Coralline Hydroxyapatite as an Ocular Implant JONATHAN J. DUTTON, MD, PhD
Abstract: Fifty patients received a coralline hydroxyapatite sphere as a buried integrated ocular implant after enucleation or evisceration surgery. The surgical technique is described and the results discussed. All patients obtained final prosthetic motility superior to that possible with simple spherical methylmeth acrylate implants. After a follow-up of 2 to 27 months (mean, 10.4 months) there have been no cases of migration or extrusion. Complications have been minimal and easily managed. The hydroxyapatite implant appears to offer ex cellent cosmetic reconstruction without the unacceptable infection and extrusion rates seen with other integrated implants. Ophthalmology 1991; 98:370-377
Enucleation has been performed at least since the 16th century. 1The modern form of the operation was proposed in 1841 and has been clinically practiced since 1851. This technique allowed placement of an ocular implant for restoration of orbital volume and some prosthetic motil ity.2·3 In an attempt to further improve motility, direct coupled, partially exposed integrated implants were in troduced in 1941. 4 High extrusion rates and infections led to the design ofcompletely buried integrated implants beginning in 1950. Although the buried implants resulted in fewer complications than the exposed types, motility was not as good as with the direct coupled implants, and extrusion rates remained unacceptably high. 5 Since the late 1950s, most surgeons have returned to the simple spherical implant, which is associated with the lowest complication rates but provides relatively poor prosthetic motility. During the past decade, coralline hydroxyapatite has been used as a bone graft substitute in a variety ofsurgical procedures.6- 10 It is highly biocompatible, causes minimal tissue inflammation, is not resorbed, and allows rapid host tissue ingrowth, resulting in a close approximation to normal human bone. 11 ·12 Since 1985, porous hydroxyapatite has been used as an ocular implant for reconstruction after enucleation and evisceration. The technique was developed by Dr. Arthur Originally received: September 20, 1990. Revision accepted: November 15, 1990. From the Department of Ophthalmology, Duke University Eye Center, Dur ham. Reprint requests to Jonathan J. Dutton, MD, Duke University Eye Center, Box 3802, Durham, NC 27710.
370
Perry, who demonstrated its value and safety in prelim inary experimental studies (unpublished data). Since that time, numerous patients have been implanted without significant complication. In August 1989, coralline hy droxyapatite was approved by the Food and Drug Ad ministration for orbital implantation, and the technique is slowly gaining wide acceptance for uncomplicated enu cleations. This study describes an experience with 50 patients un dergoing enucleation or evisceration, who had recon struction with hydroxyapatite fashioned as a buried in tegrated ocular implant. The functional and cosmetic re sults to date have been excellent, and complications have been minimal. The technique appears to offer all the ad vantages of the partially exposed, direct coupled implants, without any of their complications.
MATERIALS During the 25 months between May 1988 and June 1990, 83 patients were referred to the oculoplastic service of the Duke Eye Center for enucleation or evisceration. An additional ll patients with extruding or migrated ocular implants were referred for reconstructive orbital surgery. Of the 94 patients, 50 underwent hydroxyapatite implantation. The percentage of our patients receiving this implant rose from 22% in 1988 to 84% in 1990. Patients were considered suitable candidates for hy droxyapatite implantation as long as function of the ex traocular muscles was sufficient to provide good motility of the globe or previously placed implant. Those patients with severe orbital trauma or repeated orbital surgery re
DUTTON
•
CORALLINE HYDROXYAPATITE
Fig I. A whole scleral shell is obtained from the eye bank or prepared by removing the cornea and eviscerating all uveal tissue.
Fig 4. Four 2-mm X 3-mm windows are cut through the sclera at the proposed sites of rectus muscle attachment.
from endstage glaucoma, diabetes, or trauma in 17 pa tients, and endophthalmitis in 4 patients. In 2 patients, hydroxyapatite was used as a secondary implant after the removal of an extruding or migrated sphere, and in one patient, a methylmethacrylate sphere was replaced with hydroxyapatite for improved motility. The implant consisted of coralline hydroxyapatite carved into a sphere. The first 15 implants were provided by Dr. Arthur Perry under a research protocol. The re maining 35 implants were placed after FDA approval and were obtained from Integrated Orbital Implants (San Diego, CA). Most of the implants measured 20 mm in diameter, although, in some cases, 18- or 22-mm spheres were used depending on orbital volume. Fig 2. An eviscerated donor scleral shell is opened with relaxing incisions, and a 20-mm hydroxyapatite sphere is placed inside.
Fig 3. The relaxing incisions are sutured with a running stitch of 5-0 Vicryl to form a baseball-like covering of sclera over the implant.
suiting in fibrosis of ocular muscles received a standard polymerized methylmethacrylate sphere. Of the 50 patients, enucleation was performed in 48 and evisceration in 2. The indications for surgery were intraocular malignancy in 26 patients, a blind painful eye
SURGICAL TECHNIQUE Before beginning the surgery, the implant was prepared. This preparation has been modified over the last 2 years to allow more rapid host tissue ingrowth, and our current recommended method is summarized here. The gas ster ilized hydroxyapatite sphere was soaked in a solution of gentamicin, 80 mg diluted in 10 ml of balanced salt so lution for 15 minutes before use. An eviscerated scleral shell preserved in I 00% alcohol was obtained from the local eye bank (Fig 1). Thirty minutes before use, the shell was reconstituted in several changes of saline, the last containing 80 mg of gentamicin. Two relaxing incisions were cut 180° apart from the corneal defect toward the optic nerve for a distance of approximately I em. The hydroxyapatite sphere was placed into the scleral shell (Fig 2). The edges ofthe relaxing incisions were imbricated and sutured with a running stitch of 5-0 Vicryl to form a baseball-like covering (Fig 3). The sphere remained bare only at the site of the corneal defect. With the optic nerve stump facing forward and cut flush with the outer scleral wall, four rectangular windows, each measuring 2 X 3 mm, were cut through the sclera with a scalpel and Wes cott scissors (Fig 4). These windows were placed 90° apart and approximately 12 to 15 mm from the optic nerve stump to approximate the positions of the rectus muscle 371
OPHTHALMOLOGY
•
MARCH 1991
Fig 5. A 1-mm diameter hole is drilled to the center of the sphere at each window and at the corneal defect.
