Distraction Osteogenesis of the Mandible 

Updated: Mar 08, 2016
Author: Dale A Baur, MD, DDS; Chief Editor: Arlen D Meyers, MD, MBA 

Overview

Background

Distraction osteogenesis, also termed callotasis, callus distraction, and osteodistraction, is the surgical technique of generating new bone by progressive stretching of divided segments. Following its introduction, distraction osteogenesis gained immediate interest and has been widely performed in the maxillofacial complex.

History of the Procedure

A crude method of distraction osteogenesis first appeared in the literature in 1905 and was described by Codivilla, who used the technique to elongate a femur.

Ilizarov is the father of modern distraction osteogenesis. In 1951, Ilizarov developed a technique for repairing complex fractures or nonunions of the long bones. While treating a patient with a short amputation stump, Ilizarov performed an osteotomy and applied an external fixator to lengthen the stump with the intention of placing a bone graft. However, by chance, he discovered that the bone grew in the distraction gap, eliminating the need for a bone graft. Later research by Ilizarov demonstrated that the tension-stress effect caused an increase in metabolic activity, an increase in cellular proliferation, and a neovascular ingrowth similar to normal endochondral ossification. Over the ensuing years, Ilizarov perfected the technique in long bones.[1]

Distraction osteogenesis of the mandible is shown in the image below.

Distraction osteogenesis of the mandible. Alveolar Distraction osteogenesis of the mandible. Alveolar distractor used to increase the height of the alveolar bone. Courtesy of K.L.S. Martin, LP.

In 1992, McCarthy reported a series of 4 young patients (average age, 78 mo) who successfully underwent gradual distraction of the mandible without grafting, transfusion, or intermaxillary fixation.[2] Early in the history of this procedure, distraction osteogenesis of the mandible involved using bulky external distractors. Although these external distractors still have a place in certain applications, a wide variety of intraoral internal distractors are now available; these distractors are small and compact, with increased patient comfort and acceptance.

Distraction osteogenesis is now a feasible treatment option for adults and children with unilateral or bilateral mandibular hypoplasia. It is a treatment option for widening an excessively narrow mandible. Distraction osteogenesis is also a treatment alternative for the management of airway obstruction (eg, obstructive sleep apnea [OSA]), continuity defects of the mandible, reconstruction after a resection, and alveolar crest augmentation.

Problem

Mandibular retrognathia is one of the most common craniofacial deformities; approximately 10% of the population have significant dental overjet. Mandibular retrognathia can be congenital or acquired. Congenital causes include hemifacial microsomia, Treacher Collins syndrome, Pierre Robin syndrome, Goldenhar syndrome, Nager syndrome, and mandibular hypoplasia. Acquired causes of mandibular retrognathia include trauma (ie, condylar fractures occurring at an early age and resulting in bony ankylosis or disrupted growth) and previous surgery for developmental cysts or tumors.

Although less common than retrognathia, the mandible can also exhibit a transverse deficiency, resulting in a severe malocclusion and anterior dental crowding. This condition is difficult to correct with traditional osteotomies, and multiple extractions are often necessary. Distraction osteogenesis of the mandible has become a commonplace procedure with the flexibility to allow the surgeon to address a wide variety of mandibular defects.

Epidemiology

Frequency

Approximately 10% of the population has significant dental overjet. Craniofacial defects amenable to treatment with distraction osteogenesis are not highly prevalent. It is estimated that OSA affects 12 million people in the United States.

Pathophysiology

After a low power osteotomy is performed, distraction osteogenesis begins with the formation of a hematoma between and around the bone segments. The hematoma is converted to a clot, and bone necrosis occurs at the end of the fracture segments. An ingrowth of vasoformative elements and capillaries for the restoration of blood supply forms a soft callus.

