Principles of Internal Fixation of the Craniomaxillofacial Skeleton (eBook)

2.1 Symphyseal and parasymphyseal fractures

2.2 Body and angle fractures of the mandible

2.3 Condyle, ascending ramus, and coronoid process fractures

2.4 Fractures in bone of reduced quality

2.5 References and suggested reading

2 Mandibular fractures

1 Anatomy and definition

2 Imaging

3 Surgical approaches

4 Osteosynthesis techniques

4.1 Plate osteosynthesis

4.2 Compression plate osteosynthesis

4.3 Lag screw osteosynthesis

5 Perioperative and postoperative treatment

6 Complications and pitfalls

2.1 Symphyseal and parasymphyseal fractures

1 Anatomy and definition

The symphysis of the mandible is defined as the region between the roots of the central incisors, and the parasymphysis as the region between the lateral roots of the canines and the central incisors. Together they can be referred to as the chin or mental region (Fig 2.1-1).

This region is characterized by very vascular bone whose blood supply comes from the lingual side of the chin via the attached lingual and sublingual muscles. In addition terminal branches of the lingual artery may enter the bone directly. Under masticatory load rotational forces may occasionally be observed in this particular region; this must be considered when internal fixation is performed.

Linear and oblique fractures are the characteristic injury in this region. Comminution or bone loss is relatively rare. Occasionally, there is an inferior butterfly fragment which, if large, may involve the insertion of the suprahyoid musculature, and usually is associated with high-energy trauma seen in high-speed injuries such as motor-vehicle accidents and gun shots.

Fig 2.1-1 Anatomy of the symphysis (red) and parasymphysis (green).

2 Imaging

X-rays in two planes, such as an orthopantomogram (OPT) and a Clementschitsch view, are sufficient (Fig 2.1-2 a–b). A panorex view tends to blur the center (symphysis section), whereas a CT is the only image giving a clear picture of both cortices (Fig 2.1-3). In cases where a CT scan of the head has to be taken because of additional injuries, axial scans are usually sufficient and can be used instead of plain films.

Fig 2.1-2a–b

a Orthopantomogram (OPT) of a midline fracture.

b X-ray according to Clementschitsch with subcondylar fracture on the left.

Fig 2.1-3 CT of a midline fracture.

3 Surgical approaches

Typically, a transoral approach is used, however, under special circumstances a transcutaneous approach should be considered.

The standard approach to the chin area is via a transoral vestibular approach. In dentate patients the incision line usually lies in the mobile gingiva at a distance of 8–10 mm to the junction between attached and mobile mucosa (Fig 2.1-4). In edentulous patients a crestal incision is preferred. Initially, a smaller incision from canine to canine is made. Some surgeons prefer to cut through the mucosa, underlying facial muscles and periosteum right to the bone, others prefer to mobilize the mucosa first and to incise muscles and periosteum on a different level (Fig 2.1-5a–b). From the central smaller incision the more lateral soft tissues can be elevated subperiostally to identify the mental nerves and mental foramina. Then the cut can be extended laterally without major risk of permanently damaging the mental nerve. The complete labial surface of the chin including the inferior mandibular border may be exposed via this approach. However, this approach does not permit visual control of the lingual cortex. Consequently, under some circumstances an external approach should be considered.

Fig 2.1-4 Incision line for a transoral vestibular approach (incision with an electric needle).

Transcutaneous approaches may also be considered in cases of preexisting lacerations in the chin area. From time to time they are indicated when significant comminution or bone loss is present. In rare cases they are performed secondary to a transoral approach, when the repositioning is difficult and the lingual aspect has to be visualized. A planned trans-cutaneous incision is performed in the submental area taking the relaxed skin tension lines into account. An isolated submental incision can also be made in a curved line directly posterior to the border of the mandible. Care must be taken not to extend it too laterally in order to avoid damage to the marginal branch of the facial nerve. In cases when a more extended submandibular approach is required an incision in the submandibular fold is recommended (Fig 2.1-6).

Transoral and transcutaneous approaches are always closed in layers with resorbable or nonresorbable suture material (skin and mucosa only) depending on the surgeon's preference. It is important to repair the transected mentalis muscle with meticulous suturing to avoid a drooping chin.

Fig 2.1-5a–b

a Stepwise incision through the mucosa first, followed by the incision through the muscles and the periosteum.

b Two-layer wound closure for muscle and mucosa.

Fig 2.1-6 Incision lines for transcutaneous approaches following skin creases.

4 Osteosynthesis techniques

In healthy bone, fractures in the symphyseal and parasymphyseal region can be successfully treated with a variety of options. These include miniplate, compression plate, or lag screw osteosynthesis. Multifragmentary, defect, and infected fractures as well as fractures of an atrophic mandible should be treated with reconstruction plates according to the techniques described in chapter 2.4 (Fractures in bone of reduced quality). In nondisplaced and nonmobile fractures, nonsurgical therapy may occasionally be considered.

Before internal fixation with plates and screws is performed, mandibulomaxillary fixation (MMF) should be applied with arch bars or splints. IMF screws can also be used.

Fragment reduction in the chin area can be performed manually, with the help of reduction forceps, or with a positioning wire.

4.1 Plate osteosynthesis

Miniplate osteosynthesis is probably the technique most frequently applied for these fractures worldwide. The standard technique involves the placement of two miniplates 2.0 or corresponding plates from the Matrix system with 4 or 5 holes. One plate is placed directly above the inferior border, the second plate is placed considerably higher in the central portion of the mandible underneath the tooth roots (Fig 2.1-7a). Both locking and nonlocking plates can be used.

One plate is bent and contoured to the bone surface first. This plate may be placed either at the upper or lower border.

In bilateral subcondylar fractures in combination with a midline fracture, pressing on the angles and upper ramus bilaterally creates a gap in the labial cortex. The lingual cortex of the mandibular fracture is approximated and the width of the mandible is corrected.

The screw fixation for the superior plate is always monocortical to avoid damage to tooth roots (Fig 2.1-7b). For the inferior plate fixation both monocortical and bicortical screw placement is possible.

Miniscrews are inserted monocortically (without pretapping) in the self-tapping mode. If screws are inserted bicortically, pretapping reduces the torque. Without pretapping, there is a risk of fracture or sheering of screw heads when using miniscrews.

Fig 2.1-7a–b

a Standard technique in plate osteosynthesis of the chin involves two 4- or 5-hole miniplates 2.0.

b The screw fixation for the superior plate is always monocortical to avoid damage to tooth roots.

4.2 Compression plate osteosynthesis

Compression plates in the chin area can be placed in the center of the symphysis at a safe distance from the tooth roots. Biomechanically, one compression plate in the center (neutral zone) of the mandible is sufficient to neutralize all forces within a normal range. In this area a 4-hole compression plate is usually used, either a limited contact dynamic compression plate (LC-DCP) 2.4, a universal fracture plate 2.4, or a compression plate from the Matrix Mandible system. The use of a tension band splint or at least a bridal wire is strongly recommended to neutralize distraction forces at the superior border of the mandible (Fig 2.1-8).

Alternatively, if placement of a tension band splint is not possible or not acceptable, a compression plate osteosynthesis can be performed in a 2-plate technique. In a 2-plate compression osteosynthesis one...