Correction of Post-traumatic Enophthalmos

Enophthalmos is the recession of the ocular globe within the bony orbit. Two to three millimeters of enophthalmos is clinically detectable, and more than 5 mm is disfiguring. The principal mechanism in its development is the displacement of a relatively con­stant volume of orbital soft tissue into an enlarged bony orbit. Fat atrophy and scar contracture are less important factors in causing a mismatch of soft tissue and orbital volume.1-3 Because enophthalmos most often presents with an inadequately treated orbital fracture where the orbital floor is disrupted, the condition is characteristically accompanied by inferior displacement of the globe. Recession of the globe changes the drape of the upper lid on the globe, tending to deepen the superior tarsal fold and cause a ptosis of the upper lid

(Figure 1).

Patient with post-traumatic enophthalmos. Note recession and inferior displacement of globe, deepened superior tarsal fold, and ptosis of upper lid
Patient with post-traumatic enophthalmos. Note recession
and inferior displacement of globe, deepened superior tarsal fold, and ptosis of upper lid

Because post-traumatic enophthalmos is primarily due to alterations in the configuration of the bony internal orbit rather than to changes in the amount or character of its soft tissue contents, the treatment strategy for restoring eye position is the anatomic reconstruction of the internal orbit. This is best accomplished by defining the location and extent of injury preoperatively with computed tomographic (CT) scans, wide exposure of the injured area and retrieval of orbital soft tissues, and replacement of the invariably comminuted displaced fractures with auto­genous or alloplastic material.

 Applied anatomy

The internal orbit may be conceptualized as a modified pyramid. The lateral wall consists of thick bone created by articulation of the greater wing of the sphenoid and the orbital process of the zygoma. However, the floor, medial wall, and roof can be divided into concentric thirds based on bone thick­ness. The anterior third of the internal orbit consists of increasingly thicker bone as it merges with the orbital rim. Immediately behind the rim, the anterior third of the orbit has a concave shape, and so the widest orbital diameter is approximately 1.5 cm within the orbital cavity. The posterior third also consists of thick bone with relatively flat walls. The middle third consists of thin bone and allows this portion of the orbit to act as a crush zone, thereby protecting the optic nerve and globe by absorbing impact forces. The floor medial to the infraorbital canal and the inferior portion of the medial wall is typically involved in the `blow-out’ fracture. This area has a convex shape that produces a constriction behind the globe. Loss of this convexity transforms the intraorbital shape from pyramidal to spherical, increasing orbital volume and tending towards enoph­thalmos (Figures 2, 3). Certain injuries, usually involving the lateral orbital wall or roof, may result in inward displacement of larger fracture segments. These ‘blow-in’ fractures decrease orbital volume, resulting in globe proptosis.

Diagnosis

The clinical diagnosis of significant internal orbital disruption is based on globe malposition. When the lateral orbital rim is intact (isolated floor or medial wall blow-out fractures) and soft tissue swelling has subsided, the severity of enophthalmos can be deter­mined with a Hertel exophthalmometer which measures the difference between the anterior corneal surface and the lateral orbital rim. In the uninjured state, the cornea extends approximately 16-17 mm anterior. to the lateral orbital rim. Immediately after injury, however, globe position may appear normal or proptotic owing to soft tissue swelling. Radiologic imaging is therefore the key to defining the presence and extent of injury. Plain x-rays will confirm the presence of fractures but cannot define the extent of injury or the status of the soft tissues. The ideal pre­operative evaluation consists of axial and coronal CT sections using both bone and soft tissue windows. Thin-sliced coronal CT images allow measurement of a floor or wall defect. Defects’greater than 25% of the orbital floor will result in measurable enophthalmos. Those involving more than half of the floor will result in significant enophthalmos.4

Diplopia may result from extra muscle contusion or entrapment. This can be differentiated by forced duction test and CT scan.

Indications for surgery

In the acute phase, CT findings coupled with forced duction testing provide the best guide to the need for surgery. A CT scan can define the amount of floor disruption and, therefore, predict the likelihood of enophthalmos. It can also define the relation of the extraocular muscles to the fracture segments.

If surgery is thought appropriate, it should be performed in the acute phase when dissection is more straightforward, and soft tissue scarring and contracture are not problems. Late or secondary reconstructions, in general, are less successful than appropriate recon­struction performed in the acute phase.