Tension is then applied to the soft callus and a dynamic microenvironment is created. Pluripotential mesenchymal cells are activated into fibroblasts and osteoblasts, and type I collagen is laid down parallel to the vector of distraction. Bony trabeculae grow into the fibrous area from the periphery, parallel to the line of tension that occurs during the distraction phase. A bridge of immature bone forms across the distraction gap. A poorly mineralized, radiolucent fibrous interzone is located in the middle of the distraction gap, where the influence of tensional stress is maximal. The interzone functions as the center of fibroblast proliferation and fibrous tissue formation. During the consolidation phase, bony remodeling begins. The regenerate eventually matures into osseous tissue similar to the native bone.

Ilizarov’s study proved that the success of the distraction depended on the rate and rhythm of the force applied on site. The optimal rate of distraction is often reported to be 1 mm/day. Although the majority of authors agree with the distraction rate of 1 mm/day, there are reports suggesting different rates. Chin and Toth applied a distraction rate of up to 3 mm/day and Ramichel et al reported establishing a rate of 2 mm/day.[3, 4] However, distraction of more than 1.5 mm/day may cause delayed ossification or pseudoarthrosis due to local ischemia in the interzone. In their study of 39 patients, Meyer et al reported one failure, defending the approach of setting the rate on a case-by-case basis considering individual variables.[5] A rate of distraction of 0.5 mm or less per day may cause premature consolidation of the bone.

Soft tissue also has the ability to grow linearly along lines of tension. This is referred to as distraction histogenesis. Skin, muscle, nerves, and vascular tissue are generated, not stretched. The advantage is obvious, especially for severe retrognathia, in which the stretched soft tissue envelope can contribute to relapse when a traditional mandibular osteotomy is performed for a large (>10 mm) advancement.

Presentation

Distraction osteogenesis has many advantages over traditional mandibular osteotomies, as delineated below.

Distraction osteogenesis decreases the need for bone grafting for large (>10 mm) mandibular advancements; one can achieve 20 mm or more of advancement without a bone graft and the associated donor site morbidity, scarring, and potential for infection.

The procedure can be performed in infants and children, who would otherwise not be candidates for mandibular osteotomy because of the interference with the developing tooth buds and/or insufficient bone to safely perform a traditional osteotomy. In addition, distraction osteogenesis often has obviated the need for a tracheotomy in newborns and infants with micrognathia and airway obstruction.

This procedure also results in less distortion and loading of the temporomandibular joint than sagittal split osteotomy.

Distraction osteogenesis can be performed in 3 dimensions, that is, advancing, widening, and increasing vertical height of the basal mandibular bone. In addition, the vector and the amount of movement can be tailored to each patient, especially in those with significant facial asymmetry.

Distraction osteogenesis can be used to rotate the anterior portion of the mandible to correct open bites related with mandibular deficiencies.

Greater patient acceptance exists with this procedure, especially with the development of low-profile intraoral devices.

Distraction osteogenesis appears to have a decreased potential for relapse, especially with large advancements; this is because the transported portion experiences a progressively increased movement, instead of being transported in one large block. Due to the process of distraction histogenesis, resistance to advancement by the soft tissue envelope is decreased.

Distraction osteogenesis seems to limit the likelihood of damaging the inferior alveolar nerve.

Widening the mandible, which is difficult to do with traditional osteotomies and presents multiple complications, is possible with distraction osteogenesis.

Bone grafts are not required; hence, there is no donor site morbidity.

Mandibular distraction osteogenesis also has the following limitations[6, 7] :

  • Relative difficulty in performing osteotomies owing to potential damage to lingual mucoperiosteum or vascular plexuses of the floor of the mouth

  • Difficulty in obtaining correct vector of distraction

  • Although rare, relapse and/or resorption of the transport segment

  • Patient discomfort and psychological burden due to the retained distractor device

Indications

Distraction osteogenesis is indicated in the following cases:

  • Severe retrognathia associated with a syndrome (eg, Pierre Robin syndrome, Treacher Collins syndrome, Goldenhar syndrome), especially in infants and children who are not candidates for traditional osteotomies

  • Patients who have unilateral hypoplasia of the mandible (eg, hemifacial microsomia)

  • Nonsyndromic mandibular hypoplasia associated with a dental malocclusion (especially if the advancement exceeds the capabilities of a traditional osteotomy or if the patient is hesitant to undergo a bone graft harvest with the associated morbidity)

  • Mandibular transverse deficiency associated with a dental malocclusion and dental crowding

  • Patients with severe OSA (respiratory disturbance index [RDI] >60) and patients who are obese (body mass index [BMI] >28).

