Orbital fractures secondary to trauma are not uncommon. The most common orbital walls to be affected by trauma are the floor and the medial wall, the thinnest bone in the body. Clinical indications for repair of a fracture include diplopia or extraocular muscle entrapment, a large fracture (greater than 50% of the wall), and enophthalmos greater than 2mm.
If surgical correction is indicated, the surgeon must decide which material to use to cover the defect. Choices vary from autogenous bone grafts to synthetic implants such as silastic sheeting, porous polyethylene and titanium. Each accomplishes the same goal of coverage of the bony defect and prevention of prolapse of orbital tissues into the sinuses. Factors that weigh in the surgeons decision on what material to use include extrusion rate, infection rate, difficulty of harvesting material, and need for a foreign body.
The disadvantage of using a bone graft is that it takes extra time and increased morbidity in the surgery to harvest the graft, most commonly from the skull. The advantage is that the patient’s own tissue is being used and the chances of rejection are small.
The available synthetic implants have shown to be very biocompatible. Extrusion rates are small and the difference between extrusion rates between silastic sheeting and porous polyethylene seem to be negligible. Advantages of silastic sheeting are that a nice capsule forms around the implant, decreasing the chance of extrusion. As well, because of its smooth surface, the orbital tissues superior to the implant will not adhere to the implant and become incorporated into the sheet, thereby decreasing the chance of diplopia occurring secondary to fibrovascular ingrowth of tissues. For some, fibrovascular ingrowth is a plus. Many feel that this ingrowth of orbital tissues actually decreases the chance of extrusion of the implant. Again, the difference in extrusion rates between the two seems clinically insignificant. I have used both myself, equally, and have been pleased with each. Pliability is similar, ease of shaping, conforming and placement are comparable and both have been readily available in different thicknesses. These are the two implants that I most commonly use in my practice. One advantage of porous polyethylene for use in large defects is that the companies make implants in various shapes to conform to the natural shape of the orbit. For instance, Porex Surgical has developed ½ orbits, ¾ orbits and whole orbits to fit the needs depending on the size of the defect, either secondary to trauma or orbital tumor resection.
Titanium can also be used, but must be fixed to the surrounding, stable bone with screws. I find titanium sheets useful in large fractures or fractures involving the orbital rim where more reconstruction is needed. Various shapes and sizes are available, including an angel plate that fits the orbital floor nicely. There are two caveats to using titanium. One is that when you cut the edges to conform to the shape and size of the defect, you are left with sharp edges that must be burred down or cut to be less abrasive. The second is that the surface will allow a considerable amount of tissue ingrowth through the holes. In order to prevent the tissue from ‘sticking’ down to the surface, the implant can be covered with another material, such as a porous polyethylene sheet, a silastic sheet, banked dura mater, or pericranium.
A new device has recently become available which allows the surgeon to avoid the hassles mentioned above with the use of titanium implants. This device is a titanium sheet covered on both sides by thin sheets of porous polyethylene. The new design provides a smooth surface on both the superior and inferior aspects of the implant, and when cut, hides the sharp edges of the cut titanium, eliminating the need to burr down the edges. Again, I find this implant useful in the repair of large orbital floor fractures involving the inferior orbital rim. This implant is currently on the market and manufactured by Porex Surgical, and is also under construction by Synthes, the company largely responsible for titanium implants.
Choice of orbital wall implants has to be individualized, of course. Size of the fracture matters, presence of adequate surrounding stable bone makes a difference and whether the rim needs to be reconstructed also plays a role in the decision making.
To summarize, I find silastic sheeting (Supramid) and porous polyethylene (Medpor) to be the best for fractures not involving the orbital rim and not involving the entire wall of the orbit, which happen to constitute the majority of orbital fractures. For very large reconstructions, I prefer to use either a combination of titanium sheeting covered in a nonabrasive material or the various orbital models offered by Porex surgical if a very large defect is present secondary to tumor resection. I do feel that the new porous polyethylene covered titanium implants show promise in large reconstructions. Currently, they are available in square pieces and must be tailored to fit the needs of your patient, a relatively simple task in the scheme of orbital fracture repair. The new material is definitely worth a try in these large reconstructions.
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