Pegging the Bioceramic Orbital Implant
(InSIGHT Newsletter Special Edition/ Update)
Pegging will allow coupling of the Bioceramic implant to the overlying prosthetic eye and as a result, an increased range of movement as well as simultaneous movement of the artificial eye with the normal eye. The small dart-like tracking movements that occur give the artificial eye a more life-like appearance. Although pegging increases the movement, potential problems (most of which are minor) can occur in up to 1/3 of patients.1 To peg or not to peg is up to the surgeon and patient.
The Bioceramic orbital implant (aluminum oxide, Al2O3, alumina) represents a new generation of porous orbital implant.2 It is structurally strong, free of contaminants and easy to work with. It has a more extensive uniform pore structure (with excellent pore interconnectivity) than either the Bio-Eye® or FCI3 synthetic HA. The implant is coated with the body's own protein on implantation allowing it to become immunologically camouflaged. The implant was approved by the US Food and Drug Administration in April 2000 and by Health and Welfare Canada in February 2001.
The most common type of peg system used at this time involves a Titanium peg and sleeve system. Earlier models of the peg and sleeve were polycarbonate, however titanium has proven to be more bioinert.3 The titanium peg and sleeve system available through FCI has a hydroxyapatite coating on the titanium sleeve [Fig. 1]. This coating allows fibroblasts to gain a stronger attachment to the sleeve as compared to uncoated titanium (i.e. retention strength is improved). A Bioceramic sleeve (made of the same aluminum oxide material as the implant) in association with a titanium peg will also be available shortly. Either system works well and replaces the older polycarbonate or polymethylmethacrylate peg systems.
THE DRILLING TECHNIQUE
Pegging of the Bioceramic orbital implant is done once complete vascularization takes place. This generally occurs by 6 months in healthy patients. To confirm vascularization, an MRI scan can be done. This author no longer pegs patients with chronic disease such as Diabetes, collagen vascular diseases, or in sockets having previous radiation, where vascularization of the implant may take a prolonged time (6 to 12 months or longer).
The Bioceramic implant can be drilled by a simple manual technique. Some patients can be drilled in a minor room under local infiltrative anesthesia whereas others may require local standby anesthesia with the use of intravenous sedation in addition to the local infiltrative anesthesia in order to settle any anxiety. Prior to drilling, the patient is sat up and asked to look into the 3, 6, 9 and 12 o’clock positions. The conjunctiva over the center of the implant is marked with a gentian violet marker. Alternatively, a conformer with a central hole can be made by the ocularist preoperatively to identify the ideal drill hole position. The patient is then placed in the supine position. Topical anesthetic drops (ex. alcaine, proprocaine, tetracaine, etc.) are placed on the conjunctival surface in addition to a couple of drops of 2.5% topical epinephrine (MydfrinÒ) to vasoconstrict the conjunctival vessels. Next, 2 to 3 cc of 2% lidocaine in combination with epinephrine is infiltrated into the skin of the central lower lid, central upper lid and lateral canthus to anesthetize the orbicularis muscle (1cc in each location). After a few minutes of pressure, a 30 gauge, half-inch needle is used to infiltrate a small amount of local anesthesia (1/4 cc 2% lidocaine in combination with epinephrine) 5 to 8mm away from the implant centre at the 3, 6, 9 and 12 o’clock sub-conjunctival positions. The needle tip is pointed toward the fornix in each of these positions. After waiting 5 minutes and holding light pressure to the socket area, the central conjunctiva is incised for 5 mm with Westcott scissors. Sharp dissection is carried out to the implant surface. Any minor bleeding vessels are cauterized with bipolar cautery. A 25 gauge, 1½-inch needle is held between the thumb and index finger and placed at the implant center. With a light twisting downward movement between the thumb and index finger, the needle enters the implant. Once the needle is into the implant by 10 mm, the needle is released. It is important not to drill beyond the 10 mm. The patient is sat up and the needle is viewed to see if it is centrally placed. The patient is asked to look up, down, left and right. If the needle is not centrally placed or is on an angle, it is removed and realigned by re-entering the needle into the implant. This process is repeated until the needle is straight while the patient is looking straight. The 25-gauge needle is then replaced with an 18-gauge needle in a similar fashion [Fig. 2]. Following this, the supplied drill bit is placed between the thumb and index finger and, with a gentle downward rotating motion, the drill hole is increased in diameter to a 10 mm depth [Fig. 3]. The surgeon should do this with care as he/she does not want to make a drill hole bigger than the sleeve. The drill hole is rinsed with antibiotic solution (ex. Bacitracin) and the sleeve is screwed into the implant [Fig. 4]. I prefer to leave the sleeve shaft flush with the implant surface and it should be tight. Next, a flat-headed peg is slipped into the sleeve. The subconjunctival tissues are then closed with 6-0 polyglactin while conjunctiva is closed with 6-0 plain. The patient is seen by the ocularist in 8 weeks time to have the flat-headed peg exchanged with a round-headed peg. The peg is then coupled to the artificial eye.
Peg system availability:
In Canada: Oculo-Plastik, 200 Sauve West, Montreal, Quebec V3L 1Y9, Tel: 1-888-381-3292, Fax: 1-800-879-1849, In U.S.: FCI Ophthalmics, P.O. Box 465, 76 Prospect Street, Marshfield Hills, MA 02051, Tel: 1-800-826-9060, Fax: 1-800-879-1849, e-mail:firstname.lastname@example.org
1. Jordan DR, Chan S, Mawn L, Gilberg S, Dean T, Brownstein S, Hill VE. Complications associated with pegging hydroxyapatite orbital implants. Ophthalmology 1999:106:505-512.
2. Jordan DR, Mawn LA, Brownstein S, McEachren TM, Gilberg SM, Hill VE, Grahovac SZ, Adenis JP. The Bioceramic orbital implant: a new generation of porous implant. Ophthal Plast Reconstr Surg 2000:16:5:347-355.
3. Jordan DR, Klapper SR. A new titanium peg system for hydroxyapatite orbital implants. Ophthal Plast Reconstr Surg 2000:15:5:380-387
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