Comparison Between Internal and External Distractors in Osteogenesis

Distraction osteogenesis is a powerful technique for creating new bone during significant lengthening of the mandible without the need for bone grafting and associated donor site morbidity.

The idea of distraction osteogenesis was largely abandoned by many until the 1950s. Ilizarov minimized complications by performing a corticotomy with minimal disruption of the surrounding blood supply and using a system of tension ring fixators to control the distraction in multiple planes. Through a series of experimental studies and clinical applications, Ilizarov established the foundation of distraction osteogenesis and its role in orthopedic management.

Applications in craniofacial surgery were first seen in 1973, when Synder et al applied the approach to mandibular lengthening in a canine animal model. Almost another 20 years passed before McCarthy and colleagues published, in 1992, the first report of mandibular lengthening in 4 children with congenital mandibular deficiency, 3 with hemifacial microsomia, and 1 with Nager syndrome. Thereafter, its role rapidly expanded to the midface and nearly all classic approaches to craniofacial reconstruction.

In general, mandibular distraction can be performed in the ramus for ramus lengthening, in the mandibular angle for downward and forward advancement, or in the mandibular body. Ramus or gonial angle distraction are mainly used to treat facial asymmetries as in hemifacial macrosomia.

Severe mandibular retrognathia can be classified as congenital or acquired. Congenital abnormalities that are associated with severe mandibular retrognathia or micrognathia include craniofacial syndromes such as hemifacial microsomia, Pierre-Robin syndrome, Treacher-Collins syndrome, and Nager syndrome. Adult patients with craniofacial syndromes may have undergone previous surgery at an earlier age, but unfavorable postsurgical growth or skeletal relapse may have occurred.

Severe mandibular retrognathia also can develop following maxillofacial trauma and mandibular fractures, which may have occurred in an adult or as a child Condylar fractures occurring at an early age can result in subsequent bony and/or fibrous temporomandibular joint ankylosis and/or deficient mandibular growth, also adult patients with complications from previous mandibular tumor resection and reconstruction can also present with acquired severe mandibular retrognathia that may require distraction osteogenesis as well.

Despite the advantages of extra-oral distraction devices in the hands of clinicians (application for very small children, simplicity of attachment, ease of manipulation, bidirectional and multidirectional dis- traction), patients are apprehensive about wearing bulky external appliances because of the social inconvenience and the potential of permanent facial scars, these disadvantages and limitations were the primary force driving the evolution of mandibular lengthening and widening toward the development of intra-oral devices.

However nowadays both internal and external distractors are used in a variety of indications in these cases each of the two types of distractor devices has its own advantages and disadvantages.

Aim of the work:

The aim of this study is to compare external and internal distraction devices for mandibular lengthening in terms of bone lengthening, patient comfort, and complications.

The study will be conducted on 30 patients who are suffering mandibular problems either congenital acquired or post tumor mandibular resection that requires lengthening of the mandible, attending the outpatient clinic of Plastic Surgery Department in Ain Shams University Hospital \& Assiut University Hospital.

Preoperative assessment:

* Informed consent will be obtained from all patients before their inclusion in the study.
* Photographs will be taken for the patient in lateral, antro-posterior and oblique positions preoperative.
* Lateral cephalometric radiographs or computed tomography (CT) or cone beam CT scans will be done for each patient pre-operatively.
* The decision to perform internal or external device will be based on preoperative and intraoperative considerations, such as anatomical bony characteristics affecting the possibility to place internal devices and patient cooperation.

Principles of the operation:

* anaesthesia: general anesthesia.
* Intraoperative consideration of internal versus external distractor is decided depending on the availability of bone stock.
* Osteotomy will be done according to each case individually making sure that it suits the vector of distraction required for each case.
* The approach for the external devices will be intraoral between the mental nerve anteriorly and gonial area posteriorly on both sides of the mandible.
* The approach for internal devices will be intraoral. While preserving the mandibular branch of the facial nerve.
* After 3-5 days of latency period for callus organization, gradual lengthening of the mandible will be performed at a rate of 0.5 mm twice a day for a total of 1 mm per day until achieving desired length.

Postoperative management and assessment:

* The patient will take broad spectrum and anaerobic antibiotics, anti-edematous, analgesic in addition to supportive treatment.
* After 3-5 days of latency period for callus organization according to patient age and condition, gradual lengthening of the mandible was performed at a rate of 0.5 mm twice a day for a total of 1 mm per day until achieving desired length.
* Following distraction phase there will be consolidation phase that will not be less than 8 weeks.
* Removing of internal or external distractor device and start retention phase if required with assistance of orthodontic appliances to avoid relapse.
* The patients will be evaluated with lateral cephalograms and head CT to assess the changes and amount of new bone formation following distraction.

Eligibility Criteria:
Inclusion Criteria:

1. Males or females with congenital retrognathia or micrognathia.
2. Males and females between one month and 50 years.
3. Patients with acquired mandibular deformities as post traumatic (temporomandibular ankyloses), asymmetries, post-surgical as after mandibular tumor resection and irradiation.

Exclusion Criteria:

1. Patients with systemic illness as cardiac diseases, or mental disorders \& hepatic patients (generally debilitating diseases).