  • Mandibular hypoplasia due to trauma and/or ankylosis of the temporomandibular joint

  • Mandibular continuity defects resulting from excision of tumors and/or aggressive developmental cysts

  • Shortened vertical height of the alveolar bone (Distraction of the alveolar segment can be performed to increase the vertical height in preparation for osteointegrated dental implant placement. In patients who have had a mandibular reconstruction with a free fibular bone graft, the fibular segment can be distracted vertically to facilitate dental implant placement, as depicted in the image below.)

    Distraction osteogenesis of the mandible. Alveolar Distraction osteogenesis of the mandible. Alveolar distractor used to increase the height of the alveolar bone. Courtesy of K.L.S. Martin, LP.
  • Mandibular angle deformity. (The correction includes a rotational component and a distraction component. The rotational component is a hinge mechanism that allows free movement around its center of rotation. The distraction component for angular deformity correction usually consists of a distraction rod with two pivotable connectors at both ends. Type of hinges can be identified based on their location as follows: 1) the opening wedge hinge, 2) the closing wedge hinge, and 3) the translation hinge.)

Relevant Anatomy

The mandible is a U-shaped bone. It is the only mobile bone of the facial skeleton, and, since it houses the lower teeth, its motion is essential for mastication. It is formed by intramembranous ossification. The mandible is composed of 2 hemimandibles joined at the midline by a vertical symphysis. The hemimandibles fuse to form a single bone by age 2 years. Each hemimandible is composed of a horizontal body with a posterior vertical extension termed the ramus.

Placement of the osteotomy depends on the desired vector of distraction. However, certain anatomic structures must be avoided. The osteotomy is best placed either anterior or superior to the mandibular angle; the angle is maintained and the flattening of that portion of the patient's face is prevented. Tooth roots or developing teeth must be avoided when performing the osteotomy or placing the distraction device screw fixation. When the osteotomy is performed, the inferior alveolar nerve must also be avoided. Care must be taken to avoid damaging the lingual nerve when one extends the osteotomy through the lingual aspect of the mandible where the nerve lies in close proximity.

For more information about the relevant anatomy, see Facial Bone Anatomy.

Contraindications

No absolute contraindications to treatment exist. However, relative contraindications are as follows:

  • Patients who are unable or unwilling to comply with the distraction schedule are not ideal candidates for this procedure.

  • Mandibular distraction osteogenesis has been performed on infants as young as 9 days old,[3] but more difficulty is encountered when dealing with small fragile bones in the placement of the distraction device, especially children under 6 years of age.

  • Patients who have inadequate bone structure are not ideal. Adequate bone stock must be available to accept the device and to provide adequate surface area of the osteotomy sites for regeneration. Several authors suggest that distraction may not be a good treatment option if the bone height above the inferior alveolar nerve is less than 6-8 mm or if the transport segment will be shorter than 4-5 mm.[8, 9, 10]

  • Distraction osteogenesis of the mandible may be used on patients who have received prior radiation treatment. However, this procedure must be performed with caution because these patients are more likely to develop complications and to experience delays in wound healing.[4, 11]

  • In older patients, a decreased number of mesenchymal stem cells may impair bone healing at the distraction site.

  • Patients who have metal allergies are not ideal.

 

Workup

Laboratory Studies

Depending on the patient's age, at a minimum, complete blood count, platelet count, and coagulation studies should be performed.

