Distraction Osteogenesis 

Updated: Jan 06, 2015
Author: Pravin K Patel, MD; Chief Editor: Jorge I de la Torre, MD, FACS 

Overview

Background

Distraction osteogenesis is a technique that relies on the normal healing process that occurs between controlled, surgically osteotomized bone segments. De novo bone lengthening occurs by gradual, controlled distraction. In contrast to traditional approaches, the soft tissue envelope (the skin, muscle, and neurovascular structures) is simultaneously expanded, which stabilizes the skeletal reconstruction. The technique today is an important part of the reconstructive surgeon's armamentarium.

History of the Procedure

The idea of gradual bone lengthening is not new. The concept originated with orthopedic colleagues solving the problem of leg length discrepancies. In 1905, Codivilla lengthened a femur through serial application of casts that were cut and advanced using bed-frame traction. In 1927, Abbot replaced the casts with large pins placed through fractured femur segments and used springs to lengthen limb. In 1948, Allan incorporated a screw device that more accurately controlled the rate of distraction. However, these early attempts frequently were complicated by infection, ischemic necrosis of skin and muscle, malunion, and delayed ossification with fibrous union.

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.[1] 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.[2] Thereafter, its role rapidly expanded to the midface and nearly all classic approaches to craniofacial reconstruction.

Pathophysiology

As an underlying principle, Ilizarov proposed the tension-stress model where "slow steady traction of tissues causes them to become metabolically activated, resulting in an increase in the proliferative and biosynthetic functions."[1] The premise is that the newly generated bone between distracted bony ends will result in a stable lengthening and behave as "new" bone, appropriately responding and adapting to the regional environmental loads placed on it.

Osteogenesis may be through a cartilaginous or fibrous intermediate. The former, known as endochondral bone formation, is found in the axial skeleton; the latter, intramembranous ossification, is primarily in the craniofacial skeleton. Distraction osteogenesis mimics intramembranous ossification where recruitment and differentiation of primitive cells create a new bony framework. Histologic studies identified 4 stages that result in the eventual formation of mature bone.

  • Stage I, Fibrous tissue precursor: The intervening gap initially is composed of fibrous tissue comprised of longitudinally oriented collagen with spindle-shaped fibroblasts within a mesenchymal matrix of undifferentiated cells.

  • Stage II, Creation of bony scaffold: Slender trabeculae of bone are observed extending from the bony edges. Early bone formation advances along collagen fibers with osteoblasts on the surface of these early bony spicules laying down bone matrix. Histochemically, significantly increased levels of alkaline phosphatase, pyruvic acid, and lactic acid are noted.

  • Stage III, Bony remodeling: Remodeling begins with advancing zones of bone apposition and resorption and an increase in the number of osteoclasts.

  • Stage IV: Structural modification: Compact cortical bone is formed adjacent to the mature bone of the sectioned bone ends, with increasingly less longitudinally oriented bony spicules; this resembles the normal architecture.

As the bone undergoes lengthening, each of these stages is observed to overlap from the central zone of primarily fibrous tissue to the zone of increasingly mature bone adjacent to the bony edges. By 8 months, the intervening bone within the distraction zone achieves 90% of the normal bony architecture. Its architecture is believed to be able to withstand normal functional loads.

Indications

Indications for the use of distraction are broad, and it is applied to solve a wide range of craniofacial deformities. While its use continues to evolve, its appropriateness depends on the particular clinical problem that needs to be addressed.

Distraction osteogenesis is an essential procedure in children with craniofacial/hemifacial microsomia. Its indication is based on the severity of the mandibular deficiency. It is ideal in children with Pruzansky class II mandibular deformity if there is sufficient ramus to allow for osteotomy and placement of the distraction device. In Pruzansky class I there is typically sufficient bone to allow for conventional orthognathic surgery. In class III, in which there is insufficient bone for distraction, conventional costochondral rib grafts or vascularized fibula grafts are necessary, followed by distraction osteogenesis when needed.