When indications for acute _ management are unclear, the following algorithm has been proposed. Exploration is performed if enophthalmos greater than 2 mm develops at any time within the first 6 weeks following injury, or if diplopia in the primary gaze or down-gaze reading position does not clear within 2 weeks.5

In late presentations, when globe malposition is the raison d’etre, CT evaluation is critical in preoperative assessment. It defines not only the location and extent of internal orbital injuries but also any adjacent facial skeletal injuries. This is crucial in planning the opera­tive approach and the method of reconstruction.

Surgical techniques Exposure

Proper repositioning of the globe requires exposure and anatomic reconstruction of the internal orbit. Craniofacial approaches afford exposure of both the external and internal orbit. A transconjunctival incision, usually with a lateral canthotomy extension, is used to approach the orbital floor and lower medial and lateral walls. The coronal flap is used to approach the upper medial and lateral walls as well as the orbital roof. Extensive subperiosteal dissection of the lateral orbit will detach the lateral canthus, which should be repositioned at closure. The blepharoplasty subciliary skin incision and skin muscle flap are an alternative to the transconjunctival approach. The former provides an inconspicuous scar but may cause lid retraction, usually transient, if retraction is vigor­ous, particularly in the reoperated orbit.

Orbital rim repositioning

Because a small change in rim position leads to a large change in orbital volume, accurate orbital rim positioning is an important first step in the recon­struction of the internal orbit. The repositioned segments are stabilized with plates and screws. In the acute setting, the fracture segments are anatom­ically realigned. Keys in accurate repositioning are the zygomaticosphenoid articulation and the zygomatic arch. Unlike the narrow zygomaticofrontal articulation, the zygoma’s articulation with the sphenoid is a relatively long one, making edge-to­edge coaption more likely to reflect proper zygomatic repositioning. Proper alignment of the zygomatic arch assures restoration of facial width (which tends to be increased in these injuries)

while, reciprocally, restoring malar projection. In late reconstructions, restoration of orbital rim anatomy usually requires osteotomy and repositioning. In situations where comminution and displacement are extensive, replacement with autogenous grafts is usually most appropriate. Less often, onlay grafting may be sufficient to restore rim positioning.

Mobilization of orbital contents

The contents of the orbit are freed from the injured area by subperiosteal dissection, usually under loupe magnification. Care is taken to avoid damaging the lacrimal sac and structures in the inferior orbital fissure. Ideally, intact bony edges should be identified as the basis for orientation and to provide stable constructs on which to position grafts. This dissection can be exceedingly difficult in extensive injuries, particularly when surgery has been delayed and prolapsed orbital fat has healed to damaged mucosa in the maxillary or ethmoid sinuses, or to temporalis muscle in the temporal fossa. The orbital contents must be separated from these structures, returned and replaced in the orbit.

The intact bony landmark which is usually most difficult to identify is the posterior ledge of the remaining intact orbital floor. To best visualize the area, the author almost routinely performs an inferior orbitotomy (Figure 4).7 This access greatly simplifies this dissection. The posterior rim can also be located by placing the end of an elevator against the poste­rior wall of the maxillary sinus and elevating it until it meets resistance, which will be this rim. This ledge, which is usually 30-38 mm from the infraorbital rim, may be unstable (Figure 5).

Once the prolapsed contents of the orbit are removed from the maxillary or ethmoid sinuses, temporarily interpositioning a piece of silicone sheet­ing between the soft tissues and the area to be recon­structed is helpful (Figure 6). This maneuver prevents the soft tissues falling back into the sinus, thereby lessening their subsequent handling and allows easier control during placement of the implant or graft. Once reconstruction is complete, the silicone sheet is removed.8

Internal orbit reconstruction

The internal orbit is reconstructed to restore its preinjury anatomy with the anticipation that proper globe position will result. When reconstructing injuries to one orbital wall, the surgeon simply defines the defect by identifying intact bone edges and spanning the defect with an implant or auto­genous graft (Figure 7). Reconstruction with auto­genous materials has the conceptual advantage that they will, in time, become revascularized and incor­porated into the skeleton, thereby resisting migra­tion, extrusion, and infection. Revascularization, however, also predisposes the graft towards resorp­tion; the extent to which this occurs is unpre­dictable, making ultimate globe position also unpredictable. Clinical experience has shown that calvarial grafts tend to resorb less than grafts taken from other donor sites. Cranial bone grafts have more dense cortical bone than ilium or rib, which tend to be predominantly cancellous. Experimental evidence suggests that the volume persistence of calvarial grafts may result from the fact that cortical bone is less well vascularized and hence less suscep­tible to osteoclastic activity than cancellous bone.9 Unfortunately, calvarial bone is much more difficult to shape and control during internal orbit recon­struction. To avoid changes in graft shape, volume, and position, this author often uses alloplastic implants made of expanded polyethylene (Medpor, Porex Co, Atlanta, GA, USA) to reconstruct the inter­nal orbit. This implant has a pore size which allows vascular ingrowth

