Maxillofacial Distraction Osteogenesis

Maxillofacial Distraction Osteogenesis » By: Dr. Hatem W. AL Rashdan, BDS, MSc Jordanian Board, Oral & Maxillofacial Surgeon Private practice, Irbid, Jordan. Definition and historical background Distraction Osteogenesis can be defined as the technique in which bone generation and soft tissue proliferation are achieved by means of gradual, controlled distraction of pre-existing native bone. The first who reported a method for expansion of bone by Distraction osteogenesis is Codivilla (1905) who gradually lengthened a femur. Abbot (1927) contributed in the improvement of Codivilla method by incorporating pins instead of casts used by Codivilla. Allan (1948) was the first to incorporate a screw device to control the rate of distraction. Ilizarov a Russian orthopedician was the one who popularized DO; during the period between 1950-1970 Ilizarov conceptualized the basis of DO. The first report concerning utilization of DO in the maxillofacial area was published in 1973, when Snyder et al applied this technique to lengthen a dog mandible. McCarthy et al reported the first clinical cases of gradual distraction of the human mandible in 1992. Main Concept and Histophysiolgy DO involves creating a surgical osteotomy (fracture) in cortical bone, placement of the distraction device, and then gradual distraction of the osteomatized segment, depending on self repair mechanisms to fill the gap created in the cortical bone. At this point Dr. Kameel was asking about the osteotomy and what would guarantee that the osteomized segments stay in place, the answer was clear that the osteotomy involves the cortical bone alone and the cancellous bone is kept intact, Dr. Gharaibeh also said that the elasticity of the cancellous bone will permit some mobility of the osteomized segment. This illustration (Fig. 1) shows the creation of the cortical osteotomy: » (Fig. 1) A special device the distractor is used to obtain controlled gradual movement of the osteomized segment, see Fig. 2. The Histophysiolgy of Distraction Osteogenesis is based on the slow steady traction of tissues, which causes them to become metabolically activated, resulting in an increase in the proliferative and biosynthetic functions. The premise then 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. Distraction Osteogenesis takes place primarily through intramembranous ossification. Histological studies identified 4 stages that result in the eventual formation of mature bone. Stage I: The intervening gap initially is composed of fibrous tissue (longitudinally oriented collagen with spindle-shaped fibroblasts within a mesenchymal matrix of undifferentiated cells). Stage II: 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: Remodeling begins with advancing zones of bone apposition and resorption and an increase in the number of osteoclasts. Stage IV: Early 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 are 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. It is believed that the architecture is maintained and that the bone responds to normally applied functional loads. Indications Indications for the use of distraction are broad, and its applicability depends on the particular clinical problem. As the technique is in its infancy, the indications are evolving, and it is applied to solving a wide range of craniofacial deformities. In hemifacial microsomia, distraction osteogenesis should be considered in children with mild to moderate mandibular deformity. However, a child with a sever bone deformity will not have sufficient bone to allow for a corticotomy and/or osteotomy and placement of pins for external or internal distraction devices. In such situations, conventional costochondral rib grafts may be necessary that later may be followed by distraction osteogenesis if appropriate. Similarly, minimal mandibular deformities may be treated with conventional orthognathic surgery in the appropriate age range. In children with significant bilateral mandibular hypoplasia in whom the airway may be an issue or in those who are tracheostomy-dependent, early bone lengthening through distraction may be beneficial. Distraction allows for correction of the hypoplastic mandible earlier in childhood rather than waiting until adolescence for maturity of the facial skeleton required with traditional approaches. Children with severe midfacial deformities also may benefit from distraction earlier in childhood rather than waiting until adolescence, as it can be applied to lessen the deformity. In adolescence, when the maxillary-mandibular discrepancy is significant and stability through conventional approaches is a concern, consider distraction. Retraction during orthodontic treatment Can be utilized via Distraction, which may save time and prevent pulp necrosis. With the evolution of innovative devices, the technique is applied to an ever-increasing range of reconstructive problems, from the deficient alveolar ridge to the frontofacial advancement. Nevertheless, as with any approach to solving a clinical problem, weigh the advantages and disadvantages of any technique 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 blood loss and morbidity associated with bone grafts. Treatment Phases 1. Presurgical Phase Which involves planning of our process, this depends on radiography mainly, this includes: - Routine radiographic studies typically include CT with 3-D reconstructions. - Routine radiographic studies also typically include dental radiographs (orthopanorex, frontal and lateral cephalometric films). - Decide whether sufficient bony stock is present for fixation of the devices and the direction of the primary vector of lengthening. Consulting the Orthodontist is essential in this phase to guide the distraction at the occlusal level since the skeletal component is controlled by the device mechanism. 2. Operative Phase Osteotomies used with distraction are well described with the conventional reconstructive approaches and need only be modified to accommodate the specifics of the device being used. 