Injuries of the Middle Third of the Face

By Dr. Vishaal Bhat on Wednesday 28 November 2007 with 0 comments

The middle third of the face is at its upper part divided from the neurocranial part of the skull by a line that connects both zygomatic-frontal sutures with front-maxillar sutures and naso-frontal sutures. On sides, it is bordered by lines running from the zygomatic-frontal towards the zygomatic-temporal suture and further back to tuber maxillae and pterygoid process of the sphenoid bone. The bottom boundary is formed by the occlusal plane of the upper teeth.

The basic structure of this part of face is body of the upper jaw. The upper jaw together with the hard palate span above the oral cavity and form the bottom of nasal and orbital cavities. Similar to the lower jaw that determines shapes of chin and lower lip, the upper jaw influences formation of the mouth, upper lip, nose and position and size of orbits.

Extension of an injury to the skull’s base.

The boundary between the middle and upper thirds of face, formed by the frontal, sphenoid and ethmoid bones that moreover encompass the pneumatic system of secondary nasal sinuses, enables for fractures affecting the middle third to extend to the skull’s base (craniomaxillar fractures) with all consequences of such an injury (liquorrhea, infection of brain meninges, pneumo-cephalus etc.).

Fractures of the middle facial third.

Fractures of the middle third of face differ from fractures of the lower jaw. Reasons include both different anatomical layout of this area and composition of bones. The lower jawbone is a movable bone with a thick cortical bone tissue and well developed spongy tissue. Skeleton of the facial middle third is firmly connected to the skull and it is formed by thin bony lamellas reinforced at certain places by bony trabeculae. Except the maxilla and palatal processes of the upper jaw, there is no developed compact bone. At this region, it is very rare to find isolated injuries of particular bones (except the nasal skeleton), more often groups of bony structures (complexes) are damaged, that break up as a whole unit. Fractures are often of a comminuted character. The presence of the nasal cavity and secondary nasal sinuses whose epithelium can easily be damaged during fractures, make all injuries of the facial middle third to be open fractures with a risk of infection. A honeycomb structure of bones of the middle face with its large periosteum make all healing processes to proceed very rapidly. Dislocated fragments may get fixed at wrong positions that makes later reposition difficult. Serious functional and cosmetic malformations appear as a result.

Anatomical notes.

Skeleton of the facial middle third is composed of many bones (the upper maxilla, palatal bone, nasal bones, lachrymal bone, vomer, ethmoidal bone, upper, middle and lower ethmoturbinal conchae, zygomatic bone, sphenoid bone, zygomatic arches). Bones are held together by sutures to form one unit, with bony lamellae closing various cavities. The skeleton of the facial middle third protects important sensorial organs (vision, hearing, olfaction) and it is a place where airways and alimentary tract begin.

Mechanisms of injuries.

The upper jaw is exposed to shocks from the lower jaw during chewing. The upper jaw’s teeth absorb shocks from occlusal teeth and distribute them along the skull’s base. Pillars that are made by thicker and stronger lamellae at walls of cavities are positioned in such a way to allow for this absorption. The core and hub of pressures at the middle third is the sphenoid bone that transfers shocks and distributes them to all lamellae, processes and cavities. The bone itself participates at formation of walls of all cavities of this facial region. The middle third skeleton is very resistant to forceful hits at direction from the bottom upwards but it is less resistant to hits coming from the front and sides. Majority of fractures are caused by impacts at horizontal direction. A direction and strength of an impact that causes fractures influence character of fractures and dislocation of fragments. A muscle tonus does not play a role. A reason that participates at fragments dislocation is their own weight. In case of the whole middle third breaking off the neurocranium it may drop down and cause breathing problems by airways closure and dislocation backwards at the direction of causative force. The face then obtains a shape of inverted dish or bowl (a dish face). Most frequent causes of injuries are impacts of moving head onto a barrier. An extent and location of injury are determined by the head position (turn) at the moment of impact and the size of area onto which a force acts. With increased kinetic energy of an impact the extent and comminuted character of injuries of bony structures magnify. An impact of a moving object to the face has a similar effect. A force of a hit by fist directed at the nasal or cheek bones areas already causes an extensive destruction of bones.

Category: Oro-Maxillo Facial Surgery Notes



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