insertions on an intact globe. Using a 1-mm diameter twist bit and an electric drill, five holes were cut to the core of the hydroxyapatite sphere, one in the center of each window, and one at the corneal defect (Fig 5). The prepared implant was placed in a solution of gentamicin until needed. Enucleation was performed by opening the conjunctiva for 360° around the corneal limbus. Anterior Tenon's capsule was separated from its attachments to sclera just behind the limbus and bluntly dissected from the globe in four quadrants between the rectus muscles using Ste vens scissors. Each of the four rectus muscles were isolated with a muscle hook, and a double-armed 6-0 Vicryl suture passed through its insertion and secured with a locking stitch at each side (Fig 6). The muscle was then cut from the globe. In cases of intraocular malignancy, care was taken not to put traction on the muscles so as not to elevate intraocular pressure. In these cases, the muscles were cut from the sclera without hooking and before plac ing the 6-0 Vicryl suture. Posterior Tenon's capsule was button-holed adjacent to the optic nerve with enucleation scissors, and the optic nerve was severed about 2 to 4 mm behind the sclera. As the globe was removed, the superior and inferior oblique muscles were cut from its surface. The orbit was packed with cottonoid pledgets soaked with 0.25% phenylephrine, and pressure was applied for 5 minutes. Using malleable retractors, the pledgets were re moved, and any remaining bleeding points, including the central retinal artery, were individually cauterized (Fig 7). The prepared hydroxyapatite implant was passed into the orbit using an introducer, with the optic nerve stump facing anterior. The scleral windows were aligned with the four rectus muscles, and each muscle was secured to the anterior lip ofthe window using the preplaced double armed vicryl suture (Fig 8). Tenon's capsule was closed with interrupted stitches of 5-0 Vicryl, and conjunctiva with a running suture of 6-0 plain catgut. A methylmeth acrylate conformer was placed in the fornices, and the socket was patched with a pressure dressing and head roll for 48 hours. In the two patients undergoing evisceration, the surgery was performed by making a full-thickness scleral incision 372
•
VOLUME 98
•
NUMBER 3
Fig 6. After opening conjunctiva, the four rectus muscles are tagged with double-armed 6-0 Vicryl sutures and cut from the globe.
Fig 7. The globe is removed and all bleeding is cauterized. Posterior Tenon's is opened to show the intraconal fat compartment.
Fig 8. The implant is placed into the orbit and the superior rectus muscle (arrow) is sutured to the anterior lip of the prepared scleral window.
1 mm behind the limbus for 360° around the cornea. Using an evisceration spoon, a surgical plane was estab lished around the ciliary body in the suprachoroidal space. At the posterior aspect of the globe the optic nerve was
DUTION
•
CORALLINE HYDROXYAPATITE
Fig 9. Technetium 99m MDP static bone scan of a patient 6 months after implantation of hydroxyapatite into the right orbit. The implant shows complete vascularization to its center.
Fig 10. After removal of a small circle of conjunctiva and Tenon's, a 3 mm cutting burr is used to drill a central hole for the motility peg.
Fig 11. The central motility hole is 10-mm deep and is aligned along a radius of the sphere.
cut with the sharp edge of the spoon. The uveal contents with the cornea attached were removed unruptured as a single piece. The vortex veins and central retinal vessels were cauterized directly, and the scleral shell was scrubbed
Fig 12. A temporary flat-headed methylmethacrylate peg is placed into the motility hole to allow wearing of the prosthesis until the latter is modified.
with 100% alcohol to remove all traces of adherent uveal tissue. Five full-thickness windows, each measuring 2 mm X 3 mm, were cut in the scleral shell to allow more rapid vascular ingrowth. Two relaxing incisions were cut 180° apart in the superotemporal and inferonasal quadrants. A 16- to 18-mm hydroxyapatite sphere with five 1-mm holes drilled to its center was placed into the shell. The sclera was imbricated over the surface of the implant and sutured with 5-0 Vicryl stitches. Tenon's capsule and conjunctiva were closed as separate layers in the usual fashion. In three patients, previously placed spherical implants were removed and replaced with hydroxyapatite. In one case, the extraocular muscles were identified after dissec tion in the walls of Tenon's capsule. These were isolated, and sutured to the implant as described above. In two patients, the muscles could not be clearly identified. In these patients, Tenon's capsule in the region ofthe fibrosed muscle insertions was sutured directly to the scleral cov ering of the implant. In all patients, a custom-fitted ocular prosthesis was placed 6 weeks after surgery. After 6 months, vascular ization and fibrous ingrowth of the implant was complete. In 18 cases this was confirmed by static and dynamic bone scan studies (Fig 9) after intravenous injection of 20 mCi of 99 mTc MDP. 13 At this time, a secondary drilling procedure was per(ormed in a minor room setting. With the patient fixating the normal eye in primary gaze, the center of the implant was marked on the conjunctiva with a surgical marking pen. Local anesthetic (0.1 ml) was in filtrated beneath conjunctiva at this point. A small 3-mm circle of conjunctiva and Tenon's was removed to expose the implant. Using a 3- to 4-mm cutting burr on an electric drill, a hole was drilled radially to a depth of 10 mm toward the center of the implant (Figs 10, 11 ). A methylmeth acrylate peg with an 8-mm long shaft measuring 2 to 3 mm in diameter, and a flat head measuring 5 mm in diameter was pushed into the hole (Fig 12), and the pros thesis was replaced into the socket. After 4 to 6 weeks, the hole was lined with conjunctiva. The flat-headed peg 373
OPHTHALMOLOGY
•
MARCH 1991
•
VOLUME 98
•
NUMBER 3
was replaced with one bearing a high rounded head. The ocular prosthesis was simultaneously modified with a co~ responding circular depression on its posterior surfac~ (Fig 13), placed so as to maintain alignment with the pupillary axis of the contralateral eye.
RESULTS Of the 50 patients treated, 21 have not yet been drilled to receive the central motility peg. However, at last follow up, motility of the orbital tissues and conjunctival fornices was judged to be nearly full in all positions of gaze. Of the 29 remaining patients, 7 elected not to have the sec ondary drilling procedure because motility of the ~nitial prosthesis was already considered excellent, even without final integration to the implant. In 22 patients, the second stage drilling was completed and the prosthesis ?Iodified. In all, prosthetic motility was subjectively supenor to that obtainable with plain spherical implants (Fig 14). The overall motility was so good in many patients that the edge ofthe prosthesis became visible in extreme horizontal gaze positions. There were no complications from the surgery. In fol low-up intervals of 2 to 27 months (mean, 10.4 months), there have been no extrusions, and no migrations of the implant. We have seen no unusual orbital inflammatory reactions. In the first 10 cases, we were using 22-mm hy droxyapatite spheres placed into Tenon's capsule. How ever, this left little room for adequate anterior chamber depth on the prosthesis, and insufficient room for prep aration of the hemispherical depression for reception of the final peg without obvious proptosis. The use of an 18 mm sphere placed into Tenon's capsule or a 20-mm sphere placed behind posterior Tenon's provided adequate orbital volume, with enough orbital depth to allow a deep anterior chamber and later modification for the peg. In two patients, granulation tissue growth occurred within the central hole, pushing out the motility peg. In both cases, this was treated with the C02 laser and topical steroids. In one patient, conjunctiva grew over the surface of the final round-headed peg but did not require treat ment. One patient complained of decreased motility after removing the prosthesis for cleaning. On examination, the peg was noted to be missing. This was replaced without difficulty with restoration of full motility. In two cases, drilling of the central hole for the temporary flat-headed peg was not radial but oblique. This resulted in the peg not seating flush, and some discomfort on replacing the prosthesis. However, with placement of final round headed peg and modification of the prosthesis, this prob lem disappeared.
