Biomaterials in Craniofacial Reconstruction
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Clin Plastic Surg 31 (2004) 377–385 Biomaterials in craniofacial reconstruction Younghoon R. Cho, MD, PhD, Arun K. Gosain, MD* Department of Plastic Surgery, Medical College of Wisconsin, 9200 West Wisconsin Avenue, Milwaukee, WI 53226, USA Biomaterials have become an integral component quent infection, Wolfe [16] describes the safety and of craniofacial reconstruction. Their increasing ease efficacy of autogenous bone graft reconstruction. It of use, long ‘‘shelf-life,’’ and safety enables them to has been noted that resorption of autogenous bone be used effectively and play an important role in re- graft can be particularly problematic in certain situ- ducing operating times [1]. The ideal biomaterial is ations, particularly in reconstruction of the malar biocompatible with surrounding tissue, radiolucent, eminence in patients with Treacher Collins Syndrome, easily shaped or molded, strong enough to endure and when bone grafts are placed for augmentation of trauma, stable over time, able to maintain volume, and the chin [1]. However, difficulties may also be en- osteoactive [1–5]. There are various biomaterials cur- countered with the use of alloplastic materials in these rently available and specific usages have been charac- reconstructive situations, as they may result in erosion terized well in the literature. This article reviews of the underlying recipient bone. different biomaterials that can be used in craniofacial In experimental studies in which alloplastic reconstruction, including autogenous bone, methyl implants were removed, it was noted that the under- methacrylate and hard tissue replacement, hydroxy- lying recipient bone underwent transformation to a apatite, porous polyethylene, bioactive glass, and de- trabecular architecture with decreased bone density mineralized bone. [17]. This may be particularly troublesome if an alloplastic implant must be removed following infec- tion or dislodgment, which would result in greater Autogenous bone deformity than was initially present. Although some cite the morbidity involved in harvesting cranial bone, The first documented bone autograft was described it has been documented that with proper training, by Walther in 1821 where he replaced the bone plug plastic surgeons can harvest bone grafts easily and after trephination and noted partial healing [6,7]. Full comfortably with minimal morbidity [18]. healing of the wound was prevented by subsequent Cranial bone, iliac bone, ribs, and tibia are the wound suppuration. In 1885, Macewen [8] reported a most commonly used bone graft donor sites. In certain successful reimplantation of bone pieces into a cranial clinical circumstances, vascularized bone grafts, such defect. Other donor sites have been attempted for as free fibula or free iliac bone, provide distinct ad- repairing cranial defects, including the tibia (1889), vantages over nonvascularized bone grafts. The clini- cranium (1890), fascia (1906), rib (1911), scapula cal setting in which vascularized bone grafts have (1912), illium (1914), and sternum (1915) [6,9–15]. been used most frequently has been for reconstruction Today, many physicians believe that autogenous of large segments of the mandible. However, vascu- bone remains the biomaterial of choice for cranio- larized bone grafts require greater amounts of time facial reconstruction. In a series of 73 cranioplasties and skill and are not necessary in most clinical cir- reconstructed with autogenous bone with no subse- cumstances. Disadvantages of the autogenous bone grafts that are not seen with other biomaterials are the potential morbidity of the donor site and the * Corresponding author. additional time required to harvest the graft. In addi- E-mail address: [email protected] (A.K. Gosain). tion, autogenous bone graft often undergoes signi- 0094-1298/04/$ – see front matter D 2004 Elsevier Inc. All rights reserved. doi:10.1016/j.cps.2004.03.001 378 Y.R. Cho, A.K. Gosain / Clin Plastic Surg 31 (2004) 377–385 ficant resorption when used for augmentation of posite consisting of a polymethylmethacrylate sub- the facial skeleton, rendering it unreliable for long- strate sintered with polyhydroxyethyl and a calcium term augmentation. hydroxide coating shielding the poylmethylmetha- crylate from the external surface. It has a 20% to 30% material porosity (150 to 350 microns), holds Methyl methacrylate a negative surface charge (À8toÀ15 mV) and has substantial compressive strength (50,000 lb/in2 Methyl methacrylate is an acrylic-based resin that in particulate form and 5000 lb/ in2 in molded form) has found many uses in today’s craniofacial recon- [21]. Its porosity promotes vascular ingrowth. The struction. Its use in craniofacial reconstruction was hydrophilic