LOCATION

• 1.

  Symphysis: Occurring in the midline, between the central incisors.

• 2.

  Parasymphysis: Area bound between vertical lines distal to the canines.

• 3.

  Body: Area bound from the distal symphysis of the canine to the anterior border of the masseter muscle (distal of the second molar).

• 4.

  Angle: Area bound from the anterior border of the masseter (distal of the second molar) to the posterior border of the masseter. Third molars, if present, are typically involved in angle fractures.

• 5.

  Ramus: Area from the posterior border of the masseter to the height of the sigmoid notch; the term “subcondylar fracture” is typically within the region of the ramus.

• 6.

  Condylar:

  • Intracapsular: A fracture of the condylar head, which is bound by the capsule.

  • Condylar neck : A fracture from the height of the sigmoid notch to the attachment of the capsule. These fractures are further subdivided:

  • Dislocated: The head of the condyle is dislocated from the glenoid fossa.

  • Displaced: The head of the condyle remains in the glenoid fossa, but the neck of the condyle has been pulled out of alignment with the ramus. This can be in any direction, but most commonly is anteromedial because of the pull of the lateral pterygoid muscle.

• 7.

  Coronoid: The area of the coronoid process superior to the height of the sigmoid notch.

• 8.

  Dentoalveolar: A fracture of the alveolar bone and supporting root structure; it does not involve the basal bone of the mandible.

The distribution of fractures has also been examined, with the angle and parasymphyseal regions being most common, followed by condyle fractures. The least common fracture is the coronoid process; these fractures often are associated with a fracture of the zygomatic arch ( Figure 10-7 ).

Fractures of the mandible according to anatomic region.

FRACTURE PATTERNS

• 1.

  Open fracture (compound): This type of fracture has communication with the external environment, either through skin or through mucosa, including the periodontal ligament. Any fracture involving a tooth-bearing segment is an open fracture by definition.

• 2.

  Closed fracture (simple): This type of fracture has no communication with the external environment.

• 3.

  Comminuted: Multiple segments of bone are shattered, crushed, or splintered in this type of fracture.

• 4.

  Greenstick: This fracture is incomplete and only involves one cortex.

• 5.

  Pathologic: A fracture occurring from pre-existing disease that has structurally weakened the bone is pathologic.

• 6.

  Complex (complicated): This can be either a simple or a compound fracture that is associated with significant adjacent soft tissue injury.

• 7.

  Multiple: In a multiple fracture, there are two or more fractures within the same bone, but the fractures do not communicate with each other. A mandible fracture will typically have at least two fractures. An analogy typically used is the mandible being like a ring or pretzel; it is very difficult to break in only one place.

• 8.

  Atrophic: An atrophic fracture is a spontaneous fracture resulting from mechanical weakening because of atrophy. An atrophic mandible is defined as an edentulous mandible that has 20 mm or less in height.

• 9.

  Indirect: This is a fracture that occurs at a site distant from the area of impact (for example, the classic “guardsmen fracture,” having bilateral condylar necks and a symphyseal fracture). The point of impact at the chin creates multiple fractures—a direct symphysis fracture and indirect condylar neck fractures.

• 10. Impacted: A fracture in which segments have “telescoped” upon each other is impacted.

BIOMECHANICS

Mandibular fracture displacement is defined as follows:

• 1.

  Favorable (stable): The fracture line and the vector of the muscle pull keep the fracture buttressed and appropriately reduced.

• 2.

  Unfavorable (unstable): The fracture line and the vector of the muscle pull cause displacement ( Figure 10-8 ).

  

  A, Horizontally favorable fracture. B, Horizontally unfavorable fracture. C, Vertically favorable fracture. D, Vertically unfavorable fracture.

Understanding muscle attachments and the forces imposed upon the mandible will aid the surgeon in the management decisions. A mandible fracture has three forces acting upon it: compression, tension, and torsion ( Figure 10-9 ). These forces vary in magnitude depending upon the location of the fracture. The muscles responsible for the vertical displacement are the masseter, temporalis, and, to a degree, the medial pterygoid. Horizontal displacement can be caused by the lateral and medial pterygoid and torsion by the mylohyoid, digastrics, and geniohyoid. The favorability and unfavorability are described based on the plane of the films obtained; so a “horizontally unfavorable” fracture is displacement noted on an orthopantomogram. Conversely, a “vertically unfavorable” fracture is displacement noted on an anteroposterior film. This can be confusing at times because the vectors of the muscle pull are opposite to the plane of the film. It is probably more important to denote simply whether or not a fracture is favorable or unfavorable in nature. This feature of the fracture significantly impacts the treatment plan. For example, the buttressing effect seen in some favorable fractures will make these more amenable to closed reduction and MMF. In contrast, unfavorable fractures are typically more amenable to open reduction and internal fixation because of lack of buttressing.

