Authors of section

Author

Boaz Arzi

Executive Editor

Amy Kapatkin

General Editor

Frank Verstraete

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Intermaxillary fixation (IMF) screw and elastic chain

1. Principles

Restoring functionality and range of motion as well as maintaining occlusion are the primary goals of fixation of TMJ fractures.

Decision making on treatment of TMJ fractures is complex. It should be based on anatomical site, patient size and age, fracture configuration and desired function. CT imaging is essential. Skull or dental radiographs are not adequate to assess the extent of TMJ fractures.

Evidence-based approach to TMJ fractures in dogs and cats is lacking. The treatments recommended here are based on clinical experience of veterinary and human CMF surgeons.

CT of a dog mandible with TMJ fracture

Elastic therapy uses special bone screws joined by elastic bands or chains, to allow controlled movement of the TMJ joint. It allows proprioception input and physiological movement to maintain mandibular function. If proprioception input is delayed due to rigid maxillo-mandibular immobilization, malocclusion may be the final result because the mandible fails to re-establish its proper position.

Elastic therapy in a dog with mandible TMJ fracture

2. Technique

Placement of anchors

With the patient in dorsal recumbency, a small skin incision is made at the alveolar bone, between the canine and the first premolar teeth, on both maxillae and mandibles.

Note: this technique cannot be used in small dogs and cats because the screws are too large.

Skin incision for placement of Intermaxillary fixation (IMF) screws in a dog with caudal mandible fracture

Intermaxillary fixation (IMF) screws are made of 316L stainless steel. They are self-drilling and self-tapping. Pre-drilling may be necessary due to density of the bone.

Placement of Intermaxillary fixation (IMF) screws in a dog with caudal mandible fracture

The IMF screw is designed with a large flat head and a short shaft. The holes are used for elastic bands. When using a chain, the screw head holds it in place.

In medium to large breed dogs, the 8 mm size is the correct screw.
Intermaxillary fixation (IMF) screws in a dog with mandible TMJ fracture

The IMF screw is fully inserted through the drill holes.

Intermaxillary fixation (IMF) screws insertion in a dog with caudal mandible fracture

Elastic chains application

2-4 orthodontic elastic chains are passed between the screws placed on the mandible and maxilla. The screw holds the elastic chain either by passing through the hole or the chain goes around the screw head.

Elastic application on intermaxillary fixation (IMF) screws in a dog with caudal mandible fracture

A flowable dental composite may be applied to cover the screws to avoid soft tissue trauma and to help keep the chain in place.

Dental composite application on intermaxillary fixation (IMF) screws in a dog with caudal mandible fracture

3. Case example

IMF pins and elastic chain placed in a dog with bilateral TMJ fracture.

Example of IMF screw and elastic chain in a dog with mandible TMJ fracture

4. Aftercare

The patient should wear an Elizabethan collar until removal of the construct.

Multimodal analgesia is recommended. Non-steroidal medication for 10-14 days and opioids for the first 5 days post-surgery as needed.

The construct should be cleaned at least once daily using 0.12% chlorhexidine gluconate solution. Another option is to use a water-flossing device.

Weekly clinical recheck to assess function and to gradually loosen the chain is indicated. The goal is to gradually increase the range of motion allowing return to normal function.

The construct is kept in place for 4-6 weeks. Follow-up CT at 6 weeks is recommended. The construct is removed when normal range of motion is achieved.

After screw removal, the mucosa can be sutured with 5-0 poliglecaprone 25 in a simple interrupted fashion.

Panting is not possible, therefore exposure to heat is avoided. To prevent damage to the construct, avoid toys and contact with other animals. If the patient vomits, remove the chains and allow the patient to open its mouth to avoid aspiration pneumonia.