1-Year-Old Neutered Male Mixed breed

Signalment & History

  • This patient presents to your clinic because of an inability to completely open its mouth.
  • You order skull radiographs.

skull-oblique-1 skull-oblique-2 skull-dv



  • There is an osseous proliferation on the ventral aspect of the right mandible. This osseous proliferation extends dorsally from the right mandible to the level of the zygomatic arch.
  • There is smoothly margined osseous proliferation superimposed on the right zygomatic arch and the lateral aspect of the right mandible.


  • It is a chronic malunion of the caudal aspect of the right mandible and a suspected synostosis of the zygomatic arch


  • What is your diagnosis JAVMA. Vol 249,7,2016.
  • Thrall DE. Principles of radiographic interpretation of the axial skeleton. In: Thrall DE, ed. Textbook of veterinary diagnostic radiology. 6th ed. St Louis: Elsevier Health Science, 2013;101–113.
  • Mandibular fractures in the dog. A retrospective study of 157 cases. Vet Surg, 19, 4, 272-275, 1990

Malunion fractures result when fragments of bone heal but in an abnormal anatomical alignment. These can occur from poor initial reduction, shifting of the fragments during early healing phase, or premature removal or fixation devices before the fracture is stable. Malunion can have a negative effect on the function if they are moderate to severe and may require correction.

Radiographic Signs of Secondary Bone Healing

  • 5-10 days after reduction: Fracture fragments lose sharp margins. Demineralization of fracture fragments ends results in slight fracture line widening.
  • 10-20 days after reduction: Formation of endostial and peristeal callus. Decreasing size of fracture gap and variable loss in opacity of free fracture fragments.
  • >30 days after reduction: Fracture lines gradually disappear. External callus increase in opacity and remodels.
  • >3 months after reduction: Continuing remodeling of external callus. Trabecular pattern may develop within the callus. Cortical shadow becomes visible through the callus. Medullary cavity continuity gradually re-establish. Cortical remodeling along the line of stress.

Mandibule fractures location