Fractures and Dislocations of the Mandible

Chapter 97 Fractures and Dislocations of the Mandible

Richard M. Jerram

Mandibular fractures account for approximately 2% of all fractures in dogs and 15% of all fractures in cats. Most mandibular fractures occur as a result of automobile trauma, although dog bites and gunshots are also reported causes. Pathologic fractures can occur with severe dental or metabolic disease. Young cats and dogs (<2 years of age) are more likely to have mandibular fractures. Mandibular fractures present the veterinarian with some unique clinical management considerations. Concurrent head and thoracic trauma make anesthe-tic management challenging, the placement of oral endotracheal tubes makes an accurate assessment of occlusion difficult, and providing postoperative oral nutrition can be critical in determining clinical success. Dislocations of the temporomandibular joints occur less frequently and can occur in conjunction with mandibular fractures or other facial trauma.

ANATOMY

The mandible consists of left and right halves that are joined by a rigid fibrous symphysis at the rostral midline. Each half is further divided into the horizontal body and the vertical ramus.

• The horizontal body contains the teeth along the alveolar border. The alveolar border is the tension surface of the mandible.
• The mandible has a mandibular canal (not a medullary cavity like axial long bones) that contains the mandibular artery and vein as well as the mandibular alveolar nerve that supply the teeth and soft tissues of the lower jaw.
• The mandibular vessels and nerve enter the canal caudally at the mandibular foramen on the medial side at the junction of the body and ramus.
• The mandibular canal opens cranially at three mental foramina located lateral to the premolar teeth.
• The condyloid process of the ramus articulates with the temporal bone in the mandibular fossa forming the temporomandibular joint. This joint contains a thin articular disc (meniscus) in the dog.
• The muscles of mastication (masseter, temporalis, pterygoideus, and digastricus) insert on the coronoid and angular processes of the vertical ramus.

CLINICAL SIGNS

Clinical signs can vary but include the following:

• Asymmetry of the jaw
• Crepitus on mandible manipulation
• Oral hemorrhage
• Oral pain
• Concurrent head and thoracic trauma

DIAGNOSIS

• Diagnosis is usually based on history and clinical examination.
• Careful oral examination is necessary as there may be more than one fracture present.
• Standard dorsoventral and lateral radiographs are performed first.
• Oblique and open-mouthed views may highlight fractures undetected on standard radiographs.
• Carefully evaluate radiographs to identify other skull fractures.
• Computed tomography (CT) scans, where available, can provide a three-dimensional impression of the fracture(s) present.

SURGICAL PROCEDURES

Preoperative Considerations

Key Point

Manage concurrent head, upper airway, and thoracic trauma prior to performing mandibular fracture repair.

• Establish a patent airway, control hemorrhage, and treat shock.
• Obtain thoracic radiographs and manage any pleural space disease—that is, pneumothorax, hemothorax, diaphragmatic hernia, or pulmonary contusion.
• Record an electrocardiogram to assess for the presence of cardiac arrhythmias secondary to traumatic myocarditis.
• Complete a neurologic examination of the head and treat any possible brain edema or hemorrhage.

Anesthetic Considerations

• Endotracheal intubation is essential to reduce the risk of aspiration of blood and debris.
• To assess dental occlusion intraoperatively, place the endotracheal tube through a pharyngotomy incision.

Key Point

Use an endotracheal tube placed through a pharyngotomy incision to help establish normal occlusion during fracture repair.

• Most mandibular fractures are open; therefore, prophylactic antibiotics are recommended prior to surgery. Cefazolin (20 mg/kg IV) is preferred.

Surgical Principles

Adherence to several basic principles of mandibular fracture management will improve clinical success and reduce complication rates.

• Restore dental occlusion. Accurate anatomic reconstruction of fracture fragments will restore normal occlusion. Use an endotracheal tube placed through a pharyngotomy incision.

Key Point

The goal of mandibular fracture repair is to restore normal dental occlusion.

• Rigid fixation and neutralization of the fracture forces provides a rapid return to function.
• Carefully handle soft tissues. Avoid entrapment of soft tissues, remove devitalized tissue, and avoid excessive elevation of soft tissues from bone.
• Avoid further dental trauma. Remove only teeth that are luxated or fractured. Leave teeth in the fracture site that will contribute to stabilization of the fracture.
• Intramedullary pinning of mandibular fractures is not recommended due to the shape of the mandibular canal and the presence of the tooth roots, major vessels, and nerves.

Equipment

• Standard general surgical pack
• Orthopedic wire (various sizes) and wire twisters
• External skeletal fixation devices (generally small size)
• Bone plates and screws (generally sizes 1.5 mm to 2.7 mm)

Postoperative Care

• Provide appropriate nutrition during the recovery period.
• Cats, particularly, are less willing to eat after facial trauma. Place an esophagostomy feeding tube at the time of mandibular surgery.

Key Point

In cats, place an esophagostomy feeding tube for postoperative nutrition (see Chapter 3).

• Gastrostomy feeding tubes may be placed endoscopically if long-term tube feeding is expected (see Chapter 3).
• If a feeding tube is not used, feed a soft gruel for 4 weeks after surgery.
• Prevent animals from chewing toys or hard objects such as bones and sticks.
• Daily oral flushing with a dilute chlorhexidine solution will reduce oral bacterial contamination and clean implants placed around the teeth.

Complications

• Malocclusion is the most important complication postoperatively. Evaluate patients every 2 weeks to ensure normal occlusion is being maintained. Further surgery may be necessary if malocclusion occurs.
• Osteomyelitis occurs rarely; long-term (6–8 weeks) treatment with appropriate antibiotics is required.
• Implant failure and non-union can occur and are generally related to poor preoperative planning and implant choice.
• Damage to remaining teeth from either the original trauma or the surgery may result in dental pain or infection after the fracture has healed. Tooth extraction or endodontic therapy may be indicated.
• Temporomandibular joint ankylosis can occur following trauma to the condyloid process of the mandible. Resection of the condyloid process (condylectomy) or osteophytes may be necessary.

MANDIBULAR SYMPHYSEAL SEPARATIONS

Separation of the mandibular symphysis accounts for the majority of the mandible fractures identified in cats. Care should be taken to ensure that there is no concurrent trauma to the caudal aspect of the mandible, particularly in the area of the condyloid processes. The fixation method should provide normal occlusion. Wire stabilization is the technique of choice.

Technique

1. Place the animal in dorsal recumbency and clip and prepare the chin for aseptic surgery.
2. Make a small stab incision in the ventral mandibular skin at the level of the caudal edge of the mandibular symphysis.

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Aug 27, 2016 | Posted by in SMALL ANIMAL | Comments Off on Fractures and Dislocations of the Mandible

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