Imaging Studies

A panoramic radiograph should be obtained. This imaging provides the surgeon with better visualization of mandible morphology. A preoperative planned osteotomy is drawn in the diagnosis tracing; it should include maxilla and mandible. The PA cephalometric radiograph is another diagnostic tool, used to determine the amount of vertical and transverse (horizontal) mandibular distraction. It is the best film for determining vertical distraction due to better visualization of both mandibular angles. A diagnostic tracing of the PA cephalometric radiograph is made, as well as a drawing of the osteotomy to correspond with the diagnostic tracing of the Panorex.

Complicated cases may require CT scans with 3-dimensional reconstruction and stereolithographic models to help in planning the location of the osteotomy and the vector of distraction.

Mounted dental models on a semiadjustable articulator are often helpful in determining the vector of distraction, and optimizing the dental occlusion.

 

Treatment

Surgical Therapy

Costantino and Friedman classify possible distraction approaches to bone defects as follows[12] :

  • Monofocal: A surgical fracture creates a distraction gap (the interval between 2 bone surfaces where the healing events will happen) for posterior traction of the separated bone segments. This is the conventional for vertical alveolar augmentation prior to implant placement.

  • Bifocal: A solution of continuity is treated by moving a surgically produced bone segment along the defect from one extremity to the other. The moving segment is a transport disc. This approach is frequently used for mandibular reconstructions after tumor ablation.

  • Trifocal: Two transport discs are created from 2 extremities of defect and moved until they meet. Usually major corrections are done with trifocal processes.

The orthodontist and the surgeon must have frequent communication throughout the entire planning process, and must share the same treatment objectives.

Preoperative Details

After the workup is completed, the placement of the osteotomy and the selection of the distraction device should be determined. Either an internal (intraoral) device or an external device is used, though most routine cases can be done intraorally. Patients accept internal devices better than external ones, but the former are difficult to use in patients with small bones. External devices offer flexibility and vector selection but often cause scarring of the skin.

On the basis of the mandibular defect, the surgeon must determine where to place the osteotomy. As a general rule, if the mandible is defective in a ramus height, the osteotomy should be placed superior to the angle on the ramus, with a distractor placed in a vertical plane. If the mandible is deficient in body length, the osteotomy should be placed anterior to the angle, with the distractor device placed across the defect in a horizontal plane. If the mandible has a combination of defects, the device needs to be placed in an oblique plane. As an alternative, the surgeon may use an external multivector device with 2 osteotomies, 1 anterior and 1 superior to the angle, and 3 pins placed to obtain a multivector advancement.

Intraoperative Details

The patient receives prophylactic antibiotics and nasoendotracheal general anesthesia. An incision is made in the facial vestibule of the mandible, perpendicular to the osteotomy site. A subperiosteal plane is carefully developed to expose the osteotomy site, while an intact periosteal layer is maintained. The osteotomy is placed in the predetermined position on the basis of the findings on the preoperative workup.

Depending on the surgeon's preference, a reciprocating saw or a fissure bur can be used to perform the osteotomy, staying clear of the inferior alveolar nerve bundle by 3-5 mm. Lateral, superior, and inferior aspects of the mandible are cut, leaving the mid portion of the lingual cortex intact, as depicted in the 1st image below. Care should be taken to preserve as much osteogenic tissue as possible, including periosteal and endosteal blood supply. The intraoral distraction device is now secured to the mandible with screw fixation, as depicted in the 2nd image below. The osteotomy is then completed by using a series of osteotomes on the inferior and superior borders and on the lingual aspect. At this point, activation is attempted to ensure movement of the proximal and distal segments. The device is then returned to its starting position. The tissue is carefully closed over the device.

Distraction osteogenesis of the mandible. A recipr Distraction osteogenesis of the mandible. A reciprocating saw is used to osteotomize inferior, lateral, and superior portions of the mandible. An osteotome is then used to complete the bony cut. Courtesy of Jordan Mastrodonato, MS, Medical Illustrator, Eisenhower Army Medical Center.
Distraction osteogenesis of the mandible. Intraora Distraction osteogenesis of the mandible. Intraoral distraction device in place. Courtesy of K.L.S. Martin, LP.

