CT of the canine temporomandibular joint

Why the jaw joint needs cross-sectional imaging

The temporomandibular joint (TMJ) is small and deep, and other parts of the skull overlap it on radiographs. In a prospective study of 9 dogs and 15 cats with maxillofacial trauma (Bar-Am et al., Veterinary Surgery, 2008), CT showed 1.6 times more injuries than four-view skull radiographs in dogs, and 2.0 times more in cats. All predefined anatomic features were easy or very easy to identify on CT, while 6 of 26 were very difficult or impossible to identify on any radiographic view. Radiographs scored better than CT for dental occlusion and the integrity of the mandibular body.

When CT is indicated

The authors of the largest CT case series (Arzi et al., Journal of the American Veterinary Medical Association, 2013) describe high-definition CT of the TMJ as an essential part of the work-up for dogs and cats with:

• skull trauma
• malocclusion
• reduced range of motion of the joint
• jaw pain at rest or when opening or closing the mouth

A common presentation is a dog that cannot open or close its mouth. In 37 dogs and cats with locked jaw (Gatineau et al., Journal of Veterinary Dentistry, 2008), 84.0% were dogs, and TMJ ankylosis after fracture was the most common cause (54.0%). Other causes were masticatory muscle myositis, neoplasia, trigeminal nerve paralysis and central neurological lesions, TMJ luxation and dysplasia, osteoarthritis, retrobulbar abscess, tetanus and severe ear disease. Several of these lie outside the joint, so it is usually worth scanning the whole head, not only the joints.

What CT shows

Of 142 dogs that had skull CT at a dentistry and oral surgery service, 43 (30%) had CT findings of a TMJ disorder. In the 41 dogs analysed, disorders were usually present in combination.

Disorder	What the evidence shows
Osteoarthritis	The most common disorder: 32 of 41 dogs (78%), bilateral in 26 of them. Osteophytes were more frequent at the medial than the lateral aspect of the joint (Arzi et al., 2013). In 38 cadaver joints from 19 asymptomatic dogs (McKay et al., Frontiers in Veterinary Science, 2021), subchondral sclerosis was the most prevalent finding on cone-beam CT, and agreement with histology rose with the severity of degenerative change.
Fracture	In 11 dogs, the mandibular fossa (4), the condylar process (3) or both (4) were fractured, at similar frequency (Arzi et al., 2013).
Ankylosis and pseudoankylosis	Confirmed by helical or cone-beam CT in a multicentre series of 12 dogs and 14 cats (Kocsis et al., Frontiers in Veterinary Science, 2025). After surgery, 50% (13 of 26) had complications, and 15.4% (4 of 26) developed re-ankylosis that needed revision.
Dysplasia	In 153 asymptomatic brachycephalic dogs (Paran et al., Journal of Veterinary Dentistry, 2024), CT showed a spectrum of joint shapes. Severe dysplasia was common in Cavalier King Charles Spaniels (69.2%) and French Bulldogs (53.8%). The authors suggest marked changes in these breeds be considered a breed variation.
Tumour	2 of 41 dogs: a multilobular tumour of bone and an osteosarcoma (Arzi et al., 2013).
Septic arthritis	Rare, and typically associated with notable pain, swelling and difficulty opening the mouth. CT, cone-beam CT and/or MRI help reach the diagnosis and plan treatment (Arzi et al., Frontiers in Veterinary Science, 2021).

Fractures: why detail changes the plan

A 2023 review (Arzi, Journal of the American Veterinary Medical Association) states that precise imaging, with conventional or cone-beam CT and potentially MRI, is pivotal for medical and surgical decisions and for prognosis in TMJ fractures. Options include condylectomy, open reduction with internal fixation, or conservative management. Known complications include infection, malocclusion, ankylosis, fibrosis and osteoarthritis. A report that maps every fragment and both joints supports that choice.

TMJ CT protocol at a glance

The key principle is thin slices and a symmetrically positioned skull. The 58-case series found that thick slices or an asymmetrical head make TMJ disorders harder to diagnose, and used 3D reconstructions when needed to assess how the joint bones relate, for example in luxation or subluxation.

What the radiologist looks at

• Is the finding the cause? Only 4 of 15 dogs with osteoarthritis as their only TMJ disorder had clinical signs. In contrast, all dogs and cats with fracture, dysplasia, ankylosis, luxation or tumour had signs. Dysplastic shapes are also common in asymptomatic brachycephalic dogs.
• Bone more than soft tissue. CT shows bone better than the joint’s soft tissues. In veterinary patients, the role of the articular disc and its attachments in TMJ disorders is unknown.
• Every fragment and both joints. Fracture configuration on both sides feeds the choice between surgery and conservative management.
• Causes outside the joint. Ear disease, retrobulbar abscess and neoplasia are listed causes of locked jaw, so the rest of the head is read too.

What your report will include

Every Veheri case is read by a radiologist or neurologist, and when you order you can choose Diplomate-only reporting or the full specialist panel. You can chat directly with the specialist assigned to your case, and a simplified pet owner report helps you explain the findings to the owner.

When you take the report forward:

• Match the findings to the examination. CT findings need to be matched to the oral and orthopaedic examination, because osteoarthritis and dysplasia are often found without signs.
• Intermittent locking with a normal CT does not end the work-up. In an English Bulldog with intermittent closed-mouth jaw locking (Frazho et al., Journal of the American Veterinary Medical Association, 2008), CT with the jaw open and closed showed no TMJ abnormality. Fluoroscopy then showed the coronoid process catching on the zygomatic bone or orbital ligament.
• Muscle and nerve causes of locked jaw, such as masticatory muscle myositis or trigeminal paralysis, usually need other tests alongside imaging.

What to include when you request a TMJ CT report

• signalment: age, breed and sex
• onset and any trauma, including date and mechanism
• whether the jaw locks open or closed, and whether this is constant or intermittent
• range of motion, pain or crepitus on opening, and the occlusion
• skull shape, alongside the breed
• previous fracture treatment or TMJ surgery
• history of ear disease, a listed cause of locked jaw

How Veheri can help

Veheri’s radiologists report veterinary CT studies remotely for clinics. For related problems, see MRI of the masticatory muscles for suspected myositis and CT of the canine skull after head trauma.