Symphysiotomy, Symphysiectomy, and Intermandibular Arthrodesis in a Cat with Open-Mouth Jaw Locking — Case Report and Literature Review

Open-mouth jaw locking in a 5-year-old Persian cat: a case report

Open-mouth jaw locking is an uncommon condition in feline patients. A 5-year-old neutered male Persian cat was evaluated for an acute inability to close its mouth and ptyalism. The general physical examination was unremarkable. A complete oral examination revealed a reduced vertical range of motion, as well as an asymmetric malocclusion with severe displacement of the mandibles to the left. Advanced diagnostic imaging included computed tomography (CT), which revealed a typical brachycephalic conformation, skeletal malocclusion and a bilateral temporomandibular joint (TMJ) subluxation, with the left coronoid process of the mandible abnormally positioned ventrolateral to the zygomatic arch. The open-mouth jaw locking was manually reduced and resolved. Once the coronoid process was repositioned, a second CT scan was performed and confirmed complete reduction of the TMJ subluxation. Supportive treatment with meloxicam was administered and a loose-fitting tape muzzle and Elizabethan collar were applied for two weeks. There was no recurrence of open-mouth jaw locking at long-term follow-up. This case report highlights the relevance of CT imaging and 3-dimensional reconstruction in the diagnosis of this unusual condition.

Normal variation of clinical mobility of the mandibular symphysis in cats

Introduction

The primary objective of this retrospective study was to document the normal variation of clinical mobility of the mandibular symphysis in cats and possible associations with bodyweight, age, sex, sexual status, breed and skull morphology. Secondarily, the radiographic appearance of the mandibular symphysis and possible associations with the analyzed data were evaluated.

Materials and methods

Two hundred and sixteen cats of 15 different breeds that underwent maxillofacial, oral and dental procedures from April 2015 to December 2021 were included. Clinical mobility was evaluated under general anesthesia using a 0 to 3 scale in lateromedial (LM) and dorsoventral (DV) directions. The symphysis was radiographically classified on the occlusal radiographic view of the rostral mandibles as fused or open, and with parallel or divergent margins.

Results

Bodyweight ranged from 2.2 to 12.5 kg (median 4.0 kg), age from 4 months to 17 years and 4 months (median 6 years and 4 months). At the first evaluation DV symphyseal mobility was 0 in 177 cases (82%), 1 in 32 cases (14.8%) and 2 in 7 cases (3.2%), LM mobility was 0 in 61 cases (28.3%), 1 in 110 cases (50.9%) and 2 in 45 cases (20.8%). 81.1% of the radiographs were included in the statistical analysis. Three symphyses (1.6%) were classified as fused and 190 (98.4%) as open, 129 (68.8%) having divergent margins and 61 (31.6%) parallel. One hundred and forty-eight cases (76.7%) did not show the presence of odontoclastic replacement resorption on the canine teeth (TR subgroup 1), 23 (11.9%) showed stage ≤3 lesions (TR subgroup 2) and 22 (11.4%) stage 4 lesions (TR subgroup 3). Logistic regression models exploring factors that affected DV and LM mobility were statistically significant (p < 0.0001; p < 0.0001) with an increase in LM mobility predicting an increase in DV mobility, and vice versa. An increase in DV mobility was associated with an increase in age and in having resorptive lesions. A decrease in LM symphyseal mobility was associated with being brachycephalic.

Conclusion

The great majority of cases showed some degree of LM symphyseal mobility, and 18% showed DV mobility. Symphyseal bony fusion is rare but possible.

Etiology, clinical presentation, and outcome of temporomandibular joint luxation in cats: 21 cases (2000-2018)

This study was performed to report etiology, clinical presentation, treatment, and outcome of temporomandibular joint (TMJ) luxation in 21 cats (2000-2018). TMJ luxation was diagnosed by either dental radiography or computed tomography (CT). Causes for TMJ luxation included altercation with a dog (38%), hit-by-car (19%), unknown (19%), fall (19%), and ran into inanimate object (5%). The most common complication was development of permanent malocclusion (24%), followed by reduced vertical mandibular range of motion (5%). Reduction of TMJ luxation was successful in 94.7% of the cases. Reduction of the TMJ luxation was significantly associated with time from injury to treatment. No other significant associations were observed between cause of injury, type of TMJ stabilization, and outcome. TMJ luxation in cats carries an excellent prognosis with early joint reduction and supportive care. Concurrent dental trauma and maxillofacial injuries are common, and all patients with head trauma must be stabilized and evaluated with a thorough examination.

