Reconstruction of mandibular defects

Dr. Ahmed M. Adawy Professor Emeritus, Dep. Oral & Maxillofacial Surg.

Former Dean, Faculty of Dental MedicineAl-Azhar University

Mandibular defectsBone defect is a lack of bone where it should normally occur. Numerous etiologies lie behind mandibular defects including pathologic lesions, trauma related, infectious diseases and congenital defects. Meanwhile, the most common indication for mandibular reconstruction remains resection of benign or malignant lesions, posttraumatic deformities and osteoradionecrosis

Etiology of mandibular defects

Locally invasive benign tumors such as ameloblastoma, giant cell granuloma, keratocystic odontogenic tumor, and odontogenic myxoma are a benign, invasive, lesions of the jaws that predominantly affects the mandible. Despite the benign nature of these lesions, there is a high rate of local recurrence after curettage, which usually requires resection. Resection leads to segmental defects. Even, when treated conservatively, curettage results in the so called “critical size defects”. Critical sized defect has been defined as a defect which shows less than 10 percent bony regeneration during the lifetime of the animal (1)

Mandibular defects

Mandibular defects can generally be considered by their location and extent and can be divided into defects involving the anterior mandible ( Central defects “C”) and lateral mandible ( Lateral segment “L” ). When the condyle is resected together with the lateral mandible, the defect is designated ‘‘H”. Eight permutations of these capital letters; C, L, H, LC, HC, LCL, HCL, and HH- are encountered for mandibular defects (2). The classification was modified to include a soft tissue description as well, with ‘‘t’’ representing a significant tongue defect, ‘‘m’’ a mucosal defect, and ‘‘s’’ an external skin defect (3)

Mandibular defects

Classification of mandibular defects

Mandibular reconstruction

When undertaking mandibular reconstruction, the restoration of bony continuity alone should not be considered the measure of success. The functions of chewing, swallowing, speech articulation, and oral competence must also be addressed. The goals of mandibular reconstruction are: 1) establishment of mandibular continuity, 2) establishment of an osseous-alveolar base, 3) correction of soft-tissue defects, and 4) establishment of mandibular function

The first step in undertaking mandibular reconstruction involves careful evaluation of the patients’ anatomy in order to define the full extent of the existing or proposed defect. The quality and quantity of the remaining hard and soft tissue components must be examined. Advances in diagnostic technologies can be very helpful when formulating a plan for mandibular reconstruction. Virtual surgical planning (VSP) and computer aided design (CAD) / computer aided modeling (CAM) is an exciting new technology that presents advantages in complex craniomaxillofacial reconstruction (4)

Mandibular reconstruction

Diagnostic aids

CAD / CAM technology

In previous decades, delayed reconstruction of mandibular defects was favored over primary reconstruction. The believe was that primary reconstruction could potentially mask tumor recurrence. Further, the success rates following primary reconstruction were not very high. The defects were bridged by reconstruction plates. The most common complications were plate exposure, loose osteosynthesis screws and fractures of the reconstruction plate. Low success rates of plate-only reconstruction have been reported, ranging from 34% at 6 months, and 13 to 64% at 1-year follow-up (5)

Reconstruction plates

Plate exposure

Fracture of reconstruction plate

At present, the methods to restore mandibular defects can be classified into four basic categories: 1.Autogenous bone grafts in the form of nonvascularized free bone transfer, or vascularized tissue transfer, either pedicled or based on microvascular anastomosis 2. Distraction osteogenesis3. Alloplastic materials (with or without bone) 4. Tissue engineered graftsThe proper selection of the graft materials and technique is based on the size, site, shape, and dimensions of the defect

Mandibular reconstruction

Nonvascularized bone grafts

Bone grafts are often described by the terms osteogenicity, osteoinductivity and osteoconductivity. Osteogenicity is the presence of bone forming cells within the bone graft. Osteoinductivity is the ability of a graft to stimulate or promote bone formation. Osteoconductivity is the ability of the graft to function as a scaffold for ingrowth of new bone and migration of local osteocompetent cells originate from the endostium or residual periostium of the host bone