DISCUSSION The first description of enucleation as a surgical tech nique was by Bartisch in 1583. 2 This barbaric operation was performed without anesthesia and consisted of gross 374
Fig 13. The posterior surface of the prosthesis is modified with a circular depression for integration with the final round-headed peg.
extirpation of the globe along with associated conjuncti_va, orbital fascia, and portions ofextraocular muscles, maki~g it impossible to successfully wear an ocular prosthesis. The modern technique evolved during the 19th century, following clarification of Tenon's capsule as an anatomic layer separating the globe from deeper orbital structures. The concept on anatomical grounds is generally attributed to O'Ferrall in Dublin and Bonnet in Paris, both published in 1841, 2 although the first actual surgery has been credited to Cleoburey as early as 1826. 1 Critchett introduced the term enucleation, and was apparently the first to use the operation on a routine basis at Moorfields Eye Hospital beginning in 1851. 2 Ocular implants to restore volume and improve pros thetic motility were introduced by Mules in 1884 following evisceration ofthe globe, 3 and in 1887 by Frost 14 following enucleation. These early implants consisted of a hollow glass sphere, which extruded in 55 to 93% of proce dures.3·14 With improved techniques of wound closure, Verrey 15 reported an extrusion rate of21.3% in 343 ca_ses receiving the Mules implant up to 1898. Over the ensumg decades, a wide variety of implant materials were used in an attempt to reduce the extrusion rate and improve the cosmetic results. These included gold, silver, vitallium, platinum, aluminum, cartilage, bone, fat, fascia lata, sponge, wool, rubber, silk, catgut, reat, agar, asbestos, cork, ivory, paraffin, and cellulose. Although n?ne of these proved very successful, the anatomic necessity for some type of implant became well established. 16 Ruedemann 17 introduced the first partially exposed in tegrated implant in 1941. Extraocular muscles were at tached for improved motility. Numerous variations were developed over the following decade. Muscles were at tached via tantalum mesh screens, Dacron strips, or spe cially designed grooves and tunnels, and the implant was integrated to the prosthesis through various arrangements of male-female type pegs and sockets and even magnets. Extrusion, migration, and infection rates remained ex cessive, however, and these types ofimplants were largely abandoned by the 1950s.
DUTTON
•
CORALLINE HYDROXYAPATITE
Fig 14. A patient 3 months after final modification of the prosthesis. Top /eji, primary position ofgaze. Top right. left lateral gaze. Center leji, right lateral gaze. Center right, upgaze. Bou om , downgaze.
The completely buried integrated implants were first used by Cutler in 1945, 4 and, like their exposed counter parts, were succeeded by numerous variations in design and materials. Motility was not as good as with the ex posed implants, but significantly better than with the clas sic Mules sphere. Extrusion and migration rates were less than with exposed implants.5 These buried implants relied on variations in shape of the anterior implant face adapted to matching surfaces on the back of the prosthesis for integration of movement through the intact conjunctiva. Despite the cosmetic advantages, most of the buried im
plants still resulted in unacceptable rates of conjunctival erosion and extrusion. To date, the simple spherical im plant has given the lowest complication rate, although it provides more limited motility. Coralline hydroxyapatite porous ceramic has been un der investigation as an alloplastic bone substitute since 1975. 19 Early experiments demonstrated that pore size and distribution was a major determinant of tissue-type ingrowth.20 The replamineform process2 1 has been adapted to the production of such porous hydroxyapatite ceramics. Using this technique, the aragonite (CaC03) 375
OPHTHALMOLOGY
•
MARCH 1991
skeletal structure of the common marine reef-building coral of the genus Porites is converted hydrothermally to calcium phosphate hydroxyapatite (Ca 10(P04 )6(0H)zf, with a regular system of interconnecting pores of approx imately 500 J,Lm diameter. 19·22 These resemble the haver sian system of normal lamellar bone. When implanted into human tissue, the hydroxyapatite acts as a passive latticework for fibrovascular ingrowth. In blocks measur ing 5 X 5 X 10 mm, Grenga22 showed complete vascu larization within 4 weeks of implantation. When placed subperiosteally, this material allows bony ingrowth with out inducing osteoclastic activity. 7 Hydroxyapatite has been shown to be completely biocompatible, nontoxic, and nonallergenic. 7 •19 It does not become encapsulated and is not associated with significant foreign body inflam matory reaction. 23 When used as a bone substitute, hy droxyapatite is resistant to mild to moderate compressive forces and shows no significant resorption after 48 months. 24 Although hydroxyapatite is highly resistant to infection, under conditions of experimental bacterial in fections, Reznick and Gilmore25 showed that this material did interfere with normal host tissue response and led to chronic mild inflammation that did not completely re solve. Hydroxyapatite implants have been used for maxillo facial onlay grafting, alveolar ridge augmentation, 24•26 cranial reconstruction over bare dura, 27 middle ear re construction,9 and laryngeal framework support. 10 Zide6 used dense, nonporous hydroxyapatite blocks to repair orbital floor fractures and to augment orbital volume. Block and Kent28 applied similar implants subperiosteally to elevate the globe for the correction of vertical ocular dystopia. The use of hydroxyapatite as an ocular implant after evisceration and enucleation was mentioned by Pratt, 29 but no details of the procedure were given. The idea of using porous hydroxyapatite as an ocular implant to improve motility was devised by Dr. Arthur Perry in San Diego. In clinical trials over the past several years, the technique has proven to be safe and effective, with no significant complications. In August 1989, the use ofthis material in the orbit was approved by the FDA, and since that time the author has used this implant in the majority of enucleation procedures. Over the past 2 years, we have modified the technique of preparation and implantation to allow more rapid vascular ingrowth. The ideal ocular implant should be completely buried, simple in construction without projecting or angulated surfaces that might erode through conjunctiva, light weight, and smaller than the globe to allow for a prosthesis of adequate anterior chamber depth. In addition, it should be centered within the muscle cone, and anchored to or bital tissues to minimize extrusion. It should have extra ocular muscles attached, and should be directly integrated in some way with the prosthesis for a 1: 1 transfer of mo tility. It should induce minimal tissue inflammation and should not resorb over time. Hydroxyapatite implanted as described above fulfills all of these criteria. Unlike early integrated implants, hy droxyapatite is completely buried beneath Tenon's capsule and conjunctiva. The central hole for the motility peg is
376
•
VOLUME 98
•
NUMBER 3
lined with conjunctival mucosa so that no portion of the implant is exposed. The implant itself is a simple sphere, without projecting mounds or sharp angles. The implant is positioned within the muscle cone with extraocular muscles attached to the scleral covering. With time, this donor sclera is largely replaced by host collagen, and the implant becomes infiltrated with fibrovascular tissue so that it resembles normal bone. Thus, anchored to orbital tissues, the implant is more resistant to migration and extrusion. Attachment ofthe extraocular muscles in their approximate anatomic positions allows nearly full motility of the implant. Integration of the implant and prosthesis through the motility peg allows translation of this move ment to the artificial eye. In several patients, excursion of the prosthesis was so extreme that the edge of the pros thesis was easily visible on lateral and medial gaze, de tracting from the overall cosmetic result. In these cases, the prosthesis can be made larger, but this may reduce motility. Wrapping the coral sphere in a scleral shell is necessary to allow attachment of extraocular muscles. Alternatively, fascia or banked dura should work equally well. Cutting small windows through the scleral shell and attaching the rectus muscles to their anterior lips aligns the muscle stump and associated ciliary arteries into the window and against the hydroxyapatite. Drilling 1-mm holes to the spherical center allows more rapid access of vasculature into the implant. Before our development of this tech nique, complete vascularization often required 6 to 10 months or longer. Since we began drilling access holes, all cases in which bone scans have been performed have been completely vascularized by 5 to 6 months. At the present time, we are investigating the time course for this process, which may require as little as 2 to 3 months. Complications have been minimal and easily managed. Drilling of the central motility hole as a secondary pro cedure is performed in a minor room setting under local anesthetic. Care must be taken to sink the hole perpen dicular to the surface and radial to the sphere. In two cases this hole was drilled oblique to the surface so that the temporary peg could not be seated properly. This re sults in some discomfort in attempting to wear the un modified prosthesis. A second hole can be drilled coin cident with the first, and fibrous tissue will fill in the poorly aligned and unused hole. However, once the final peg is placed and the prosthesis modified, the rounded head eliminates any problems caused by the skewed alignment of the peg shaft. Granulation tissue may form within the central motility hole, and in two cases was prolific enough to dislodge the peg. In one case, we excised the abnormal growth with fine scissors, but it recurred 2 weeks later. The C02 laser was used to vaporize this tissue successfully in this patient and also in another patient. The cause ofthis complication is unclear but may be related to a loose fit of the peg resulting in irritation of the conjunctiva growing into the hole. It is important to drill the motility hole only 1 mm larger in diameter than the peg shaft. Initially, we used pegs with a shaft measuring 2 mm in diameter. The pegs now supplied with the implants have a 3-mm shaft.