Many children are likely to require staged procedures, with secondary distraction and/or conventional orthognathic surgery, to be able to control the symmetry in multiple planes. In many cases, simultaneous maxillary-mandibular distraction, in which mandibular distraction device drives the maxillary distraction, can be beneficial.

In children with significant bilateral mandibular hypoplasia in whom the airway may be compromised or in those who are dependent on tracheostomy, early bone lengthening through distraction may be beneficial.[3] Increasing experience with neonatal distraction has shown that in selected cases (eg, Pierre Robin sequence), the need for tracheostomy can be avoided or the tracheostomy tube can be decannulated. See the image below.[4, 5, 6]

Infant with Pierre Robin sequence. Infant with Pierre Robin sequence.

Children with severe midfacial deformities in the context of facial clefts and craniofacial conditions may also benefit from distraction.[5, 7] . It is believed that problems from rebounding forces of the soft tissue envelope and skeletal relapse are less likely to occur with gradual advancement, in contrast to conventional approaches.

With the evolution of innovative devices, distraction is applied to an ever-increasing range of reconstructive problems, from deficient alveolar ridges to orbitofrontal advancement. Nevertheless, as with any promising innovation, the benefits and risks of distraction must be weighed carefully. Advantages cited in the literature include minimal likelihood of relapse, increased stability with large movements, simultaneous expansion of soft tissue, decreased operative time, and decreased blood loss and morbidity associated with bone grafts.

However, from the placement of the device to its removal, distraction typically requires a period of months; this required length of time needs to be balanced against the procedure’s psychosocial impact on the child or adolescent.

Contraindications

Disadvantages of distraction osteogenesis include device failure, cutaneous scars with external pin-based devices, necessity of a secondary procedure for removal of internal devices, limited control of the distracting vector with internal devices, patient compliance and acceptance of the device, and the increased overall treatment time. Additional issues are related to the specifics of the osteotomies, such as neurovascular injury and dental injury.

The most significant contraindication to the use of distraction osteogenesis involves the difficulties that patients and their parents may have accepting the distraction device and the treatment process itself. For many children and adolescents, as well as their parents, the significant commitment, compliance, and management required during the distraction procedure may at times be difficult to balance with day-to-day activities. Moreover, children may have significant fear of the procedure, and parents can be hesitant to activate the device.

When distraction is performed during the school year, it can significantly impact peer acceptance and the patient’s education. When it is carried out during the summer, the procedure affects summer athletic activities and family vacations. Patients must be thoughtfully selected and fully informed about the treatment process. At our institution, the psychologist is an integral member of the treatment team, and parents and patients are encouraged to meet and talk with families who have had experience with a similar distraction procedure.

 

Workup

Consultations

Children who are potential candidates for skeletal distraction are evaluated and managed in a multidisciplinary setting that primarily includes the following clinicians:

  • Plastic/craniofacial surgeon

  • Orthodontist

  • Psychologist

  • Speech/language pathologist

Other specialists, including in otolaryngology, neurosurgery, and sleep medicine, are involved depending on the specific circumstances.

Imaging Studies

The workup primarily relies on radiographic information to define the anatomic deformity and to assess whether distraction osteogenesis is a viable alternative to conventional surgery. Routine radiographic studies typically include computed tomography (CT) scanning with three-dimensional (3-D) reconstructions and dental radiographs (Panorex, frontal, and lateral cephalometric films). These studies serve to give a 3-D representation of the craniofacial abnormality and to determine whether sufficient bony stock is present for device fixation (see the image below).[8] Moreover, with current advancements in software, osteotomies and distraction devices can be virtually simulated.

CT imaging illustrating skeletal deformity and air CT imaging illustrating skeletal deformity and airway compromise in infant with Pierre Robin sequence.

Other Tests

Neonates and infants with obstructive apnea may require polysomnography, flexible nasoendoscopy, and direct bronchoscopy for the diagnosis of retroglossal obstruction and synchronous tracheomalacia.[7] Failure of conservative measures should be documented.