Nonvascularized autologous bone grafts can be used for reconstruction of small to medium size L- defects of the mandible. Many donor sites are available for autologous bone graft harvest such as calvarium, rib, ilium, tibia, fibula, scapula, humerus, radius, metatarsus, and mandibular symphysis, and provide viable and immunocompatible osteoblastic cells. These sites are different in terms of embryologic characteristics, type of bone and architecture. This could be the potential source of advantages and disadvantages (6)

Nonvascularized bone grafts

Cranial bone is an acceptable site for obtaining bone for grafting. The technique can yield considerable amounts of cortical bone but limited amounts of cancellous bone. Obtaining grafts from the ribs is another option that yield both bony and cartilaginous tissues. The cartilaginous component is useful for providing an articular surface for the temporomandibular joint and as a growth center in growing patients. However, rib graft is limited by the size, curvature, and strength of the rib plus donor site complications, such as pneumothorax, rib fracture, and pleural puncture

Nonvascularized bone grafts

Harvesting calvarium bone graft

Costochondoral rib graft for ramusand condyle reconstruction

Many surgeons choose a cortico-cancellous block grafttaken from the anterior or posterior iliac crest for jaw reconstruction. These grafts contain the greatest absolute cancellous bone volume and have the highest cancellous-to-cortical bone ratio. From a single side, the maximum amount of obtainable bone from the anterior ilium approaches 50 cc. From the posterior ilium, the maximum obtainable bone volume is about 90 cc. Donor site complications include hematoma, seroma, nerve and arterial injuries, gait disturbances, fractures of the iliac wing, peritoneal perforation, infection, sacroiliac instability, and pain (7)

Nonvascularized bone grafts

Bone graft harvested from the anterior part of the iliac crest

However, there are two major limitation of using an autogenous bone graft: poor osteointegration andexcessive resorption when the defect is larger than 6 to 9 cm. Insufficient blood supply for the surrounding tissues secondary to irradiation, scarring, and infection is major detrimental factor. Moreover, donor site morbidity limits the use of autogenous bone graft (8)

Nonvascularized bone grafts

Vascularized bone grafts The use of vascularized bone grafts has considerably improved treatment outcomes for patients with significant mandibular and soft tissue defects, particularly after ongoing radiation therapy. Direct comparisons of nonvasculized bone grafts and vascularized bone grafts have shown superiority of the latter in terms of bony union (69% vs. 96% ) (9), as well as superior functional and aesthetic scores for diet, speech, and midline symmetry (10). Superiority increases significantly in case of mandibular defects greater than 6 cm. Today the most commonly used grafts with microvascular anastomosis are: fibula; iliac crest; scapula; and radial forearm with the fibula graft being the most popular for mandibular reconstruction

The use of free vascularized fibula has become the “gold standard” for mandibular reconstruction since its introduction in 1989 (11). The fibula graft offers a good length of dense cortical bone, up to 25 cm in adults, as well as a long pedicle based on the peroneal artery for the reconstruction of long bony defects. Further, the graft may provide skin islands, up to 25 cm long and 14 cm wide, suitable for reconstruction of associated soft tissue defects. Moreover, the technique permits  two team approach. This decreases the time of operation, and reduces the critical ischemia time (5 hours) of the graft. A 98% graft survival and good aesthetic and functional outcomes have been reported (12). Morbidity is mostly avoidable with careful planning and appropriate technique

Free vascularized fibular graft

One disadvantage of the free fibula graft is the height discrepancy between the native mandible and the transplanted fibula, especially at the anterior segment. The ‘double-barreling’ of the fibula to create equal struts is a useful modification with good aesthetic and functional outcomes (12). The ‘double-barreling’ of the fibula enables immediate osseointegrated dental implantation, obtaining better results and lower complication rates compared to vertical distraction devices (13)

Free vascularized fibula graft

Diagrammatic representation of harvesting vascularized fibula

graft

Double-barreling fibula graft

Distraction osteogenesisDistraction osteogenesis is a biologic process of new bone formation in a gap between two separated bone segments. The gap is gradually filled by incremental traction. A callus forms between the separated bone segments as long as the traction proceeds. There have been a number of small series describing success with transport-disk distraction osteogenesis. One study described a two-step transport-disk distraction technique with internal distracters to reconstruct body or ramus defects in both horizontal and vertical dimensions (14). All patients had benign odontogenic tumors, which allowed preservation of periosteum and no required radiation. Also, the distraction requires 14–18 months of treatment