DUTION
•
CORALLINE HYDROXYAPATITE
We observed only one case of the motility peg being lost upon removal of the prosthesis. Again, this was clearly related to a hole that was too large for the peg diameter. In the future, a set of pegs with variable shaft sizes should be available to compensate for such situations. In one patient, conjunctiva grew over the surface ofthe final peg. This did not interfere with motility and no treatment was offered. In such situations, any conjunctival mucosa trapped in the motility hole might be expected to form an inclusion cyst, although this patient has had no further problems after 8 months. Hydroxyapatite has been used in three patients as a secondary implant after removal of a previously placed methylmethacrylate sphere. In two patients, the original spheres extruded, and in one patient, replacement was for improved motility. In all cases, motility was more limited due to some fibrosis of the extraocular muscles. However, the motility that was possible with these muscles was transferred to the prosthesis, and the overall effect was an improvement over the original sphere. Our current practice is to offer hydroxyapatite as a pri mary implant in all cases of enucleation or evisceration in which the extraocular muscles allow for adequate mo tility. The only contraindications are cases ofsevere orbital trauma with scarred muscles, cases where orbital malig nancy, such as retinoblastoma, may recur and the presence of a bone density implant might obscure radiologic im aging, and cases of orbital infection. The use of donor sclera, however well screened, presents some minimal risk, and we have had several patients refuse this implant be cause of the fear of HIV contamination. Alternative methods of attaching muscles directly to the hydroxy apatite, as for example with fibrin glue, or coating the sphere with an inert soft biocompatible shell, are being investigated. Coralline hydroxyapatite as an ocular implant appears to offer a significant improvement over all previously used materials. The cosmetic results equal those of the best integrated implants, but with fewer potential complica tions. The long-term benefits, as well as risks, however, remain to be determined. The use of hydroxyapatite sig nificantly raises the cost of enucleation. Even without a confirmatory bone scan, the costs of the implant, sclera, additional surgical time, secondary drilling procedure, and modification of the prosthesis can add $1500 to $2500 to the usual charges. Nevertheless, the benefits of this ma terial extend beyond its obvious cosmetic value. If long term studies confirm its lower migration and extrusion rate, and its relative resistance to infection, the medical advantages of hydroxyapatite will make the cost worth while.
REFERENCES 1. Luce CM. A short history of enucleation. lnt Ophthalmol Clin 1970; 10:681-7. 2. Snyder C. An operation designated "The Extirpation of the Eye." Arch Ophthalmol1965; 74:429-32.
3. Mules PH. Evisceration of the globe, with artificial vitreous. Trans Ophthalmol Soc UK 1885; 5:200-6. 4. Gougelmann HP. The evolution of the ocular motility implant. lnt Ophthalmol Clin 1976; 10:689-711. 5. Troutman RC. End results of implant surgery. Trans Am Acad Ophthalmol Otolaryng 1952; 56:30-4. 6. Zide MF. Late posttraumatic enophthalmos corrected by dense hy droxylapatite blocks. J Oral Maxillofac Surg 1986; 44:804-6. 7. Rosen HM, McFarland MM. The biological behavior of hydroxyapatite implanted into the maxillofacial skeleton. Plast Reconstr Surg 1990; 85:718-23. 8. Matukas VJ, Clinton JT, Langford KH, Aaronin PA. Hydroxylapatite: an adjunct to cranial bone grafting. J Neurosurg 1988; 69:514-7. 9. Grote JJ. Reconstruction of the middle ear with hydroxylapatite im plants: long-term results. Ann Otol Rhinal Laryngol 1990; 99 (no. 2, pt. 2, suppl144). 10. Hirano M, Yoshida T, Sakaguchi S. Hydroxylapatite for laryngotracheal framework reconstruction. Ann Otol Rhinal Laryngol 1989; 98:713 7. 11. Holmes RE, Wardrop RW, Wolford LM. Hydroxylapatite as a bone graft substitute in orthognathic surgery: histologic and histometric findings. J Oral Maxillofac Surg 1988; 46:661-71. 12. van Blitterswijk CA. Grote JJ. Biocompatibility of clinically applied hy droxylapatite ceramic. Ann Otol Rhinal Laryngol 1990; 99 (no. 2, pt. 2, suppl144). 13. Patka P, Hollander, WD, Otter GO, et al. Scintigraphic studies to eval uate stability of ceramics (hydroxyapatite) in bone replacement. J Nucl Med 1985; 26:263-71. 14. Frost WA. What is the best method of dealing with a lost eye? Br Med J 1887; 1:1153-4. 15. Wood CA, ed. The American Encyclopedia and Dictionary of Oph thalmology. vol. VI: Dioptric System to Exophthalmos, Chicago, Cleveland Press, 1915; 4418-56. 16. Culler AM. Basic principles of anatomy and physiology of the orbit and relation to implant surgery. Trans Am Acad Ophthalmol Otolaryngol 1952; 56:17-20. 17. Ruedemann AD. Plastic eye implant. Am J Ophthalmol1946; 29:947 52. 18. Cutler NL. A basket type implant for use after enucleation. Arch Ophthalmol1946; 35:71-83. 19. Piecuch JF. Extraskeletal implantation of a porous hydroxyapatite ce ramic. J Dent Res 1982; 61:1458-60. 20. Klawitter JJ. A Basic Investigation of Bone Growth into a Porous Ce ramic Material. [Thesis], Clemson, SC: Clemson University, 1970. 21. White EW, Weber JN, Roy, OM, et al. Replamineform porous bio materials for hard tissue implantation applications. J Biomed Mater Res 1975; 9:23-7. 22. Grenga TE, Zin JE, Bauer TW. The rate of vascularization of coralline hydroxyapatite. Plast Reconstr Surg 1989; 84:245-9. 23. Holmes RE. Bone regeneration within a coralline hydroxyapatite im plant. Plast Reconstr Surg 1979; 63:626-33. 24. Holmes RE, Hagler HK. Porous hydroxylapatite as a bone graft sub stitute in mandibular contour augmentation: a histometric study. J Oral Maxillofac Surg 1987; 45:421-9. 25. Reznick JB, Gilmore WC. Host response to infection of a subperiosteal hydroxylapatite implant. Oral Surg Oral Med Oral Pathol 1989; 67: 665-72. 26. Butts TE, Peterson LJ, Allen CM. Early soft tissue ingrowth into porous block hydroxyapatite. J Oral Maxillofac Surg 1989; 47:475-9. 27. Zide MF, Kent JN, Machado L. Hydroxylapatite cranioplasty directly over dura. J Oral Maxillofac Surg 1987; 45:481-6. 28. Block MS. Kent JN. Correction of vertical orbital dystopia with a hy droxylapatite orbital floor graft. J Oral Maxillofac Surg 1988; 46:420
5. 29. Pratt SG. Evisceration techniques. Adv Ophthal Plast Reconstr Surg 1988; 7:247-53.
