Introduction
Distraction osteogenesis is a surgical process for reconstruction of skeletal deformities. It involves gradual, controlled displacement of surgically created fractures which results in simultaneous expansion of soft tissue and bone volume. It is the ability to reconstruct combined deficiencies in bone and soft tissue that makes this process unique and invaluable to all types of reconstructive surgeons. Ilizarov developed a procedure based on the biology of the bone and on the ability of the surrounding soft tissue to regenerate under tension ; the technique involved an external fixator, the Illizarov apparatus, structured as a modular ring. Although the types of complications remained the same infection, the most common complication occurring particularly along the pin tracks, pain, nerve and soft tissue irritation the Ilizarov technique reduced the frequency and severity of the complications.The Ilizarov technique made the surgery safer, and allowed the goal of lengthening the limb to be achieved.
Gavriel Ilizarov, a Russian orthopedic surgeon, is credited with developing the armamentarium and describing the biologic basis of this process for the management of orthopedic limb deformities. The concepts described by Ilizarov have been adapted and modified for use in maxillofacial surgery. Although the majority of surgical experience with distraction technology has been in orthopedics, early results indicate the process to be equally effective in facial skeletal reconstruction. It is now possible to apply distraction technology to deformities of the jaws and dentoalveolar process. Development of miniature, internal distraction devices have made this clinically feasible and practical.
Modern distraction osteogenesis evolved primarily from the work of Gavriel Ilizarov. Starting in the 1960’s in his modest clinic in
Development of distraction osteogenesis required defining new concepts in regeneration of bone and soft tissue. To initiate and control the distraction process, surgical instruments specific to the biomechanical requirements of the technique needed to be developed. Rigorous analysis of the initial results were needed to define the biologic basis of the process. To reach the current state of this technology required many years. Over a period of thirty years, the clinic consisting of a single wooden building was replaced by a modern, state-of-the-art medical center engaged in a combination of patient care, clinical research, basic science research, and instrument development. In the beginning, the treatments involved use of available instruments and basic surgical techniques. The use of percutaneous wires to manipulate bone fragments is still an important part of the Ilizarov method. To gain control of the wires and thereby the bones, Ilizarov developed the ring fixator. The rings could be joined by a variety of threaded rods and hinges providing fixation which was versatile and adaptable.
After Ilizarov’s work was recognized by the Soviet medical establishment, the modest wooden clinic evolved into a state-of-the-art medical center and research facility. Over a period of 30 years, Ilizarov explored the basic science, defined parameters for clinical application, and improved the instrumentation for the distraction osteogenesis process. Restricted communication between Soviet and western medical communities limited dissemination of the work outside of
The process involved creation of surgical fractures with minimal tissue reflection and manipulation of the fragments with percutaneous rods supported by an external frame. The technique combined minimally invasive surgery and application of a unique device which could manipulate bones and maintain fixation simultaneously. The device evolved into the components of the Ilizarov ring fixator used by orthopedic surgeons today. Ilizarov found that combining minimal tissue dissection, slow transport of skeletal fragments, near rigid fixation, and maintenance of skeletal loading, resulted in formation of both new bone and adjacent soft tissue. Achievement of stable, functional rehabilitation of combined osseous and soft tissue deformities represents a major achievement in reconstruction surgery.
Distraction rate
The distraction rate must be gradual, as a rapid rate of distraction will result in a fibrous union in which the bone pieces are joined by fibrous, rather than osseous tissue.
Too slow of a distraction rate would result in early bone consolidation. A common distraction rate for lower limbs is 1 millimeter per day
Distraction Osteogenesis for maxillofacial application
Why not apply the Ilizarov method directly to maxillofacial skeletal reconstruction? There are a number of unique features of the facial skeleton that require special consideration when applying distraction osteogenesis. When confronting a length deficiency of the leg, for example, the anatomical structures are generally related in a linear, coaxial arrangement. Lengthening using an Ilizarov ring fixator is appropriate because the structure and function of the device allows great control of axial movements while maintaining coaxial alignment of bones. Limb lengthening most often involves creation of an osteotomy perpendicular to the transport direction. Given the linear anatomy of extremities, the ring fixator is ideal in generating skeletal transport and fixation under an axial load.
Application of Ilizarov ring fixators with transcutaneous rods is not ideal in the facial region. The face concentrates many functions into overlapping anatomical units. Many anatomical structures are involved with multiple functions. Transfixation of skeletal elements with transcutaneous rods is generally not possible because of the interference with these other facial functions. In addition, esthetics is an important function of facial structures. Scarring of cosmetically important facial structures may result from external, transcutaneous devices.