When mandibular symphyseal osteotomy is performed, access is obtained through the usual genioplasty incision. The osteotomy is started through the body of the mandible with a saw. The device is secured in position, and a thin osteotome is then used to complete the bony cut through the alveolar process and between the teeth, attempting to maintain the integrity of the soft tissue and avoid damaging teeth.

When a continuity defect of the mandible is encountered, the surgeon can use distraction osteogenesis or, more specifically, transport osteogenesis (instead of a bone graft) to address this problem. An osteotomy is performed on either the proximal segment or the distal segment, resulting in a transport disk of bone at least 1.5-2 cm in thickness. After the latency period, this disk is transported across the mandibular defect, following the usual rate and rhythm protocol. After the entire defect has been traversed with the disk, the surgeon allows for consolidation. On occasion, a small bone graft is placed at the interface of the disk and on the opposite side, where consolidation is not always complete.

Postoperative Details

The traditional latency period is 5-7 days. Young children have an increased bone metabolism and may have a latency period as short as 24-48 hours, without affecting ultimate consolidation. Waiting too long increases the risk of bony union; waiting 7 days is advised if the periosteum is excessively traumatized. In addition, if both hard tissue and soft tissue are less than ideal in quality or quantity, increasing the latency period may be considered.

As mentioned before and according to most study results, the recommended rate of distraction is 1 mm per day. A slower rate could result in premature bony union, whereas a faster rate could result in a fibrous union. The inferior alveolar nerve seems to tolerate a distraction rate of 1 mm/d. Ilizarov recommended a continuous rhythm for distraction; however, this is not feasible in the clinical setting, so a rhythm of 1-2 times per day is recommended. The surgeon or a responsible adult should activate the appliance. During a bilateral mandibular advancement, an anterior open bite tends to develop; this can be corrected at the end of advancement with orthodontic elastics.

The consolidation phase is typically 8 weeks, although some adults may require up to 12 weeks of consolidation. Reports have described the use of adjunctive therapies and their potential to enhance optimization of the consolidation period. Among these, bone morphogenic protein 2 (BMP-2), growth hormones, osteoblastlike cells, and therapeutic low-level laser are reported to demonstrate improved bone healing.[13, 14, 15, 16, 17] Thus, these supportive treatments remain as viable strategies to provide high-quality regenerate and shorten overall healing. During the consolidation phase, the fixation must be rigid enough to prevent the formation of fibrous tissue but not too rigid to prevent physiologic loading of the new bone. The formation of the regenerate can be monitored with serial radiographs or CT scans.

These procedures can often be performed on an outpatient basis, although some patients may require 1-2 days of hospitalization for postoperative care. After the consolidation phase is complete, the device can be removed using intravenous sedation and local anesthesia. Orthodontic detailing of the occlusion can begin 3-6 months after the consolidation phase.

In bilateral expansion of the mandible, the patient should be distracted until a slight class III dental occlusion exists (edge-edge incisal relationship). In a unilateral expansion, a slight overcorrection of the mandibular midline is recommended to overcome the deficient soft tissue envelope.

During the distraction phase, the patient is examined every 2-3 days to monitor the advancement and to detect potential occlusal discrepancies. During the consolidation phase, the patient should be seen on a weekly basis to monitor healing and ossification of the regenerate.

Follow-up

See Postoperative details.

Complications

With experience, the overall complication rate is low. Complications include the following: fibrous nonunion or premature union of bone, infection that may hinder osteogenesis, noncompliant patient with treatment failure, scarring of the skin with external devices, hardware failure, and malocclusion because of improper vectors.

Although rare, relapses, temporomandibular joint ankylosis, fracture of the mandible or the transport segment and resorption of the transport segment have also been reported.[18, 19, 20] See the image below.

