An orbital blowout fracture is a traumatic deformity of the orbital floor or medial wall that typically results from the impact of a blunt object larger than the orbital aperture, or eye socket. Most commonly this results in a herniation of orbital contents through the orbital fractures. The proximity of maxillary and ethmoidal sinus increases the susceptibility of the floor and medial wall for the orbital blowout fracture in these anatomical sites. Most commonly, the inferior orbital wall, or the floor, is likely to collapse, because the bones of the roof and lateral walls are robust. Although the bone forming the medial wall is the thinnest, it is buttressed by the bone separating the ethmoidal air cells. The comparatively thin bone of the floor of the orbit and roof of the maxillary sinus has no support and so the inferior wall collapses mostly. Therefore, medial wall blowout fractures are the second-most common, and superior wall, or roof and lateral wall, blowout fractures are uncommon and rare, respectively. They are characterized by double vision, sunken ocular globes, and loss of sensation of the cheek and upper gums from infraorbital nerve injury.

The two broad categories of blowout fractures are open door and trapdoor fractures. Open door fractures are large, displaced and comminuted, and trapdoor fractures are linear, hinged, and minimally displaced. The hinged orbital blowout fracture is a fracture with an edge of the fractured bone attached on either side.

In pure orbital blowout fractures, the orbital rim (the most anterior bony margin of the orbit) is preserved, but with impure fractures, the orbital rim is also injured. With the trapdoor variant, there is a high frequency of extra-ocular muscle entrapment despite minimal signs of external trauma, a phenomenon that is referred to as a "white-eyed" orbital blowout fracture. The fractures can occur of pure floor, pure medial wall or combined floor and medial wall. They can occur with other injuries such as transfacial Le Fort fractures or zygomaticomaxillary complex fractures. The most common causes are assault and motor vehicle accidents. In children, the trapdoor subtype are more common. Smaller fractures are associated with a higher risk of entrapment of the nerve and therefore often smaller fracture are more serious injuries. Large orbital floor fractures have less chance of restrictive strabismus due to nerve entrapment but a greater chance of enopthalmus.

There are a lot of controversies in the management of orbital fractures. the controversies debate on the topics of timing of surgery, indications for surgery, and surgical approach used. Surgical intervention may be required to prevent diplopia and enophthalmos. Patients not experiencing enophthalmos or diplopia and having good extraocular mobility may be closely followed by ophthalmology without surgery.

Some clinically observed signs and symptoms include:

Common medical causes of blowout fracture may include:

There are two prevailing theories to how orbital fractures occur. The first theory is the hydraulic theory. The hydraulic theory states that a force is applied to the globe which results in equatorial expansion of the globe due to increasing hydrostatic pressure. The pressure is eventually released at the weaker point in the orbit (the medial and inferior walls). Theoretically, this mechanism should lead to more fractures of the medial wall than the floor, since the medial wall is slightly thinner (0.25 mm vs 0.50 mm). However, it is known that pure blowout fractures most frequently involve the orbital floor. This may be attributed to the honeycomb structure of the numerous bony septa of the ethmoid sinuses, which support the lamina papyracea, thus allowing it to withstand the sudden rise in intraorbital hydraulic pressure better than the orbital floor.

The second prevailing theory is known as the buckling theory. The buckling theory states that a force is transmitted directly to the facial skeleton and then a ripple effect is transmitted to the orbit and causes buckling at the weakest points as described above.