Page 94 - Advanced concepts in orbital wall fractures

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Chapter 5
below the ledge, which makes the error in deviation small. As far as the pitch is concerned, it is particularly important to see if the implant is not positioned too cranially at the apex or below the posterior ledge. This can be easily seen on the sagittal images. Translation is difficult to see as expected.
The position of the implants that the surgeon was satisfied with also had a significantly better yaw and roll compared with the implants with which the surgeon was not satisfied, which shows that the surgeon was able to identify when there was a deviation in the yaw or roll of the implant.
About 1.6 CT scans were required until the surgeon was satisfied (maximum n=3). This was comparable for both surgeons. When intraoperative and postoperative scans have a comparable dose of radiation, this implies only a minimal increase in radiation for the usual reconstruction, as a postoperative scan is no longer necessary. In our opinion, the possibility of changing the position of the implant and reducing the need for revision outweighs the increase in dose of radiation.
The primary reason for adjusting an implant was usually the observed deviation in roll and yaw. This was expected because they are best assessed in multiplanar view and the results also show that they improved significantly. The degree of translation is difficult to estimate with minimal displacements and was therefore only once the reason to change the implant. The rotation pitch was never a reason, as the deviations remained limited. The implant was never placed below the posterior ledge and only in a few reconstructions slightly too far cranially.
In the retrospective case series by Borad et al., 44 % of their implants were repositioned during operation after intraoperative imaging9. This is comparable to the half in our study. Unfortunately, the authors did not calculate if there was an actual improvement in the position of the implant. Blumer et al. stated that orbital floor fractures that had been reduced anatomically incorrectly can be reliably detected using intraoperative imaging. Between 29 and 47 % of the implants would have been adjusted if intraoperative imaging had been used5. Both studies imply that when