The mandible is a unique intramembranous bone that crosses the facial midline terminating in fibrocartilage-covered joints articulating against the cranial base. The basal portion of the mandible—the condylar neck, ramus, body, and symphysis—functions to support facial, oral, and pharyngeal soft tissues. The basal portions serve as attachments for muscles of facial expression and the muscles of mastication and the muscles of the tongue. The alveolar process is uniquely adapted to support the development and function of the dentition and periodontium. The mandible is in near constant motion as a result of the normal functions of swallowing, breathing, speaking, chewing, and expression. During these functional activities, the mandible is stressed or loaded by tensile and compressive forces, which vary with protrusive and right and left lateral excursive movements. A loss of continuity of the mandible and a breach of its ability to support the face and perform these important functions can occur as a result of trauma, infection, and benign and malignant neoplasms. Selection of the appropriate reconstruction technique for a mandibular continuity defects is based on many issues, including the host characteristics. Host characteristics that can influence successful reconstruction include patient age, metabolic status, tissue vascularity, and availability of stem cells. Ideally there is an absence of infection, minimal scar tissue, and minimal tissue damage as a result of radiation. Considerations when reconstructing the mandible include appropriate stability, isolation from the oral cavity, and a source of inducible stem cells. The result of the reconstruction should provide patients with a mandible of appropriate size, shape, and maxillary mandibular relationship.
Continuity defects of the mandible
Traditional approaches to achieve mandible reconstruction have been the use of autogenous bone from the iliac crest together with a reconstruction plate, a metal or alloplastic tray, or allograft bone to achieve the appropriate shape of the mandible. These approaches, although successful, require large amounts of autogenous bone and often require time-consuming intraoperative procedures, such as rolling a patient over to access posterior iliac crest. An alternative choice is the use of viable fibula osteomyocutaneous grafts, which requires a significant donor site and substantial operating time and expertise associated with graft procurement and vascular anastomosis. Current trends in mandibular reconstruction aim to achieve reestablishment of a viable mandible of proper form and maxillary mandibular relationship while decreasing the need for invasive autogenous graft procurement. To date the need for autogenous bone has not been completely eliminated in mandible reconstructions, but the amount needed has been substantially decreased and, thus, the morbidity and time associated with graft procurement improved. In addition, when grafts are used they are combined with recombinant human bone morphogenetic protein-2 (rhBMP2)/absorbable collagen sponge (ACS) (1.5 mg/mL) (Infuse, Medtronic, Minneapolis, Minnesota) or transport distraction osteogenesis. This article’s Further Readings lists articles on mandible reconstruction using rhBMP-2/ACS and transport distraction osteogenesis.
Transport distraction
The purpose of this atlas article is to provide relevant principles and technique information regarding approaches to mandible reconstruction by transport distraction osteogenesis. The use of transport distraction osteogenesis for reconstruction of the temporomandibular joint was published in a previous issue of Atlas of the Oral and Maxillofacial Surgery Clinics of North America ; thus, the focus of this article is on reconstruction of defects of the mandibular body with transport distraction. I discuss these concepts by reviewing four cases. The complexity of these cases does not vary greatly with the complexity of the defect or surgery but more with regard to the important host (patient) factors. Transport distraction for reconstruction of continuity defects is most efficient for defects of the mandibular body. When used to reconstruct a defect of the body of the mandible, the transported segment not only achieves bone continuity but also, through histiogenesis, the associated attached tissue is reconstructed achieving a natural ridge with a vestibule. Transport distraction is limited to reconstruction of a relatively straight line defects as seen with defects of the mandibular body. This is because the connective tissue stroma within regenerate dictates the shape of the reconstructed tissue. If attempts are made to move a transport disc around a curve, the regenerate forms a straight segment between the point of transport origin and completion. Thus, if it is necessary to reconstruct a defect of the symphysis, the best plan is to create transport discs from the right and left posterior stumps of the mandible and move them toward the symphysis. The residual defect in the symphysis requires a bone graft. An alternative plan is to transport right and left transport discs forward from the body with a vector that lets them consolidate in the midline and then follow that procedure with a second midline osteotomy and application of a midline distracter to widen the symphysis.
Figs. 1–4 provide information regarding the basic features of a transport distracter, (Threadlock design, KLS Martin, Jacksonville, Florida) and the concepts of transport distraction. The design of this transporter is universal in nature. It can be used to transport segments of the right or left body of the mandible from anterior to posterior or from posterior to anterior. The transport shaft is available in a variety of lengths, including 30, 40, 50, and 60 mm, and can be attached above the bone plate, below the bone plate for continuity defects, or to native mandible in cases of marginal resection with remaining basal bone. In Fig. 1 , the components of the device are labeled. Component 1 is a fixed titanium mesh that extends above and below the transport shaft 5. It can be attached to residual bone to provide additional stability or removed if not needed. Component 2 is the transport segment attachment mesh that moves along the variable length transport shaft 5 at 0.5 mm per complete turn of the activation arm 4. The activation arm is attached to the transport shaft and includes multiple ball joints to permit unstressed alignment of the activation arm during turning of the device. The activation arm can remain intraoral and emerge through mucosa or it can emerge through the skin for percutaneous activation. Component 3 is the attachment arm that provides an attachment for the transport shaft 5 to a reconstruction plate or basal mandible. The attachment location of the attachment arm to the transport shaft relative to the defect or its attachment to a plate or mandible can be adjusted anterior or posterior by loosening the set screw and sliding it along the groove in the transport shaft and then tightening the set screw to fix it in the desired location. It is best to attach the arm (see Fig. 3 ) to the plate or mandible at the point of greatest curvature if a curve exists, to avoid binding of the transport segment as it moves along the transport arm. The attachment arm accepts a screw designed to attach it to a locking plate or a locking screw for attachment to the mandible. The attachment arm can be removed from its slot in the transport shaft and flipped for cases where it is best to have the transport arm located below the reconstruction plate. Fig. 2 shows the transporter configured for anterior to posterior transport with attachments to the reconstruction plate proximal mandible and the transport segment. The transport bone segment should be 1.5 cm wide ± 0.5 cm and equal to the full thickness of the mandible. Care should be taken during preparation of the transport segment to maintain its vascular supply by not detaching periosteum or soft tissue attached to its coronal or lingual surfaces. Transport usually is initiated after a latency of 5 to 7 days at a rate of 1 mm per day ± 0.5 mm. In Fig. 3 , there is a partially transported segment showing the clearance between the transport segment and the curvature of the bone plate. In Fig. 4 , the linear relationship of the transport shaft between the points of initiation and completion of distraction is shown. The principles of distraction can be applied by using a system such as the one described previously. These principles include linear transport of a segment with appropriate dimensions and vascular supply with a mechanically smooth but rigid system that permits adaptation to the defect and minimizes micromotion.
