Kéo giãn sinh xương điều trị thiểu sản hàm dưới nặng kèm thiếu lồi cầu bẩm sinh Mandibular distraCTion osteogenesis for severe hypoplasia with congenital absence of the condyle

The management of severe jaw deformities in growing children presents a fundamental question: should we intervene early, or should treatment be postponed until skeletal growth is complete?

For many dentofacial deformities, definitive orthognathic surgery is generally delayed until growth is nearly complete. However, when a skeletal deficiency is severe enough to compromise essential functions such as breathing and mastication, simply waiting for adulthood may not always be the most appropriate strategy.

This case involved an 11-year-old patient with severe mandibular hypoplasia, craniofacial asymmetry, and congenital absence of the right mandibular condyle.

Mandibular hypoplasia is more than an aesthetic problem

The patient presented with a Tessier No. 7 transverse facial cleft associated with right-sided hemifacial hypoplasia. The right mandible was severely underdeveloped, with congenital absence of the mandibular condyle.

The mandible as a whole was markedly small and retruded. This produced not only a significant facial deformity but also several functional consequences.

The underdeveloped dental arch contributed to severe dental crowding. More importantly, mandibular retrusion contributed to restriction of the retrolingual airway, and the patient was diagnosed with obstructive sleep apnea.

Treatment had previously been deferred because the patient was still growing.

In this situation, however, the objective of early intervention was not to create the patient's definitive adult facial result at the age of 11. The immediate priorities were to improve mandibular structure, breathing, and oral function while establishing a better foundation for subsequent growth and future treatment.

A staged reconstructive strategy

Following multidisciplinary assessment with Dr. Sang Nguyen Minh regarding the patient's sleep-disordered breathing, and with guidance from Professor Imad Abu El-Naaj, a staged treatment strategy was developed.

Stage 1: Condylar reconstruction

Because of the congenital absence of the right mandibular condyle, the first step was reconstruction of the condylar region using a costochondral graft.

In a growing child, a costochondral graft can be used to reconstruct the temporomandibular region and restore ramus height. Its subsequent growth behavior, however, can vary considerably between patients, making long-term surveillance throughout craniofacial development essential.

As part of the same treatment strategy, teeth 37 and 47 together with the developing 38 and 48 tooth germs were removed to facilitate the subsequent surgical and skeletal movements.

Stage 2: Mandibular distraction osteogenesis

Following reconstruction of the condylar region, the mandible was lengthened using distraction osteogenesis.

Unlike conventional osteotomy in which skeletal segments are immediately repositioned to their final location, distraction osteogenesis gradually generates new bone between surgically created bone surfaces.

The process consisted of four phases.

1. Osteotomy and distractor placement:Bilateral mandibular osteotomies were performed in the angle regions, and Zurich II distraction devices were placed.

2. Latency:A seven-day latency period was observed after surgery before activation of the distractors. During this period, the initial healing process developed between the osteotomized bone surfaces.

3. Distraction:The mandibular segments were gradually separated at approximately 1 mm per day.

Controlled mechanical distraction stimulates new bone formation within the developing gap while allowing the surrounding soft tissues to progressively adapt to the increasing mandibular length.

4. Consolidation:Once the intended advancement had been achieved, the devices were maintained in position while the newly generated bone underwent progressive mineralization and maturation. This phase extends over several months and is monitored clinically and radiographically.

Why distraction osteogenesis?

For an 11-year-old patient with a severely deficient mandible requiring substantial lengthening, distraction osteogenesis offers an important advantage: the skeletal framework and surrounding soft tissues can be lengthened progressively rather than requiring the entire correction to be achieved during a single acute movement.

As new bone forms within the distraction gap, the muscles, mucosa, skin, and other surrounding soft tissues are given time to adapt to the changing mandibular dimensions.

In this patient, mandibular advancement was intended to achieve more than an improvement in facial appearance. Increasing mandibular length and projection was also intended to improve the relationship of the tongue and lower facial structures to the upper airway, thereby contributing to management of the patient's obstructive sleep apnea.

Four months into consolidation

At four months into the consolidation phase, CT imaging demonstrated good ossification of the regenerate within the distraction sites.

The patient's masticatory function had improved, together with a clear clinical improvement in breathing.

This, however, does not represent the end of treatment.

Orthodontic treatment is continuing to address the severe dental crowding. Maxillary expansion is also being performed to correct the transverse discrepancy between the dental arches and, in appropriately selected patients, may additionally increase dimensions of the nasal cavity.

Early intervention does not mean definitive treatment

An important distinction in cases such as this is the difference between early intervention to restore function and definitive orthognathic correction after completion of growth.

At 11 years of age, substantial craniofacial growth remains. In a patient with a complex congenital deformity and a reconstructed condyle using a costochondral graft, the future growth pattern cannot be predicted with complete accuracy.

The current objective is therefore not to create a definitive adult result during childhood.

Rather, the aim is to reconstruct essential anatomy, improve the airway and function, create additional space for the developing dentition, and establish a more favorable foundation for subsequent craniofacial growth.

As the patient approaches skeletal maturity, maxillomandibular growth and facial development will be reassessed. Definitive orthognathic surgery may then be considered to further optimize jaw relationships, occlusion, and facial symmetry.

This case demonstrates that young age does not necessarily mean that all skeletal intervention should be postponed. When a severe craniofacial deformity is already compromising breathing and function, the key is to define the objective of each treatment stage and develop a long-term strategy that evolves with the patient.