Mean Volume Loss (%)

Mean Volume Loss (%)

100

Membraneous

Endochondral

75

50

25

Monkey

at surgery

20 weeks

Fig. 10.4  Reconstruction of the supraorbital rim with a split calvarial graft from the outer table of the skull

bone grafts merely lose 17–19% of their volume (Smith and Abramson 1983; Zins and Withaker 1983; Zins et al. 1984; Craft and Sargent 1989).

The minimal resorption of calvarial bone grafts offers a superior form consistency and subsequently more reliable aesthetic results. Consequently, as a result of the difficulty in estimating resoption in the graft area, in the majority of cases iliac crest and costal bone grafts have been abandoned (Fowler et al. 1995) (Fig. 10.5).

The degree of graft resorption is also influenced by the stability of the bone graft. A rigid fixation with miniplates noticeably reduces the extent of resorption (Philipps and Rahn 1988). A rigidly fixed membranous bone graft experimentally maintains a 10% greater volume than a nonfixed membranous bone graft. Rigidly fixed enchondral bone grafts maintain 75% of their volume in comparison with 15% in nonstabilized enchon­ dral grafts (Philipps and Rahn 1990).

Despite the experimentally low to moderate graft resorption in desmal bone grafts with adequate osteosynthesis, clinically there may be an unexpectedly greater resorption in the long-run (Fowler et al. 1995).

10.2.2  Bone Dust/Bone Chips

There is experience in filling defects with bone dust (Jackson et al. 1986; Dufresne et al. 1992; Hardt et al. 1994). Small residual defects such as craniotomy holes can be filled with bone dust collected intraoperatively. Resorbable membranes or titanium craniotomy rosettes can also be used to achieve stabile contours (Greenberg and Prein 2002).

a

b1

b2

• Bone dust

The majority of residual defects filled with bone dust exhibit distinct resorption. The bone is replaced by connective tissue, often with irregular to concave depres­ sions, resulting in an uneven skull surface.

An incomplete spontaneous osseous bridging is clinically and histologically found only at the level of the inner table (Hardt et al. 1994).

There are comparable results when using bone chips, which are attained from crushing tiny, nonintegrable bony fragments in a bone-mill (Hardt et al. 1994) (Fig. 10.6).

• Bone dust and membrane coverage

A few months after covering bone dust-filled defects with reabsorbable membranes (GORETEX), a smooth, coherent, niveau of regenerative connective tissue is formed under the membrane. Again, one only finds an incomplete, defect-bridging oseous regeneration at the level of the inner table. The regenerative capacity of bone is age-dependant (Hardt et al. 1994) (Figs. 10.7 and 10.8).

• Bone dust and titanium rosettes

The combination of bone dust and craniotomy rosettes produces clinically equivalent results. After removing the titanium rosettes, there is connective tissue with or without minimal niveau loss. The mostly incomplete osseus regeneration is exclusively limited to the level of the inner table (Hardt et al. 1994) (Fig. 10.9).

Fig. 10.6  Filling cranial bone defects with bone dust. (a) Bone dust (bone particles) collected during drilling of craniotomy holes. (b) After reinsertion of the frontal bone flap, burr holes and small bone defects are filled with bone dust

10.2.3  Autogenous Grafts from the Iliac Crest

Cortico-cancellous grafts from the iliac crest are rarely used to reconstruct skull bone defects. However, the iliac crest is an excellent reservoir for large amounts of cancellous bone, which may be needed for frontal sinus obliteration or frontobasal reconstruction.

Fig. 10.8  Histological section through a burr hole which was filled with bone dust and covered with a GORETEX membrane. (a) Newly-formed bone with remnants of the membrane (arrow)

(160×). (b) Almost complete reconstruction of a trepanation defect filled with vital bone (100×)