increase in intra-cranial pressure. This is known as an extradural haematoma.
Fig 1.3 – Lateral view of the skull, showing the path of the meningeal arteries. Note the pterion, a weak point of the skull, where the anterior middle meningeal artery is at risk of damage.
The increase in intracranial pressure causes a variety of symptoms; nausea, vomiting, seizures, bradycardia and limb weakness. It is treated by diuretics in minor cases, but surgical intervention is required in cases of major haemorrhage.
Zygoma | Radiology Reference Article
The zygoma (also known as zygomatic bone or malar bone) is an important facial bone which forms the prominence of the cheek. It is roughly quadrangular in shape.
Zygoma has three surfaces, five borders, and two processes.
- anterolateral surface is convex, pierced at its orbital border by the zygomaticofacial foramen, through which the zygomaticofacial nerve and vessels pass
- temporal (posteromedial) surface articulates with the maxilla, its smooth concave posteriorly forms an incomplete wall of the infratemporal fossa
- orbital surface forms the anterolateral part of the orbital floor and bears the zygomatico-orbital foramina, openings of the canals leading to the zygomaticofacial and zygomaticotemporal foramina.
- orbital (anterosuperior) border forms the inferolateral circumference of the orbital margin
- maxillary (anteroinferior) border articulates with the maxilla, tapers just above the infraorbital foramen; the zygomaticomaxillary suture joins the maxillary margin of the zygomatic bone and the zygomatic process of the maxilla
- temporal (posterosuperior) border is of sinuous shape, convex above and concave below, and continuous with the posterior border of the frontal process and upper border of the zygomatic arch
- posteromedial border articulates with greater wing of sphenoid above and orbital surface of maxilla below and serves as attachment for masseter muscle
- frontal process articulates with the frontal bone above and greater wing of sphenoid posteriorly, and terminates at the frontozygomatic suture
- temporal process is directed backwards, has an oblique, serrated end articulating with the zygomatic process of temporal bone, forming the zygomatic arch at the temporozygomatic suture
- lateral surface attaches zygomaticus minor and major muscles
- posteroinferior border – masseter muscle
- tubercle of frontal process (of Whitnall) – lateral palpebrae ligament, a suspensory ligament and part of the aponeurosis of levator palpebrae superioris
- maxillary border gives origin to part of levator labii superioris
The zygoma ossifies from one center, appearing in fibrous tissue around the eighth week of life. Sometimes it may be divided by a horizontal suture into a larger upper and small lower division.
- the zygomaticofacial foramen can often be double or sometimes be absent
- the tubercle attaching lateral palpebrae ligament from frontal process of zygoma is absent in 5-10% of skulls