Another study reported a series of seven patients with segmental defects after composite resections for oral cavity squamous cell carcinoma (15). The initial reconstruction used soft tissue flaps and reconstructive bridging plates. At an average 20 months later, transport disk distraction osteogenesis was performed with an external fixator. One patient received radiotherapy and had insufficient callus formation. The other six patients had successful bony reconstruction.Although distraction osteogenesis has been successful in the reconstruction of large segmental defects, its application is limited by a requirement for intact soft tissue and periosteum, an incompatibility with adjuvant radiotherapy and the need for a long period of treatment

Distraction osteogenesis

Transport-disk distraction osteogenesis

Panoramic X-ray after installation of the distraction device

One year after distraction osteogenesis, very good bone formation is noted

Alloplastic materialsCurrently , there has been great interest in the development of synthetic grafting materials to be used in osseous reconstruction surgeries (16).The ideal bone substitute is osteoconductive, osteoinductive, biocompatible, and bioresorbable. Moreover, it should induce minimal or no fibrotic reaction, undergo remodeling and support new bone formation. From a mechanical point of view bone substitutes should have similar strengths to that of the bone being replaced. Finally, it should be cost-effective and be available in the amount required

Multiple products, containing combinations of hydroxyapatite, tricalcium phosphate, dicalcium phosphate, calcium sulphate, or bioactive glass are currently available for use in trauma and orthopedic surgery. The crystalline and porous qualities of these materials aid in anchoring surrounding tissues to facilitate proper fixation. However, an evidence-based guideline to assist surgeons in selecting the best product for specific clinical indications is not available yet

Alloplastic materials

Tissue engineered technology

Tissue engineering is the application of scientific principles to the design, fabrication, modification and growth of living tissues using biomaterials, cells and growth factors (17). There are many approaches to bone tissue engineering. One popular approach involves the utilization of biomaterial scaffolds combined with bone marrow-derived stromal cells and growth factors. Numerous scaffolds matrices, including allogenic, xenogenic, and synthetic graft materials have been used

Tissue engineering technology

Ideally, the scaffolds should be (1) three dimensional and highly porous with an interconnected pore network for cell growth and flow transport of nutrients and metabolic waste as well as (2) biocompatible and bioresorbable with a controllable degradation and resorption rate to match cell or tissue growth. Furthermore, these scaffolds should possess (3) suitable surface chemistry for cell attachment, proliferation, and differentiation, and (4) mechanical properties to match those of the tissues at the site of implantation (18)

Tissue engineered technology

Bone marrow derived stromal cells can be grouped under the term mesenchymal stem cells. They are characterized by their ability to self renew and differentiate into multiple cell types, including osteoblasts, adipocytes and chondrocytes. It has been widely accepted that regeneration of bone defects is advanced by bone marrow stem cells that migrate to the site of damage and undergo differentiation promoting structural and functional repair (19). Bone marrow stromal cells are induced to differentiate into osteoblasts and restore bone defects

Tissue engineered technology

 Mesenchymal stem cells have the potential to differentiate into various lineages

Many growth factors are involved in osteogenesis. Bone morphogenetic proteins (BMP-2 and BMP-7), transforming growth factor beta (TGF-β), insulin-like growth factors I and II (IGF I and II), platelet-derived growth factor (PDGF), fibroblast growth factors (FGFs), and vascular endothelial growth factor (VEGF) have been proposed for use in bone tissue engineering. Bone morphogenetic proteins; BMP-2 and BMP-7 are known for their osteoinductive qualities (20)

Tissue engineered technology

In an interesting study, Herford and Boyne (21) presented the practice of reconstruction of large defects of the mandible using rhBMP-2 on collagen carrier and titanium mesh in 14 patients. All cases achieved complete bone formation and high levels of functional rehabilitation. Radiologic indications of a newly formed bone appeared in 5-6 months after the reconstruction. Tissue bioengineering technology appears to be a very promising technique. It could have significant impact on the reconstruction of maxillofacial defects. However, more comparative studies and randomized controlled clinical trials are needed to determine the true efficacy of this technique