Case 1

A 22-year-old man was referred for treatment 4 days after suffering a complex zygomatic and internal orbital injury after being involved in a motor vehicle accident (Figure 9). Ocular function was normal. A preoperative CT scan showed massive disruption of the zygomatic complex as well as disruption of three walls of the internal orbit. Reconstruction took place on the fifth day after injury using coronal, transconjunctival with lateral canthotomy, and gingival buccal sulcus approaches. The zygomaticofrontal and zygomaticosphenoid articula­tions were aligned as well as the zygomatic arch, infraorbital rim, and lateral buttress. Microplate fixation was used for maintaining position of the zygomaticofrontal articulation, zygomatic arch, and inferior rim. A miniplate was used to maintain position of the lateral buttress. The lateral and infer­olateral portion of the orbit was reconstructed with a channel implant of expanded polyethylene. A titanium miniplate was placed in one of the prefab­ricated slots and fixated to the lateral orbital rim, thereby maintaining position of the orbital contents in this area and also providing support for a second implant, positioned to reconstruct the inferomedial convexity of the orbit.

A 44-year-old man was referred 2 years after suffering a zygomatic and heminasoethmoid fracture in a motor vehicle accident (Figure 10). The fracture was treated acutely with open reduction and rigid internal fixation. The patient had diplopia in three fields of gaze preoperatively.

Reconstruction was accomplished through bicoro­nal and transconjunctival approaches with lateral canthotomy. The medial orbital wall, with its attached medial canthal ligament, was osteotomized and reposi­tioned. The repositioned bone fragments were then fixed inferiorly with a microplate. Superiorly, the bone fragment was purchased with a transnasal wire attached to a miniscrew placed in the right supero­medial orbital rim. An inferior orbitotomy was used to access and retrieve the orbital contents from the temporal fossa, the orbital floor, and the ethmoid sinuses. Vitallium mesh was used to reconstruct the internal orbit and provide a platform for expanded polyethylene implants. In this case, some residual enophthalmos persisted owing to the surgeon’s failure to appwciate the increase in orbital volume resulting from anatomic replacement of the previously laterally displaced medial orbital rim and wall.

References

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  2. Manson PN, Clifford CM, Su CT et al. Mechanisms of global support and post-traumatic enophthalmos. I. The anatomy of the ligament sling and its relation to intramuscular cone orbital fat. Plast Reconstr Surg 1985;77:193-200.
  3. Manson PN, Grivas A, Rosenbaum A et al. Studies on enophthalmos. II. The measurement of orbital injuries and their treatment by quantitative computed tomography. Plast Reconstr Surg 1985;77:201-9.
  4. Hawes MJ, Dortzbach RK. Surgery on orbital floor fractures (influence of time and repair and fracture size). Ophthalmology 1983;90:1066-72.
  5. Wilkins RB, Havins WE. Current treatment of blow­out fractures. Ophthalmology 1982;89:464-72.
  6. Yaremchuk MJ, Kim WK. Soft tissue alterations with acute, extended open reduction and internal fixation of orbital fractures. J Craniofac Surg 1992;3:134-40.
  7. Tessier P. Inferior orbitotomy. A new approach to the orbital floor. Clin Plast Surg 1982;9:569-75.
  8. Glassman RD, Manson PN, Petty P et al. Techniques for improved visibility and lid protection in orbital explorations. J Craniofac Surg 1990;1:69-72.
  9. Chen NT, Glowacki J, Bucky LP et al. The roles of revascularization and resorption on endurance of craniofacial onlay bone grafts in the rabbit. Plast Reconstr Surg 1994;93:725-82.
  10. Glassman RD, Manson PN, Vanderkolk CA et al. Rigid fixation of internal orbital fractures. Plast Reconstr Surg 1990;86:1103-10.
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  12. Yaremchuk MJ, Manson PN. Reconstruction of the internal orbit using rigid fixation techniques. In: Yaremchuk MJ, Gruss JS, Manson PN, editors. Rigid fixation of the craniomaxillofacial skeleton. Boston: Butterworth-Heinemann; 1992.

 

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