Treating TMJ ankylosis in young cats

A case study

Ever since she was found as a stray, Phantom had a problem. The 8-month-old spayed female domestic shorthair cat was presented to me because she was having difficulty eating and drinking.

On physical examination, I was able to open her mouth only 2 millimeters on the left and 6 millimeters on the right, as measured between the maxillary and mandibular incisor teeth (Figure 1). Abnormal spacing was present between the maxillary and mandibular incisor teeth, and the right maxillary second incisor tooth was missing. An uncomplicated cusp fracture of the right maxillary canine tooth was seen.

There was a Class 4 malocclusion (maxillomandibular asymmetry) in that the left mandible was not aligned with the right mandible in the rostrocaudal, side-to-side and dorsoventral dimensions. The right mandibular canine tooth was mesioverted (tipped rostrally), likely due to chronic pressure from the tongue.

Just Getting By

Phantom ate and drank by sneaking the tongue through the 6-mm space on the right side of the mouth. The remainder of her physical exam was unremarkable except for a 2/6 systolic murmur previously evaluated by a cardiologist.

Unlike other similarly afflicted cats I have seen, Phantom was in good body condition, suggesting she was doing well getting the calories that she needed through her partially opened mouth. A now-healed laceration of the right rostral tongue had caused a forked tongue that was lined up with the right mandibular canine tooth. Palpation of the structures of the skull showed an indentation in the area of the left zygomatic arch.

I asked the owners if Phantom had sustained head trauma. They thought trauma may have occurred before adoption. We talked about the possibility of unilateral or bilateral TMJ ankylosis.

Actually, extra-articular pseudoankylosis is more common than true joint involvement. It is seen most commonly in cats that have sustained some type of maxillofacial trauma, usually at a very young age.

CT Scan

TMJ ankylosis
Figure 2-A: A three-dimensional reconstruction of a CT scan helped with the diagnosis. Here, the right side was normal. Figure 2-B: The left side showed a malformed zygomatic arch and left mandibular ramus. The area of ankylosis is medial to the rostral zygoma.

Prior to surgery, we needed to confirm our suspected diagnosis by obtaining a CT scan. Anesthesia required a tracheostomy since the mouth did not open wide enough to perform normal endotracheal intubation.

After a critical care specialist performed a tracheostomy, we moved Phantom into the CT scanner. The scan showed no ankylosis of either TMJ joint, but a large callus was present between an abnormally formed left mandibular ramus and an abnormally formed zygomatic arch (Figures 2-A, 2-B and 2-C). Three-dimensional reconstructions are helpful for visualizing the area of surgical interest and for ruling out the need for bilateral surgery.

Time for Surgery

TMJ an
Figure 2-C: A ventrodorsal view shows a bony fusion between the left mandibular ramus and malformed zygomatic arch.

Phantom was then moved to the operatory. A 3-centimeter linear incision was made from rostral to caudal, starting 5 millimeters caudal to the left lateral canthus, extending caudally directly over the zygomatic arch.

The zygomatic arch was removed with rongeurs to expose the large callus connecting the arch and the lateral surface of the mandibular ramus. The callus was slowly and methodically removed with rongeurs, along with a portion of the ramus, until the range of motion was found to be acceptable by having an assistant check this under the drape intraoperatively.

After an acceptable range of motion was achieved, and after acceptable space was established between the remaining zygoma and the remaining portion of the ramus, adjacent temporalis muscle was positioned between the two bones to decrease the chances of reankylosis. A condylectomy was not needed to achieve an acceptable range of motion, which was measured at 34 millimeters immediately postoperative.

At-Home Care

Phantom was kept overnight to provide IV fluids and opioid injections. She was discharged the following day and sent home with prednisolone—0.5 mg/kg twice daily—to utilize its catabolic effects and hopefully decrease the likelihood of reankylosis.

A week’s supply of amoxicillin/clavulanate was prescribed, and a fentanyl transdermal patch was placed for four days, followed by oral buprenorphine after the patch was removed. After allowing for a few days of healing, the owners were directed to attempt basic range of motion exercises to minimize the likelihood of reankylosis.

The range of motion was similar when Phantom was re-evaluated one week after surgery. The tracheostomy site had not fully healed. Oral medications were being administered without a problem, and Phantom seemed comfortable.

Three weeks postoperatively, Phantom presented for another recheck. The tracheostomy site was fully healed and the range of motion measured at 40 millimeters. Weight gain was noted, from 3.54 kilograms preoperatively to 4.14 kilograms at the three-week recheck.

Lessons Learned

The first time she saw that Phantom could open her mouth, the owner literally cried. Every patient we see provides the potential for a life lesson. The story of Phantom reminds us not to take for granted the little things in life, such as being able to open our mouth.

This case describes one example of how computed tomography has revolutionized our diagnosis of head and neck disease. Next month I will further discuss the importance of this advanced diagnostic tool.

Until then, happy National Pet Dental Health Month.


  1. Meomartino L, Fatone G, Brunetti A, Lamagna F, Potena A. “Temporomandibular Ankylosis in the Cat: A Review of 7 Cases.” J Small Anim Pract. 1999; 40(1):7-10.
  2. Gatineau M, El-Warrak AO, Marretta SM, Kamiya D, Moreau M. “Locked Jaw Syndrome in Dogs and Cats: 37 cases (1998-2005).” J Vet Dent. 2008; 25(1):16-22.
  3. Arzi B, Cissell DD, Verstraete FJ, Kass PH, DuRaine GD, Athanasiou KA. “Computed Tomographic Findings in Dogs and Cats With Temporomandibular Joint Disorders: 58 cases (2006-2011).” J Am Vet Med Assoc. 2013; 242(1):69-75.

Dr. John Lewis practices veterinary dentistry and oral surgery at NorthStar Vets in Robbins-ville, N.J. Columnists’ opinions do not necessarily reflect those of Veterinary Practice News. 

Originally published in the February 2017 issue of Veterinary Practice News. Did you enjoy this article? Then subscribe today! 

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One thought on “Treating TMJ ankylosis in young cats

  1. Our sweet boy Mojito Mo-Mo has suffered from Ankylosis since he was 4 months old We have done everything we could for him. We have had 27 teeth pulled which as you know is very difficult since he cannot have the normal airway anesthesia. It’s been a stressful 6 years but he weighs 10 plus pounds! His Dad makes him chicken with chicken liver pate! Anyway, I have only heard MoMo meow once, then his mouth closed. He is an amazing cat and quite the comedian. I was wondering what it would take to safely operate on the right side of his face to release the ankylossis that would allow him to live a more normal life. And yes I know that there is a possibility of reankylosis. I would love to hear from you about our wonderful and amazing MoMo We live in northeastern Oregon State