Page 1924 - Cote clinical veterinary advisor dogs and cats 4th

961.e4 Temporomandibular Joint Luxation

side, swelling and discoloration of the ipsilateral • Rare congenital or acquired malformation: Initial Database
glossopalatine region, swelling, crepitation and shallow mandibular fossa, underdeveloped/ • CBC and serum biochemistry panel: gener-
VetBooks.ir and hypersalivation. mandibular condyle, and periarticular • Head radiographs under general anesthesia:
ally unremarkable; preanesthesia
misshapen retroarticular process, flattened
pain with affected TMJ palpation, dehydration,
dorsoventral (ventrodorsal), right and left
osteophytosis; abnormal laxity in mandibular
Etiology and Pathophysiology
open-mouth jaw locking
that show displacement of the mandibular
Relevant anatomy: symphysis also reported as inciting cause of lateral oblique, and open-mouth views
• Mandibular ramus: vertical part of mandible • Open-mouth jaw locking: TMJ subluxation/ condyle or coronoid process with/without
that lies medial to the zygomatic arch, luxation, rotational movement of the man- fracture of associated bone structures
caudolateral to the orbit dibular body and locking of the coronoid
• Mandibular condyle: articular process of the process ventrolateral to the zygomatic arch; Advanced or Confirmatory Testing
mandible; articulates with mandibular fossa mouth is locked wide open, and compared CT:
of the temporal bone to form the TMJ with TMJ luxation, there is no tooth-to-tooth • Excellent imaging modality for assessing TMJ
• Retroarticular process: ventral extension contact (p. 708). disease
of the mandibular fossa of the temporal • Subtle abnormalities not identified on
bone preventing caudal dislocation of the DIAGNOSIS radiographs easily demonstrated on CT
mandibular condyle • 3D reconstruction is beneficial for diag-
• Coronoid process: dorsal protuberance of Diagnostic Overview nosis, treatment planning, and owner
the mandibular ramus providing insertion Clinical presentation and head radiographs education.
for the temporal muscle (under general anesthesia) provide the basis for
Luxation with/without regional fracture: a conclusive diagnosis. If subluxation/luxation TREATMENT
• Trauma is the most common inciting cause; due to TMJ dysplasia is suspected, CT scan
TMJ dysplasia may predispose the animal to with three-dimensional (3D) reconstruction Treatment Overview
subluxation/luxation without obvious outside or fluoroscopic imaging may be necessary for Treatment goals are to alleviate discomfort
force. diagnosis. General anesthesia for diagnostic and obtain functional lower jaw movement
• Luxation in a rostrodorsal direction is most imaging also provides an opportunity for and occlusion.
common because the prominent retroarticu- esophagostomy tube placement if prehension
lar process prevents caudoventral movement and chewing functions are unlikely to be Acute General Treatment
of the mandibular condyle. reestablished immediately. Acute TMJ luxation:
• The more tightly seated mandibular condyle • Manual reduction of rostrodorsal luxation
in the mandibular fossa of the temporal Differential Diagnosis ○ Chemical restraint (sedation or anesthesia)
bone makes luxation in cats more common • TMJ luxation with/without regional fracture ○ Place a wooden dowel (hexagonal soft-
when there is an associated regional fracture. • TMJ dysplasia with/without coronoid process wooded pencil works best in small pets)
Dogs have a more loosely seated mandibular displacement between the upper and lower carnassial
condyle, and luxations usually occur without • Mandibular neurapraxia (dysfunction of teeth of the affected side only (i.e., maxil-
regional fracture. mandibular branch of cranial nerve V) lary fourth premolar and mandibular first
• In rostrodorsal luxation, the lower jaw is • Neurogenic atrophy of temporal, masseter, molar), and gently force the mouth closed
shifted rostrally and laterally to the unaffected and digastricus muscles until the joint is reduced.
side. • Mandibular ramus/zygomatic arch fracture ○ Rotating the dowel clockwise (if the
• With complete luxation, the joint capsule • Masticatory myositis luxation is on the left side) or counter-
is damaged; serious injury to the articular • Dental/skeletal malocclusion clockwise (if the luxation is on the right
disk may occur. • Periorbital/caudal mandibular/caudal maxil- side) facilitates movement of the man-
TMJ dysplasia with/without coronoid process lary neoplasia dibular condyle back into its mandibular
displacement: • Foreign body fossa.

A B C
TEMPOROMANDIBULAR JOINT LUXATION A, Clinical photograph of a cat with its mouth incompletely closed
shows the lower jaw shifted slightly to the right, causing the upper and lower canine (thick circle) and cheek teeth
(thin circle) to make contact. B, Dorsoventral radiographic view of the same cat shows the left mandibular condylar
process (asterisk) being displaced rostrally (and dorsally). C, Skull of a cat, ventral view. shows that the right mandibular
condyle (asterisk) is luxated rostrally and dorsally, causing the lower jaw to shift toward the left side (arrows). For
comparison, note the normal left temporomandibular joint (dotted oval), with the mandibular condyle articulating with
the mandibular fossa of the temporal bone. (Copyright Dr. Alexander M. Reiter, University of Pennsylvania.)

www.ExpertConsult.com