Keywords
Enophthalmos - Orbital fractures - Orbital implants
INTRODUCTION
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 [[1]]. Fat atrophy and scar contracture are less important factors in causing a mismatch
of soft tissue and orbital volume [[1]
[2]
[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.
Because posttraumatic 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 tomography (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.
PERTINENT 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 ([Fig. 1]). 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 ([Fig. 2]).
Fig. 1 Pertinent anatomy of the orbit
A cadaveric dissection of the orbit demonstrating the convex shape of the inferomedial
aspect of the internal orbit. An average distance of approximately 40 mm between the
inferior orbital rim and the posterior ledge of the posterior maxillary wall is shown.
Fig. 2 Cadaveric dissection of the orbital floor
The disrupted orbital floor in this cadaveric specimen illustrates the thin, eggshell-like,
consistency of the middle third as compared to the uninjured anterior and posterior
portions of the floor.
The floor of the orbit is a frequent site of fracture [[4],[5]]. 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 enoph-thalmos.
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, coronal, and sagittal 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 [[6]]. Diplopia may result from extra muscle contusion or entrapment. A Forced duction
test and a CT scan can differentiate between diplopia that results from rectus muscle
entrapment and diplopia that is secondary to post injury soft tissue swelling.
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 [[7]].
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, often with a lateral canthotomy or transcaruncular
extension is used to approach the orbital floor, as well as the medial and lateral
walls. The coronal approach will provide exposure of the upper orbit. Extensive subperiosteal
dissection of the lateral orbit will detach the lateral canthus. If it is detached,
the lateral canthus should be repositioned at closure. The blepharoplasty subciliary
skin incision and skin muscle flap are an alternative to the transconjunctival approach.
The These transcutaneous lid incisions are more prone to post operative lid retraction.
Insicions directly over the orbital rim at the junction of the eyelid and cheek can
leave an inconspicuous scar in older individuals.
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-to-edge 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 may require osteotomy
and repositioning. In situations where comminution and displacement are extensive,
replacement with autogenous grafts is often necessary. Onlay grafting may be used
to restore orbital contour and rim position.
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 [[8]]. 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 ([Fig. 3]). By elevating the end until it meets resistance allows for identification of this
rim. The ledge, which is usually 30-38 mm from the infraorbital rim, may be unstable.
Fig. 3 Mobilization of orbital contents
Identification of the intact posterior ledge is performed by placing an elevator against
the posterior wall of the maxillary antrum and elevating it until it meets restriction.
The presence of this intact bony landmark must be confirmed preoperatively by CT scanning
to avoid an inadvertant injury to the optic nerve.
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. 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 [[9]].
INTERNAL ORBIT RECONSTRUCTION
INTERNAL ORBIT RECONSTRUCTION
The internal orbit is reconstructed to restore its preinjury anatomy with the anticipation
that proper globe position will result ([Fig. 4]). 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
auto-genous graft. 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.
Fig. 4 Case
Case of a 25-year-old gentleman with significant left medial orbital wall and orbital
floor fracture. The pre- and postoperative CT findings are shown. (A) Coronal preoperative
view. (B) Postoperative coronal view demonstrating significant improvement in the
contour of the left orbit after placement of an anatomical pre-bent medial orbital
wall and floor implant. (C) Preoperative sagittal view. (D) Postoperative sagittal
view.
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 [[10]]. 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 and some incorporation into the recipient
bed. In a personal experience of 70 patients over a 4-year period, there has been
no known instance of infection or graft extrusion using this material.
Injuries involving two or more walls of the orbit are problematic. Rigid fixation
techniques are useful in these injuries by allowing, in effect, these complex injuries
to be subdivided into a series of smaller, more manageable areas [[11]]. Metallic implants are attached to the orbital rim and are used to span large defects
and provide a platform to support grafts for implants. This support function can be
accomplished with a number of designs ([Fig. 5]). The implant alone may be used to restore the internal orbital contour or may serve
as a platform on which to place grafts [[12]]. Clinical experience has shown that prolapse of orbital soft tissues through mesh
platforms has not led to motility problems or made subsequent reoperation difficult.
