10.1.3  Orbital Region (Jackson et al. 1986; Serletti and Manson 1992; Hammer and Prein 1998)

•Frontal defects in the eyebrow region interfere with eyelid mobility and functionally disturb perspiration. An efficiently reconstructed supraorbital arch protects the globe.

•In orbital roof defects, bridging the gaps with convex bone transplants prevents the development of an enophthalmus and the transmission of cerebral pulsations to the orbital soft tissues and a potential cerebral prolapse (Mohr et al. 1994).

•Orbital wall defects have to be reconstructed with bone grafts, mesh systems or alloplastic sheets to avoid herniation of orbital soft tissue with subsequent enophthalmus or muscle imbalance or incarceration (Korneef 1982; Gruss et al. 1985; Ilankovan and Jackson 1992; Mathog 1992; Serletti and Manson 1992; Sugar et al. 1992; Merten and Luhr 1994; Piotowski and Beck-Manntagetta 1995; Gehrke et al. 1996; Hammer and Prein 1998; Dietz et al. 2001; Dempf et al. 2001).

Prolapsed periorbital soft tissues are carefully relocated and incarcerated eye mucles are released and replaced. Bone grafts may both be directly integrated and wedged into the defect in a self-stabilizing manner or as a cantiever,­ stabilized by a microplate at the orbital margin (Gruss et al. 1985; Antonyshyn et al. 1989; Mathog 1992; Hammer 1995; Reinert and Gellrich 1997; Markowitz and Manson 1998; Manson 1998b; Hammer 2002; Greenberg and Prein 2002; Frodel 2002).

10.2  Autogenous Bone Grafts

Due to the proximity to the operation field in a coronal approach, it is advisable to preferentially harvest autogenous bone grafts from the calvarium (Jackson et al. 1982; Dufresne et al. 1992). Various bone grafting tech­ niques are used to bridge bony defects.

10.2.1  Split Calvarial Grafts

These grafts are obtained by splitting bicortical calvarial bone.

The inner table is used as a graft to reconstruct defects and can in itself be variably altered in size and shape, whereas the outer table is used to restore the skull contour of the donor side. Split calvarial grafts are particularly used in large defects (Froherg and Deatherage 1991; Dufresne et al. 1992; Salyer 1992; Hardt et al. 1994; Greenberg and Prein 2002; Frodel et al. 1993; Frodel 2002) (Fig. 10.1).

Technique of harvesting split calvarial grafts (Kellman and Marentete 1995)

Placing craniotomy holes and connecting osteot­ omies

Detaching the dura and extracting the bicortical bone flap

Splitting the bicortical bone flap through the diploic space into inner and outer table using microsaw and chisels

• Inner table grafts

Tabula interna grafts have the advantage of providing a sufficient amount of donor bone without leaving a cosmetic defect in the calvarium. Inner table grafts are most commonly harvested from the inner table of the skull when intracranial-extracranial procedures are being performed.

According to Kellman and Marentete (1995) a piece of skull bone analogical to the size of the defect has to be determined and harvested to reconstruct the defect. For resecting the inner table of the double-layered skull bone, an oscillating or reciprocating saw may be used. After outlining the size of the graft on the inner table, the diploic layer is divided carefully with the saw. After circular incision, a chisel may be used to separate inner and outer table (Figs. 10.2 and 10.3).

• Outer table grafts

Grafts of the outer table can be harvested without performing a craniotomy.

The desired graft size is outlined with a burr until the diploic space is reached. Then the marked bone graft is removed with special chisels (sledge-shaped osteotomes), an oszillating saw or a piezo surgical device. The parietal skull region — as the preferred donor site — is generally sufficiently thick to harvest outer

Fig. 10.1  Technique of harvesting calvarial bone grafts (mod. a. Kellman and Marentete 1995). (a) Splitting the fronto-temporal bone flap with chisels or saw to obtain monocortical calvarial grafts. (b) Harvesting of monocortical bone grafts from the outer table of the skull. After creating a groove with a round burr, the split skull graft is elevated with chisels or a sagittal saw. The

separation requires a precise technique with correct insertion of the osteotome into the diploic space at a correct angle, parallel to the inner and outer table. (c) Splitting the bicortical calvaria in the interconnecting diploe into monocortical tabula externa and tabula interna grafts

table grafts. The defect can be filled with bone cement if necessary (Jackson 1986; Jackson et al. 1987; Frohberg and Deatherage 1991; Hardt et al. 1992; Dempf et al. 1998).

The donor site should be located on the parietal bone between the temporal line and a point 1.5 cm lateral to the sagittal suture. The bone below the temporal line is too thin to allow safe harvesting of the graft. lt is crucial to avoid the midline, because then the superior sagittal sinus is located beneath the sagittal suture and inadvertent penetration of the inner table during graft harvest could result in laceration of the sinus, which would result in significant

bleeding and possibly an air embolism and/or sinus thrombosis.

Donor site bleeding may be controlled by using either bone wax or a resorbable collagen sponge. During harvesting, small emissary veins may be encountered in the diploic layer, causing significant bleeding. If this occurs early during the harvesting of the graft, then bone wax is placed at the edges of the graft to control the bleeding, and another donor site may be chosen.

However, if an emissary vein is encountered during harvesting the outer table, then the procedure should be finished as quickly as possible and the graft

Fig. 10.3  Reconstruction of an extensive defect of the orbital roof with split calvarial graft (inner table). (a) Harvested graft. (b) Reconstructed orbital roof after frontofacial osteotomy, cranial debridement and canalization of the frontal sinus. The bone

graft is fixed with two miniplates. (c) Reintegration of the fron- to-facial bone segment. (d) The reconstructed orbital roof is covered with a pericranial flap

removed. Immediate hemostasis is accomplished by using bone wax.

Technique of harvesting monocortical outer table transplants (Kellman and Marentete 1995)

The maximum circumference of the transplant is outlined with a large round burr until the diploic space is reached

Elevation of the graft is carried out using a flexible saw, chisels, or piezosurgical device

The convex form of the thin outer table of the skull facillitates fitting of the graft particularly into regions of disrupted concave midfacial contours (orbital wall defects). Designed bone grafts can be used to reconstruct the load-bearing facial pillars or the nasal dorsum.

Grafts harvested in an anteroposterior direction are straighter and best suited for the reconstruction of the medial buttresses and nasal dorsum. Grafts oriented in a superoinferior direction along the lateral skull are more curved and generally better suited for reconstruction of the lateral buttresses in the zygomatic region and the orbital walls.

The carefully inserted bone grafts have to be stabilized with minior microplates. The local morbidity rate, mostly in the form of small wound complications, may reach 4.6% (Ilankovan and Jackson 1992) (Fig. 10.4).

• Graft resorption

In contrast to iliac crest or costal grafts, the membranous, desmal calvarian bone grafts exhibit a considerably lower resorption rate (Withacker 1989). The enchondral iliac and costal grafts display resorption rates of 60-80% of their original volume, whilst the desmal calvarian