TMJ luxations occur in both the dog and cat as a result of trauma or dysplasia. Malocclusion will be present, resulting in
the inability of the animal to close its mouth fully. With rostrodorsal luxation, the mandible will shift rostrally and laterally
to the contralateral side. This shift may go unnoticed if the mandibular body is fractured. The cat has a higher incidence
of TMJ luxation due to decreased mandibular symphyseal movement and shorter jaw length.
A well-developed retroarticular process and articular eminence cradles the feline condyle and assumes most of the responsibility
in resisting displacement of the joint. Consequently, fracture of the mandibular condyle, articular eminence or surrounding
bony structures may be obligatory for TMJ luxation to occur in the cat.
Luxation and fracture of the TMJ in dogs is less common due to greater mandibular symphyseal mobility, stronger lateral ligamentous
support preventing rostral condylar displacement and a smaller articular eminence. The retroarticular process in both dogs
and cats naturally prevents caudal luxation of the mandibular condyle. Therefore, luxation of the mandibular condyle usually
occurs in a rostrodorsal direction. A dorsoventral radiograph best demonstrates a TMJ luxation. Radiographic findings include
increased width of the TMJ space and a rostral shift of the mandibular condyle on the affected side.
Reduction of a rostrodorsal TMJ luxation is obtained by placing a wood dowel (pencil in smaller animals) between the carnassial
teeth (dowel acts as a fulcrum) and closing the jaw against the dowel while simultaneously easing the jaw caudally.
The reduction usually is unstable, and a tape muzzle for one to two weeks is indicated. Fractures of the mandibular condyle,
mandibular fossa or temporal bone usually are treated conservatively, because they may heal by bony union or as a pain-free
and functional nonunion.
Comminuted and intra-articular fractures that can lead to joint arthrosis and ankylosis may be treated with a condylectomy,
although it is controversial whether to perform this surgery at the time of trauma or later if healing complications occur.
Tape muzzles may be contraindicated in these situations as immobility of the joint may promote ankylosis.
This disease is seen primarily in 3- to 7-month-old West Highland White, Scottish and Cairn Terriers (rarely in other breeds),
and it is of unknown cause associated with development.
Puppies may present with swelling of the jaws, inappetence, lethargy and fever. They will be resentful on palpation of the
cranium and mandible and are reluctant to open their mouths.
Its distinctive radiographic feature is an extensive, bilateral, irregular, periosteal reaction of the mandible that can extend
to the TMJ, tympanic bullae and calvarium.
Radiographs reveal the extent of the TMJ involvement. Long-term treatment with non-steroidal anti-inflammatory drugs or corticosteroids
is recommended. The condition tends to run an undulant course, and signs may regress at about one year of age.
Temporomandibular joint ankylosis usually occurs as a complication following trauma to the region of the TMJ. Ankylosis also
has been reported as a sequel to extensive new bone formation associated with otitis media and craniomandibular osteopathy.
Ankylosis results in a progressive inability to open the mouth, often resulting malnutrition, weight loss, dehydration, atrophy
of the muscles of mastication and respiratory obstruction.
Two types have been recognized — true or intracapsular ankylosis, and false or extracapsular ankylosis.
An example of extracapsular would be ankylosis between the zygomatic arch and coronoid process without true TMJ involvement.
Key radiographic features of true ankylosis are the loss of a regular TMJ space and mandibular condyle contour and associated
irregular new bone formation. Treatment for intracapsular ankylosis consists of condylectomy and excision of all associated
osteophytes. Prognosis is guarded due to high rates of re-ankylosis of cut bony surfaces. Treatment for extracapsular ankylosis
is completely dependent on the nature and location of the lesion.
Fracture of the zygomatic arch
Fractures of the zygomatic arch toward the cranium or fractures that have been allowed to heal in a depressed position can
inhibit rostral movement of the coronoid process. A decreased range of motion will be noted on physical exam, as well as an
irregular zygomatic arch.
Range of motion is contingent on the severity and angulation of the fracture and/or callus formation. Cats are less prone
to this type of injury because of the wide curvature of the zygomatic arch. Treatment entails removal of the offending section
of arch or rigid fixation of a fresh fracture.
Though rare, osteoarthritis of the TMJ in dogs and cats has been reported. It can be a sequel to TMJ dysplasia or contralateral
mandibulectomy. Sometimes proliferative changes of an adjacent tympanic bulla may extend to include the TMJ. Osteophyte formation
can be severe, and it may surround the articular surfaces of the temporal bone and mandibular condyle. These animals will
have proper alignment of dentition, but they will be extremely reluctant to open their mouths. Treatment is limited to medical
Dr. Hoskins is owner of Docu-Tech Services. He is a diplomate of the American College of Veterinary Internal Medicine with
specialities in small animal pediatrics. He can be reached at (225) 955-3252, fax: (214) 242-2200 or e-mail: