Orbital trapdoor fracture

Case contributed by Alejandro Planas Callao
Diagnosis certain

Presentation

Direct left orbit impact while playing in the playground. Limited and painful ocular motility.

Patient Data

Age: 9 years
Gender: Male
ct

Slightly displaced left orbital floor fracture with infraorbital nerve involvement.

Herniation and entrapment of intraorbital fatty tissue and inferior rectus muscle, which adopts an hourglass-like morphology.

Case Discussion

Orbital trapdoor fractures are blow-out fractures that are characteristic of children and young adults. It mainly affects the inferior orbital wall and less frequently the medial wall.

A direct impact to the orbit increases intraorbital pressure producing a linear fracture trace that allows inferior displacement and subsequent repositioning of the orbital floor. Children possess more elastic bones due to a lower proportion of cortical bone and a higher proportion of cancellous bone, allowing fractured bone flaps to more easily return to their original position. This fracture mechanism favors the entrapment of herniated fatty tissue and, characteristically, the muscle belly of the inferior rectus muscle.

Although this fracture has also been reported in adults, their bones allow for a smaller range of displacement and therefore a much lower rate of entrapment of intraorbital structures 1.

When the inferior rectus muscle is trapped, as in our case, there is a limitation of infraduction and an even more evident limitation of supraduction. Early surgical release of the muscle is necessary to avoid permanent impairment of extraocular motility due to ischemia or scarring of the muscle belly 2. Our patient presented the characteristic ocular motility impairment and was successfully treated with no residual functional deficit.

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