Temporomandibular joint ankylosis following distra Temporomandibular joint ankylosis following distraction osteogenesis

Soft tissue dehiscence or device exposure is not necessarily considered as a complication.

Outcome and Prognosis

Distraction osteogenesis of the mandible has become a commonplace procedure with the flexibility to allow the surgeon to address a wide variety of mandibular defects. The sophistication of the distraction devices has increased in the last few years, allowing multivector movement of the mandible. A high percentage of patients accept intraoral distraction with a small, low-profile distraction device.

Although traditional mandibular osteotomy, such as bilateral sagittal split osteotomy, will always have a role, distraction osteogenesis allows a surgeon to treat patients who are unable or unwilling to undergo traditional osteotomy. Distraction osteogenesis is a highly predictable and reliable method of increasing the bone in a deficient mandible.

Future and Controversies

With technologic advancements, distraction devices have become smaller and more sophisticated than early versions. Distraction osteogenesis may even be teamed with endoscopic techniques to allow the placement of these devices with minimal surgery.

Preliminary studies of rabbits have shown that distraction performed in the presence of recombinant human bone morphogenetic protein placed into the distraction site accelerates bone formation.

Distraction osteogenesis is showing great promise in the treatment of OSA. Although traditional combined maxillary and mandibular osteotomy are effective in treating mild-to-moderate OSA, the results are disappointing in patients with severe OSA (RDI >60) and/or a high BMI (>28). This is likely because traditional mandibular osteotomy has a physiologic limit of about 10 mm of advancement, which may be insufficient to open the airway for effective relief of the obstruction in the obese patient or in those with severe disease.

Distraction osteogenesis allows for advancement of up to 25 mm by using a specially designed distraction device, as depicted in the image below. In effect, the amount of distraction is individualized for each patient by performing polysomnography (PSG) after about 15-18 mm of advancement. If the PSG demonstrates a normal RDI, distraction is stopped to allow for consolidation. If the RDI is still elevated, distraction continues for the full 25 mm.

Mandibular distractor used for maxillomandibular a Mandibular distractor used for maxillomandibular advancement for the treatment of OSA. Courtesy of K.L.S. Martin, LP.

As part of this treatment protocol, the patient undergoes a LeFort I osteotomy with down fracture and then placed in intermaxillary fixation to allow the distraction device to move the maxilla and mandible as a unit and maintain the preexisting dental occlusion. In addition, the patient receives elective tracheotomy for airway protection. During PSG, the tracheotomy is occluded to avoid confounding the results.

When the distraction phase is completed, the cannula is removed. The consolidation phase is approximately 4 months, after which the device is removed. In 1 case series, this protocol was highly effective in the management of severe OSA. Patient selection and compliance are important for the success of this procedure.

One controversy involves the use of distraction osteogenesis instead of traditional bilateral sagittal split osteotomy. Some authors have stated that bilateral sagittal split osteotomy is an obsolete procedure with no role in current practice. In reality, traditional mandibular osteotomies will always have a role; however, distraction osteogenesis gives the surgeon another option in treating a wide variety of mandibular deficiencies.

Other research directions on distraction osteogenesis are as follows:

  • Administration of growth factors to enhance bone healing: Bone morphogenic proteins 2 and 4, transforming growth factor-beta (TGF-beta), platelet-derived growth factor (PDGF), vascular endothelial growth factor (VEGF), and fibroblast growth factor (FGF) applications have demonstrated promising results to accelerate bone healing in distraction osteogenesis.[21, 22, 23, 24]

  • Resorbable distractors: Resorbable mandibular distractors, when combined with advances in resorbable materials and distraction, may enable predictable distraction with a single operation.[25, 26]

  • Continuous distraction osteogenesis: Automatic distraction systems that can activate continuous distraction are a promising alternative in distraction osteogenesis. Bone healing is accelerated with continuous distraction when compared with intermitted distraction.[27, 28]