Osteotomies necessary to mobilize facial bone fragments are complex in shape. The osteotomy is rarely perpendicular to the axis of transport. The transport geometry is therefore complex which complicates the determination of transport rate. As such, the response of the osteotomy to transport is also complex. The regeneration chambers in the orthopedic model differ from the maxillofacial model. The consolidation rate for facial bone transports may be affected by many factors. First, the complex morphology of the distraction chamber, second is the inherent difference in bone healing in the facial skeleton, and third is the effect of functional load on the consolidating site.
To allow practical, clinical use of distraction osteogenesis to intraoral and maxillofacial applications requires modification in both armamentarium and surgical technique. Direct application of Ilizarov’s distraction osteogenesis method is not possible in the maxillofacial region. This is because the facial bones differ from the extremities in morphology and function. The key is to incorporate the positive regenerative capability of orthopedic distraction osteogenesis into a practical method for facial bone reconstruction.
The Process of Alveolar Distraction Osteogenesis
The process of alveolar distraction osteogenesis involves mobilization, transport, and fixation of a healthy segment of bone adjacent the deficient site. A mechanical device, the alveolar distraction device, is used to provide gradual, controlled transport of a mobilized alveolar segment. When the desired repositioning of the bone segment is achieved, the distraction device is left in a static mode to act as a fixation device. Displacement of the osseous segment results in positioning of a healthy portion of bone into a previously deficient site. Because the soft tissue is left attached to the transport segment, the movement of the bone also results in expansion of the soft tissue adjacent the bone segment. At the original location of the segment is left a regeneration chamber which has a natural capacity to heal by filling with bone. This propensity of the regeneration chamber to heal by filling with bone instead of fibrous tissue is a function of the surrounding, healthy cancellous bone walls and location within the skeletal functional matrix. As a result of the gradual distraction, the alveolar housing, including the osseous and soft tissue components are enlarged in a single, simultaneous process.
Alveolar Distraction Device
Development of miniature, internal distraction devices has made transport of alveolar segments possible. The alveolar distraction device has been developed for reconstruction of alveolar process deformities using the distraction osteogenesis process. The implantable components of the alveolar distraction device consists three components.
When placed into a properly formed segmental osteotomy, the distraction device allows for controlled elevation of the segment resulting in coronal displacement of the alveolar crest. The transport slowly displaces the overlying soft tissue producing expansion. A regeneration chamber is established in the portion of the osteotomy that is perpendicular to the transport axis. The portion of the osteotomy that is parallel to the transport acts to maintain alignment of the segment. After the desired amount of transport has been achieved, the lead screw is left in place until bone healing occurs across the sliding component of the osteotomy. The regeneration chamber fills with bone of several weeks. As a result of the distraction process the volume of both bone and soft tissue has been increased. The reconstructed site is them suitable for further rehabilitation with osseointegrated implants, prosthetic pontic placement, or movement of a tooth with orthodontics.
Model simulated surgery using the Alveolar Distraction Device.
Indications:
1. Primary indications. Combined deficiencies in bone and soft tissue.
2. Secondary indications.
Alternative treatments.
Expansion of the alveolar housing for:
Create site for dental implant placement
Improve ridge esthetics for pontic
Improve periodontal enviornenvironmentacent teeth
Expand alveolus for orthodontic tooth movement
Limitations
Must have a minimum quantity of bone
transport and anchorage segment must have adequate strength to withstand forces of mobilization and transport.
Expansion occurs only in the direction of transport.
Patient must cooperate with activation process
Complications
fracture of transport segment
fracture of anchorage segment
premature consolidation
undesirable transport vector
Objectives of Distraction Process
1. expansion of bone and soft tissue volume
2. displacement of bone into deficient site
Combining Distraction with other techniques
The distraction process may not produce the anatomical objective in a single step. Maxillofacial skeletal deformities are most often complex and three dimensional in nature. Alveolar deformities are not an exception. It is rare that the distraction process alone would result in an alveolar ridge of ideal shape and size. Usually additional osteoplasty is indicated. The distraction process results in the substrate, increased bone volume and expanded soft tissue, which makes creation of an appropriate alveolar morphology possible. Knife edge bony alveolar ridges are usually removed and discarded. If the ridge crest is slightly palatal to the ideal position, the labial cortex may require labial displacement. The distraction process has raised the medullary component of the alveolus allowing the labial plate to be displaced. The resultant increase in alveolar volume is accommodated by the expanded gingiva so that a nontension soft tissue closure is possible.
