The paranasal sinuses as a protective crumple zone for the orbit

The purpose of this study is to test the theory that the paranasal sinuses serve a protective function for the central nervous system and special sensory organs.

Nonrandomized experimental trauma study with fresh human cadavers.

Fresh human cadaver heads were obtained and the sinuses on one side underwent endoscopic endonasal sinus surgery and were then filled with radio-opaque bone cement to obliterate them. The contralateral sinuses were not operated upon to allow both for comparison to the experimental side and to serve as an intraspecimen control. The cadavers underwent serial computed tomography (CT) scans. Scans were performed prior to surgery, after surgery, and after unilateral sinus obliteration to obtain baseline CT studies prior to any impact testing. Sequential drops of increasing energy were then performed directing the impacts onto the globes. Initial endpoints were either orbital fractures or ocular injury. Trauma was induced by impacting a weighted rod onto the globes using a guided drop technique. Orbital rim impact was avoided, so that the effect of direct globe trauma could be assessed; fractures were thus induced via the hydraulic mechanism, in which force is transmitted through the globe to the surrounding tissues and orbital walls. After initial injury endpoints were met, additional impact testing was performed on globes, in which fractures occurred with lower drop forces to ensure impact energy equivalence between the control and the experimental sides.

All the experimentally obliterated paranasal sinus orbits tested suffered trauma-induced globe ruptures, and no orbital wall fractures were encountered. On the control sides, no globe ruptures occurred at either an equivalent or higher energy than the energy needed to induce globe ruptures on the experimental side orbits, although orbital floor fractures on the control sides occurred after lower energy impacts in some cases.

This study demonstrates that the thin orbital floor fractures preferentially, thereby protecting the globe from rupture as a result of the directed trauma. When the sinus crumple zones were eliminated, globe ruptures occurred.