Comminuted fractures of the caudal maxillary area can be nondisplaced (left), but are usually displaced and depressed (right). The pattern of the fracture lines will vary according to the direction of the insult. Malocclusion may be seen.
Displaced fractures of the caudal midface may affect the occlusion of the caudal premolar and molar teeth. If the integrity of the infraorbital margin is disturbed, the orbit and eye are affected.
General information for all midfacial fractures
Human craniomaxillofacial surgeons use the Le Fort classification for midface fractures. Veterinary medicine lacks a classification system. Therefore, the authors have divided the midface arbitrarily based on a variety of cases that they have treated in the past 10 years.
From a biomechanical standpoint, the maxillofacial structures are relatively lightweight. Yet they have strong frames made of thin bones that also form the nasal cavity and paranasal sinuses. These maxillofacial frames are strengthened by the buttresses, which are thicker areas of the bones, designed to distribute the forces of mastication. The buttresses also help to maintain the position of the maxilla in the appropriate relationship with the base of the skull and the mandible. There are lateral, medial and caudal buttresses. The objective of reconstructing midfacial fractures is to restore these buttresses as well as the orbit and frontonasal vault. Fixation of bone fragments is done from the most unstable to more stable, in order to ‘simplify’ the fracture.
Midfacial fracture classification
The frontonasal area: Frontal bone and part of nasal bone
The zygomatic arch: Zygomatic process of the temporal bone and zygomatic bone
Caudal midface: Maxilla and part of nasal bone
Rostral midface: Maxilla, nasal and incisive bones
Palatal: Incisive, maxilla, palatine
Panfacial: When more than one region is involved
The midface is unique because of its 3D complexity and the interaction of its hard and soft tissues. This area has a large number of blood vessels and cranial nerves.
In the midface, form and function are interdependent; even minor disruption of the anatomy may be obvious, especially if it affects the occlusion of the teeth.
The degree of fracture comminution in the midface and the degree of injury to the soft tissue envelope contribute to the complexity of the repair.
Modern imaging technologies allow analysis of fracture patterns and assessment of the fracture complexity. The gold standard for assessment of a fracture pattern is computed tomography (CT), that can produce thin section images with CT-based 3D data sets.
It is strongly advised to obtain postoperative CT scans to assess the surgical result.
Cone beam CT technology is an evolving imaging modality in veterinary dental and craniomaxillofacial surgery. It gives a 3D view of all craniomaxillofacial structures in less time with less cost than a full CT. The resolution is not as good as the CT and its use for fracture planning is not well established.
3D printing of the skull for surgical planning is very useful. The surgeon can visualize the trauma in 3D, perform the planned surgery on the model and evaluate the results before it is done on the patient.
DICOM voxel data set, 3D image analysis, and professional software are available for free on the internet.
If visualization software for the DICOM datasets is not available, CT views of the midface (axial, coronal, and oblique parasagittal) are still recommended for simple fractures. 3D views are recommended for more complex fractures.
Plain X-rays alone are only adequate for structures such as dentition, and should only be used alone if CT is unavailable.
MRI or ultrasound can be helpful for soft tissue injuries but are not included in the standard diagnostic work up.
Special fracture consideration
If the entire upper jaw is fractured or dislocated, there will be a pronounced malocclusion at the frontonasal and frontomaxillary sutures. This is typically seen in young dogs.
Patients with simple caudal midface fractures may have malocclusion leading to difficulty in eating.
Patients with comminuted fractures can have subcutaneous emphysema, crepitus, and nasal bleeding. Soft tissue trauma may be present at the site of injury. Extensive bleeding may occur as a result of damage to the maxillary artery or infraorbital vessels.