Page 1402 - Cote clinical veterinary advisor dogs and cats 4th

Open-Mouth Jaw Locking 709

GENETICS, BREED PREDISPOSITION • Hair accumulation at dorsocaudal tongue • Lateral oblique radiographic view (showing
• Cats: primarily Persian surface (in cats that continue grooming but TMJ dysplasia when present)
VetBooks.ir other breeds • Bilateral exophthalmos and reduced retropul- ○ Shallow, flat, or irregular mandibular Diseases and Disorders
○ Wide joint space
cannot swallow)
• Dogs: primarily basset hound; occasionally
fossa
sion of globes
RISK FACTORS
• Head shape (e.g., brachycephalic cats) Etiology and Pathophysiology ○ Hypoplastic articular eminence
○ Flattened or enlarged condylar process
• Specific anatomic configuration of the TMJ Dysplasia of TMJ or adjacent tissues: ○ Hypoplastic or thickened retroarticular
(relating to capsule, articular disk, condylar • Resulting in progressive TMJ laxity and process
process, mandibular fossa, retroarticular subluxation/luxation of the condylar process
process) and adjacent tissues (coronoid • Medial pulling of the mandibular body TREATMENT
process of mandible, zygomatic arch, mastica- on contraction of pterygoid muscles at
tory muscles) maximal mouth opening (e.g., immediately Treatment Overview
• Dysplasia, subluxation/luxation of the TMJ, after yawning) and lateral flaring of the Immediate relief by manual unlocking in the
and laxity of the mandibular symphysis coronoid process of the mandibular ramus sedated or anesthetized patient and temporary
eventually causing displacement of the tip maxillomandibular fixation to avoid recurrence
ASSOCIATED DISORDERS of the coronoid process ventrolateral to the of locking, followed by definitive surgery the
• TMJ luxation zygomatic arch same or next day
• TMJ dysplasia (bony and/or soft tissue) Trauma of TMJ or adjacent tissues:
• Abnormal extrusion of maxillary and/or • Flattening of the zygomatic arch Acute General Treatment
mandibular canine teeth • Displacement of the coronoid process • Manual unlocking by opening the mouth a
• Trauma to TMJ, mandible (condylar process, • Thickening (callus formation) of the zygo- little further, carefully pressing the affected
coronoid process), and mandibular symphysis matic arch and/or coronoid process mandible medially, and gently closing the
• Laxity of the mandibular symphysis mouth
Clinical Presentation • Laxity of the TMJ • Maxillomandibular fixation (e.g., place-
DISEASE FORMS/SUBTYPES Iatrogenic: ment of a tape muzzle to restrict full
• TMJ dysplasia without mandibular • After unilateral total mandibulectomy range of mouth opening until definitive
displacement Other: surgery)
• TMJ dysplasia with subluxation/luxation of • Abnormal extrusion of maxillary and/or
the TMJ but no open-mouth jaw locking mandibular canine teeth, causing them to Chronic Treatment
• Open-mouth jaw locking with the mouth contact the opposing canine teeth on closure Recommended:
locked wide open due to displacement of the mouth; subsequent levering forces • Partial resection of the zygomatic arch
of the coronoid process of the mandible resulting in increased mandibular symphyseal • Partial reduction of the coronoid process
ventrolateral to the zygomatic arch laxity, TMJ laxity, and rotational movement • Combination of zygomatic arch resection
of the mandibular body and coronoid process reduction (preferred
HISTORY, CHIEF COMPLAINT by the author)
• Episodes of open-mouth jaw locking after DIAGNOSIS • Symphysiotomy, symphysiectomy, and
yawning, grooming, or vocalizing intermandibular fixation (if laxity of the
• Frequency: once per month to several times Diagnostic Overview mandibular symphysis was the leading cause
per day • History, clinical signs, and radiography (often of open-mouth jaw locking)
• Duration: a few seconds/minutes to many sufficient to make a diagnosis) • Skin suture removal 10-14 days postopera-
hours/days • CT is of academic interest but not required tively
• Spontaneous correction possible, sometimes for diagnosis. Not recommended:
associated with an audible click • Imbrication/plication of the lateral TMJ
• Drooling of saliva and dropping of food due Differential Diagnosis capsule
to inability to close mouth and swallow • Traumatic TMJ luxation with rostrodorsal • Mandibular condylectomy
• Pawing at face, rubbing muzzle on ground, displacement of the mandibular condyle
shaking head, and vocalizing during locking (lower jaw shifting to opposite side, inability Nutrition/Diet
episodes to fully close mouth due to contact between Soft food for 2 weeks postoperatively
• Dehydration and weight loss due to inability upper and lower teeth, dorsoventral radio-
to swallow water and food (if untreated) graphic view showing no contact between Possible Complications
mandibular coronoid process and zygomatic Recurrence of open-mouth jaw locking
PHYSICAL EXAM FINDINGS arch) • Unlikely if resective surgery was properly
Usual presentation (compare with TMJ luxation): • Mandibular neurapraxia (trigeminal neuritis) performed
• Mouth locked wide open (lower jaw cannot • Bilateral mandibular fracture (similar • Possible with partial zygomectomy only
be closed when pushed against the upper to mandibular neurapraxia, lower jaw or partial coronoidectomy only (par-
jaw) can usually be moved against the upper ticularly when insufficient bony tissue was
• No contact between upper and lower teeth jaw) removed)
• Slight rostral protrusion of ipsilateral mandible • Periorbital/caudal mandibular/caudal maxil- Open-mouth jaw locking occurring on
• More ventrally positioned dental arch at lary neoplasia opposite side:
ipsilateral mandible • Mandibular ramus/zygomatic arch fracture • If possibility of bilateral locking had not
• Facial protuberance from displaced coronoid been evaluated before surgery of one side
process sometimes palpable (and occasion- Initial Database only
ally even visible under skin) ventrolateral to Routine preanesthetic blood tests
ipsilateral zygomatic arch Recommended Monitoring
• Drooling of saliva (due to inability to close Advanced or Confirmatory Testing Observing animal closely when yawning,
the mouth and difficulty to swallow) and • Dorsoventral/ventrodorsal radiographic view particularly when having had history of open-
moist fur at chin and neck region of the head (most useful) mouth jaw locking

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