377
Abstract: Fifty patients received a coralline hydroxyapatite sphere as a buried integrated ocular implant after enucleation or evisceration surgery. The surgical technique is described and the results discussed. All patients obtained final prosthetic motility superior to that possible with simple spherical methylmeth acrylate implants. After a follow-up of 2 to 27 months (mean, 10.4 months) there have been no cases of migration or extrusion. Complications have been minimal and easily managed. The hydroxyapatite implant appears to offer ex cellent cosmetic reconstruction without the unacceptable infection and extrusion rates seen with other integrated implants. Ophthalmology 1991; 98:370-377
Enucleation has been performed at least since the 16th century. 1The modern form of the operation was proposed in 1841 and has been clinically practiced since 1851. This technique allowed placement of an ocular implant for restoration of orbital volume and some prosthetic motil ity.2·3 In an attempt to further improve motility, direct coupled, partially exposed integrated implants were in troduced in 1941. 4 High extrusion rates and infections led to the design ofcompletely buried integrated implants beginning in 1950. Although the buried implants resulted in fewer complications than the exposed types, motility was not as good as with the direct coupled implants, and extrusion rates remained unacceptably high. 5 Since the late 1950s, most surgeons have returned to the simple spherical implant, which is associated with the lowest complication rates but provides relatively poor prosthetic motility. During the past decade, coralline hydroxyapatite has been used as a bone graft substitute in a variety ofsurgical procedures.6- 10 It is highly biocompatible, causes minimal tissue inflammation, is not resorbed, and allows rapid host tissue ingrowth, resulting in a close approximation to normal human bone. 11 ·12 Since 1985, porous hydroxyapatite has been used as an ocular implant for reconstruction after enucleation and evisceration. The technique was developed by Dr. Arthur Originally received: September 20, 1990. Revision accepted: November 15, 1990. From the Department of Ophthalmology, Duke University Eye Center, Dur ham. Reprint requests to Jonathan J. Dutton, MD, Duke University Eye Center, Box 3802, Durham, NC 27710.
370
Perry, who demonstrated its value and safety in prelim inary experimental studies (unpublished data). Since that time, numerous patients have been implanted without significant complication. In August 1989, coralline hy droxyapatite was approved by the Food and Drug Ad ministration for orbital implantation, and the technique is slowly gaining wide acceptance for uncomplicated enu cleations. This study describes an experience with 50 patients un dergoing enucleation or evisceration, who had recon struction with hydroxyapatite fashioned as a buried in tegrated ocular implant. The functional and cosmetic re sults to date have been excellent, and complications have been minimal. The technique appears to offer all the ad vantages of the partially exposed, direct coupled implants, without any of their complications.
MATERIALS During the 25 months between May 1988 and June 1990, 83 patients were referred to the oculoplastic service of the Duke Eye Center for enucleation or evisceration. An additional ll patients with extruding or migrated ocular implants were referred for reconstructive orbital surgery. Of the 94 patients, 50 underwent hydroxyapatite implantation. The percentage of our patients receiving this implant rose from 22% in 1988 to 84% in 1990. Patients were considered suitable candidates for hy droxyapatite implantation as long as function of the ex traocular muscles was sufficient to provide good motility of the globe or previously placed implant. Those patients with severe orbital trauma or repeated orbital surgery re
DUTTON
•
CORALLINE HYDROXYAPATITE
Fig I. A whole scleral shell is obtained from the eye bank or prepared by removing the cornea and eviscerating all uveal tissue.
Fig 4. Four 2-mm X 3-mm windows are cut through the sclera at the proposed sites of rectus muscle attachment.
from endstage glaucoma, diabetes, or trauma in 17 pa tients, and endophthalmitis in 4 patients. In 2 patients, hydroxyapatite was used as a secondary implant after the removal of an extruding or migrated sphere, and in one patient, a methylmethacrylate sphere was replaced with hydroxyapatite for improved motility. The implant consisted of coralline hydroxyapatite carved into a sphere. The first 15 implants were provided by Dr. Arthur Perry under a research protocol. The re maining 35 implants were placed after FDA approval and were obtained from Integrated Orbital Implants (San Diego, CA). Most of the implants measured 20 mm in diameter, although, in some cases, 18- or 22-mm spheres were used depending on orbital volume. Fig 2. An eviscerated donor scleral shell is opened with relaxing incisions, and a 20-mm hydroxyapatite sphere is placed inside.
Fig 3. The relaxing incisions are sutured with a running stitch of 5-0 Vicryl to form a baseball-like covering of sclera over the implant.
suiting in fibrosis of ocular muscles received a standard polymerized methylmethacrylate sphere. Of the 50 patients, enucleation was performed in 48 and evisceration in 2. The indications for surgery were intraocular malignancy in 26 patients, a blind painful eye
SURGICAL TECHNIQUE Before beginning the surgery, the implant was prepared. This preparation has been modified over the last 2 years to allow more rapid host tissue ingrowth, and our current recommended method is summarized here. The gas ster ilized hydroxyapatite sphere was soaked in a solution of gentamicin, 80 mg diluted in 10 ml of balanced salt so lution for 15 minutes before use. An eviscerated scleral shell preserved in I 00% alcohol was obtained from the local eye bank (Fig 1). Thirty minutes before use, the shell was reconstituted in several changes of saline, the last containing 80 mg of gentamicin. Two relaxing incisions were cut 180° apart from the corneal defect toward the optic nerve for a distance of approximately I em. The hydroxyapatite sphere was placed into the scleral shell (Fig 2). The edges ofthe relaxing incisions were imbricated and sutured with a running stitch of 5-0 Vicryl to form a baseball-like covering (Fig 3). The sphere remained bare only at the site of the corneal defect. With the optic nerve stump facing forward and cut flush with the outer scleral wall, four rectangular windows, each measuring 2 X 3 mm, were cut through the sclera with a scalpel and Wes cott scissors (Fig 4). These windows were placed 90° apart and approximately 12 to 15 mm from the optic nerve stump to approximate the positions of the rectus muscle 371
OPHTHALMOLOGY
•
MARCH 1991
Fig 5. A 1-mm diameter hole is drilled to the center of the sphere at each window and at the corneal defect.
