Calvarial bone grafting is an established method of craniofacial reconstruction in facial plastic surgery. Konig and Muller were the first to describe autogenous calvarial bone grafting in 1890, advocating a combined osteocutaneous flap. Smith, Abramson, and Tessier popularized the technique for modern craniofacial reconstruction. More recently, split calvarial bone grafts have been shown to be safe and effective grafts for nasal reconstruction and a viable alternative to autogenous cartilage and alloplastic implants for dorsal nasal augmentation.
Two groups of patients undergoing rhinoplasty and/or nasal reconstruction require materials to augment the nasal dorsum. The first group has saddle nose deformity, arising from traumatic, infectious, idiopathic, or iatrogenic conditions. The second group of patients has a congenitally platyrrhine nose, characterized by a low, wide dorsum, poor tip projection and definition, and an acute nasolabial angle. In modern reconstruction of the nasal dorsum, an ideal implant provides structural support, long-lasting augmentation, limited mobility, and reasonable resistance to infection.
Four categories of facial implants are in use today: alloplastic materials, homografts, xenografts, and autografts. Alloplasts are implants made of chemically composed polymers. Homografts refer to grafts obtained from a donor of the same species and include irradiated and nonirradiated cartilage, bone, and soft tissue. Xenografts refer to materials obtained from different species and are not used in contemporary augmentation rhinoplasty. Autografts are materials harvested from the patient’s own body and include bone, cartilage, and soft tissue grafts.
Alloplasts
Presently, the literature supports the use of both alloplastic and autogenous material for nasal reconstruction. Employing alloplastic materials shortens the length of an operation by eliminating the harvesting step, eliminates donor site morbidity, and can be easily tailored to conform to the defect. These materials are available in unlimited quantities and undergo minimal resorption. However, there are several important disadvantages to their use that have prompted many surgeons to avoid their use when possible. These disadvantages include foreign body reaction at the implant–tissue interface, a limited ability to withstand infection, and a tendency to migrate. These implants must be placed under highly sterile conditions, preferably in a bed of healthy, robust native tissue; tension over the implant and compromise to the vascular supply of the recipient bed must be avoided.
Homografts
Homografts represent another option for nasal reconstruction, and irradiated costal cartilage has been advocated as the preferred graft for dorsal nasal reconstruction by some surgeons, especially for those with extruded nasal alloplastic implants. Irradiated costal cartilage is harvested from cadavers that meet the same criteria required for organ donation (Venereal Disease Research Laboratory, hepatitis B, human immunodeficiency virus, tuberculosis, and slow virus testing). After harvest, the graft is irradiated with 30,000 to 40,000 Gy of ionizing radiation to eradicate potential pathogens. Benefits of homografts include their availability, low infection rates, minimal host immunogenic response, and decreased operative times. The use of homografts is limited by their tendency to resorb, sometimes unpredictably; resorption rates as high as 80% have been reported at 2 years. Symmetric contouring of the graft, placement in areas of low mobility (such as the nasal dorsum), and K-wire insertion are techniques that have been developed to decrease the rate of absorption. Homologous rib is best reserved for the elderly, to decrease operative times and donor site morbidity.
Autologous Implants
Given the shortcomings of allopasts and homografts, many nasal surgeons believe that the preferred type of implant for correction of saddle nose deformities or severe structural deficiencies is autogenous cartilage or bone. Autologous tissue is favored for its biocompatibility, low rate of infection and extrusion, and limited inflammatory response. It also lacks the risk of disease transmission that is present in homologous implants. Despite the limited availability and donor site morbidity, autologous implants remain the standard to which all other implants are compared.
Cartilage
Cartilages is an extremely popular graft material for most rhinoplasty surgeons and can be harvested from the septum, concha, or rib. Septal and conchal cartilages do not provide sufficient material for repair of most saddle nose deformities or severe tip structural deficiencies. Rib is the only source of cartilage that provides the structural support required for major nasal reconstruction. A significant advantage of rib is that it is readily available, although moderate absorption rates and a tendency to warp have been reported. Removal of the perichondrium, accompanied by symmetric carving using the central core of cartilage for dorsal augmentation, is one technique described to reduce warping. Internal fixation of the graft with a K-wire can also potentially reduce warping and decrease delayed graft malposition. Donor site morbidities include the possibility of pneumothorax, a likelihood of postoperative pain, temporary atelectasis, potential chest wall deformity, and a visible scar. In older patients, ossification of the cartilage can make carving and shaping of costal cartilage difficult.