Transport distraction
The purpose of this atlas article is to provide relevant principles and technique information regarding approaches to mandible reconstruction by transport distraction osteogenesis. The use of transport distraction osteogenesis for reconstruction of the temporomandibular joint was published in a previous issue of Atlas of the Oral and Maxillofacial Surgery Clinics of North America ; thus, the focus of this article is on reconstruction of defects of the mandibular body with transport distraction. I discuss these concepts by reviewing four cases. The complexity of these cases does not vary greatly with the complexity of the defect or surgery but more with regard to the important host (patient) factors. Transport distraction for reconstruction of continuity defects is most efficient for defects of the mandibular body. When used to reconstruct a defect of the body of the mandible, the transported segment not only achieves bone continuity but also, through histiogenesis, the associated attached tissue is reconstructed achieving a natural ridge with a vestibule. Transport distraction is limited to reconstruction of a relatively straight line defects as seen with defects of the mandibular body. This is because the connective tissue stroma within regenerate dictates the shape of the reconstructed tissue. If attempts are made to move a transport disc around a curve, the regenerate forms a straight segment between the point of transport origin and completion. Thus, if it is necessary to reconstruct a defect of the symphysis, the best plan is to create transport discs from the right and left posterior stumps of the mandible and move them toward the symphysis. The residual defect in the symphysis requires a bone graft. An alternative plan is to transport right and left transport discs forward from the body with a vector that lets them consolidate in the midline and then follow that procedure with a second midline osteotomy and application of a midline distracter to widen the symphysis.
Figs. 1–4 provide information regarding the basic features of a transport distracter, (Threadlock design, KLS Martin, Jacksonville, Florida) and the concepts of transport distraction. The design of this transporter is universal in nature. It can be used to transport segments of the right or left body of the mandible from anterior to posterior or from posterior to anterior. The transport shaft is available in a variety of lengths, including 30, 40, 50, and 60 mm, and can be attached above the bone plate, below the bone plate for continuity defects, or to native mandible in cases of marginal resection with remaining basal bone. In Fig. 1 , the components of the device are labeled. Component 1 is a fixed titanium mesh that extends above and below the transport shaft 5. It can be attached to residual bone to provide additional stability or removed if not needed. Component 2 is the transport segment attachment mesh that moves along the variable length transport shaft 5 at 0.5 mm per complete turn of the activation arm 4. The activation arm is attached to the transport shaft and includes multiple ball joints to permit unstressed alignment of the activation arm during turning of the device. The activation arm can remain intraoral and emerge through mucosa or it can emerge through the skin for percutaneous activation. Component 3 is the attachment arm that provides an attachment for the transport shaft 5 to a reconstruction plate or basal mandible. The attachment location of the attachment arm to the transport shaft relative to the defect or its attachment to a plate or mandible can be adjusted anterior or posterior by loosening the set screw and sliding it along the groove in the transport shaft and then tightening the set screw to fix it in the desired location. It is best to attach the arm (see Fig. 3 ) to the plate or mandible at the point of greatest curvature if a curve exists, to avoid binding of the transport segment as it moves along the transport arm. The attachment arm accepts a screw designed to attach it to a locking plate or a locking screw for attachment to the mandible. The attachment arm can be removed from its slot in the transport shaft and flipped for cases where it is best to have the transport arm located below the reconstruction plate. Fig. 2 shows the transporter configured for anterior to posterior transport with attachments to the reconstruction plate proximal mandible and the transport segment. The transport bone segment should be 1.5 cm wide ± 0.5 cm and equal to the full thickness of the mandible. Care should be taken during preparation of the transport segment to maintain its vascular supply by not detaching periosteum or soft tissue attached to its coronal or lingual surfaces. Transport usually is initiated after a latency of 5 to 7 days at a rate of 1 mm per day ± 0.5 mm. In Fig. 3 , there is a partially transported segment showing the clearance between the transport segment and the curvature of the bone plate. In Fig. 4 , the linear relationship of the transport shaft between the points of initiation and completion of distraction is shown. The principles of distraction can be applied by using a system such as the one described previously. These principles include linear transport of a segment with appropriate dimensions and vascular supply with a mechanically smooth but rigid system that permits adaptation to the defect and minimizes micromotion.
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