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Facial Fracture Management Handbook - Orbital blowout fractures

last modified on: Sat, 12/16/2017 - 17:10

Facial Fracture Management Handbook

by Dr. Gerry Funk  see also: Facial Fracture Management Handbook

Orbital Blowout Fractures

Anatomy and Mechanism of injury

Blowout fractures of the orbit most frequently affect the middle third of the orbit where the orbital walls are the thinnest. Inferior blowout fractures involving the floor of the orbit (maxillary sinus roof) are the most common followed by medial wall blowout fractures. True blowout fractures result from a rapid increase in intraorbital pressure resulting in a herniation of orbital contents out through the thin bony orbital walls. This injury most frequently results from an impact to the anterior orbit such as with a baseball or closed fist.

 In many cases blowout fractures are associated with other fractures of the orbital rim, usually a malar complex fracture. It is important to differentiate pure blowout fractures, which do not have an associated fracture of the orbital rim, from malar complex fractures associated with orbital floor fractures. A second level of differentiation is between blowout fractures with or without entrapment of orbital contents. The most commonly entrapped material following a blowout fracture is orbital fat, this alone may lead to decreased up gaze if the orbital floor is involved. The most common muscle to be entrapped by the fracture is the inferior rectus muscle. For example, a fracture might be described as a pure inferior blowout fracture with likely entrapment of the inferior rectus muscle resulting in severely limited up gaze.

Physical Exam

Head and neck trauma exam with special attention to:

1. Visual acuity and extraocular movements. An Ophthalmology consult should be obtained in all cases to evaluate the posterior chamber and to perform forced ductions if decreased EOM's are present. This involves anesthetizing the sclera and attempting to rotate the globe through full extraocular movements. Positive forced ductions suggest the eye cannot be rotated manually in one or more directions and indicate a mechanical entrapment, as opposed to decreased motion due to pain, swelling or a neurologic injury.

2. Examine the eye carefully for enophthalmos or exophthalmos and ask the patient about double vision (diplopia) in all fields of gaze.

3. Palpate for orbital rim fractures and compare facial symmetry to exclude the possibility of an associated malar fracture.

4. Cranial nerve V2 sensation.

Emergency Management

As with malar complex fractures the most important emergency management is to ensure that no significant ocular injury exists. This is accomplished with a meticulous physical exam and an emergent CT scan if decreased vision is present. The patient should be seen by an ophthalmologist prior to being discharged home from the emergency room. Most of these patients will be seen, evaluated and given follow up for definitive care. As with malar complex fractures these patients should be given a 7 day course of antibiotics.

If there is evidence for an orbital hematoma with rapidly increasing intraocular pressure (proptosis, decreased visual acuity, severe orbital pain, decreased EOM's and chemosis) a lateral canthotomy or cantholysis may need to be performed. This can be done rapidly and easily at the bedside. The patient should also be started on high dose steroids (Decadron 3/4mg/kg body weight initially followed by 1/3mg/kg every 6 hrs.)

Radiographic Work Up

The appropriate radiologic work up for an orbital blowout fracture or suspected blowout fracture is a high resolution CT scan. Fine cut, noncontrast, bone windows through the orbits should be obtained in both the axial and coronal plane. The coronal cuts are essential as they allow a straight on cross sectional view of the orbital walls. While the coronal cuts are most important in demonstrating the magnitude of the blowout injury, axial cuts allow better visualization of the distance between the posterior extent of the fracture and orbital apex structures. If there is evidence for an orbital hematoma soft tissue windows should also be obtained.

Definitive Management

There are several reasons to repair blowout fractures: 1) mobilize obviously entrapped extraocular muscles in cases presenting with positive forced ductions and severe subjective diplopia, 2) mobilize a large volume of herniated orbital fat back into the orbit in order to return the globe to its preinjury location in cases where greater than 2mm of enophthalmos and or diplopia are present and 3) restore orbital floor integrity and reduce herniated fat in cases with a large defect seen on CT scan but without acute evidence of entrapment or enophthalmos, in order to prevent late post traumatic enophthalmos. Most surgeons would accept both the first and second reasons as indications for surgery. Some controversy exists surrounding the third. This controversy revolves around the observation that in some cases a small amount of orbital contents herniating into the maxillary sinus is clinically insignificant and results in no EOM compromise, enophthalmos or diplopia. However, in other instances the herniation and disruption of orbital fat results in symptomatic orbital volume loss. This is presumably due to fat necrosis in the orbit and late post-traumatic enophthalmos. Additional factors may further complicate the situation such as equivocal forced ductions initially or the resolution of diplopia and improvement of EOM after swelling has decreased.

In equivocal cases without clear indications for surgery a watch and wait approach can be taken. The patient should be reexamined at 7 to10 days following the trauma. If after 10 days equivocal forced ductions persist or diplopia remains in straight ahead or down gaze or if there is enophthalmos greater than 2mm and the CT scan has demonstrated a blowout fracture to be present, surgery should be strongly considered (36).

Surgical management of blowout fractures is directed at replacing herniated orbital contents back into the orbit and repairing the defect through which it herniated. Approaches to the orbital floor or medial orbital wall include the subciliary (blepharoplasty) approach and the transconjunctival approach (which will occasionally require a lateral canthotomy to improve visualization). A Lynch incision (a vertical incision between the medial canthus and the dorsum of the nose) will supplement medial exposure and a lateral brow incision will supplement lateral exposure. If a Lynch incision is done in conjunction with a subciliary or transconjunctival approach the medial canthal tendon should not be detached and dissection through the Lynch incision should remain above it.

Once the orbital floor defect has been exposed herniated muscle and fat are gently disimpacted back into the orbit. The entire extent of the defect should be explored. Various materials have been used to reconstruct orbital wall defects including, Silastic, Supramid, Silicone sheets, Teflon, Marlex mesh, Gortex and Gelfilm. Free autografts of cranial bone, iliac crest, rib, anterior maxillary wall and homograft materials have also been used in the reconstruction of orbital walls. If possible, we prefer to use bone grafts to reconstruct the orbital floor defects. If a minor wound infection or bone graft exposure into the maxillary sinus occurs removal of the construct is not mandatory and may be managed with antibiotics. With many of the allograft materials an infection requires removal of the graft. Also the use of an autograft virtually eliminates the possibility of any sort of unusual host versus graft response. Marlex mesh has a long history of use in the repair of orbital floor defects with very good long term results and in selected small defects it is occasionally used (37). The material used to reconstruct the orbital floor should always be secured in place over the defect. We are currently using AO Synthes microscrews for this. Failure to secure the material used in reconstructing the orbital defect could potentially allow it to shift into an unwanted position or impinge on the optic nerve.

Most patients undergoing orbital surgery are treated with preoperative steroids and for 24 to 36 hours after surgery. The usual dose is 8 - 10 mg every eight hours. If the maxillary sinus or sinonasal passage will communicate with the wound prophylactic antibiotics should be given.