insertions on an intact globe. Using a 1-mm diameter twist bit and an electric drill, five holes were cut to the core of the hydroxyapatite sphere, one in the center of each window, and one at the corneal defect (Fig 5). The prepared implant was placed in a solution of gentamicin until needed. Enucleation was performed by opening the conjunctiva for 360° around the corneal limbus. Anterior Tenon's capsule was separated from its attachments to sclera just behind the limbus and bluntly dissected from the globe in four quadrants between the rectus muscles using Ste vens scissors. Each of the four rectus muscles were isolated with a muscle hook, and a double-armed 6-0 Vicryl suture passed through its insertion and secured with a locking stitch at each side (Fig 6). The muscle was then cut from the globe. In cases of intraocular malignancy, care was taken not to put traction on the muscles so as not to elevate intraocular pressure. In these cases, the muscles were cut from the sclera without hooking and before plac ing the 6-0 Vicryl suture. Posterior Tenon's capsule was button-holed adjacent to the optic nerve with enucleation scissors, and the optic nerve was severed about 2 to 4 mm behind the sclera. As the globe was removed, the superior and inferior oblique muscles were cut from its surface. The orbit was packed with cottonoid pledgets soaked with 0.25% phenylephrine, and pressure was applied for 5 minutes. Using malleable retractors, the pledgets were re moved, and any remaining bleeding points, including the central retinal artery, were individually cauterized (Fig 7). The prepared hydroxyapatite implant was passed into the orbit using an introducer, with the optic nerve stump facing anterior. The scleral windows were aligned with the four rectus muscles, and each muscle was secured to the anterior lip ofthe window using the preplaced double armed vicryl suture (Fig 8). Tenon's capsule was closed with interrupted stitches of 5-0 Vicryl, and conjunctiva with a running suture of 6-0 plain catgut. A methylmeth acrylate conformer was placed in the fornices, and the socket was patched with a pressure dressing and head roll for 48 hours. In the two patients undergoing evisceration, the surgery was performed by making a full-thickness scleral incision 372
•
VOLUME 98
•
NUMBER 3
Fig 6. After opening conjunctiva, the four rectus muscles are tagged with double-armed 6-0 Vicryl sutures and cut from the globe.
Fig 7. The globe is removed and all bleeding is cauterized. Posterior Tenon's is opened to show the intraconal fat compartment.
Fig 8. The implant is placed into the orbit and the superior rectus muscle (arrow) is sutured to the anterior lip of the prepared scleral window.
1 mm behind the limbus for 360° around the cornea. Using an evisceration spoon, a surgical plane was estab lished around the ciliary body in the suprachoroidal space. At the posterior aspect of the globe the optic nerve was
DUTION
•
CORALLINE HYDROXYAPATITE
Fig 9. Technetium 99m MDP static bone scan of a patient 6 months after implantation of hydroxyapatite into the right orbit. The implant shows complete vascularization to its center.
Fig 10. After removal of a small circle of conjunctiva and Tenon's, a 3 mm cutting burr is used to drill a central hole for the motility peg.
Fig 11. The central motility hole is 10-mm deep and is aligned along a radius of the sphere.
cut with the sharp edge of the spoon. The uveal contents with the cornea attached were removed unruptured as a single piece. The vortex veins and central retinal vessels were cauterized directly, and the scleral shell was scrubbed
Fig 12. A temporary flat-headed methylmethacrylate peg is placed into the motility hole to allow wearing of the prosthesis until the latter is modified.
with 100% alcohol to remove all traces of adherent uveal tissue. Five full-thickness windows, each measuring 2 mm X 3 mm, were cut in the scleral shell to allow more rapid vascular ingrowth. Two relaxing incisions were cut 180° apart in the superotemporal and inferonasal quadrants. A 16- to 18-mm hydroxyapatite sphere with five 1-mm holes drilled to its center was placed into the shell. The sclera was imbricated over the surface of the implant and sutured with 5-0 Vicryl stitches. Tenon's capsule and conjunctiva were closed as separate layers in the usual fashion. In three patients, previously placed spherical implants were removed and replaced with hydroxyapatite. In one case, the extraocular muscles were identified after dissec tion in the walls of Tenon's capsule. These were isolated, and sutured to the implant as described above. In two patients, the muscles could not be clearly identified. In these patients, Tenon's capsule in the region ofthe fibrosed muscle insertions was sutured directly to the scleral cov ering of the implant. In all patients, a custom-fitted ocular prosthesis was placed 6 weeks after surgery. After 6 months, vascular ization and fibrous ingrowth of the implant was complete. In 18 cases this was confirmed by static and dynamic bone scan studies (Fig 9) after intravenous injection of 20 mCi of 99 mTc MDP. 13 At this time, a secondary drilling procedure was per(ormed in a minor room setting. With the patient fixating the normal eye in primary gaze, the center of the implant was marked on the conjunctiva with a surgical marking pen. Local anesthetic (0.1 ml) was in filtrated beneath conjunctiva at this point. A small 3-mm circle of conjunctiva and Tenon's was removed to expose the implant. Using a 3- to 4-mm cutting burr on an electric drill, a hole was drilled radially to a depth of 10 mm toward the center of the implant (Figs 10, 11 ). A methylmeth acrylate peg with an 8-mm long shaft measuring 2 to 3 mm in diameter, and a flat head measuring 5 mm in diameter was pushed into the hole (Fig 12), and the pros thesis was replaced into the socket. After 4 to 6 weeks, the hole was lined with conjunctiva. The flat-headed peg 373
OPHTHALMOLOGY
•
MARCH 1991
•
VOLUME 98
•
NUMBER 3
was replaced with one bearing a high rounded head. The ocular prosthesis was simultaneously modified with a co~ responding circular depression on its posterior surfac~ (Fig 13), placed so as to maintain alignment with the pupillary axis of the contralateral eye.
