Mandible Fracture

Etiology

The mandible is one of the most commonly fractured facial bones, along with the nasal and zygomatic bones. Most frequently, fractures are a result of trauma, such as motor vehicle accidents, physical altercations, industrial accidents, falls, and contact sports. For this reason, it is critical to evaluate patients with mandible fractures for other associated traumas, to include cervical spine and traumatic brain injuries.[1]

Epidemiology

Vehicular accidents and altercations are the primary causes of mandibular fractures in the United States and throughout the world. In an urban trauma setting, altercations account for most fractures (50%), and motor vehicle accidents are less likely (29%). Males suffer approximately three times as many mandible fractures as females, with the majority occurring in the third decade of life.[1][2]

Mandibular fractures are uncommon in children under the age of six, likely because of the relative prominence of the forehead compared to the chin. When they do occur, they are often greenstick fractures.

Pathophysiology

Because of its ring-like structure, multiple fractures are seen in more than 50% of cases. The most common combination of injuries is a parasymphyseal fracture with a contralateral angle or subcondylar fracture. While studies vary in reported fracture frequencies, the most common individual fracture sites are the body, the condyle, and the angle. The symphyseal/parasymphyseal area is less commonly fractured, and the ramus and coronoid process are rarely involved. In automobile accidents, the condyle was the most common fracture site; whereas, the symphysis was most commonly fractured in motorcycle accidents. In assault cases, the angle is the most common fractured site.[3]

Mandible fractures can be classified by favorableness, based on the association between the direction of the fracture line and the way muscle action either reduces or distracts the fracture fragments. Mandibular fractures are favorable when muscles tend to draw the fracture fragments together and unfavorable when muscle forces displace fracture fragments. An example of a favorable fracture is an obliquely-oriented fracture just anterior to the angle, with the superior aspect of the fracture line situated posterior to the inferior aspect; this configuration causes the masseter to pull the fragments together and stabilize the fracture, meaning that surgical reduction may not be required.[4]

Depending on the fracture locations, the patient can present with trismus, dental malocclusion, swelling, and tenderness externally and intraorally. Damage to the inferior alveolar nerve may result in anesthesia to the lower lip and chin. Loose teeth and intraoral lacerations with or without bony step-offs may be present as well.

Patients with mandibular fractures frequently have other associated injuries (43%). The most common associated injuries include head injuries (39%), head and neck laceration (30%), midface fractures (28%), ocular injuries (16%), nasal fractures (12%), and cervical spine fractures (11%)[1]

The presence of lower wisdom teeth may increase the risk of fracture of the angle of the mandible. Patients with a mandibular fracture that have wisdom teeth also have a higher infection risk (16.6%) when compared with the ones without wisdom teeth (9.5%).[1]

In the pediatric population, any fracture of the mandible may damage permanent teeth. Follow up with the oral and maxillofacial surgeon or pediatric dentist is indicated.

History and Physical

Patients will present with mandibular pain, facial asymmetry, deformity, and dysphagia. Malocclusion, a decreased range of movement of the temporomandibular joint, trismus, or lower lip numbness can also be present. Determining the mechanism of injury is important. In a motor vehicle accident, the patient usually suffers from multiple, compound, or communicated mandibular fractures. Mandibular fracture from an altercation is more likely to be single, simple, and nondisplaced.

On physical examination, one should inspect the maxillofacial area for deformity, including ecchymosis and edema. A careful intraoral examination should be performed; sublingual hematoma is suggestive of an occult mandibular fracture. One should also look for any malocclusion, trismus, or facial asymmetry.

