Theoretically, the mandibular external fixator could be used to achieve definitive bone healing. Nevertheless, the external fixator does not offer the same degree of stability compared to internal devices.
The external fixator device will often only be applied temporarily, with subsequent replacement by an internal fixation system.
The external pin fixation device gives a high degree of freedom for the frame assembly as the pins can be placed selectively into each segment and connected with short bars to constitute a subunit. Subsequently, the subunits are joined with additional connecting elements to make up the complete framework. In this process, each subunit can be manipulated into a reduced position until the whole construct's final tightening.
Limitations of external fixators
Some disadvantages of an external fixator are:
The extensive amount of hardware necessary for the complex construction
The quality of the bony reduction is not guaranteed as the reduction is often not visualized (closed reduction)
Alternative: biphasic pin fixation
An alternative to the modular technique is the biphasic pin fixation (also known as Joe Hall Morris fixation).
Fracture alignment is first achieved with adjustable connecting rods between the pin pairs (not shown in the illustration).
The aligned pins are then covered with a silicon tube (eg, endotracheal tube, chest tube) and then injected with methyl methacrylate resin.
Alternatively, the pins can be connected with a molded methyl methacrylate block that sets after application.
Finally, after adequate bone healing, the pin fixation and adjustable rods are removed.
This image shows an example of this technique following a self-inflicted gunshot wound, where a plating system or modern fixator was not available.
In this case, the fixation is nonrigid and can lead to instability of the framework. However, it is readily available and may be considered when nothing else is available. Larger threaded Steinmann-type pins would be preferable over K-wires.
The following recommendations apply to optimize the framework stability:
Choose large pin diameters (Schanz screws or Steinmann pins may be considered)
Use at least two pins in each fragment
Keep a large distance between the pin pairs
When possible, place pins at least 1 cm from the fracture line
Place the connecting rods or plastic bar close to the skin surface to keep the lever arms short.
2. Patient preparation
This procedure is typically performed with the patient placed in a supine position.
If the major fragments can be aligned using any of the MMF techniques, MMF is used to simplify the overall assembly process.
4. Pin insertion
The pins are inserted through the soft-tissue envelope overlaying the safe zones into the mandible's lower border.
For more information on the anatomy of the mandible, click here.
Two pins are inserted into each major fragment at an appropriate distance to each other and the adjacent fracture lines.
The length of the threaded portion of the pins is chosen to attain bicortical engagement.
Make a small stab incision to prepare for pin insertion at the predetermined screw locations in the posterior mandible. The stab incision is done with the blade parallel to the RSTL (relaxed skin tension lines).
Soft-tissue dissection and protection
Bluntly dissect a soft-tissue channel onto the underlying bone and insert a trocar for soft-tissue protection through the channel until it contacts the bone.
A self-drilling pin is loaded into a handle. Use the trocar as a guide and drive the pin into the bone down to the pin's base.
If a self-drilling pin is not available or not advisable due to fragment instability, make sure to pre-drill before pin insertion.
The clinical photograph shows pin insertion with a trochar.
5. Frame assembly
Creation of subunits
The two pins in each fragment are connected with a rod and two clamps (as illustrated). The example here shows four subunits.
Linking the two posterior subunits
Apply a connecting rod loosely between two subunits using rod-to-rod clamps.
One fracture is manually reduced by manipulating two subunits, tighten the rod-to-rod clamps
Linking the anterior subunits
The anterior subunits are linked in the same way as the posterior subunits.
Final frame assembly
Only one fracture gap is left between two large assembled mandibular portions to connect the anterior and posterior subunits. This gap is reduced and fixed through a connecting rod.
The illustration shows the final assembly of the external fixator using the modular technique.
MMF is removed after the final external fixator assembly to allow for mandibular function.
Alternative: using a bow
When a large circumference of the mandible requires external fixation, a pre-contoured rod can be directly attached to the pins.
A template rod is first inserted into the combination clamps.
This template rod is then used to make further adjustments in the bending of the bow-shaped rod.
This clinical picture shows an alternative placement on the inferior border with a history of comminution and multiple infections, and a parasymphyseal defect, after multiple failed attempts at treatment using ORIF and traditional plating techniques.
The postoperative orthopantomogram shows Schanz screws. Note that the screw on the far left is too close to the inferior alveolar nerve.
6. Aftercare following external fixation
Release of MMF and elastics
The patient should be instructed how to release the MMF in case of an emergency. Some surgeons prefer to provide wire cutters to the patient for the period of MMF. During this period, wire fatigue and loosening can occur. The patient should report any loosening of the MMF to the surgeon immediately.
As an alternative, the MMF may be achieved by using elastics instead of wires. With an adequate number of elastics, the same level of reliability can be reached minimizing the risk of inability to release the MMF during an emergency situation.
Postoperative x-rays are taken within the first days after surgery. In an uneventful course, follow-up x-rays are taken prior to releasing the MMF.
It will be necessary to see the patient approximately 1 week postoperatively to assess the stability of the occlusion and to check for infection of the surgical wound. The intermaxillary fixation wires or elastics must be assessed and proven to hold the patient tightly in occlusion. Patients also have to be periodically re-examined to rule out signs of infection. At each visit, the surgeon must evaluate the patient's ability to perform adequate oral cleaning. It may be necessary to provide additional instruction to assure appropriate hygiene and wound care.
There should be no malocclusion detected as occlusion is determined and secured in the operating room.
Release of MMF
On releasing the MMF, physiotherapy can be prescribed. The mandible will be hypomobile after the period of MMF, and the muscles will be atrophic and “tight.” Opening and excursive exercises should be demonstrated and implemented. Goals should be set, and typically, 40 mm of maximum interincisal mouth opening should be attained by 4 weeks postoperatively. If the patient cannot fully open his or her mouth, additional passive physical therapy may be required.
Basic postoperative instructions
The diet has to be in a liquid or semi-liquid form. For patients with a full complement of teeth, the diet must be more liquefied than when there are gaps with teeth missing. Because the diet will be no-chew, more fluids are required to assist in swallowing the food. A blender, or preferably, a juicer is useful. Anything can be made into a liquid or semi-liquid form with these tools. Liquid dietary supplements from the grocery store help maintain caloric intake. The patient should monitor their body weight on a weekly basis during the period of MMF to evaluate any dramatic changes.
Patients must be instructed in oral hygiene procedures. The presence of the arch-bars and MMF wires makes this a much more difficult procedure, and the inside of the teeth cannot be reached with a toothbrush. A soft toothbrush (dipping in warm water makes softer) should be used to clean the buccal/labial surfaces of the teeth, arch-bars and wires. Chlorhexidine oral rinses should be prescribed and used at least 3 times each day to help sanitize the mouth.
Dental follow up
The patient should be warned to continue routine follow up with their dentist. Fractures near the dental roots can often result in delayed loss of tooth viability, requiring periapical films and additional dental procedures.