The orbital floor is formed predominantly by the orbital plate of the maxilla, with contributions from the zygomatic bone anterolaterally and the palatine bone posteriorly. It slopes upward from front to back and medially, and is the thinnest wall of the orbit, measuring only 0.5-1 mm overlying the maxillary sinus. The infraorbital groove and canal traverse the floor from posterior to anterior, carrying the infraorbital nerve and artery to the infraorbital foramen.
The orbital floor is the most common site of blowout fractures in orbital trauma, where direct globe compression raises intraorbital pressure and the thin floor fractures inferiorly into the maxillary sinus. Herniation of orbital fat and occasionally the inferior rectus or inferior oblique muscle into the sinus produces enophthalmos and restricted upgaze (tethering of the inferior rectus). Diplopia on upgaze from muscle entrapment is the primary indication for surgical repair with an orbital floor implant. The infraorbital nerve is invariably traumatised, causing infraorbital cheek numbness.
Hydraulic pressure from globe impact fractures the thin orbital floor into the maxillary sinus, producing enophthalmos, restricted upgaze from inferior rectus or fat entrapment, and infraorbital numbness from nerve injury, managed surgically with floor implant if significant enophthalmos or muscle entrapment is present.
Herniation of the inferior rectus muscle through the orbital floor fracture into the maxillary sinus causes restricted and painful upgaze with diplopia, a surgical emergency in children (trapdoor fracture) requiring urgent reduction of the muscle to prevent ischaemic necrosis.
