Distraction osteogenesis (DO) may be the most versatile tool to become available to the craniofacial surgeon in recent years. It can be used in an ever-expanding register of clinical scenarios and offers major advantages over conventional craniofacial techniques in some circumstances. Craniofacial surgery has significant complications, some of which can be mitigated but not eliminated by choosing DO over conventional approaches. Although some DO applications are in their infancy with limited data, this article provides an overview of current uses of this versatile technology.
Key points
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Distraction osteogenesis has a wide variety of applications in the craniofacial skeleton.
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Greater degrees of skeletal movement can be achieved with distraction osteogenesis compared with conventional techniques.
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The decision to use distraction osteogenesis, conventional osteotomy, or a combination of techniques should be based on individual patient situations.
Overview
Distraction osteogenesis (DO) is a method of inducing new bone formation within a gap between 2 bony surfaces of an osteotomy via gradual application of an external separating force. Orthopedic surgeons have used this technique for nearly a century to lengthen long bones, and much of the current understanding of the biomechanics involved and progression of the osteoneogenesis has been extrapolated from this literature. Initial interest in application of DO to surgical osteotomies in the craniofacial skeleton centered on lengthening the mandible or on repairing segmental mandibular defects. In the early 20th century, European surgeons pioneered mandibular DO in animal models. From the 1970s through the 1990s, various canine models were used to develop techniques to lengthen the mandible via distraction at a surgically created osteotomy. Rosenthal reported the first clinical results of DO of the human mandible in 1927, and since then DO has been applied to an ever-expanding list of locations and clinical scenarios throughout the craniofacial skeleton.
The underlying goal of DO, regardless of specific anatomic location, is to lengthen the chosen bone, thereby establishing more normal anatomic size and position relative to surrounding structures. The surgical osteotomy is created (or the distractor can be placed across an existing suture), the distractor device is applied, and a latency period is allowed to elapse before beginning distraction. This latency phase allows initial bone healing to begin at the osteotomy gap via bony callus formation. The bony segments are gradually separated by activating the distractor device over a period of several days. This is the distraction phase, gradually stretching the callus, inducing osteoneogenesis. Once the desired length is achieved, distraction stops, and the soft immature bone now present in the distraction gap mineralizes, eventually resembling mature bone. This newly formed bone is likely never as strong as native bone. The cross-section of the regenerate can only be as big as the cross-section of the bone at the osteotomy and is frequently smaller. This should factor into the planning of the osteotomy location. During this consolidation phase, the distractor device is left in situ to provide rigid fixation to the bony segments, facilitating maturation of the bony regenerate and preventing skeletal relapse and pseudoarthrosis.
Overview
Distraction osteogenesis (DO) is a method of inducing new bone formation within a gap between 2 bony surfaces of an osteotomy via gradual application of an external separating force. Orthopedic surgeons have used this technique for nearly a century to lengthen long bones, and much of the current understanding of the biomechanics involved and progression of the osteoneogenesis has been extrapolated from this literature. Initial interest in application of DO to surgical osteotomies in the craniofacial skeleton centered on lengthening the mandible or on repairing segmental mandibular defects. In the early 20th century, European surgeons pioneered mandibular DO in animal models. From the 1970s through the 1990s, various canine models were used to develop techniques to lengthen the mandible via distraction at a surgically created osteotomy. Rosenthal reported the first clinical results of DO of the human mandible in 1927, and since then DO has been applied to an ever-expanding list of locations and clinical scenarios throughout the craniofacial skeleton.
The underlying goal of DO, regardless of specific anatomic location, is to lengthen the chosen bone, thereby establishing more normal anatomic size and position relative to surrounding structures. The surgical osteotomy is created (or the distractor can be placed across an existing suture), the distractor device is applied, and a latency period is allowed to elapse before beginning distraction. This latency phase allows initial bone healing to begin at the osteotomy gap via bony callus formation. The bony segments are gradually separated by activating the distractor device over a period of several days. This is the distraction phase, gradually stretching the callus, inducing osteoneogenesis. Once the desired length is achieved, distraction stops, and the soft immature bone now present in the distraction gap mineralizes, eventually resembling mature bone. This newly formed bone is likely never as strong as native bone. The cross-section of the regenerate can only be as big as the cross-section of the bone at the osteotomy and is frequently smaller. This should factor into the planning of the osteotomy location. During this consolidation phase, the distractor device is left in situ to provide rigid fixation to the bony segments, facilitating maturation of the bony regenerate and preventing skeletal relapse and pseudoarthrosis.
