1. When considering the anatomy of the mandible, which one of the following reresents the region between the The mandible has a number of discrete anatomic subunits and fracture sites are classified and treated according to these locations. The body forms the horizontal part of the mandible between the first or second premolar and the third molar. The angle forms the junction between these two subunits. The condyle forms part of the temporomandibular joint (TMJ) where it articulates with the glenoid fossa of the temporal bone. The coronoid is the site of attachment of the temporalis muscle. The sigmoid notch is found between these two points. The mandible also has muscle attachments from the masseter, pterygoids, digastric, stylohyoid, and geniohyoid. The symphysis is the midline region anteriorly between the central incisors. The parasymphysis is the region on either side of the symphysis between the midline and mental foramen. The alveolus is the site where dentition is located (Fig. 36.1).1 Fig. 36.1 A, Anatomic regions of the mandible. B, Frequency of fractures in those regions. A B Coronoid process Alveolus Symphysis Body Angle Ramus Condylar process 14% 21% 3% 20% 3% 2% 36%
Mandibular fractures are a common injury especially in young adult males and are classified by anatomic location. The most common sites are the condyle, body, angle, and symphysis. The fracture site is dependent upon the mechanism of injury and is related to both the direction and magnitude of force. For example, assaults commonly result in angle fractures, while motor vehicle crashes more commonly result in body fractures. The mandible frequently fractures at two sites simultaneously (50% of cases). The coronoid is the least commonly fractured site in adults representing around 2% of cases.1–3
3. Aston SJ, Beasley RW, Thorne CH, eds. Grabb and Smith’s Plastic Surgery. 6th ed. Philadelphia: Lippincott-Raven; 2007 All of the above may be seen in conjunction with a mandibular fracture but ecchymosis to the floor of the mouth is said to be pathognomonic of this condition. When assessing patients with suspected mandibular fractures, external and internal examinations are required. A noticeable step-off is often visible between the teeth at the site of fracture in addition to the bruising. Asking patients whether their bite feels normal is a very useful and highly sensitive test. The mental nerve is a continuation of the inferior alveolar nerve that supplies sensation to the skin overlying the anterior mandible. Paresthesia in this region indicates that the fracture has resulted in damage to this nerve. This must be documented preoperatively. Trismus refers to a reduced ability to open the mouth and is often seen following a mandibular fracture as a result of pain, swelling, and muscle spasm. It may also be due to a mechanical problem where a displaced fracture is present and there is disruption of the normal mandibular U shape. Loose teeth are common following facial trauma and again this must be documented during initial assessment. Dental assessment is advised in such cases.1,2
Although the panoramic view of the mandible is excellent and will enable the vast majority of fractures to be diagnosed, it should be supplemented with a mandibular series. This will typically include a posteroanterior (PA) and lateral skull view, right and left lateral oblique views, Towne projection, and submental vertex views. CT scans are not usually required for isolated mandibular fractures, but they may be useful in situations where plain radiographs are inadequate, such as when cervical collars are still in place. MRI is better for imaging soft tissue than bone and is not required in mandibular fractures. Radiographs may be useful to identify the inferior alveolar nerve relationships, but nerve injury is best diagnosed during clinical examination.1,2
fracture? There are five typical indications for tooth removal: 1. Grossly mobile teeth in which periapical pathology or advanced periodontal disease is present 2. Partially erupted third molars with an associated dental pathologic condition 3. Teeth that prevent adequate reduction of the fracture 4. Teeth with fractured roots 5. Teeth with exposed root apices Nonrestorable teeth and bony impactions should be retained if this assists in reduction. For example, extraction of bony impactions can result in removal of excessive amounts of bone that may compromise both the fracture site and the potential placement points for plate or screw fixation.1–3
There are a number of definitions of the stability required for optimal fracture healing to occur. Rigid or absolute stability means there is no movement occurring across the fracture site. This allows for primary bone healing without callus formation. Rigid stability may be an ideal therapeutic principle in some situations, but in the mandible, it mandates the use of large reconstruction plates, multiple miniplates, or lag/locking screws. The lack of movement stimulation at the fracture ends may reduce the osteogenic healing process of the bone in some situations. Absolute stability is not usually achieved in mandibular fractures, as a subtle amount of movement at the fracture site is preferred. Load-bearing stability occurs where all load is transmitted through the construct rather than the bone. This is required in situations where there is bony insufficiency either in terms of quality or quantity, such as extreme comminution or atrophic mandibles. Load-bearing stability is most often accomplished by large reconstruction plates such as those used when reconstructing segmental mandibular defects with free bone transfer. Load-sharing stability is where stability is achieved by the fixation system in conjunction with stabilizing forces provided by anatomic abutment of noncomminuted fracture segments. Some callous is likely to be formed with each of these approaches. Functional or nonrigid stability enables micromotion to occur across the fracture gap but is balanced by external forces and remains within limits so as to allow the fracture to progress satisfactorily to union. There will be formation of callus and secondary ossification. There are advantages and disadvantages of having rigid or semirigid fixations and the benefits of each will depend on factors including location and type of fracture/s and bone quality. In general load-sharing approaches with miniplates are still most often used in mandible fractures.1
