Key words: bone block, bone defect, bone harvesting, bone shell technique, bony gap, cancellous bone cylinder, corticocancelleous bone graft, iliac crest anterior, iliac crest posterior, mixture of cancellous bone graft and hydroxyapatite (eg, Bio-Oss, Geistlich) osteosynthesis for graft fixation, reconstruction of canine fossa
An indication for bone harvesting from the iliac crest exists if sufficient bone graft cannot be obtained locally from the surgical area of the facial skull. This occurs mainly in the correction of congenital malformations or dentofacial growth disorders of greater severity, when larger grafts are required at several sites of the maxilla and mandible to bridge bone gaps or defects.
During surgical augmentation of hypoplastic jaw structures, bone gaps may occur or, if bone lamellae are displaced in relation to each other, nesting may occur. These gaps are bridged by stable bone blocks or filled with cancellous grafts. Stabilization with osteosyntheses is usually required. In orthognathic surgery, bone harvesting can be performed simultaneously from the iliac crest and individually depending on the defect size.
The extent of the necessary bone harvesting is not predictable (even based on the surgical planning) in all cases of severe dentofacial malformation. It can often only be determined intraoperatively from a 3D overview in the surgical region. Therefore, when planning the surgical procedure, care should be taken to ensure that simultaneous bone harvesting is performed only after surgical visualization of the bone defect, if possible.
Both the extent of the dentofacial deformity and the extent of the planned corrections result in bone defects of varying sizes that can be filled with cortical or cancellous or combined bone grafts.
Cortical grafts are used as thinly as possible to cover bone defects in the canine fossa of the midface after LeFort I osteotomy, and are fixed by microscrews to cover the maxillary sinuses.
Cortical bone blocks are also used in the posterior maxilla after CCWR of the maxilla for defect bridging and stable anchorage of the maxilla. If a caudal displacement of the maxilla is performed in a “short face,” cortical bone blocks should also be interposed in the piriform aperture.
Bony fissures, which occur, for example, after sagittal mandibular splitting due to displacement of the mandible or after chin wing corrections, are preferably filled with cancellous bone cylinders. In such cases it is also possible to use additional hydroxyapatite granules, which will be mixed with spongy crumbs to augment the volume of the graft.
Corticocancellous grafts are preferred to create a new stable bone surface with the cortical portion to act as a barrier against bone resorption, for example because the covering soft tissue no longer has periosteum. The cancellous bone fills the underlying bone defect and leads to rapid graft growth. This shell-technique has been perfected in the augmentation of alveolar defects or atrophic areas of the alveolar ridge.
24.2 Methodology of bone block harvesting
With the patient under general anesthetic and in the supine position, local anesthetic and vasoconstrictor (eg, prilocaine 1% with epinephrine 1:200,000) are injected along the palpable anterior hip scapula while the skin is moved medially. This allows the lateral femoral cutaneous nerve, which supplies sensation to the lateral anterior femoral skin (Fig 24-1a), to be displaced medially and reliably spared during the procedure. Again shifting the skin medially, an approximately 4-cm skin incision is made with a 15-gauge scalpel from the anterior superior iliac spine over the palpable iliac crest to the craniolateral. The scar will later be 2- to 3-cm lateral to the iliac spine contour. After periosteal slitting tangentially approximately in the middle of the iliac crest, subperiosteal free dissection of the upper part of the iliac fossa, ie the inner side of the iliac bone, is performed (Fig 24-1b). At a distance of 1 to 1.5 cm cranial to the anterior superior iliac spine, a piezoelectric or longitudinal oscillating saw is used to perform a box-shaped osteotomy of a corticocancellous block from the inner surface of the iliac blade. This block can be several centimeters long and wide, as needed (Fig 24-1c). Depending on the size of the bone block, the iliac crest should be preserved if possible. Even if the inner lip of the iliac crest up to the intermediate line is also removed, the bone harvest site will not remain palpable later. Similarly, the outer cortical layer of the iliac crest should also be preserved to avoid fenestration with injury to the gluteus medius muscle insertion. This is followed by deepening of the box-shaped osteotomy and undermining of the corticocancellous bone block with the gouge (Fig 24-1d), and finally complete mobilization and harvesting. Further cancellous bone material is harvested from the surrounding area with the gouge or small sharp spoon, again without perforating the thin outer cortical layer in depth (Fig 24-1e). Then the open cancellous bone spaces are manually closed with collagen fleece as a hemostyptic (Fig 24-1f) and the access is closed layer by layer: periosteum (Fig 24-1g), fat tissue, connective tissue, with absorbable single button sutures. Skin suturing is performed intracutaneously (Fig 24-1h), with single (Fig 2-24-1i) or even double with additional 6-0 single button sutures and wound closure strip adaptation, depending on the situation. A drainage is usually not necessary. Suture removal is performed after 2 weeks.