Open-mouth jaw locking in cats: a literature review and use of CT in three cases

Abstract

Case series summary: This report summarises and reviews the published cases of open-mouth jaw locking in cats and describes three further cases. Case 1 was a 5-year-old, 5.3 kg male neutered domestic shorthair cat. CT identified changes consistent with temporomandibular joint (TMJ) dysplasia with osseous degenerative changes, and the cat subsequently underwent bilateral partial zygomectomy with bilateral partial coronoidectomy. Case 2 was a 10-year-old, 6.0 kg male neutered Exotic Shorthair. Aside from a fracture of the left maxillary canine tooth crown and absence of the left maxillary fourth premolar tooth, no abnormalities were found on CT scan. The cat also underwent bilateral partial zygomectomy with bilateral partial coronoidectomy. The third case was a 1-year-old, 4.0 kg male neutered Persian cat. Changes on CT were consistent with bilateral TMJ dysplasia, and the cat underwent staged bilateral partial zygomectomy with bilateral partial coronoidectomy. There was no recurrence of open-mouth jaw locking in any of the cases on long-term follow-up.

Relevance and novel information: Open-mouth jaw locking has been reported in cats of a wide range of ages, from 1-10 years. Cats with all skull types (brachycephalic, mesaticephalic and dolichocephalic) may be affected, but brachycephalic breeds seem to be over-represented. A CT scan with the jaw locked in place is recommended for diagnosis and surgical planning purposes; two of the cases reported here document the first cases of TMJ dysplasia in cats to be definitively diagnosed using CT. Trauma and symphyseal or TMJ laxity may also predispose to development of the condition. Partial coronoidectomy and partial zygomatic arch resection performed alone or in combination are generally successful at preventing recurrence. Bilateral partial zygomectomy with bilateral partial coronoidectomy has not previously been reported as a surgical treatment, and is recommended when open-mouth jaw locking occurs bilaterally.

Figure 1

(a) Case 1, sagittal CT scan showing subluxation of the left temporomandibular joint (arrow), retroarticular process elongation (arrowhead) and dorsally flattened condyloid process. (b) Sagittal CT of a normal feline skull at the same level for comparison. 1 = condyloid process; 2 = mandibular fossa of the temporal bone; 3 = temporal bone; 4 = mandible; 5 = external acoustic meatus; 6 = orbit

Figure 2

Case 1, CT three-dimensional reconstruction of the skull showing displacement of the left coronoid process ventrolateral to the zygomatic arch (arrow)

Figure 3

Case 1, intraoperative photograph showing ventrolateral displacement of the left coronoid process (arrow). Z = zygomatic arch; C = coronoid process

Figure 4

Case 2, CT three-dimensional reconstruction of the skull showing luxation of the right temporomandibular joint (arrowhead) and displacement of the right coronoid process ventrolateral to the zygomatic arch (arrow)

Figure 5

Case 2, transverse CT scan showing displacement of the right coronoid process ventrolateral to the zygomatic arch (arrow). Z = zygomatic arch, C = coronoid process, M = mandible, O = orbit, NP = nasopharynx

Figure 6

(a) Case 3, three-dimensional CT reconstruction of the skull showing the subluxated left temporomandibular joint during left open-mouth jaw locking. Flattening of the left condyloid process and mandibular fossa of the temporal bone (arrow) is evident and there is widening of the joint space. Courtesy of Clinica Veterinaria dell'Orologio, Sasso Marconi, Bologna, Italy. (b) Three-dimensional CT reconstruction of a normal feline skull for comparison. 1 = condyloid process; 2 = mandibular fossa of the temporal bone; 3 = zygomatic arch; 4 = mandible; 5 = external acoustic meatus; 6 = hyoid apparatus; 7 = temporal bone

Figure 7

(a) Case 3, ventrodorsal extraoral radiograph of the right temporomandibular joint showing displacement of the right coronoid process ventrolateral to the zygomatic arch (arrow) during right open-mouth jaw locking. The mandible is rotated and appears oblique because of the jaw locking. (b) Ventrodorsal extraoral radiograph of a normal feline skull for comparison. Z = zygomatic arch; C = coronoid process