Preoperative planning
When considering DO of the craniofacial skeleton, planning begins with a thorough history and physical examination. Particular attention should be given to occlusion, cranial vault shape, and position of the orbits (and globes within them), as well as the overall shape and symmetry of the maxillofacial region. Photographs are taken and placed in the medical record. Cephalograms, both lateral and frontal, are useful in nearly all patients. Pantomograms of the tooth-bearing areas are helpful as well. High-resolution 3D computed tomograms are most useful for analysis and planning although the radiation particularly of children should be considered and minimized. Computer-aided design/computer-aided manufacturing systems are widely available to construct life-size acrylic models or perform virtual surgery for planning purposes. Detailed anatomy, including defect or malposition magnitude and precise location of brain, eye, tooth, and other important structures, are well visualized. An additional advantage is the ability to clearly evaluate surrounding bone stock to ensure adequate amounts are available to generate bone and secure the selected distractor devices. This technology allows planning osteotomy sites, device placement, and final desired position of the distracted bones. Plastic jigs or guides can be constructive for intraoperative guiding of these steps. The distractors in some cases can be custom made or shaped for a specific situation.
Surgical Technique
A detailed discussion of the individual procedures performed for craniomaxillofacial distraction osteogenesis is not the purpose here. Certain important points bear mention. With regard to positioning and prepping, there are 2 points. Regardless of the approach chosen, there is a reasonable chance the aerodigestive tract will be traversed at some point. Therefore, we prefer complete irrigation of the nasal, oral, and pharyngeal cavities with 3% hydrogen peroxide solution, including brushing teeth if present. A second irrigation of the same areas is done with 10% povidone-iodine solution (Betadine, Purdue Pharma, LP, Stamford, CT), and the teeth if present are brushed again. For scalp incisions the hair is washed with Betadine scrub. Then the external field is prepped with the same povidone-iodine solution.
Patient positioning
For the majority of craniofacial DO surgeries, the patient is placed supine, with the head of the operating table rotated about 120° away from the anesthesiologist to allow the surgical team maximum access to all sides of the head. For bilateral mandibular distraction, the table usually is not turned. The head of the operating table is extended, and the whole table is placed in reverse Trendelenburg position.
Although we have found this positioning to be amenable to nearly all DO surgeries (including some posterior cranial vault distractions), some authors prefer either the standard prone position or the “sphinx” position, wherein the patient is placed prone with the neck maximally extended and head elevated with the arms placed anteriorly. These positions allow better access to the entire skull and posterior cranium, but special care must be taken to pad the multiple pressure points created along the chin and mandible and especially to secure the endotracheal tube, which can be disastrous if dislodged in this position. Air embolism might be more likely with the sphinx position as well, owing to the open circulation of the medullary space and the skull osteotomies being elevated significantly above the heart. In the senior author’s practice, the prone position is reserved for cases where successful posterior distraction requires osteotomy to the level of the foramen magnum.
Distractor selection
The first choice is (semi)internal versus external devices. The prefix “semi-“ refers to intraoral devices where all or part of the body of the device is not buried under the tissues but remains contained in the mouth. Otherwise the internal devices are buried, but there is always a partially exposed activator mechanism. The external devices are outside the patient connected to the bone percutaneously.
External Distractors
In the current practice of the senior author (S.A.T.), the majority of DO performed utilizes internal devices; however, some situations exist wherein external devices may be superior. Arguments for internal or external devices exist throughout the literature. Internal devices may increase long-term patient compliance because they are less conspicuous and less likely to be dislodged by patient activity. Some authors feel the distraction forces are better transmitted via the direct fixation of the device to bone with screws rather than the more distant percutaneous fixation of external devices. The internal devices require more exposure and dissection to place. Their vector cannot be altered once placed (some designs offer limited adjustability), and perhaps most important, they require a second frequently difficult procedure for removal. Often the distraction process has moved the devices away from the incision used to place them, making their exposure even more difficult.
External devices allow more fine tuning of distraction vectors, better facilitate multivector distraction, and may be used when inadequate bone stock exists for implanted devices to be anchored. There are external scars at every percutaneous entry site and some of these pins and wires migrate through the soft tissue, amplifying the scarring. The halo devices ( Fig. 1 ) often require transcutaneous facial attachments, but some are used exclusively with custom intraoral appliances having builtin attachments. They are not at all hidden, and they are more subject to dislodgement by patient activity. If placed away from the typical mandibular osteotomy site, the pins might present less harm to the dentition than the screws of an internal device placed right over the osteotomy. Additionally, their removal is typically a minor procedure, often appropriately done in the office.
In some direct comparative series, these devices were found to be less effective than external, percutaneous systems; however, both DO devices outperformed traditional orthognathic surgery in long-term outcomes. The authors prefer to utilize internal distractors whenever possible, with the understanding that removal of these devices is a more significant operation than removal of external distractors. The benefits of improved transmission of distraction force and increased patient comfort and compliance are felt to outweigh these drawbacks.
Mandibular Distraction
For infant distraction when airway compromise persists through nonoperative measures and a tracheotomy is being contemplated, mandibular distraction offers another option. External multivector devices anchored percutaneously with osteotomies performed through intraoral incisions have been traditional. New internal devices are available that are small enough to fit on the bone stock of the neonatal mandible. These are typically placed through retromandibular or submandibular incisions.
In older patients, there is greater variety in distractor type and technique applied. For asymmetry problems like craniofacial microsomia, the movements can be very complex and require careful planning. There is often a combination of ramus lengthening, body lengthening, and gonial angle rotation. This type of movement requires external multivector devices. Symmetric mandibular distraction with gonial angle rotation is frequently performed with curvilinear, internal distractor devices placed via intraoral incisions.
