Step 9 Subperiosteal Dissection of Anterior Maxilla andor Orbit

The sharp end of a periosteal elevator is pulled across the full length of the periosteal incision to separate the incised edges. Periosteal elevators are then used to strip the periosteum from the underlying osseous skeleton, both along the anterior surface of the maxilla and zygoma and inside the orbit. The inferior orbital rim is superior to the orbital floor just behind it. After the periosteum of the infraorbital rim is elevated, the elevator is positioned vertically, stripping inferiorly as it proceeds posteriorly for the first centimeter or so (Figs. 2-22 and 2-23). The bony origin of the inferior oblique muscle, the only muscle in the orbit that does not arise from its apex, will be

Figure 2-22 Subperiosteal dissection of anterior maxilla and orbital floor. Note that the periosteal elevator entering the orbit is placed almost vertically as dissection proceeds behind the rim. In the anterior region, the floor of the orbit is at a lower level than the crest of the rim, necessitating dissection inferiorly just behind the crest of the rim.

Figure 2-22 Subperiosteal dissection of anterior maxilla and orbital floor. Note that the periosteal elevator entering the orbit is placed almost vertically as dissection proceeds behind the rim. In the anterior region, the floor of the orbit is at a lower level than the crest of the rim, necessitating dissection inferiorly just behind the crest of the rim.

Subperiosteal Dissection Lamina
Figure 2-23 Sagital plane through orbit showing subperiosteal dissection of the anterior maxilla and orbital floor.

just posterior to the orbital rim and lateral to the upper aperture of the nasolacrimal canal, and may also arise partly from the lacrimal fascia over the lacrimal sac (Fig. 2-24). During dissection, one will readily encounter the inferior orbital fissure. The periosteum of the orbit (periorbita) sweeps downward into the fissure. If necessary, the contents of the inferior orbital fissure can be incised to provide more exposure (Figs. 2-25 and 2-26)

Subperiosteal Dissection
Figure 2-25 Anatomic dissection showing incision through the contents of the inferior orbital fissure to facilitate orbital dissection. These tissues should first be cauterized with bipolar electrocoagulation to prevent bleeding when incised.
Figure 2-26 Anatomic dissection showing increased exposure of orbit after incision of contents of inferior orbital fissure.

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