While it is often difficult to determine the patient’s preoperative dental occlusion status, it is helpful if dental records are available to serve as a guideline for surgical reduction of the fracture or fractures. The system most commonly used to characterize dental occlusion is the Angle classification. In class I occlusion, the mesiobuccal cusp of the first maxillary molar fits into the buccal groove of the first mandibular molar. In class II occlusion – an overbite – the mesiobuccal cusp of the first maxillary molar sits mesial (anterior) to the buccal groove of the first mandibular molar. In class III occlusion – an underbite – the mesiobuccal cusp of the first maxillary molar sits distal (posterior) to the buccal groove of the first mandibular molar.[5]

The tongue-blade bite test is a quick and inexpensive diagnostic tool for predicting mandibular fractures. It has a sensitivity of 88.5% and a specificity of 95%. It can be performed by asking the patient to bite down firmly on a tongue depressor and keep the tongue depressor clenched between the teeth. The examiner should twist the tongue blade. If there is no fracture of the mandible, the examiner should be able to break the blade. In the presence of a mandibular fracture, the patient opens his or her mouth because they experience pain from the fracture, and the tongue depressor remains intact.[6]

Evaluation

Diagnosis of mandibular fractures requires radiographic imaging studies, including mandibular series, panorex, and computed tomography (CT) scan. A mandibular series includes an anteroposterior view, bilateral oblique views, and a Towne view. They are best for evaluating the condyles and neck of the mandible. Dental panoramic view, or panorex, is best for evaluating the symphysis and the body of the mandible. CT scan is indicated if associated facial fractures are suspected. A chest radiograph is necessary for an unconscious patient with missing teeth to rule out aspiration. Laboratory studies are generally not indicated unless urgent or emergency surgery is anticipated. In those situations, basic screening labs should be obtained including complete blood count, complete or basic metabolic panel, type and screen, and prothrombin time or INR for patients who are on warfarin for anticoagulation.[7]

Treatment / Management

Patients with mandibular fractures frequently have associated injuries. Initial treatment should be directed toward immediate, potentially life-threatening injuries such as airway obstruction, major hemorrhage, cervical spine injury, and intracranial injury. If oral intubation cannot be performed, indicated surgical airway may be required. Nasotracheal intubation should not be performed if midface, nasal, or anterior skull base fractures are suspected. Patients with mandibular fractures should observe cervical spine precautions until cleared.[8][9][10](B2)

Mandibular fractures with mucosal, gingival, or tooth socket disruption are considered open fractures, and antibiotics with intraoral anaerobic pathogen coverage should be administered to reduce the risk of infection. Appropriate antibiotic agents include ampicillin/sulbactam, amoxicillin/clavulanate, and clindamycin for penicillin-allergic patients. Tetanus prophylaxis should also be considered in open fractures. Pain control should be achieved with acetaminophen, NSAIDs, and/or opioids. Steroids and ice packs are useful for reducing edema.

Patients with linear, nondisplaced, or greenstick fractures can be treated as outpatients with soft diet, analgesics, and urgent follow up with the otolaryngologist, oral and maxillofacial surgeon, or plastic surgeon for elective operative repair that can be performed as an outpatient procedure in 3 to 5 days, leaving time for some of the edema to subside and facilitate surgery. A Barton dressing, an ace wrap over the top of the head and underneath the mandible, may be used to stabilize the fracture and help relieve pain. These comparatively uncomplicated fractures are often treated with maxillomandibular fixation (MMF), in which the upper and lower jaw are wired together for a period of time in order to stabilize the fracture during the healing process. MMF can be achieved in several ways, with one of the most common being Erich arch bars and wires, although bridle wires, Ivy loops, intermaxillary fixation screws, and hybrid arch bars are also used. Wire loops are also useful for alveolar ridge fractures, providing interdental fixation to stabilize the fracture segments. Historically, MMF would last for 6-8 weeks; nowadays, many surgeons will only use rigid MMF with steel wires for 2 weeks or less and then replace the wires with elastic bands, or even do away with rigid MMF altogether. The advantage to MMF is that it avoids the risks of placing plates and screws, but requires a compliant patient to follow a prolonged regimen that often results in weight loss and may cause ankylosis of the temporomandibular joint. MMF is also a poor choice for malnourished patients, such as alcoholics, and patients likely to vomit, such as pregnant women and patients with seizure disorders, because they could aspirate. For this reason, it is imperative to provide even seemingly low-risk patients with wire cutters to release the MMF in the event of vomiting. Patients who are likely to be noncompliant and cut the MMF wires in the absence of vomiting or who are liable to not follow up as directed should undergo open reduction and internal fixation (ORIF) instead.