RESULTS Of the 50 patients treated, 21 have not yet been drilled to receive the central motility peg. However, at last follow up, motility of the orbital tissues and conjunctival fornices was judged to be nearly full in all positions of gaze. Of the 29 remaining patients, 7 elected not to have the sec ondary drilling procedure because motility of the ~nitial prosthesis was already considered excellent, even without final integration to the implant. In 22 patients, the second stage drilling was completed and the prosthesis ?Iodified. In all, prosthetic motility was subjectively supenor to that obtainable with plain spherical implants (Fig 14). The overall motility was so good in many patients that the edge ofthe prosthesis became visible in extreme horizontal gaze positions. There were no complications from the surgery. In fol low-up intervals of 2 to 27 months (mean, 10.4 months), there have been no extrusions, and no migrations of the implant. We have seen no unusual orbital inflammatory reactions. In the first 10 cases, we were using 22-mm hy droxyapatite spheres placed into Tenon's capsule. How ever, this left little room for adequate anterior chamber depth on the prosthesis, and insufficient room for prep aration of the hemispherical depression for reception of the final peg without obvious proptosis. The use of an 18 mm sphere placed into Tenon's capsule or a 20-mm sphere placed behind posterior Tenon's provided adequate orbital volume, with enough orbital depth to allow a deep anterior chamber and later modification for the peg. In two patients, granulation tissue growth occurred within the central hole, pushing out the motility peg. In both cases, this was treated with the C02 laser and topical steroids. In one patient, conjunctiva grew over the surface of the final round-headed peg but did not require treat ment. One patient complained of decreased motility after removing the prosthesis for cleaning. On examination, the peg was noted to be missing. This was replaced without difficulty with restoration of full motility. In two cases, drilling of the central hole for the temporary flat-headed peg was not radial but oblique. This resulted in the peg not seating flush, and some discomfort on replacing the prosthesis. However, with placement of final round headed peg and modification of the prosthesis, this prob lem disappeared.
DISCUSSION The first description of enucleation as a surgical tech nique was by Bartisch in 1583. 2 This barbaric operation was performed without anesthesia and consisted of gross 374
Fig 13. The posterior surface of the prosthesis is modified with a circular depression for integration with the final round-headed peg.
extirpation of the globe along with associated conjuncti_va, orbital fascia, and portions ofextraocular muscles, maki~g it impossible to successfully wear an ocular prosthesis. The modern technique evolved during the 19th century, following clarification of Tenon's capsule as an anatomic layer separating the globe from deeper orbital structures. The concept on anatomical grounds is generally attributed to O'Ferrall in Dublin and Bonnet in Paris, both published in 1841, 2 although the first actual surgery has been credited to Cleoburey as early as 1826. 1 Critchett introduced the term enucleation, and was apparently the first to use the operation on a routine basis at Moorfields Eye Hospital beginning in 1851. 2 Ocular implants to restore volume and improve pros thetic motility were introduced by Mules in 1884 following evisceration ofthe globe, 3 and in 1887 by Frost 14 following enucleation. These early implants consisted of a hollow glass sphere, which extruded in 55 to 93% of proce dures.3·14 With improved techniques of wound closure, Verrey 15 reported an extrusion rate of21.3% in 343 ca_ses receiving the Mules implant up to 1898. Over the ensumg decades, a wide variety of implant materials were used in an attempt to reduce the extrusion rate and improve the cosmetic results. These included gold, silver, vitallium, platinum, aluminum, cartilage, bone, fat, fascia lata, sponge, wool, rubber, silk, catgut, reat, agar, asbestos, cork, ivory, paraffin, and cellulose. Although n?ne of these proved very successful, the anatomic necessity for some type of implant became well established. 16 Ruedemann 17 introduced the first partially exposed in tegrated implant in 1941. Extraocular muscles were at tached for improved motility. Numerous variations were developed over the following decade. Muscles were at tached via tantalum mesh screens, Dacron strips, or spe cially designed grooves and tunnels, and the implant was integrated to the prosthesis through various arrangements of male-female type pegs and sockets and even magnets. Extrusion, migration, and infection rates remained ex cessive, however, and these types ofimplants were largely abandoned by the 1950s.
DUTTON
•
CORALLINE HYDROXYAPATITE
Fig 14. A patient 3 months after final modification of the prosthesis. Top /eji, primary position ofgaze. Top right. left lateral gaze. Center leji, right lateral gaze. Center right, upgaze. Bou om , downgaze.
The completely buried integrated implants were first used by Cutler in 1945, 4 and, like their exposed counter parts, were succeeded by numerous variations in design and materials. Motility was not as good as with the ex posed implants, but significantly better than with the clas sic Mules sphere. Extrusion and migration rates were less than with exposed implants.5 These buried implants relied on variations in shape of the anterior implant face adapted to matching surfaces on the back of the prosthesis for integration of movement through the intact conjunctiva. Despite the cosmetic advantages, most of the buried im
plants still resulted in unacceptable rates of conjunctival erosion and extrusion. To date, the simple spherical im plant has given the lowest complication rate, although it provides more limited motility. Coralline hydroxyapatite porous ceramic has been un der investigation as an alloplastic bone substitute since 1975. 19 Early experiments demonstrated that pore size and distribution was a major determinant of tissue-type ingrowth.20 The replamineform process2 1 has been adapted to the production of such porous hydroxyapatite ceramics. Using this technique, the aragonite (CaC03) 375
OPHTHALMOLOGY
•
MARCH 1991
skeletal structure of the common marine reef-building coral of the genus Porites is converted hydrothermally to calcium phosphate hydroxyapatite (Ca 10(P04 )6(0H)zf, with a regular system of interconnecting pores of approx imately 500 J,Lm diameter. 19·22 These resemble the haver sian system of normal lamellar bone. When implanted into human tissue, the hydroxyapatite acts as a passive latticework for fibrovascular ingrowth. In blocks measur ing 5 X 5 X 10 mm, Grenga22 showed complete vascu larization within 4 weeks of implantation. When placed subperiosteally, this material allows bony ingrowth with out inducing osteoclastic activity. 7 Hydroxyapatite has been shown to be completely biocompatible, nontoxic, and nonallergenic. 7 •19 It does not become encapsulated and is not associated with significant foreign body inflam matory reaction. 23 When used as a bone substitute, hy droxyapatite is resistant to mild to moderate compressive forces and shows no significant resorption after 48 months. 24 Although hydroxyapatite is highly resistant to infection, under conditions of experimental bacterial in fections, Reznick and Gilmore25 showed that this material did interfere with normal host tissue response and led to chronic mild inflammation that did not completely re solve. Hydroxyapatite implants have been used for maxillo facial onlay grafting, alveolar ridge augmentation, 24•26 cranial reconstruction over bare dura, 27 middle ear re construction,9 and laryngeal framework support. 10 Zide6 used dense, nonporous hydroxyapatite blocks to repair orbital floor fractures and to augment orbital volume. Block and Kent28 applied similar implants subperiosteally to elevate the globe for the correction of vertical ocular dystopia. The use of hydroxyapatite as an ocular implant after evisceration and enucleation was mentioned by Pratt, 29 but no details of the procedure were given. The idea of using porous hydroxyapatite as an ocular implant to improve motility was devised by Dr. Arthur Perry in San Diego. In clinical trials over the past several years, the technique has proven to be safe and effective, with no significant complications. In August 1989, the use ofthis material in the orbit was approved by the FDA, and since that time the author has used this implant in the majority of enucleation procedures. Over the past 2 years, we have modified the technique of preparation and implantation to allow more rapid vascular ingrowth. The ideal ocular implant should be completely buried, simple in construction without projecting or angulated surfaces that might erode through conjunctiva, light weight, and smaller than the globe to allow for a prosthesis of adequate anterior chamber depth. In addition, it should be centered within the muscle cone, and anchored to or bital tissues to minimize extrusion. It should have extra ocular muscles attached, and should be directly integrated in some way with the prosthesis for a 1: 1 transfer of mo tility. It should induce minimal tissue inflammation and should not resorb over time. Hydroxyapatite implanted as described above fulfills all of these criteria. Unlike early integrated implants, hy droxyapatite is completely buried beneath Tenon's capsule and conjunctiva. The central hole for the motility peg is