Zones of compression and tension within the fractured mandible are determined by the muscles inserting onto the mandible and the forces exerted by these muscles during function. The four smaller arrows demonstrate the direction of muscular forces placed on the mandible by the lateral pterygoid, temporalis, pterygomasseteric sling, and the suprahyoid musculature. The larger arrows demonstrate the load placed on the mandible during function. Because of these forces, the zone of compression is located at the inferior border, the zone of tension is located at the superior border, and the neutral axis is approximately at the level of the inferior alveolar canal.

(From Baker S, Dalrymple D, Betts NJ: Concepts and techniques of rigid fixation. In Fonseca RJ, Walker RV, editors: Oral and maxillofacial trauma , ed 2, vol 2, Philadelphia, 1997, WB Saunders.)

PHYSICAL EXAM

After the patient is stabilized and an appropriate history is ascertained, including the mechanism (energy) of injury, a complete head and neck exam should occur. Some of the signs and symptoms of a mandible fracture include the following:

• 1.

  Pain: Examination should include a complete head and neck exam with palpation of the mandible along its entire contour, including the temporomandibular joints. The exam should also include intraoral palpation along the alveolus, external oblique ridges, and anterior border of the ramus.

• 2.

  Swelling: Upon extraoral (resulting in facial asymmetry) or intraoral examination, one may note vestibular or floor of mouth edema.

• 3.

  Paresthesia of the mental distribution

• 4.

  Trismus

• 5.

  Malocclusion

• 6.

  Ecchymosis of vestibule and/or floor of mouth

• 7.

  Gingival laceration

• 8.

  Mobility of bone segments or teeth

• 9.

  Palpable bony steps

• 10. Deviation of the mandible; changes in facial contour or arch form

RADIOGRAPHIC EXAM

Radiographic imaging is additional objective data that should confirm (or complement) the practitioner’s working diagnosis. The plain film is still the most cost-effective and accurate radiographic modality. When obtaining plain films, two views at right angles must be obtained in order to assess fracture displacement. A “mandible series” consists of the orthopantomogram (or it can be substituted with right and left lateral oblique views), posterior/anterior view, and reverse Towne’s view ( Figures 10-10 through 10-13 ). A reverse Towne’s view will aid in the assessment for a condylar fracture. In many institutions computerized tomographic (CT) scans are readily available and can be viewed in three planes: axial, coronal, and sagittal. Additionally, they now can be reconstructed into three-dimensional images ( Figures 10-14, 10-15, and 10-16 ). CTs are obtained in circumstances in which the patient has suffered multisystem trauma and may need to be scanned for other injuries, or when the patient is unable to be appropriately positioned for conventional radiographs.

Panoramic radiograph, the single most informative radiograph in diagnosis of mandibular fractures.

The lateral oblique view of the mandible is helpful in diagnosing ramus, angle, and posterior body fractures.

The Caldwell posteroanterior view shows medial or lateral displacement of fractures of the ramus, angle, body, and symphysis.

The reverse Towne’s view is most helpful for showing medial displacement of the condyle and condylar neck fractures.

Axial view of right parasymphyseal and left body fractures.

Three-dimensional CT scan illustrating a comminuted mandible fracture secondary to a gunshot wound.

Computed tomography (CT) scan is ideal for condylar fractures.

SECONDARY (INDIRECT) BONE HEALING

Secondary bone healing occurs through a process of remodeling and callus formation when the fracture is immobilized without the use of rigid fixation. Bone healing occurs according to the principles of Wolff’s law. Julius Wolff proposed that mechanical stress was responsible for determining the architecture of bone. Remodeling of bone occurs in response to physical stresses (or lack thereof) from the soft tissue envelope and musculature, whereby bone is deposited at sites subjected to stress and is resorbed at sites where there is little stress. In contrast to second intention healing of soft tissue, which will not return the tissue to its pre-injury state (i.e., formation of scar tissue), secondary bone healing will regenerate the injured bone to its pre-injury state. Remodeling of the mandible to a full load-bearing state requires 4 to 6 months (a diminished time frame compared to long bones). The initial healing process, in order to return to normal function, typically takes an average of 4 to 6 weeks (depending on the type and severity of the fracture) and occurs in four stages ( Figure 10-17 ).

• 1.

  Inflammatory stage: The fracture causes a disruption of the vascular supply within the bone. Initially the fracture site hemorrhages, with the formation of a hematoma throughout the fracture. This is followed by an inflammatory process with the presence of macrophages, monocytes, neutrophils, and platelets. The vascular compromise initially causes necrosis of bone at the fractured edges, but a reparative process of angiogenesis ensues, as well as the formation of osteoprogenitor cells, mesenchymal cells, and fibroblasts.