ORIF with plates and screws is often employed when it is not practical to leave a patient in MMF for a prolonged period of time, if there are comminuted fractures, if some of the bony fragments are edentulous and therefore not reduced with MMF, or if MMF otherwise does not provide sufficient reduction. Common situations include a fracture at the angle or in the subcondylar region, or if a fracture spans the entire height of the body or symphysis so that when the MMF wires are placed, the tension along the alveolar ridge causes the fracture line at the inferior margin of the mandible to splay apart. In the latter scenario, the arch bar used for MMF functions as a tension band along the alveolar ridge, but compressive forces are needed along the inferior margin of the mandible for stability, and a robust plate is known as a “recon bar” is often required in that location. Two to three lag screws can also be used to fixate fractures of the parasymphyseal region, which will avoid the use of palpable plates. In contrast, angle fractures that traverse the oblique ridge of the mandible can often be fixated using only a single thin Champy plate that takes advantage of the muscles of mastication to keep the fractured segments stabilized. Another frequently cited set of indications for ORIF were described by Zide and Kent in 1983, which pertain to condylar fractures. The absolute indications for ORIF include: displacement of the condyle into the middle cranial fossa, inadequate reduction with MMF, lateral extracapsular displacement of the condyle, and foreign body in the temporomandibular joint. The relative indications include: bilateral condylar fractures with a comminuted midface, bilateral fractures with history of malocclusion, bilateral fractures in an edentulous patient, and when splinting is not recommended. [11][12](B3)

Bilateral mandibular fractures are not uncommon, but edentulous patients make for a unique challenge. While there is no concern for malocclusion in edentulous patients, the lack of teeth mean that MMF cannot be used to stabilize fracture segments. In these cases, Gunning splints or external fixators may be used. Bilateral fractures of the mandibular body or ramus can also result in retraction of the anterior fracture segment, due to the action of the mylohyoid muscle, resulting in airway compromise and a potential need for emergent intubation or a surgical airway. Another special situation is the pediatric mandible fracture; most of these cases can be treated conservatively with a soft diet. Fortunately, it is very rare that children require MMF. Occasionally, ORIF is required, and many surgeons prefer to use resorbable plates and screws rather than titanium in order to minimize the potential for growth anomalies or injury to tooth buds. [13](B2)

Hospital admission may be indicated in patients with significantly displaced fractures. Patients with airway compromise, patients who are unable to tolerate oral feeding or secretions, and patients with inadequate pain control will also require hospital admission.[14][15]

Differential Diagnosis

Differential diagnosis includes mandibular contusion, mandibular dislocation, and isolated dental trauma. In a mandibular dislocation, if a single condyle is dislocated, the jaw will deviate away from the side of the dislocation. In a subcondylar fracture, the jaw will deviate toward the side of the fracture, resulting in premature contact on the fractured side and an open bite on the normal side.

Prognosis

The overall prognosis for patients who suffer mandible fractures is good, particularly in the absence of other associated injuries. While the perioperative complication rate in patients who undergo ORIF is fairly high due to the complexity of the repair (~20%), the long term results are good, with only 7% of patients reporting long term complications, such as abscess, malunion/nonunion, and hardware exposure. Smoking and alcohol use, the latter of which frequently contributed to the original cause of the mandible fracture, are associated with a higher rate of complications; patient age, gender, and type of injury do not appear correlated with outcomes.[16]

Complications

Regardless of treatment modality - conservative management, closed reduction with MMF, or ORIF - the most common complication of mandibular fractures and their treatment is malocclusion. ORIF has a higher risk of developing complications than a closed reduction - 21% vs 17%, particularly when performed by surgeons without a high-volume facial trauma practice. Hypesthesia of the lower lip and chin is also extremely common, with some studies reporting rates as high as 50%. Other less common complications include infection, bony malunion/nonunion, hardware extrusion, persistent trismus or mandibular deviation with opening, and facial nerve injury. Fractures at the angle are associated with the highest rate of developing complications.[17][18][19]