Additional associated presenting clinical signs could be pain on mastication, resulting in a reluctance to chew, audible "click"
with jaw movement, pain on palpation of the TMJ or surrounding soft tissues, swelling of the TMJ area, malocclusion of teeth,
decreased range of motion and/or enophthalmos/exophthalmos. A good otic examination (and possibly imaging of the inner ear)
should be included on initial work-up to rule out ear disease as the cause for pain in the region of the TMJ.
Obtaining detailed images of the TMJ usually expedites the search for a diagnosis. Extra-oral radiographic technique is used
to image the TMJ. Multiple views are required to assess the joint. Dorsoventral (or ventrodorsal) and right- and left-lateral
oblique views are standard. Some veterinarians find it useful to add an open-mouth view to a series.
Positioning for the oblique views has been described in many ways. Two commonly accepted oblique views are the lateral rostrodorsal
and the laterodorsal oblique.
By convention, the joint imaged is always the TMJ closest to the film/table. To obtain the first view, the animal is positioned
in lateral recumbency with the nose raised 20 degrees off the table and supported by a foam wedge or sandbag (different angulations
from 15 to 35 degrees have been suggested for various skull shapes), projecting the TMJ through the masseter fossa of the
To obtain the second view, the animal is positioned in lateral recumbency with the nose raised slightly (7 to 10 degrees),
and the head is rotated 20 degrees along its median axis, projecting the TMJ ventral to other bony structures.
The second view is most commonly advocated in the cat. The oblique views are challenging to position and reproduce. Interpretation
of TMJ radiographs can be difficult due to the complexity of surrounding structures and superimposition.
When extra-oral radiographs do not provide enough detail of the TMJ, computed tomography (CT) and magnetic resonance imaging
(MRI) may be necessary. CT is indicated when more information is needed about the three-dimensional shape and internal structure
of the osseous components of the joint.
This modality may be considered for evaluating ankylosis, osteoarthritis, dysplasia, neoplasms, fractures, luxations and subluxations.
Intravenous iodinated contrast medium may be useful with CT to investigate neoplasms or mass lesions, masticatory myositis,
neighboring middle-ear disease and possible cerebral involvement of any lesion. MRI is only used when information about the
soft-tissue structures of the joint (meniscus, joint capsule, articular cartilage and lateral ligament) are necessary. The
use of MRI, though common in man, has yet to be reported for use in dogs and cats for the investigation of TMJ disorders.
Other TMJ disorders follow.
Reported in Bassett Hounds, Dachshunds, Irish Setters and a handful of additional dog and cat breeds, dysplasia is a rare
congenital or developmental condition. It generally consists of malformation of the bony structures of the TMJ, and it results
in brief to extended periods of intermittent open-mouth jaw locking. Yawning usually precipitates an event.
The mandible will be laterally shifted and an ipsilateral protuberance on the lateral, ventral aspect of the zygomatic arch
may be noted. The protuberance is the displaced coronoid process of the mandible.
The shift and the protuberance are located on the opposite side of the dysplastic joint. Both joints can be affected; therefore,
dogs may present with alternating signs. A shallow mandibular fossa, underdeveloped retroarticular process and/or articular
eminence, abnormally angled and flattened mandibular condyle, slack lateral ligament and excessively mobile mandibular symphysis
are required to create open-mouth jaw locking due to TMJ luxation or subluxation with or without lateral dislocation of the
coronoid process over the zygomatic arch.
Radiographic features of dysplasia consist of flattening of the mandibular condyle and fossa with a hypoplastic or misshapen
retroarticular process, a widened irregular joint space with periarticular osteophytosis and an increased obliquity of the
articular surface of the mandibular condyle. Immediate treatment for coronoid displacement consists of manually opening the
jaw even further to release the coronoid process from the lateral aspect of the zygomatic arch; sedation may be necessary.
Long-term recommended treatment consists of surgical reduction of the coronoid process, surgical resection of portions of
the zygomatic arch or a combination of both techniques.
Open-mouth jaw locking with coronoid displacement can occur as sequelae to traumatic or developmental flattening of the zygomatic
arch, malunion fracture of the mandibular body, mandibular symphyseal laxity and brachycephalic skull conformation without