Introduction:
It is an elongation technique that uses the same principle of bone repair seen after a fracture. A fracture is a bone break that commonly happens in accidents, falls, or sports injuries. It is treated by approximating and aligning the broken pieces and immobilizing them in a cast.
During healing, new bone forms between the broken pieces, forming a soft callus that ultimately ossifies (hardens) and joins the fragments. This healing process, with the formation of new bone, is known as osteogenesis.
During CDO, an undersized bone is intentionally fractured, which will initiate osteogenesis, but instead of a cast, a mechanical device (distractor) is fixed to connect the broken fragments. This is done because the direction of the new bone that will form between the fractured parts will be under the surgeon's control. The entire process of breaking and forming new bone is done until the undersized bone has reached its desired length. This part of the process is called distraction osteogenesis (DO), and if it is done in the head and face, it is called craniofacial distraction osteogenesis (CDO).
Who Needs a CDO?
Patients with bone deformities in the face and the head will benefit from CDO. Most often, these deformities are congenital (present at birth) and occur due to genetic abnormalities. A few defects are mentioned below:
- Mandibular Hypoplasia- Hypoplasia means arrested development, and when this happens in the mandible (lower jaw), it is known as mandibular hypoplasia. The arrested development results in a small-sized mandible called micrognathia. Micrognathia does not occur alone; it is always combined with glossoptosis (tongue pushed back into the throat) and cleft palate (a split in the roof of the mouth). All three signs occur in a sequence known as the Pierre Robin sequence. A genetic abnormality may have just the signs of the Pierre Robin sequence or can be in combination with other defects; for example, patients with stickler syndrome have the three cardinal signs of the Pierre Robin sequence along with eye defects, hearing impairments, and joint deformities.
- Midface Hypoplasia- Another set of bone deformities, but this time they are seen in the bones in the middle of the face. The associated features of midface hypoplasia are hypoplastic nasal bone, small maxilla (upper jaw), and cleft lip and palate. The presence of these signs depends on the penetrance of the abnormal gene. Penetrance in the proportion of the abnormal gene, for a better understanding of the same stickler syndrome, can be used; if the abnormal gene is present superficially, it may cause only the Pierre robin sequence, but if it gets completely mutated, then the same patient with stickler syndrome will have midface hypoplasia as well.
- Craniosynostosis- This is a cranial defect due to the early fusion of the bones in the baby's skull. The skull is not one huge bone; it is made of six bones (a total of eight in number), fusing together at different times after birth. The location of the fusion is known as a suture.
The fusion timing may range from three months to three years, facilitating the baby's brain growth after birth. However, if there is a genetic anomaly, the sutures fuse beforehand (craniosynostosis) and retard brain development. With CDO, the surgeon can correct the structural deformity in the conditions mentioned above, thereby improving the quality of life.
Does CDO Only Restore the Shape of the Deformed Bones?
Craniofacial distraction osteogenesis (CDO) is more than an aesthetic treatment; it helps to restore normal physiology and brain development, emotional well-being, and overall quality of life. Patients with mandibular and midface dysplasia have their tongues pushed into the throat due to underdeveloped jaws; this will cause airway obstruction, sleep apnea, and difficulty swallowing.
If left untreated, craniosynostosis will lead to severe craniofacial (skull and face) deformity, intracranial (inside the skull) hypertension, cognitive impairment, developmental delays, seizures, blindness, and death. With CDO's help, patients can avoid possible tracheostomy (a surgical procedure to relieve airway obstruction) and craniotomy (brain surgery to relieve intracranial hypertension).
What Happens During CDO?
The entire process of intentionally breaking the deformed bone and forming and stabilization of the new bone takes place in four stages, they are-
- Initial Osteotomy/Distractor Placement Phase- The surgeon creates an osteotomy (cutting the bone) in the desired bone and places the distractor device. In cases of craniosynostosis, the surgeon will use the existing suture line as a guide to place the distractor. A distractor comes in different forms and sizes and can be external or internal; it is chosen depending on the type of deformity. This ends phase one of CDO.
- Latency Phase- This is a waiting period for the broken bone to begin to heal; a soft callus (a type of soft bone) forms during this time. This phase can last from 24 hours to 5 days after phase 1.
- Active Distraction Phase- The distractor placed in phase one is activated in this phase. It gently pulls the soft callus by applying traction at intervals in the desired direction, leading to osteogenesis. The activation is done twice per day for a few weeks.
- Consolidation Phase-The soft callus pulled during the distraction phase is now left in place to mineralize, remodel and mature into an ossified bone. During this phase, the distractor is kept in place to provide rigid fixation of the bony fragments. Once the consolidation phase is over, the distractor device is removed.
The surgeon will always extend the deformed bone beyond the normal measurements in account of relapse, which will happen in almost all bone remodeling procedures. Although the phases mentioned above outline the underlying principle of CDO, the interdisciplinary team managing the patient will always customize CDO depending on individual needs.
What Are the Complications of CDO?
The following are a few complications associated with CDO:
- Device Failure- This rarely happens when the distractor device breaks; the location of the distraction plays an important role in the device failure.
- Device Extrusion- Also a rare complication, happens when the orthodontic forces (force applied by the teeth) exceed orthopedic forces (force applied by the bone). This will result in the movement of the device by the bone instead of the device moving the bone.
- Relapse- This happens more often than other complications, especially in the mandible. This is why the distraction is always done in excess to compensate for the reduction during relapse.
- Injury to the Tooth Buds- Thishappens when osteotomy extends beyond the cortical (outer) part of the bone in the mandible and maxilla and can be avoided with proper planning and 3D imaging.
- Malocclusion- This is more of a consequence rather than a complication because patients with mandibular and midface dysplasia already have distorted teeth; CDO only improves the size of the bone in which the distorted teeth are present; it does not align the teeth. Orthodontic treatment is essential for these patients after CDO.
- Nerve Injury- This happens in the mandible because the preferred site of osteotomy is at the angle (junction between the lower border of the ramus and the inferior border of the body) of the mandible, which is where the inferior alveolar nerve passes through.
- Cerebrospinal Fluid Leak- Extremely rare and can occur during cranial vault (skull) expansion.
- Scarring- Is seen when external distraction devices are used and can be minimized by placing tension-free sutures after the device placement.
- Infection- Can be prevented by prescribing prophylactic pre and post-op antibiotics.
Conclusion-
Managing genetic abnormalities with congenital defects requires an interdisciplinary team of craniofacial surgeons, otolaryngologists, neurosurgeons, ophthalmologists, plastic surgeons, dentists, geneticists, physical therapists, etc. The success of CDO depends on all of them. Preoperative assessment with computed tomographic (CT) scans and magnetic resonance imaging (MRI) are essential for treatment planning. CDO is a well-tolerated procedure, and with a standardized postoperative pathway, it can improve the patient's overall well-being.
