Ординатура / Офтальмология / Английские материалы / Oculoplasty and Reconstructive Surgery Made Easy_Garg,Touky, Nasralla_2009
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Orbital Implants 339
Figure 14: Alumina with vicryl mesh wrapping
Figure 15: Bioceramic-orbital
Figure 16: Preoperative dermis fat graft
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Figure 17: Postoperative dermis fat graft
Figure 18: Silicone-orbital
Figure 19: Expandable implant
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Expandable Orbital Implant
Expandable orbital implant has an anterior injection portal, rectus muscle placement grooves, and 4 independently expandable/deflatable quadrants. An expandable orbital implant will have the capacity to be enlarged as the surrounding orbital tissues atrophy. An enlarging prosthesis should help correct ptosis (drooping eyelid), enophthalmos (sunken eye) and motility (movement). It is still in the pipeline for commercial production but seems to be a promising choice.
INTRODUCTION
Orbital injuries may be part of panfacial trauma that range from mild even non significant to severe and debilitating, however, such injuries are of secondary importance to securing airway, stabilizing the circulation and protecting the cervical spine. Trauma to the orbit can involve the globe, eyelid, sinuses and the brain. The nature and severity of the injury depend on the mechanism of trauma.
After securing the lifesaving measures, a team approach incorporating a plastic surgeon, otolaryngologist, a neurosurgeon in addition to the ophthalmologist is needed for the facial trauma patient’s evaluation. A systematic ocular and orbital examination is necessary to delineate any subtle injuries as delay in the diagnosis of orbital and ocular problems may worsen the prognosis.
ANATOMIC CONSIDERATIONS
The orbit is a four-sided conical structure with its base directed forwards and apex projecting medially towards the optic foramen. The base or the orbital rim is outlined by thick strong bone: the supraorbital arch of the frontal bone above, the zygoma and maxilla inferiorly, the zygoma laterally and the frontal process of the maxilla medially. The walls of the orbit
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consist of relatively thin bone. The orbital volume is about 30 ml and the orbital depth is approximately 4.5 cm. Consequently, slight change in the bony anatomy will be reflected on soft tissue and globe position.
The medial wall is formed of the frontal process of the maxilla and the lacrimal bone forming the lacrimal fossa behind which is the extremely thin, less than 0.5 mm, lamina paparycea of the ethmoids and finally the lesser wing of the sphenoid and the optic foramen (Figure 1). Being exceptionally thin and fragile, medial wall fractures are usually subtle and accompany many orbital injuries. The medial wall transmits the anterior and posterior ethmoidal arteries and nerves at the junction between the ethmoidal bone and the orbital plate of the frontal bone. Trauma to this wall
Figure 1: Bones forming the medial wall
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is frequently associated with orbital hemorrhage, epistaxis and surgical emphysema.
The roof is composed mainly of the orbital plate of the frontal bone and posteriorly the lesser wing of sphenoid separating the orbit from the frontal lobes of the brain. It is thinnest anteriorly where it is related to the frontal sinus.
The orbital floor is composed of the orbital plates of the maxilla and zygomatic bones with a small contribution from the palatine bone posteriorly. The posterior limit of the floor is defined by the inferior orbital fissure and a small vertical component of the palatine bone posteromedially. Near the apex the inferior orbital fissure transmits venous channels as well as the infraorbital and zygomatic nerves. Contained entirely in the maxilla, the infraorbital groove posteriorly becomes the infraorbital canal as it gains a roof (Figure 2). It opens 4 mm below the orbital rim as the infraorbital foramen that transmits the infraorbital nerve and vessels. The floor is
Figure 2: Diagram of the orbital floor
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also thin, 0.5 to 1.0 mm thus it easily fractures especially medial to the infraorbital canal.
The lateral wall is thick formed of the frontal process of the zygomatic bone and the frontal bone anteriorly and the greater wing of sphenoid posteriorly. It transmits the zygomatic nerve and artery which often splits into the zygomaticotemporal and zygomaticofacial branches before entering the bone.
EVALUATION OF ACUTE ORBITAL AND PERIORBITAL INJURIES
Initial evaluation starts with complete history to determine the circumstances of the present injuries. Low velocity impact such as a human punch usually produces injury limited to the region of impact. High velocity injury such as motor vehicle accidents is often associated with soft tissues and skeletal injuries that are more extensive and may be remote from the impact. With projectile injuries such as with shattered glass or missiles, intraocular, subcutaneous and orbital foreign bodies should be ruled out.
It is better to remove blood and debris as well as any superficial foreign bodies to do a careful and precise examination of the injured area as well as the surrounding areas. Blunt low velocity trauma usually cause edema and contusions and the extent of the facial fractures is often more than in cases associated with extensive lacerations as the energy of the impacting force in the former is dissipated by the skeleton rather than soft tissue. Palpation of the orbital rims, malar eminences, zygomatic arches and nose may show fractures and surgical emphysema.
