February 2012
Dr Gerhard Steenkamp

A cat is presented after some unknown head trauma. Radiographically you confirmed a luxation of the left condyle.

a) Discuss the procedure to replace the condyle.

b) What post reduction protocol should be followed?

a) Replacing the condyle.

During temporomandibular joint luxation, the condyle of the mandible usually gets displaced rostro-dorsally. In order to replace the condyle there has to be 2 forces applied, one to move the condyle ventral, and another to move it caudal. In order to illustrate this I have used a dog skull, but the principle is exactly the same in cats:

In this lateral view of the skull of a dog, you can clearly see the simulated position of the condyle after luxation (blue pointing hand). It usually luxates dorsally and rostrally. This is due to the fact that the retro-articular process (red arrow) very seldom fractures, making it difficult to luxated ventrally and caudally. The muscles of mastication also contributes to the more common dorso-rostral luxation.

With the patient in dorsal recumbency, a round object, like a pen or pencil, is placed between the first mandibular molar and the 4th maxillary premolar. Do not use objects that are hard, like steel pins, as this may cause damage to the teeth.
A force is then applied to the rostral part of the mandible (green arrow) in a dorsal direction. Because of the fulcrum effect of the pen, the caudal part of the mandible is deflected ventrally (red arrow) and thereby dislodging the condyle from the rostro-caudal position. Once the condyle has been dislodged, the pen is rotated in a clockwise direction (open blue arrow) in order to force the condyle back into its socket.

b) What post reduction protocol should be followed?

1 You should always take a post operative view immediately. This will help you decide if the condyle was replaced or not

                            Pre closed reduction                              Post closed reduction

2 Once you have radiographic confirmation that the reduction was   successful, you need to stabilise the jaws, reducing the size the mouth can open and thereby decreasing the risk of relaxation. To achieve this you can either use interarcade bonding (see photo) in small patients like cats, or a canvas muzzle can be used for dogs. This should be kept in place for at least 3 to 4 weeks in which time fibrosis around the joint will stabilise it and prevent relaxation.

3 Pain control should be optimal for these patients. Use of opioids would strongly be advised, combined with a potent anti-inflammatory drug.

4 Soft food should be offered as these patients cannot chew normally.

5 When the animal is presented 3 to 4 weeks later, a follow-up radiograph should be made to confirm the status of the TMJ.

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