Upper and Midface Distraction
Midface distraction can be performed at the Le Fort I, II, or III or monobloc levels. When DO is being entertained for midface hypoplasia, it is essential to consider cranial volume, periorbital aesthetics and function, and occlusal needs separately. Cranial volume and periorbital function and aesthetics include the position of the anterior cranium, the frontoorbital bar, the malar eminence, and the infraorbital rim relative to the globe position. Retro positioning of these structures can result in increases in intracranial and intraorbital pressures damaging both brain and eye function if left untreated. This analysis dictates the specific distraction level necessary to achieve the desired result. If only the lower midface is retruded, a LeFort I advancement may suffice to correct the occlusion. If the forehead and frontoorbital complex, as well as the malar eminences, lie in a normal anatomic position, but the “central face ” (nasal and lower maxillary structures) are retruded, a LeFort II-type osteotomy can be used to correct this. Parts of this can be measured empirically via the sella-nasion A angle on a lateral cephalogram ( Fig. 2 ), understanding that the position of the malar eminence will go unnoticed with this measurement, and clinical judgment must be employed regarding its relative position. Additionally, some of the craniofacial dysostosis syndromes have abnormal orientation of the anterior cranial fossa rendering sella-nasion a poor reference line. The normal sella-nasion A angle is 81° ± 3°. If the nasal complex, inferior orbits, and malar eminences are also retruded, a Le Fort III osteotomy will be required to correct this. If the entirety of the frontoorbital complex, in addition to the midface structures, is retruded, monobloc advancement may be required to restore normal contour and relieve abnormal stresses on the eyes and frontal lobes ( Fig. 3 ). In this case, the sella-nasion A angle may be overly obtuse or normal, but such judgment is often made based on an overall clinical and radiographic examination of the skull and skull base in its entirety. The occlusion might need to be set separately from the upper and midface aesthetics with later Le Fort I level or mandibular movement.
Approaches
Necessary exposure of the skeleton for these procedures can be achieved through a combination of coronal, periorbital, and intraoral incisions and subperiosteal dissection. As with the mandible, use of external devices requires less exposure, and internal devices require more exposure. Internal devices for Le Fort I and II distraction can be placed intraorally. Internal devices for Le Fort III and monobloc distraction are placed in the temporal fossae. A Le Fort I is performed through an upper vestibular sulcus incision that also provides exposure for intraoral device placement.
For LeFort II advancement, nasoorbital exposure in additional to the intraoral incision is needed. It is possible to perform the nasal and orbital osteotomies without the use of a coronal approach, either via nasal root incision or Lynch incisions, although either of these approaches will result in visible scars that may be unacceptable to some patients. Transconjunctival and transcaruncular incision avoid this. Midface degloving is another option. The LeFort III can be done with these approaches as well if an external halo type distractor is to be used. For a Le Fort III with internal devices or a monobloc distraction with either an internal or external device, a coronal incision is necessary. A camouflaged sigmoid or saw tooth type of incision is recommended.
Osteotomies and Device Placement
The osteotomies are performed no differently for distraction than for standard skeletal movements, although many surgeons prefer to place the devices and drill the anchoring screw holes before performing osteotomies. The most important point is that the need for complete segment mobility is obvious when the segment is to be moved. However, when it is not to be initially moved but to be moved by distraction, it is a pitfall not to ensure totally the mobility of the segment as well. Distraction will fail if the mobilized segment is not totally mobilized. Another point worth mentioning is sealing of the anterior cranial fossa during a monobloc. When traditional monobloc advancement is done, the cranial cavity is generally sealed with a pericranial flap and fibrin glue. When the osteotomy is done without initial advancement, it should still be sealed at least with glue if not also the flap to separate the sinonasal contents from the dura.
Once complete segment mobilization is assured, the devices are placed. Previously drilled holes or custom drill guides from computer planning determine internal device placement for the desired vector of distraction. Generally, 3 or 4 screws on each side of the osteotomy are required, with care being taken to avoid underlying neurovascular and dental structures. If a halo device is to be used, careful planning of bandeau and craniotomy osteotomies is required to ensure adequate stable skull posterior to these cuts to support the distractor hardware. The devices should be test activated once placed to ensure proper function.
Cranial Vault Distraction
The use of DO as an alternative to conventional surgery for singlesuture and multisuture craniosynostosis is a recent development and an area of active research. Although they work slightly differently than distractors, springs should be mentioned as a less invasive method for cranial alteration as well. It may be possible to achieve similar results in terms of cranial growth and stability to standard surgical methods using DO or springs with the potential for shorter operative times and fewer complications. Thus far, available data from some centers suggest that there is no difference in terms of outcomes, complications, length of stay, or blood loss. Given the rarity of the underlying conditions, it has been proposed a certain learning curve exists, and as surgeons’ experience increases, some of these anticipated benefits might be demonstrated ( Fig. 4 ).
