Management of acute feline temporomandibular luxation

The lower jaw of the cat on your exam table is displaced to the left (Photo 1). Is the mandible or maxilla fractured? Or is the mandible luxated? If so, right or left? What is the best way to diagnose and treat this problem? Can you as a general practitioner handle it, or must the case be referred to a boarded orthopedic or dental specialist?

Jan Bellows DVM, Dipl. AVDC, Dipl. ABVP

First, the patient needs to be stabilized. In that trauma probably caused this presentation, the patient should be evaluated and treated for life-threatening non-oral injuries if present. Once stable, anesthesia is needed for a thorough oral evaluation.

Anatomically, the condyloid process articulates in the mandibular fossa of the temporal bone. The mandibular fossa, which receives the mandibular condyle, is bordered by the articular eminence (part of the pterygoid bone) on the rostral aspect and the retro-articular process caudally.

Photo 1: Marked trauma to the rostral mandible and maxilla, including right temporomandibular luxation.

The masseter, temporalis and pterygoid muscles hold the condyle tight in the fossa. Between the condyle and fossa there is a meniscus. The joint capsule attaches to the edge of the meniscus, forming two separate compartments, the meniscotemporal and meniscomandibular. The lateral temporomandibular ligament originates from the posterior ventral aspect of the zygomatic arch and inserts on the lateral aspect of the condyloid and retroarticular processes.

Photo 2: DV closed-mouth radiograph revealing rostrodorsal condyloid process luxation (red circle), normal appearing TMJ ( green circle).

Acute lower-jaw displacement commonly occurs secondary to mandibular luxation of the condyloid process, either rostral dorsal or caudal ventrally out of the mandibular fossa. Rarely mandibular ramus fracture, symphyseal separation and maxillary fractures cause acute jaw displacement.

Photo 3: 3-D CAT scan image of different patient with luxated condyloid process.

In most cases it is a unilateral rostral dorsal luxation, where the mandible deviates to the side opposite the luxated joint. Condylar process luxation usually can be confirmed with dorsoventral or ventrodorsal closed-mouth radiographs where the tube head is positioned perpendicular to the temporomandibular joints aimed at the caudal zygoma. Symmetry is critical (Photos 2 and 3).

Photo 4: Insertion of TB syringe between the right carnasial teeth.

Additional rostrocaudal, open mouth, left and right lateral views with the nose raised about 15 degrees off the table, may also be exposed and examined. CT or MRI examination often is helpful to evaluate pathology in cases where plain films are not diagnostic.

The goal of treatment is to return the luxated condylar process into the joint cavity. While the patient is under general anesthesia, a fulcrum (a tuberculin syringe, pencil or non-metallic tubular device) is inserted between the maxillary fourth premolar and mandibular molar on the side of the luxation (Photo 4).

Photo 5: Closure of jaws over the syringe.

The mandible of the luxated side is gently pulled rostrally to disengage the condyle from the dorsal surface of the articular eminence. Then the jaws are opposed on the fulcrum (Photo 5). This action usually causes the affected condyle(s) to pass over the articular eminence to insert into the mandibular fossa. Radiographs are exposed and examined to confirm reduction (Photos 6 and 7).

Unless unstable, post-reduction fixation is not necessary unless there are additional maxillary or mandibular fractures requiring stabilization. Even very slight rotation will distort the appearance of the nasal structures or the coronoid and articular processes of the mandible.

Photo 6: Clinical post-procedure reduction.

Occasionally the fibro-cartilaginous disc in the luxated joint will be torn and folded on itself, preventing the condyle from settling back in place or reluxating following reduction. If the condyle does not properly reduce back into the fossa, condylectomy may be indicated to allow functional occlusion. Condylectomy may also be indicated in cases of fractures of the condylar process and articular recess which are not repairable by fixation of the fragments.

Photo 7: Radiograph confirming both condyloid processes in normal locations.

Caudoventral luxation is less common. The mandibular symphysis deviates posteriorly to the same side as the luxation. These more severe luxations cause significant damage to the joint capsule and ligament. In cases of caudal luxation, open surgery usually is necessary to reconstruct the normal condyle-fossa relationship.

Dr. Bellows owns All Pets Dental in Weston, Fla. He is a diplomate of the American Veterinary Dental College and the American Board of Veterinary Practitioners. He can be reached at (954) 349-5800; e-mail: dentalvet@aol.com