Surgery – Instruments – Internal pressure applicator
Reexamination Certificate
2000-07-27
2003-07-22
Woo, Julian W. (Department: 3731)
Surgery
Instruments
Internal pressure applicator
C606S060000, C606S196000, C623S010000
Reexamination Certificate
active
06596009
ABSTRACT:
BACKGROUND OF THE INVENTION
Fractures of the orbital floor of the eye socket, particularly blow out fractures, can be difficult to diagnose, and if not promptly repaired, can result in diplopia, mismatching of the ocular level between the patient's two eyes, long term damage to the ocular nerve eye, and other conditions that cannot always be repaired by subsequent surgeries.
The orbit (eye socket) can be conceptualized as a four walled cone shaped vault. The peripheral portions of this vault (orbital rim, orbital apex and the most lateral aspect of the orbital floor) are fairly rigid and somewhat resistant to fracture. The internal portion of the orbital vault is constructed of bone analogous to a very thin egg shell (averaging 0.27 mm thick). The thinnest and weakest portions are the inferior(floor) and medial walls of the orbit.
Fractures of the orbital floor classically occur by two mechanisms. The first is called an orbital “blow out fracture”. Blow out fractures occur when kinetic energy is delivered to the globe (eye ball) in a discrete fashion. Examples could include a fist or baseball. Such a direct blow to the globe drives the globe into orbit like a piston. The hydraulic pressure is distributed within the cone shaped walls of the orbit and causes the weakest wall to fracture and rapidly decompresses the orbit. Since the weakest wall is the orbital floor, these bones fracture, and then blow out (swing inferiorly) in a trap door fashion, from periosteal hinges. This allows the contents of the orbit (periorbital fat, extraoccular muscles, and globe) to descend into the maxillary sinus below.
The second classic mechanism for orbital floor fracture is as a component to fractures of the zygomatic-maxillary complex (cheek bone or ZMC) fractures. In these cases, kinetic energy is delivered to the malar prominence of the zygoma (cheek bone) and the zygoma is driven into the maxillary sinus. The zygoma is a very thick bone that composes the lateral and inferior-lateral portions of the orbital vault. The rigid zygoma rarely fractures but the thin orbital floor, which is attached to it, buckles and shatters.
Symptoms of fractures involving the orbital floor may include 1) inability to gaze superiorly due to the tethering effect of entrapped fat and/or extraoccular muscles on the edges of fractured bone, 2) diplopia (double vision) due to either disruption of the extraoccular muscle function which coordinates binocular vision as described above, or altered pupillary alignment, 3) enophthalamos (retruded and unequal pupil levels) as the globe sags when the supporting periorbital fat herniates into the maxillary sinus and, finally, 4) paresthesia or anesthesia of the affected cheek. Since the inferior orbital nerve (the sensory nerve to the cheek) travels in a groove in the orbital floor/roof of maxillary sinus, direct injury from bone fragments or tension from sagging orbital contents disrupts normal nerve function.
To correct visual and aesthetic defects associated with orbital floor fractures, the volume of the periorbital soft tissue, and the volume of the boney vault must be equilibrated. Periorbital fat and muscles must be relocated back into the orbit and the integrity of the orbital vault must be restored. The fractured bone of the orbital floor must then be stabilized long enough for osteosynthesis to occur (approximately 4-6 weeks). The difficulty with repairing the orbital floor has to do largely with the difficulty to stabilize these paper thin bones, against the weight of the intra orbital contents, long enough for osteosynthesis to occur.
Methods typically employed in the repair of maxillofacial fractures do not work within the orbit. Even if a surgical approach allowed placement of wires, screws or bone plates, the bones are too thin and simply break into smaller pieces.
Traditional repairs of the orbital floor therefore have approached the problem from two avenues. The first method is from the orbit. This approach requires either a subciliary skin incision (2 mm below the lower eyelashes), or a transconjunctival incision (inside the eye lid) and then dissecting through the tissues of the lower eye lid to expose the fracture from the superior surface. Herniated tissue is then raised out of the maxillary sinus and the integrity of the orbital floor is restored by placing a thin implant over the hole in the floor. The implant rests on the stable peripheral edges of the fracture-analogous to a sheet of plywood temporarily placed to cover a hole in a floor. Theoretically, the best implant for the job would be autogenous cortical bone. The graft would eventually incorporate and the risk for long term complications would essentially be eliminated. In reality, such implants are often much thicker than required and do not conform to the true shape of the orbital floor. These drawbacks often prevent the implant from achieving the volumetric balance necessary for proper aesthetics and function of the globe.
Additionally, there are initial infectious risks with non stabilized bone and there is also risk of associated donor site morbidity. Alloplastic materials are by far the most common implants used to repair orbital floor fractures. Silicon sheeting, polytetrafluoroethylene (Teflon®), polyethylene, Gelfilm™, Marlex™ mesh, hydroxyapatite, methyl methacrylate and titanium mesh are a few examples.
Titanium mesh has the advantage that it may be rigidly fixed to the inferior orbital rim and therefore has less risk of infection or extrusion, and can be used when the blowout fracture is so large that stable margins are not available upon which to rest the implant. However, titanium mesh is costly, requires significantly more skill and experience to shape and place into proper position, will tether the globe if placed incorrectly, and will complicate radiologic exams post-operatively. All of the other materials are less expensive, easy to shape, easy to place, and have minimal interference with the function of the globe. But since all of the latter materials are placed passively over the fracture, and never become integrated therewith, migration, extrusion and infection become lifelong risks. It is important to note that due to the juxtaposition of these anatomic structures, any sinus infection can easily become an intraorbital infection and in a worse case scenario, an intracranial infection. Therefore, although such infections are not frequent, they can be quite serious.
Finally, all the approaches that utilize surgical dissections through the lower eye lid carry the potential sequela of a visible scar, ectropion or entropion (lower lid margin rolled outwardly or inwardly, respectively), infection, injury to neuro vascular structures, the tear duct aperatus, and to the extraoccular muscles of the globe, as well as retrobulbar hematoma and very rarely blindness.
To avoid the short and long term complications of the orbital exposure, surgeons have developed a second method and approach the orbital floor from the maxillary sinus. Since the orbital floor is also the roof of the maxillary sinus, orbital floor fractures can be exposed by making an antrostomy in the anterior maxilla just above the roots of the maxillary teeth. This approach simply requires an incision in the gingiva and removing the paper thin bone of the anterior maxilla between the zygomatic buttress and piriform rim. In cases of blowout fractures, the fractured bones and periorbital fat can be observed herniating down through an opening in the sinus roof. The orbital contents can be pushed back into the orbit from below and then the bone fragments can be aligned into proper position. Once again, the difficulty with stabilization of the bone fragments long enough for osteosynthesis is the pivotal issue. Without stabilization, gravity will pull the orbital contents back into the sinus.
Surgeons have classically employed two methods to stabilize the reduced fragments from the intrantral (antrum=sinus) approach. The oldest method is to systematically layer iodoform gauze within the sinus. The gauze will comple
Christie Parker & Hale LLP
Woo Julian W.
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