 

Treatment

Surgical Therapy

Regardless of which facial skeletal element is undergoing distraction, the treatment can be divided broadly into the following phases:

  • Presurgical phase

  • Operative phase

  • Lag phase

  • Distraction phase

  • Consolidation phase

  • Retention phase

Presurgical phase

This phase involves radiographic studies to determine the feasibility of placement of the distraction device, whether an internal or external device is more appropriate, and the vector (direction, amplitude) of the distraction. Anticipated trajectory depends directly on the distraction vector, which can be vertical, horizontal, or oblique. Multiplanar devices even allow manipulation of the vector during the distraction phase. When possible, the use of printed, patient-specific 3-D anatomic models helps to visualize the placement of the distraction device and the osteotomy and to simulate the distraction process. See the image below.

Presurgical planning to determine the distraction Presurgical planning to determine the distraction vector and osteotomies.

Involvement of the orthodontist is essential during the presurgical phase. Presurgical orthodontic preparation assists the skeletal distraction by providing an occlusal guide.

Operative phase

Osteotomies used with distraction are well described with the conventional reconstructive approaches and need only be modified to accommodate the specific device. While the exact details may vary with the procedure, the following are guidelines:

Mandibular distraction

Adequate mandibular bone stock must be available for the osteotomy and placement of the device.

Numerous factors should be considered when deciding between an internal versus external device. External devices allow for more predictable, multidirectional control of the distraction, which cannot be achieved with the currently available internal devices.[9] However, external devices require multiple skin incisions that may lead to significant facial scarring. For many children and their families, the application of sequential distraction-vectors with a series of internal devices is preferable to the risk of permanent external scars.

The approach, either intraoral or extraoral, depends upon the degree of bony and soft-tissue exposure required for placement of the device and the allowable maxillary-mandibular opening.

The placement and direction of the device dictates the distraction vector. The osteotomy line does not necessarily need to be perpendicular to the distraction vector but should be placed to avoid injury to the inferior alveolar nerve and the developing dentition. In addition, avoidance of such injury can be facilitated by an incomplete osteotomy with subsequent separation occurring during the distraction phase. See the image below.

Intraoperative photographs of distractor placement Intraoperative photographs of distractor placement.

Temporarily fixing the distractor into position before making the osteotomy can simplify distractor placement. Positioning the device after the osteotomy can be difficult because of the mobility of the proximal segment.

Employ standard principles of a sagittal split osteotomy when lengthening the mandibular body. Preserve the nerve by using a reciprocating saw for the buccal corticotomy and “green-stick” fracturing the lingual cortex with an osteotome. Complete mobilization is not always necessary, since the distraction device completes the osteotomy. Warn the patient and family of the discomfort the patient will feel until the fracture is completed.

Prior to closure, test the device and clearly mark for the family the direction (clockwise or counterclockwise) of the driver used to turn the device.

Midfacial and frontofacial distraction

The use of external devices (head frame and/or helmet) typically requires the presurgical placement of a palatal appliance to guide the distraction vector in multiple planes relative to the skull base.[10]

The midface must be completely mobilized as with conventional approaches with conventional, well-defined osteotomies. Avoid dental root disruption during the stages of primary or mixed dentition by modifying the typical Le Fort I osteotomy. Place the horizontal cut more cephalad, near the level of the inferior orbital foramen.

Midfacial advancements at the Le Fort I level with currently available internal devices are limited because of the difficulty of appropriately orienting the devices in the limited space. The fixation of the device may also injure the developing dentition. External multidirectional devices are preferred, as they allow more control over the vector of the distraction process.

Midfacial advancement at the Le Fort III level[11] and frontofacial advancements can be approached with either internal or external devices, depending on the circumstances. Place the internal devices at the level of the body and arch of the zygoma. External devices require a palatal appliance and are supported by additional traction wires at the zygoma, nasal root, and supraorbital regions.

