Page 131 - Advanced concepts in orbital wall fractures
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                                General discussion and future perspectives
comparison to other studies6,7. It is useful for research purposes and in the analysis of volume before, for example, orbital decompression surgery or reconstruction after exenteration surgery. It may also be possible to compare the postoperative volume of the reconstructed side of an orbital wall fracture with the unaffected side to quantify the volume reduction. Orbital wall fractures are often reconstructed using titanium orbital reconstruction plates. As the density of a titanium orbital implant is high and induces little scattering on a CT scan, measuring the volume after reconstruction is possible. Accuracy studies to prove the validity of measuring postoperative orbital cavities have not been performed yet.
The bony orbit is not an enclosed space due to the presence of apertures
and therefore it is difficult to measure the volume. The fracture itself is an
additional and irregular opening. The consequence is that measurement
of the orbital volume after trauma is even more complicated. Imaginary
planes and lines are necessary to delineate the fissures, optic canal,
anterior boundary, and the fracture site. One solution may be to use
method SAA with automatic segmentation minus bone and air masks
followed by manual adjustments8,9. Although this method is not as quick
and accurate, the reproducibility is high and it will still be useful in clinical assessment. This has been confirmed by a recent study with an intraclass
correlation of 0.9339. The importance of measuring volume is rather to
objectify the extensiveness of the fracture in comparison to the unaffected
side than it is to predict the outcome or serve as an indicator for surgery. C
Mirroring of the segmented unaffected bony orbit onto the fractured bony 7 orbit is an important step in computer-assisted orbital reconstruction. It
is assumed that both sides are identical and that the virtual template
of the mirrored side can be a representation of the pretraumatised
state of the affected side. Chapter 3 proves that the volume difference between the left and right orbital cavities is negligible and the orbital wall contours show high similarity. The mean orbital volume was 27.53 cc (SD 3.11) and the mean difference between the left and right cavity was 0.44 cc (SD 0.31). These results are comparable to other recent studies and probably differ mildly due to variation in measurement methods10-12. The largest asymmetry in the contour is noticed near the apex. This is
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