• 2.

  Cartilaginous stage: This stage is the initiation of a cartilaginous (soft) callus that is comprised of fibrocartilaginous tissue. At the conclusion of this stage the mobility across the fracture is eliminated.

• 3.

  Bony callus stage: This stage involves the conversion of the cartilaginous callus to a bony callus comprised of immature woven bone, which typically occurs within 3 to 4 weeks of the injury. This is initiated by the conversion of chondrocytes to osteocytes, leading to the formation of endochondral bone.

• 4.

  Remodeling stage: This stage is the return of the osseous tissue to its pre-injury state and occurs for months following the injury. It is the final stage and results in the conversion of endochondral bone to mature lamellar bone.

A, Early fracture with hematoma. B, Fibrocartilaginous (soft) callus. C, Hard callus.

PRIMARY (DIRECT) BONE HEALING

Primary bone healing is a process of directly remodeling the haversian systems of compact lamellar bone by the use of rigid fixation. The use of rigid fixation stabilizes the fracture, optimizing contact healing. This eliminates the need for the intermediate steps required for a bony callus, and more rapidly returns the fracture to a pre-injury state ( Figure 10-18 ).

Diagram demonstrating contact healing and gap healing. The middle diagram demonstrates that plate placement has resulted in the two fracture ends being in close proximity on the cortex adjacent to the plate. This situation can lead to contact healing. Unfortunately, the plate was not overbent, resulting in a gap between the fracture ends on the cortex away from the plate. This situation leads to gap healing. The bottom diagram demonstrates the histologic features of bone following contact healing and gap healing. Note how the cutting cones have passed directly across the fracture in the area of contact healing. This process does not occur primarily in the area of gap healing.

CLOSED TREATMENT TECHNIQUES

Maxillomandibular Fixation

MMF is a basic and fundamental principle in the management and treatment of the maxillofacial trauma patient. It serves as a cornerstone, providing a stable base from which facial form and function can be restored. It re-establishes the patient’s premorbid occlusion, assisting in the reduction and fixation of simple and complex facial fractures. Most mandible fractures will require 4 to 6 weeks of MMF when used as the sole means of fixation; however, depending upon the fracture pattern, location, severity, and co-morbidities, some fractures will require 8 weeks. A variety of MMF techniques are available in today’s modern practice, including the following:

• 1.

  Arch bars

• 2.

  Intermaxillary fixation (IMF) screws

• 3.

  Interdental wire fixation

• 4.

  Skeletal suspension wires

• 5.

  Various bonded and nonmetallic tooth-borne systems

Closed reduction techniques should be reserved for minimally to nondisplaced, favorable fractures, and for patients who have a complement of teeth sufficient to provide a stable occlusion. Some authors have advocated the use of MMF for comminuted mandible fractures, and in circumstances with compromised soft tissue. The concern is to avoid open techniques because of periosteal stripping, which could lead to necrosis of small bone fragments and potentially create a continuity defect and possible additional soft tissue loss. One concern with this type of management is the risk of infection, especially if there is soft tissue compromise or if the fracture involves a tooth-bearing portion of the mandible (open fracture). In addition, malunion or nonunion is possible considering that these fractures are highly unstable with inadequate bone buttressing. Lastly, severely comminuted bone does little to support the overlying soft tissue envelope. As scarring and contracture occur, regaining volume is often difficult to accomplish without recruiting distant tissue. These complications are often avoidable with early rigid stabilization, the use of external fixators, or the primary reconstruction with vascularized tissue when indicated.

Arch bars, which are the traditional workhorse for MMF, are applied to the dentition using circumdental wires. The patients are placed into their premorbid occlusion upon the final tightening of the intra-arch and inter-arch wires. Arch bars are very useful when managing dentoalveolar fracture segments because they assist in reestablishing the intra-arch contour; they also serve as a “tension band” that will resist the forces of tension seen along the alveolar level of the mandible. In addition, arch bars serve in directing vectors of force to assist in fracture reduction and reestablishment of the premorbid occlusion. While arch bars provide an effective and versatile means of MMF, their use is not without consequence. Increased surgical time both in placement and in removal, risk of penetrating injury to the surgeon, trauma to the periodontium, and compromised oral hygiene are all shortcomings of traditional arch bars. Arch bar placement in the pediatric patient can be complicated, depending on the patient’s age and stage of eruption. First, the position of the height of contour and contacts in the primary dentition may prevent application of circumdental wires. Second, there is the potential for extrusion of the primary tooth upon tightening the wire, especially in the root resorption stage for exfoliation ( Figure 10-19 ).