Blow out fracture of the orbit, most commonly leads to fracture of –
**Core Concept**
A blow out fracture of the orbit occurs when there is a rupture of the thin orbital floor or medial wall, allowing the orbital contents to herniate into the maxillary sinus or ethmoid sinus. This type of fracture is often caused by a direct blow to the globe, leading to an increase in intraorbital pressure and subsequent fracture of the orbital bones. The orbital floor is the most common site of fracture due to its thinness and the presence of the maxillary sinus.
**Why the Correct Answer is Right**
The orbital floor is composed of the orbital plate of the maxilla, which is a thin plate of bone that forms the floor of the orbit. When a blow out fracture occurs, the orbital contents, including the globe, extraocular muscles, and fat, herniate into the maxillary sinus through the fractured orbital floor. The orbital floor is more susceptible to fracture due to its thinness and the presence of the maxillary sinus, which can absorb the force of the blow and contribute to the fracture. The orbital floor is also more likely to fracture due to the presence of the inferior orbital fissure, which can provide a pathway for the orbital contents to herniate into the maxillary sinus.
**Why Each Wrong Option is Incorrect**
**Option A:** The zygomatic bone, also known as the malar bone, forms the prominence of the cheek and is not typically involved in a blow out fracture of the orbit.
**Option B:** The lacrimal bone forms the anterior part of the medial wall of the orbit and is not typically involved in a blow out fracture of the orbit.
**Option C:** The frontal bone forms the roof of the orbit and is not typically involved in a blow out fracture of the orbit.
**Clinical Pearl / High-Yield Fact**
The "three signs" of a blow out fracture of the orbit are enophthalmos (sunken eye), limited upward gaze (due to entrapment of the inferior rectus muscle), and infraorbital nerve anesthesia (due to compression of the nerve).
**Correct Answer:** D.