Fig. 5 Internal orbit reconstruction
Pre-bent anatomical orbital plate in situ [[20]].
The utility of such metallic implants has been demonstrated in the senior author's
(M.J.Y) recent experience with repair of orbital floor and medial wall fractures.
An anatomical prebent titanium plate was used to reconstruct 19 medial wall fractures
in 17 patients. Preliminary measurements of pre- and post-reconstruction orbital volume
have shown a statistically significant improvement in the reconstructed orbital volume.
Initial average orbital volume difference between the fractured and nonfractured orbit
measured approximately 11% compared to 2% in the post-reconstruction volume measurements.
This preliminary survey demonstrated the effectiveness of costum anatomical mesh plates
in restoration of orbital contour and volume with a low complication rate.
ALTERNATIVE TECHNIQUES
Zhang et al. [[13]] demonstrated the use of computed tomography-based mirroring-reconstruction images
of the orbit in 22 patients with late posttraumatic enophthalmos. The authors were
able to fabricate anatomically adaptive titanium mesh by computer-aided design and
computer-aided manufacturing techniques. Application of the implant reduced the traumainduced
orbital volume increment by 65% and corrected 50% of severe late enophthalmos. Nonetheless,
additional augmentation of orbital contents was required for further correction.
He et al. [[14]] promolgated the use of navigation-guided surgery with a 3D model, and titanium
mesh with an alloplastic implant, for the treatment for delayed orbitozygomatic fractures
with severe enophthalmos. In this retrospective review of 64 patients, good globe
projection was achieved in 74.2% of the cases of the traditional surgery, 75% in the
group undergoing computer-assisted 3D model surgery, and 90.9% in the navigationguided
surgery group.
Although enlargement of the bony orbit is the accepted pathogenesis for late enophthalmos
[[15]], several authors have recently attempted to prevent or correct the deformity with
periorbital soft tissue augmentation. Nishi et al. [[16]] have used sliced costal cartilage for the treatment of late posttraumatic enophthalmos
by placing grafts below the subperiosteum from a location posterior to the equatorial
plane of the orbit. Lee [[17]] has advocated the use of autologous, diced-cartilage graft to augment the orbital-tissue
volume in addition to the standard fracture-reduction methods in the acute setting.
In a recent case report, Cerveli et al. [[18]] demonstrated the use of retrobulbar lipofilling for correction of enophthalmos
and suggested its use as a safe alternative technique for orbital volume enhancement.
Bernardino [[19]] suggested the correction of late posttraumatic enophthalmos by using a tissue expander.
SUMMARY
Posttraumatic enophthalmos presents as a challange to the reconstrcutive surgeon given
the fuctional and aesthetic considerations that relate to the orbit. Correction of
late enophthalmos deformities requires intimate knowledge of the bony orbit and its
contour. Wide surgical exposure and retrieval of the prolapsed orbital content into
its anatomic location can facilitate restoration of the orbital shape. Given the intricate
anatomy of the internal orbit, several alloplastic implants are now available for
more accurate reconstruction of the orbital contour. Skillful planning and repair
of late enophthalmos has been demonstrated in multiple recent studies and it is likely
related to the precision with which orbital anatomy can be restored.
CASE PRESENTATIONS
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 ([Fig. 6]). 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.
Fig. 6 Case
Acute reconstruction of high-energy damage to the zygomatic complex and internal orbital
reconstruction. (A) Preoperative frontal view. (B) Postoperative frontal view. (C)
Preoperative worm's eye view. (D) Postoperative worm's eye view. (E) Preoperative
coronal CT view.
Case 2
A 44-year-old man was referred 2 years after suffering a zygomatic and heminasoethmoid
fracture in a motor vehicle accident ([Fig. 7]). The fracture was treated acutely with open reduction and rigid internal fixation.
The patient had diplopia in three fields of gaze preoperatively.
Fig. 7 Case
Late orbital reconstruction after a motor vehicle collision. (A) Preoperative frontal
view. (B) Postoperative frontal view. (C) Preoperative worm's eye view. (D) Postoperative
worm's eye view.
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.