A complete ophthalmic examination is a must to rule out globe injuries and present medicolegal problems. If the patient is conscious, the visual acuity and field by confrontation should
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be documented. Pupil diameter and responses to light as well as swinging flash light test should be also documented. Presence of afferent papillary defect denotes optic nerve injury, however if both optic nerves are equally damaged, this sign may be absent. The lid, adnexa, conjunctiva, cornea, anterior chamber, iris and lens should be examined with magnification either by slit lamp or a magnifying loupe for lacerations, tissue loss, hemorrhage, opened globe injuries, presence of foreign bodies or lens displacement. When ocular rupture is suspected, globe exploration should take place before any fracture repair.
The retina and optic nerve should be examined on both sides using the ophthalmoscope looking for retinal edema or hemorrhages as well as optic nerve pallor or edema. The caliber of the retinal vessels comparing arteries to veins is also evaluated. Engorged non-pulsatile veins may signify increased orbital pressure, similarly central retinal artery pulsations denotes increased ocular or orbital pressure. B scan ultrasound can be performed if media opacity precludes the visualization of the retina.
The position of the globe on the affected side in comparison to contralateral one should be noted and measured, if possible, by the exophthalmometer. The eye positions should be evaluated from the vertex prospective; however, significant lid edema may cause bias. Vertical globe displacement can be estimated by putting a ruler across the medial canthi and noting the point at which it crosses the globe at each side. A depressed orbital floor fracture leads to globe ptosis. Enophthalmos occurs with increased orbital volume such as in wall fractures. While proptosis occurs due to increased soft tissue contents such as hemorrhage and /or reduction of orbital volume associated with inward displacement of one or more of its walls. If the condition is associated with reduced
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vision or afferent papillary defect, computed tomography (CT) examination is immediately done and intervention should not be delayed. Presence of pulsatile proptosis suggests abnormal vascular communications or transmission of dural pulsations through a fractured displaced orbital roof.
In a conscious cooperative patient with minimal lid edema eye movements all directions of gaze should be examined. The patient is asked to report any diplopia at any direction of gaze. Gaze restriction can be caused by nerve injury, soft tissue swelling, direct muscle injury or entrapped muscle within a skeletal fracture. Forced duction and diplopia fields are performed when indicated.
Hyposthesia in areas around the orbit should be looked for especially in the cheek which is supplied by the commonly injured infraorbital nerve. Upper lid position should be noted and documented as ptosis may occur as a result of nerve injury, levator aponeurosis laceration or dehiscence or later from fibrosis.
Soft tissue landmarks of the orbit such as canthal angles may be displaced by fractures of the underlying bone. For example, increased intercanthal distance suggests nasoethmoidal fractures involving the reflected part of the medial canthal tendon while inferiorly placed lateral canthus suggests inferior dislocation of the zygoma. If the medial wall is involved, the lacrimal drainage system should be evaluated
RADIOLOGICAL EVALUATION
Radiological studies especially computed tomography (CT) play an indispensable role in evaluating the orbital trauma and detecting radio-opaque foreign bodies. Both axial and coronal CT sequences are required.
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Coronal images in 2 mm sections delineate the orbital floor, roof, medial and lateral walls, the nasoethmoid region, the orbital rim and the face surrounding the orbit. It helps delineate the size, shape and location of fractures and associated soft tissue injuries.
Axial scans permit evaluation of the lacrimal drainage pathways, nasal and paranasal sinuses, medial and lateral walls of the orbit, superior and inferior orbital rims, zygomatic arch, pterygoid plates, temporomandibular joint, base of the skull, superior orbital fissures and optic canal. It allows to show globe placement in comparison to the unaffected side.
The combination of axial and coronal scans can give most of the needed information in trauma cases. Three-dimensional scans are helpful in obtaining a more accurate evaluation and understanding of the situation, hence help in deciding the best line for treatment. They are generated from the reformatting 1.5 mm slices on conventional CT scan using a special software computer program. They are very helpful in old trauma cases as they show the deformity, the site, size and appearance of bony defects as well as bone fractures
Problems Associated with Orbital Trauma
•Orbital hemorrhages and emphysema
•Traumatic optic neuropathy
•Orbital fractures
•Septic cavernous sinus thrombosis
•Carotid cavernous fistula
•Orbital foreign bodies
PROBLEMS ASSOCIATED WITH ORBITAL TRAUMA
Orbital Hemorrhages
Bleeding is frequently associated with periorbital trauma and fractures. Blood may be found in the eyelid anterior to the