Bone
Autologous bone is rigid, provides excellent support, and can be contoured with an otologic drill to create the desired contour. For nasal reconstruction, osseous rib and iliac crest are common sources of endochondral bone, while calvarium is the most common source of membranous bone. Osseous rib has an unpredictable pattern and amount of absorption, with an inherent tendency to distort its shape over time. The iliac crest yields plentiful bone, which can be fashioned to fit a variety of defects, similar to calvarial grafts. However, absorption has been problematic, and donor site issues, including pain and walking impairment, have been substantial.
Calvarial Bone
Calvarial bone offers advantages for nasal reconstruction based on its membranous origin. Experimental evidence suggests that graft volume is more consistently maintained in bone of membranous origin than from endochondral bone grafts. When compared morphologically to endochondral bone, membranous bone demonstrates a thicker cortical plate, a smaller endocortical cancellous area, and stronger intracortical struts.
Clinical advantages to calvarial bone grafting include decreased donor site pain, a hidden donor site, proximity of the donor site to the surgical field, and excellent graft shape. An additional benefit of calvarial bone is its ability to establish a bony union, decreasing the risk of displacement. Calvarial bone can also be used safely in patients with infection, destructive infectious processes, and noninfectious inflammatory diseases.
Anatomic Considerations in Calvarial Bone Grafting
The calvarium is composed of single frontal and occipital bones, along with paired parietal and temporal bones ( Figure 16-1 ). The sagittal, coronal, lambdoid, and squamosal sutures separate these bones. There are three distinct layers in the adult human skull: the outer cortical layer, the middle spongy cancellous layer (also termed the diploic layer), and the inner cortical layer. The goal of the split calvarial bone technique is to harvest only the outer cortical layer ( Figure 16-2 ). The dura adheres very closely to the undersurface of the inner calvarial layer, making it susceptible to tearing if the inner calvarium is inadvertently violated. The undersurface of the inner cortex is imprinted with numerous concavities formed by the underlying intracranial vasculature. The venous sagittal sinus is located in the midline and is approximately 1 to 1.5 cm wide. The temporal line represents the superior attachment of the temporal muscle, and both the outer cortical and the middle diploic layers are unacceptably thin lateral to this landmark. Moreover, the area above the temporal line possesses a natural curvature that mimics the nasal dorsum. Midline calvarial bone grafts place the sagittal sinus at risk, so bone within 2 cm of the midline should be left undisturbed. The bone also becomes thin in the area of the sutures ( Figure 16-3 ). The parietal bone has been consistently noted to have the thickest bone. Bone is thicker in males than in females by 1 or 2 mm. With these anatomic areas in mind, the safest area to harvest a split calvarial bone graft is on the parietal bone between the temporal line, the sagittal sinus, and suture lines.
Methods and Surgical Techniques
The patient’s hair is not shaved but instead is parted and coated with bacitracin ointment. The donor site and the recipient are prepped with povidine-iodine or alcohol and infiltrated with lidocaine (Xylocaine) with epinephrine (1 : 100,000) to promote hemostasis. Consideration should be given to using the nondominant side of the scalp, to protect the dominant motor cortex in the event of a neurologic complication. A sagittal temporoparietal incision is made over the superior temporal line. An incision positioned medial to the superior temporal line risks exposure if male pattern baldness develops, and an incision placed laterally risks hematoma from dissection around the temporalis muscle and cerebrospinal fluid leak from calvarial dissection in the thinner bone of this region. After the incision is made to the level of the calvarium, the pericranium is elevated medially and laterally. Using an otologic cutting drill, a 1.5 × 4.5-cm graft is outlined, with the longest dimension in the sagittal plane. A trough is created around the graft with the cutting burr. The diploic level is identified when spongy bone and bleeding are encountered. The margins of the trough are beveled to facilitate the positioning of the osteotomes. The osteotomes are positioned in a plane tangential to the skull to prevent dural injury ( Figure 16-4 ). A series of sequentially larger curved osteotomes are used circumferentially to separate the outer table calvarium from the inner table through the diploic layer. If dura is exposed during elevation, the margins should be burnished with a diamond drill. Typically, no further measures are necessary. The donor site defect can be obliterated by filling with methyl methacrylate, although this may occasionally lead to a pain syndrome, and also harbors all of the usual risks of a foreign body. The defect when left untreated is frequently imperceptible, given its location under hair-bearing scalp, and most patients are not bothered by the slight palpable depression in that zone. The wound is closed in a single layer over a suction drain, and a head wrap is placed. The calvarial bone graft is then brought to a separate sterile field and irrigated copiously with a bacitracin-containing solution. At this point, the bone graft normally measures approximately 1.0 × 3.5 cm. An otologic drill is used to carve a fusiform shape to match the nasal defect. The graft is fashioned slightly wider caudally if correction of the internal nasal valve is required. The undersurface of the graft is hollowed along its central axis to prevent displacement.