Morphometry and Morphology of the Articular Surfaces of the Medial Region of the Temporomandibular Joint in the Felis Catus (Domestic cat) - A Cone Beam Computed Tomography Study

The articular surfaces of the temporomandibular joint (TMJ) in the cat consist of the articular head of the condylar process of the ramus of the mandible and the mandibular fossa of the petrous part of the temporal bone. Anatomic conformation of the TMJ articular surfaces can vary; however, this has not been studied in the cat. Thus, the aim of this study was to characterize the conformation of the medial region of the TMJ in mesocephalic adult cats as well as to determine the articular relationship by measurement of the degree of coverage of the mandibular fossa over the articular head. This was accomplished by assessing 60 TMJs from 30 mesocephalic adult cats by means of cone-beam computed tomography (CBCT). The width and depth of the mandibular fossa, and the degree of coverage of the mandibular fossa were evaluated using parasagittal reconstructions of the medial aspect of the TMJ by two observers. No statistically significant difference was observed during the intra and interobserver evaluation of the mandibular fossa width and depth and the degree of coverage of the mandibular fossa over the articular head. P-values for the studied variables were greater than 0.05. The resulting measurements demonstrated a concave mandibular fossa with a prominent retroarticular process and a poorly developed articular eminence; a well-defined rounded articular surface, and a high degree of coverage (171°) of the mandibular fossa over the articular head. In conclusion, the articular surfaces at the medial aspect of the TMJ displayed elevated geometric similarity, with an articular head of the condylar process deeply seated in the mandibular fossa.

Comparative morphometry of the temporomandibular joint in brachycephalic and mesocephalic cats using multislice CT and cone beam CT

OBJECTIVES

The purpose of this study was to analyse and compare morphometric measurements of the temporomandibular joint (TMJ) in two groups of cats with brachycephalic and mesocephalic craniofacial skull conformations using multislice CT and cone beam CT.

METHODS

CT records of 20 cats without TMJ pathology were included in the study, and were divided into two groups according to those with mesocephalic or brachycephalic skull conformation. Width and depth of the mandibular fossa, width and height of the head of the mandible, and two different angles were measured in 40 TMJs.

RESULTS

TMJ conformation differed between groups: 3/6 parameters were statistically different. Brachycephalic cats had a significantly narrower mandibular fossa, a shorter head of the mandible and a wider angle of congruence (angle 2).

CONCLUSIONS AND RELEVANCE

The results provide morphometric measurements that can serve as a reference tool for the veterinary radiologist and surgeon when TMJ evaluation is necessary. Moreover, the study identified significant differences between the two craniofacial skull conformations.

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

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.

Traumatic Dentoalveolar and Maxillofacial Injuries in Cats: Overview of diagnosis and management

PRACTICAL RELEVANCE

Maxillofacial and traumatic dentoalveolar injuries can cause pain and inflammation, and reduce function of the mouth, impacting a cat's quality of life. Many traumatically induced feline fractures have been reported to involve the mandible or skull and, in cats with maxillofacial trauma, traumatic dentoalveolar injuries are particularly prevalent. Traumatic dentoalveolar injuries can also often be found in otherwise healthy cats.

CLINICAL CHALLENGES

Some traumatic dentoalveolar injuries require emergency treatment; timely recognition and managment is therefore important for achieving the optimal outcome. Multiple approaches exist for the management and repair of maxillofacial traumatic injuries. However, those for traumatic dentoalveolar injuries may be more limited.

AUDIENCE

This review is aimed at feline and general practitioners, as well as veterinarians with expertise in dentistry.

EVIDENCE BASE

The authors draw on their clinical experience and evidence from the literature, where appropriate, to produce an overview of foundation guidelines. It is hoped that this will serve as a stimulus for deeper consideration as to what constitutes 'best practice' principles for cats with traumatic dentoalveolar and maxillofacial injuries.

Maxillofacial Injuries and Diseases That Cause an Open Mouth in Cats

Oral and maxillofacial disorders in the cat can present as an inability to close the mouth and reaching an accurate diagnosis can be challenging if all of the differentials are not systematically considered. This review focuses on the six conditions that commonly result in a cat being unable to close the mouth. Differential diagnoses include: luxation of the temporomandibular joint, fracture of the temporomandibular joint, caudal mandibular fracture, impingement of the coronoid process of the mandible on the zygomatic arch, mechanical obstruction, and neuropathy. Maxillofacial anatomy, including the temporomandibular joint, muscles of mastication and their innervation will be reviewed. This paper primarily focuses on review of the relevant literature describing each disorder and the diagnostic procedures and treatment options that should be considered when evaluating a cat that is unable to close its mouth. Emphasis is placed on the importance of a complete intraoral examination and evaluation of occlusion to allow the clinician to identify the cause for this clinical sign in cats since periodontal disease causing tooth-to-tooth contact is a common and often unrecognized cause for open mouth in cats.