surface diminishes bacterial adhesion fol- first described during the early stages of World War II lowing preimplantation soaking in antibiotic solution. when there was a growing interest in acrylic resins In addition, the negative surface charge further deters [6,19]. Its first reported human use was in 1940 by adhesion of bacteria to the implant. Zander [6,7]. Unlike autogenous bone, which can The implant can be prefabricated in custom shapes have variable resorption of between 25% and 40% for facial augmentation. When placed in a subperi- of the bone graft over time, methyl methacrylate is osteal position, the implants can be adequately held resistant to absorption [20]. A meta-analysis review- in place by closure of the overlying periosteum. Gu- ing 45 studies of routine cranioplasty with methyl yuron has extensive experience in the use of these methacrylate showed an infection rate of approxi- implants for malar augmentation, chin augmentation, mately 5%. In a series of 42 cranioplasties by Manson and augmentation of the temporal regions for correc- and colleagues [20], isolated cranioplasties showed no tion of the ‘‘hourglass’’ facial deformity [22]. The infection. However, patients who had undergone si- hourglass facial deformity may occur following tem- multaneous reconstruction of the cranial vault, the poral atrophy following elevation of the temporalis orbital walls, and nose had an infection rate of 23%. muscle and as the result of bilateral irradiation of the All patients who had infection with methyl meth- orbits and anterior cranial base during infancy. Cus- acrylate had experienced a previous infection, indicat- tom implants of HTR polymer can be placed in the ing that a history of infection in the region is a temporal region for augmentation. A recent report of significant risk factor for subsequent infection. Methyl four such cases demonstrates the successful correction methacrylate was found to be stronger than the adja- of the hourglass deformity using this technique [22]. cent skull bone to compression and torsion testing. In Eppley et al [23] described the successful use addition, they found that cranial orbital reconstruction of computer-generated HTR for cranial reconstruc- adjacent to previously infected ethmoidal sinuses were tion in fourteen patients who had large (greater than more directly related to infection than was the material 150 cm2) preexisting defects of the cranium or cranio- used for reconstruction. The authors cited an additional orbital region. They used a preoperative high-reso- advantage of methyl methacrylate to be low cost, pre- lution 3D CT scan to reconstruct the defect. The dictable resultant shape, ready availability, and suit- manufacturer then used this reconstruction to fabricate ability for complex defects.. The authors concluded the HTR implant with less than 1 mm accuracy. At the that methyl methacrylate is the cranioplasty material of time of surgery the implant was secured using metal or choice in adults with good soft tissue quality who have resorbable fixation. To minimize the risk of infection not had previous infection. However, criticism of in cases where the frontal sinus was in proximity to methyl methacrylate is that it is an inert and fixed the implant, the sinus was cranialized, covered with a substance that will not adapt to the changing cranio- pericranial flap, or obliterated with hydroxyapatite facial skeleton. This is particularly important if one cement paste. The authors reported no postoperative is considering skeletal reconstruction in a growing complications or infections and good reconstructive child. An additional disadvantage of methyl metha- results. This technique simplifies the reconstruction crylate is that there is no bone incorporation or and reduces operative time by eliminating the need ingrowth, making it susceptible to infection or dis- to harvest bone graft and to shape the graft intra- lodgement through the duration of the reconstruction. operatively [23]. Hard Tissue Replacement Hydroxyapatite Hard Tissue Replacement (HTR; Walter Lorenz Hydroxyapatite is the primary mineral component Surgical, Jacksonville, FL) is another polymeric com- of teeth and bone and comprises up to 70% of the Y.R. Cho, A.K. Gosain / Clin Plastic Surg 31 (2004) 377–385 379 calcified skeleton. It is a calcium phosphate com- forms of hydroxyapatite. The authors found that pound arranged in a hexagonal structure and can be cranial bone grafts were not reliable for long-term produced synthetically as a ceramic by a process augmentation, with complete bone graft resorption called sintering. It is one of the more common forms observed in each of the facial recipient sites. The of calcium phosphate in clinical use. It has excellent volume maintenance of the hydroxyapatite compos- tissue compatibility