The Champy system was first described by Michelet et al1 in 1973 and later validated by Champy et al2 in 1978. It advocates the use of monocortical (not bicortical) miniplates and is based on the concept that only tensile stresses are harmful to fracture healing, as these tend to open up the fracture line. Compressive forces, however, tend to pull the fracture lines together and can be used to help fracture reduction and stabilization. The system involves placement of miniplates to counteract the tensile or opening forces and utilize the compressive forces. Anterior to the first premolar, two miniplates are required, one above the other, as there are multidirectional forces acting across this site. Fractures posterior to the first premolar normally only require single plate fixation. The standard approach to ORIF of a symphyseal fracture is intraoral (not submental) within the lower lip sulcus. Care should be taken to ensure that the incision is placed away from the attached gingiva to ensure there is sufficient nonadherent mucosa to facilitate tension-free soft tissue closure. Temporary arch bars are usually only required where there are two concomitant fractures such as a symphyseal, condyle, or angle.
Prophylactic antibiotic use in mandibular fractures has been proven to significantly reduce the incidence of postoperative infection. However, antibiotics only need to be prescribed until definitive fixation. Further antibiotic use (i.e., postoperative) does not affect infection rates, nor does the use of oral chlorhexidine, even though it can reduce bacterial counts. Not all fractures will require surgical fixation; for example, some condylar fractures may be managed conservatively with a soft diet and physical rehabilitation exercises. Some body fractures are amenable to maxillomandibular fixation (MMF) only. There is usually no great urgency to stabilize mandibular fractures if antibiotics and analgesics are being given.1,2 The AO has comprehensive guidance on its website that includes approaches and fixation placement that can be a useful reference.3
Fractures of the condyle require early active range of motion (ROM) to rehabilitate TMJ articulation. In fractures such as this, where occlusion is maintained, soft diet and close observation represent the best treatment. If malocclusion subsequently develops, then arch bars or maxillomandibular fixation (MMF) should be placed and occlusion controlled with elastics. ORIF is indicated for some condylar fractures, such as bilateral cases or cases where there is significant displacement of the fracture and where occlusion cannot be established. Access to the TMJ and condyle are commonly through a preauricular approach and this can be difficult and risks damage to the facial nerve but would not be justified in this case.1–3
The angle has the highest complication rate of any single region of the mandible. These fractures can also be difficult to reduce and stabilize accurately. Approaches include transbuccal, intraoral, and maxillomandibular fixation (MMF). Isolated fractures can be reliably treated with a single miniplate along the oblique ridge through an intraoral incision to provide functional stability. A second 2-mm miniplate can be added to the lower border if more rigid fixation is needed.1,2
A vast majority of mandibular fractures seen in children involve the condyle. Condylar fractures in this population must be followed very closely because they can lead to ankylosis and growth disturbances. Management of other mandibular fractures in children require additional care when managing them operatively as it is important to avoid damage to the developing tooth buds. Roughly half of all mandibular fractures are bilateral, and due to the increased instability these fractures display, at least one fracture should be fixated with more rigid plating. However, not all sites necessarily need rigid fixation. Common fracture patterns include a body/symphysis/angle fracture with a contralateral condylar/subcondylar fracture. The condyle is often treated nonoperatively while the body/symphysis/angle fracture is chosen for rigid fixation. In situations of comminution, it is best to have bridging of the area of comminution with load-bearing fixation using larger reconstruction plates. Where bone graft is required, it is preferable to delay this in heavily contaminated wounds or where there is poor soft tissue cover. Edentulous mandibles tend to have smaller and lesser quality bone stock; however, this does not mean they should always be treated conservatively. Accuracy of reduction is perhaps not as important as in the dentate mandible, as occlusion does not need to be restored, but approaches still include the use of reconstruction plates as alternatives to nonoperative treatment. Malocclusion is a potential risk factor following mandibular fracture and is almost always the result of a technical error intraoperatively. However, it is not the most common complication. Other potential problems include hardware failure, reinjury, infection, nonunion, and ongoing pain and jaw stiffness.1–3