Jaw: open-mouth locking in Cats (Felis) | Vetlexicon
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Jaw: open-mouth locking

ISSN 2398-2950

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Introduction

  • Cause: laxity of the mandibular symphysis.
  • Head shape (brachycephalism).
  • Long coronoid processes.
  • Flattened zygomatic arches.
  • Obliquely arranged mandibular fossae and condylar processes.
  • Signs: mouth locked wide open due to displacement of the coronoid process of the mandible ventrolateral to the zygomatic arch.
  • Diagnosis: clinical signs (often pathognomonic) and diagnostic imaging features (radiography, computed tomography).
  • Treatment: partial zygomectomy, partial coronoidectomy, or a combination of both procedures (may need to be done bilaterally).
  • Prognosis: excellent.

Presenting signs

  • Mouth locked wide open due to displacement of the coronoid process of the mandible ventrolateral to the zygomatic arch.
  • No contact between maxillary and mandibular teeth.
  • Ipsilateral mandible situated more ventrally and rostrally compared to the other side.
  • Facial protuberance from displaced coronoid process palpable and/or visible at ventrolateral aspect of ipsilateral zygomatic arch.
  • Drooling of saliva, dropping of food, accumulation of hair around tongue, and dehydration and weight loss due to inability to close mouth and swallow.
  • Pawing at face, rubbing muzzle on ground, shaking head, and vocalizing during locking episodes.

Acute presentation

  • Mouth locked wide open without contact between maxillary and mandibular teeth; drooling saliva.

Geographic incidence

  • World-wide.

Age predisposition

  • Adult.

Breed/Species predisposition

Public health considerations

  • None.

Cost considerations

  • Long-term control requiring surgical correction under general anesthesia.

Special risks

  • Anesthesia-related risks.

Pathogenesis

Etiology

  • Temporomandibular joint dysplasia: rare congenital or acquired malformation manifesting as shallow mandibular fossae, underdeveloped/misshapen retroarticular processes, flattened (incongruent) mandibular condyles.
  • Laxity of the mandibular symphysis, head shape (brachycephalism), long coronoid processes, flattened zygomatic arches, obliquely arranged mandibular fossae and condylar processes.
  • Open-mouth jaw locking: medial pulling of the mandible upon contraction of the pterygoid muscles at maximal mouth opening and lateral flaring of the coronoid process (for example immediately after yawning) resulting in locking of the coronoid process ventrolateral to the zygomatic arch; mouth is locked wide open without contact between maxillary and mandibular teeth.

Predisposing factors

General

  • Temporomandibular joint dysplasia.
  • Temporomandibular joint laxity.
  • Mandibular symphyseal laxity.
  • Flattening of the zygomatic arches.

Specific

  • Trauma to temporomandibular joint or adjacent tissues.
  • After unilateral total mandibulectomy.
  • Canine tooth extrusion with abnormal contact between maxillary and mandibular canine teeth and subsequent levering forces resulting in increased temporomandibular joint and mandibular symphyseal laxity.

Pathophysiology

  • Medial pulling of the mandible upon contraction of the pterygoid muscles at maximal mouth opening and lateral flaring of the coronoid process (for example immediately after yawning) resulting in locking of the coronoid process ventrolateral to the zygomatic arch; mouth is locked wide open without contact between maxillary and mandibular teeth.

Timecourse

  • One or more episodes (once a month to several times a day, ranging from a few seconds or minutes to many hours or days) of open-mouth jaw locking after yawning, grooming, playing, eating, or vocalizing.
  • Spontaneous correction sometimes associated with an audible ‘click’.

Epidemiology

  • Rare.
  • Usually adult cats.
  • No gender predisposition.

Diagnosis

Presenting problems

  • Mouth locked wide open.

Client history

  • Episodes of open-mouth jaw locking after yawning, grooming, playing, eating, or vocalizing.
  • Audible ‘clicking’ noises.

Clinical signs

  • Mouth locked wide open.
  • No contact between maxillary and mandibular teeth.
  • More rostroventrally positioned ipsilateral mandible.
  • Facial protuberance from displaced coronoid process palpable and/or visible at ventrolateral aspect of ipsilateral zygomatic arch.
  • Drooling of saliva, dropping of food, accumulation of hair around tongue (in the cat), and dehydration and weight loss due to inability to close mouth and swallow.
  • Pawing at face, rubbing muzzle on ground, shaking head, and vocalizing during locking episodes.

Diagnostic investigation

 

Definitive diagnostic features

  • Periarticular osteophytosis at mandibular coronoid process (dorsolateral) and zygomatic arch (ventromedial) from repeated contact in the past.

Gross autopsy findings

  • Not usually done.

Histopathology findings

  • Not usually done.

Differential diagnosis

  • Rostrodorsal temporomandibular joint luxation (resulting in contact between maxillary and mandibular teeth) Temporomandibular joint: luxation.
  • Abnormal extrusion of maxillary and mandibular canine teeth.
  • Trauma to temporomandibular joint, zygomatic arch, mandible (condylar process, coronoid process), and/or mandibular symphysis.
  • Mandibular neurapraxia (trigeminal neuropathy; mouth can be closed by the examiner without effort).
  • Bilateral mandibular fracture (lower jaw can usually be moved against the upper jaw) Mandibular: fracture.
  • Periorbital/caudal mandibular/caudal maxillary neoplasia.

Treatment

Initial symptomatic treatment

  • Manual unlocking (opening the mouth fully while pressing the affected mandible medially and closing the mouth) in the sedated or anesthetized patient.
  • Temporary maxillomandibular fixation to avoid recurrence of locking (placement of a tape muzzle to restrict full range of mouth opening until definitive surgery) Mandible: fracture repair.

Standard treatment

  • Partial resection of the zygomatic arch, partial reduction of the coronoid process, or a combination of  both procedures.
  • Symphysiotomy, symphysioectomy and intermandibular fixation (if mandibular symphyseal laxity was the leading cause of open-mouth jaw locking).

Monitoring

  • Occlusion.
  • Ability to close the mouth.

Subsequent management

Treatment

  • Bilateral surgery may be required.

Monitoring

  • Look for signs indicative of bilateral involvement.

Prevention

Control

  • Selective breeding.

Prophylaxis

  • Selective breeding.

Group eradication

  • Selective breeding.

Outcomes

Prognosis

  • Poor without surgery due to high rate of recurrence.
  • Excellent with resective surgery.

Expected response to treatment

  • Complete recovery.
  • Recurrence of open-mouth jaw locking when insufficient bone was resected.
  • Open-mouth jaw locking occurring on the opposite site (in case of bilateral involvement).

Reasons for treatment failure

 
  • Insufficient bone resection.
  • Bilateral involvement was not recognized.

Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Reiter A M (2004) Symphysiotomy, symphysiectomy and intermandibular arthrodesis in a cat with open-mouth jaw locking - case report and literature review. Journal of Veterinary Dentistry 21 (3), 147-158 PubMed.