Lag phase

Before proceeding with distraction, there is a variable period (latency period) to allow for initial bone formation to occur. The period is typically 3-5 days, although in neonates and infants, the latency period may be omitted or last only 24 hours. With skeletal maturity, in contrast, the latency period is typically 5-7 days.

Distraction phase

The process of distraction is activated when bone segments are gradually pulled apart using either an internal or external device. Three variables must be set: the rate of distraction, the rhythm or frequency of distraction, and the total time of distraction. The rate of distraction is typically 1.0 mm/d.[12] Some advocate up to 2.0 mm/d in younger children to avoid early consolidation and a slower rate of 0.25-0.5 mm/d in older patients. This can be accomplished either once a day or divided throughout the day, determining the rhythm or frequency of distraction. While the distraction rate is 1.0 mm/d, ideally maintain the tissues under constant tension by dividing the total daily rate of distraction into smaller increments throughout the day to favor histogenesis.

The total time of the distraction phase is customized to the severity of the deformity and the patient’s demographics. There can be a discrepancy between the anticipated bone length and the total time of distraction. External devices that use pins to transmit the forces frequently bend, and the distance at the site of the distracting mechanism rarely equals the distance of the gap at the osteotomy sites. In hemifacial microsomia, for example, the position of the menton, distance from the lateral canthus to the commissure, and the mandibular cant should serve as clinical guidelines.

Consolidation phase

Once the desired correction is achieved with the distraction phase, allow mineralization of the immature bone to occur. Lock the distracting appliance into place to maintain stability until the newly formed bone has sufficient strength. The length of this phase varies depending on the circumstances. In general, 6-8 weeks is considered adequate. A guideline used by some centers is 2 days of consolidation to every day of distraction.

Retention phase

Remove the device and maintain stability, typically with the assistance of orthodontic appliances. In children with hemifacial microsomia, this step may require occlusal splints to guide the maxilla into position when the leveling of the mandibular cant creates a posterior open bite. In children with midfacial deformity, retention may require a face mask with elastic traction for a period of time.

Complications

Complications specific to the distraction process include the following[13] :

  • Device mechanism failure

  • Injury to the developing tooth follicles (eg, maxillary and mandibular osteotomies)

  • Injury to various branches of the facial or trigeminal nerves (eg, the inferior alveolar nerve with mandibular distraction)

  • Pin site infection with external devices or semiburied devices

  • Nonunion and premature fusion

  • Complications specific to the osteotomy

  • Psychosocial issues related to the recovery (length of treatment time and patient's physical appearance with distraction device)

Outcome and Prognosis

With increasing clinical experience, the long-term outcome and the specific role of distraction osteogenesis are better defined today. Clearly, distraction can generate bone with the capacity for remodeling and adaptation to functional loads. However, distraction osteogenesis is likely incapable of restoring the normal development of a once dysplastic pattern of craniofacial growth. Distraction techniques allow the surgeon to intervene earlier in childhood to restore the facial form and function, but the extent to which it eliminates subsequent conventional procedures remains uncertain. See the image below.

Typical airway changes after mandibular distractio Typical airway changes after mandibular distraction.

Future and Controversies

As with conventional orthognathic surgery, distraction osteogenesis of the craniofacial skeleton should be considered one of the many tools in the armamentarium of a surgeon. Compared with orthopedic lengthening and rotations of long bones, craniofacial distraction is highly complex. Challenges include careful placement of osteotomies to mobilize facial elements and the multidirectional vectors of distraction. Significant advances in computer-assisted surgery have occurred, and newly designed software can simulate osteotomies and planned distraction in difficult, asymmetrical cases.[14] Cone-beam CT scanners, which provide excellent bony resolution at a fraction of the radiation, are now available for intraoperative CT imaging and postoperative follow-up.

The extent to which distraction osteogenesis will replace conventional approaches depends largely on technical innovations that will allow for implantable multidirectional devices that can be easily activated and controlled remotely with minimal incisions.