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. • In deciding between internal versus external devices, a number of factors should be considered. External devices allow for multidirectional control of the distraction, which cannot be achieved with the currently available internal devices. However, external devices may lead to significant facial scarring, and the application of sequential different distraction vectors with a series of internal devices may be preferable to a permanent external scar. • Exposure can be obtained through either an intraoral or extraoral approach, depending upon the exposure required for the placement of the device and the allowable maxillary-mandibular opening. • The placement and/or direction of the device, not the osteotomy of the mandible, dictate 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 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. • Temporarily fix the distractor into position prior to making the osteotomy. Positioning and placement of the device after the osteotomy can be difficult because of the mobility of the proximal segment. • Make the buccal corticotomy with a reciprocating saw, and "green-stick" fracture the lingual with a fine osteotome to preserve the inferior alveolar nerve. 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. Fig.3 shows linear distraction device used in the mandible, while Fig.4 shows extra-oral multi-vector (angular) Distraction device, in Fig. 5 a Distractor is applied to the Ramus. » (Fig. 3)» (Fig. 4) » (Fig. 5) Midfacial and frontofacial distraction • With the use of external devices (head frame and/or helmet), presurgical preparation typically involves placement of a palatal appliance to guide the distraction vector. • Make the osteotomies as with conventional approaches and complete the mobilization of the mid face. • In children in the stage of primary or mixed dentition, modify the typical LeFort I osteotomy and place it well above the developing dentition at the level of the inferior orbital foramen. • Midfacial advancements at the LeFort I level with currently available internal devices are limited because of the difficulty in appropriately orienting the devices in the limited space. The fixation of the device may injure the developing dentition. External multidirectional devices are preferred as they allow more control over the distraction process. • Midfacial advancement at the LeFort III level and frontofacial advancements can be approached either with 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 additionally traction wires at the zygoma, nasal root, and supraorbital regions. A discussion was raised at this point about anchorage utilized during Distraction and what prevent the anchorage segment to move instead of the wanted segment, it is apparent that we usually move a small segment against large segment, in the case of the ramus the anchorage is obtained from the glenoid fossa which means that the whole skull will act as anchorage segment. 3. Latency Phase Fracture healing is allowed to occur before distracting forces are applied. This period typically lasts 5-7 days. In younger patients (typically, younger than 4-5 years), the latency period may be significantly shortened or omitted altogether to prevent early consolidation. At this point a discussion evolved why do not we start immediately? The answer is because we want to keep the cancellous bone vascualarity so it will heal by bone formation and not fibrous tissue. 4. Distraction Phase The process of distraction is activated with the bone segments gradually pulled apart using either an internal or external device. Three variables must be set: the rate of distraction, the rhythm and/or frequency of distraction, and the total time of distraction. The rate of distraction is typically 1.0 mm/d. Some advocate up to 2.0 mm/d in younger children to avoid early consolidation and a slower rate of 0.5 mm/d or 0.25 mm qid in older patients to avoid fibrous unions. 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. Dr. Rwashdeh directed a discussion about the frequency of distraction, a conclusion of either 0.5 mm twice daily or 0.25 four times daily can be utilized. Also an overall distraction of more than 1 mm but less than 2mm daily can be obtained with special care in some cases.  The total time of the distraction phase depends on achieving the clinical goals; individualize it to each patient and to the severity of the deformity. Remember that the total length of bone desired does not necessarily equal the total time of the distraction phase. External devices that use pins to transmit the forces frequently bend, and the distance at the site of the distracting mechanism on the device rarely equals the distance of the gap at the osteotomy sites. Use clinical guidelines (e.g., position of the chin point, distance from the lateral canthus to the commissure and the mandibular cant) to determine the end point in children with hemifacial microsomia. 5. 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. 6. Retention Phase Remove the device and maintain stability, typically with the assistance of orthodontic appliances. In children with hemifacial microsomia, this 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 facemask with elastic traction for a period of time. Limitations and Drawbacks Complications specific to the distraction process include the following: • Device mechanism failure or breakage • Loosening of the device because of inadequate bone stock • Injury to the developing tooth follicles • Injury to the nerve (inferior alveolar nerve) • Pin site infection with external devices • Relapse The long-term outcome and what role distraction osteogenesis ultimately plays in reconstruction remain unknown. Clearly, distraction can generate bone with the capacity for remodeling and adapting to the loads placed on it. Whether distraction osteogenesis is capable of restoring the normal development of a once dysplastic pattern of growth of the facial skeleton remains to be seen. 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.