Bilateral Extracapsular Soft-Tissue Ossification Affecting Range of TMJ Motion in an Airedale Terrier

A 3 mo old female Airedale terrier presented with decreased range of motion of the temporomandibular joint (TMJ), which was first recognized at weaning. Computed tomography (CT) revealed abnormal, bilateral ossification of the soft tissues extending from the region of the tympanic bullae to the medial aspect of the angular process of each mandible. Those ossified structures most closely approximated the location of the lateral pterygoid muscles. The ossified structures were present at presentation and initially manifested as complete ossification on the right side. The condition progressed to complete bilateral ossification by 3 yr of age. The mandibular condyles associated with the temporomandibular joints were malformed. The patient had severe mandibular distoclusion with deviation of the mandible to the left. The left mandibular cheek teeth were positioned in a caudal cross bite. A single treatment of manual stretching and breakdown of the ossified muscle of mastication by placement of tongue depressors within the oral cavity resulted in no increase in TMJ range of motion as measured by the incisal opening. This is the first reported case of spontaneous false ankylosis of the TMJ in an Airedale terrier.

Lip avulsion and mandibular symphyseal separation repair in an immature cat

A 12-week-old kitten was presented for symphyseal separation, comminuted rostral fractures of the mandibles, avulsion of the mandibular lip, andfractured teeth. Oral examination and intraoral dental radiographs demonstrated a mandibular symphyseal separation and the presence of developing tooth buds. Cerclage wire was placed circumferentially around the mandibles for 2-weeks to provide stabilization of the mandibular symphyseal separation. Clinical examination 9.5-months following surgery demonstrated normal occlusion with enamel hypoplasia affecting the mandibular canine teeth. Intraoral dental radiographs showed a partial bony union of the mandibular symphysis and vital, developing mandibular canine teeth.

Computed Tomography and Partial Coronoidectomy for Open-Mouth Jaw Locking in Two Cats

Open-mouth jaw locking in the cat has traditionally been minimally evaluated with diagnostic imaging. Multiple methods have been described for surgical management of this problem. This report describes the use of computed tomography to diagnose open-mouth jaw locking in 2 cats secondary to ventrolateral displacement of the coronoid process in relation to the zygomatic arch. In these 2 cases, a previously unreported surgical approach whereby the coronoid was not reduced before partial coronoidectomy was used with successful outcomes.

Significant association between tooth extrusion and tooth resorption in domestic cats

Abnormal extrusion of canine teeth is often noted in middle-aged and geriatric domestic cats. The same age group of cats also is commonly affected by tooth resorption (TR). This study explored the relationship between these two phenomena of unknown etiology. Using digital radiography, the distance between the alveolar margin (AM) and cementoenamel junction (CEJ), referred to as the AM-CEJ distance, was measured in clinically and radiographically healthy maxillary canine teeth of 24 TR-affected and 29 TR-free cats. The mean AM-CEJ distance of maxillary canine teeth of cats with and cats without TR was 2.68-mm and 2.22-mm, respectively. An analysis of covariance adjusting for age revealed a significant correlation (p = 0.02) between tooth extrusion and TR. Extrusion of the maxillary canine teeth became clinically apparent when an AM-CEJ distance of 2.5-mm or greater was evident in the absence of horizontal or vertical alveolar bone loss. Based on this criterion, 15 of 24 cats with TR (63.0 %) exhibited extrusion of maxillary canine teeth, compared to 9 of 29 cats without TR (31.0 %). Four extruded and five non-extruded maxillary canine teeth were evaluated histologically. Cementum of extruded teeth was significantly thicker compared to that of non-extruded teeth. Four of 4 canine teeth with extrusion (100 %) showed histological evidence of resorption, compared to 1 of 5 canine teeth without extrusion (20.0 %). These results suggest that tooth extrusion is linked to or may be caused by similar factors responsible for the development of TR.

Use of three-dimensional computed tomography for diagnosis and treatment planning for open-mouth jaw locking in a cat

CASE DESCRIPTION

A 2.5-year-old spayed female Persian cat was evaluated for acute inability to close its mouth.

CLINICAL FINDINGS

A wry-mouth malocclusion was evident, and the right side of the mandible was longer than the left side. The right mandibular tooth row appeared to be lowered. The lower jaw was persistently maintained in an open position. The presumptive diagnosis was open-mouth jaw locking. Diagnostic imaging with computed tomography and 3-dimensional reconstruction was performed for definitive diagnosis and to achieve a better understanding of the lesions. Imaging revealed locking of the right ramus of the mandible, which was displaced ventrolaterally, causing the coronoid process to impinge on the right zygomatic arch.

TREATMENT AND OUTCOME

A bilateral partial ostectomy of the rostroventral margins of the zygomatic arches with an autogenous fat graft implantation was performed. The cat recovered without complications and by the following morning was bright, alert, and responsive and eating canned cat food comfortably. One year after surgery, the owner reported that the cat had continued to function well, was eating normally, and had not had any observed locking episodes since surgery.

CLINICAL RELEVANCE

Unlike radiographic imaging, computed tomography may be used to create 3-dimensional reconstructions of structures in cases of suspected open-mouth jaw locking; improve evaluation of the lesions; and improve decision-making and client education for diagnosis, treatment options, and prognosis.