Tissue engineered technology

1. Hollinger JO, Kleinschmidt JC. The critical size defect as an experimental model to test bone repair materials. J Craniofac Surg; 1, 60, 1990.2. Jewer DD, Boyd JB, Manktelow RT, et al. Orofacial and mandibular reconstruction with the iliac crest free flap: a review of 60 cases and a new method of classification. Plast Reconstr Surg; 84: 391, 1989.3. Hidalgo DA, Pusic AL. Free-flap mandibular reconstruction: 10-year follow-up study. Plast. Reconstr. Surg; 110: 438, 2002.4. Sharaf B, Levine J, Hirsch D, et al. Importance of computer aided design and manufacturing technology in the multidisciplinary approach to head and neck reconstruction. J Craniofac Surg; 21: 1277, 2010.5. Maurer P, Eckert AW, Kriwalsky MS, et al. Scope and limitations of methods of mandibular reconstruction: a long-term follow-up. Br J Oral Maxillofac Surg; 48: 100, 2010.6. Scheerlinck LM, Muradin MS, van der Bilt A, et al. Donor site complications in bone grafting: comparison of iliac crest, calvarial, and mandibular ramus bone. Int J Oral Maxillofac Implants; 28: 222, 2013. 7. Ahlman E, Patzakis M, Roidis N, et al. Comparison of anterior and posterior iliac crest bone grafts in terms of harvest-site morbidity and functional outcomes. J Bone Joint Surg Am; 84: 716, 2002.

References:

8. Kessler P, Thorwarth M, Bloch-Birkholz A, et al. Harvesting of bone from the iliac crest- comparison of the anterior and posterior sites. Br J Oral Maxillofac Surg; 43: 51, 2005.9. Foster RD, Anthony JP, Sharma A, et al. Vascularized bone flaps versus nonvascularized bone grafts for mandibular reconstruction: an outcome analysis of primary bony union and endosseous implant success. Head Neck; 21: 66, 1999.10. King TW, Gallas MT, Robb GL, et al. Aesthetic and functional outcomes using osseous or soft-tissue free flaps. J Reconstr Microsurg; 18: 365, 2002. 11. Hidalgo DA. Fibula free flap: a new method of mandible reconstruction. Plast Reconstr Surg; 84: 71, 1989. 12. Shen Y, Guo XH, Sun J, et al. Double-barrel vascularised fibula graft in mandibular reconstruction: a 10-year experience with an algorithm. J Plast Reconstr Aesthet Surg; 66: 364, 2013. 13. Chang YM, Wallace CG, Hsu YM, et al. Outcome of osseointegrated dental implants in double-barrel and vertically distracted fibula osteoseptocutaneous free flaps for segmental mandibular defect reconstruction. Plast Reconstr Surg; 134: 1033, 2014. 14. Chen J, Liu Y, Zhao S, et al. Two-step trasnport-disk distraction osteogenesis in reconstruction of mandibular defect involving body and ramus. Int J Oral Maxillofac Surg; 39: 573, 2010.

References:

References:15. Seitz O, Harth M, Ghanaati S, et al. Secondary mandibular reconstruction after squamous cell carcinoma resection: clinical reevaluation of trasport disk distraction osteogenesis. J Craniofac Surg; 21: 59, 2010. 16. Cannon T.Y., Strub G.M., Yawn R.J. et al. Oromandibular Reconstruction. Clin. Anat; 25: 108, 2012. 17. Langer R, Vacanti JP. Tissue engineering. Science; 260: 920, 1993.18. Hutmacher DW. Scaffolds in tissue engineering bone and cartilage. Biomaterials; 21: 2529, 2000. 19. Abkowitz JL, Robinson AE, Kale S, et al. Mobilization of hematopoietic stem cells during homeostasis and after cytokine exposure. Blood; 102: 1249, 2003. 20. van Hout WMMT, van derMolen ABM, Breugem CC, et al. Reconstruction of the alveolar cleft: can growth factor-aided tissue engineering replace autologous bone grafting? A literature review and systematic review of results obtained with bone morphogenetic protein-2. Clin Oral Invest; 15: 297, 2011. 21. Herford AS, Boyne PJ. Reconstruction of mandibular continuity defects with bone morphogenetic protein-2 (rhBMP-2). J Oral Maxillofac Surg; 66: 616, 2008.