376
•
VOLUME 98
•
NUMBER 3
lined with conjunctival mucosa so that no portion of the implant is exposed. The implant itself is a simple sphere, without projecting mounds or sharp angles. The implant is positioned within the muscle cone with extraocular muscles attached to the scleral covering. With time, this donor sclera is largely replaced by host collagen, and the implant becomes infiltrated with fibrovascular tissue so that it resembles normal bone. Thus, anchored to orbital tissues, the implant is more resistant to migration and extrusion. Attachment ofthe extraocular muscles in their approximate anatomic positions allows nearly full motility of the implant. Integration of the implant and prosthesis through the motility peg allows translation of this move ment to the artificial eye. In several patients, excursion of the prosthesis was so extreme that the edge of the pros thesis was easily visible on lateral and medial gaze, de tracting from the overall cosmetic result. In these cases, the prosthesis can be made larger, but this may reduce motility. Wrapping the coral sphere in a scleral shell is necessary to allow attachment of extraocular muscles. Alternatively, fascia or banked dura should work equally well. Cutting small windows through the scleral shell and attaching the rectus muscles to their anterior lips aligns the muscle stump and associated ciliary arteries into the window and against the hydroxyapatite. Drilling 1-mm holes to the spherical center allows more rapid access of vasculature into the implant. Before our development of this tech nique, complete vascularization often required 6 to 10 months or longer. Since we began drilling access holes, all cases in which bone scans have been performed have been completely vascularized by 5 to 6 months. At the present time, we are investigating the time course for this process, which may require as little as 2 to 3 months. Complications have been minimal and easily managed. Drilling of the central motility hole as a secondary pro cedure is performed in a minor room setting under local anesthetic. Care must be taken to sink the hole perpen dicular to the surface and radial to the sphere. In two cases this hole was drilled oblique to the surface so that the temporary peg could not be seated properly. This re sults in some discomfort in attempting to wear the un modified prosthesis. A second hole can be drilled coin cident with the first, and fibrous tissue will fill in the poorly aligned and unused hole. However, once the final peg is placed and the prosthesis modified, the rounded head eliminates any problems caused by the skewed alignment of the peg shaft. Granulation tissue may form within the central motility hole, and in two cases was prolific enough to dislodge the peg. In one case, we excised the abnormal growth with fine scissors, but it recurred 2 weeks later. The C02 laser was used to vaporize this tissue successfully in this patient and also in another patient. The cause ofthis complication is unclear but may be related to a loose fit of the peg resulting in irritation of the conjunctiva growing into the hole. It is important to drill the motility hole only 1 mm larger in diameter than the peg shaft. Initially, we used pegs with a shaft measuring 2 mm in diameter. The pegs now supplied with the implants have a 3-mm shaft.
DUTION
•
CORALLINE HYDROXYAPATITE
We observed only one case of the motility peg being lost upon removal of the prosthesis. Again, this was clearly related to a hole that was too large for the peg diameter. In the future, a set of pegs with variable shaft sizes should be available to compensate for such situations. In one patient, conjunctiva grew over the surface ofthe final peg. This did not interfere with motility and no treatment was offered. In such situations, any conjunctival mucosa trapped in the motility hole might be expected to form an inclusion cyst, although this patient has had no further problems after 8 months. Hydroxyapatite has been used in three patients as a secondary implant after removal of a previously placed methylmethacrylate sphere. In two patients, the original spheres extruded, and in one patient, replacement was for improved motility. In all cases, motility was more limited due to some fibrosis of the extraocular muscles. However, the motility that was possible with these muscles was transferred to the prosthesis, and the overall effect was an improvement over the original sphere. Our current practice is to offer hydroxyapatite as a pri mary implant in all cases of enucleation or evisceration in which the extraocular muscles allow for adequate mo tility. The only contraindications are cases ofsevere orbital trauma with scarred muscles, cases where orbital malig nancy, such as retinoblastoma, may recur and the presence of a bone density implant might obscure radiologic im aging, and cases of orbital infection. The use of donor sclera, however well screened, presents some minimal risk, and we have had several patients refuse this implant be cause of the fear of HIV contamination. Alternative methods of attaching muscles directly to the hydroxy apatite, as for example with fibrin glue, or coating the sphere with an inert soft biocompatible shell, are being investigated. Coralline hydroxyapatite as an ocular implant appears to offer a significant improvement over all previously used materials. The cosmetic results equal those of the best integrated implants, but with fewer potential complica tions. The long-term benefits, as well as risks, however, remain to be determined. The use of hydroxyapatite sig nificantly raises the cost of enucleation. Even without a confirmatory bone scan, the costs of the implant, sclera, additional surgical time, secondary drilling procedure, and modification of the prosthesis can add $1500 to $2500 to the usual charges. Nevertheless, the benefits of this ma terial extend beyond its obvious cosmetic value. If long term studies confirm its lower migration and extrusion rate, and its relative resistance to infection, the medical advantages of hydroxyapatite will make the cost worth while.
REFERENCES 1. Luce CM. A short history of enucleation. lnt Ophthalmol Clin 1970; 10:681-7. 2. Snyder C. An operation designated "The Extirpation of the Eye." Arch Ophthalmol1965; 74:429-32.
3. Mules PH. Evisceration of the globe, with artificial vitreous. Trans Ophthalmol Soc UK 1885; 5:200-6. 4. Gougelmann HP. The evolution of the ocular motility implant. lnt Ophthalmol Clin 1976; 10:689-711. 5. Troutman RC. End results of implant surgery. Trans Am Acad Ophthalmol Otolaryng 1952; 56:30-4. 6. Zide MF. Late posttraumatic enophthalmos corrected by dense hy droxylapatite blocks. J Oral Maxillofac Surg 1986; 44:804-6. 7. Rosen HM, McFarland MM. The biological behavior of hydroxyapatite implanted into the maxillofacial skeleton. Plast Reconstr Surg 1990; 85:718-23. 8. Matukas VJ, Clinton JT, Langford KH, Aaronin PA. Hydroxylapatite: an adjunct to cranial bone grafting. J Neurosurg 1988; 69:514-7. 9. Grote JJ. Reconstruction of the middle ear with hydroxylapatite im plants: long-term results. Ann Otol Rhinal Laryngol 1990; 99 (no. 2, pt. 2, suppl144). 10. Hirano M, Yoshida T, Sakaguchi S. Hydroxylapatite for laryngotracheal framework reconstruction. Ann Otol Rhinal Laryngol 1989; 98:713 7. 11. Holmes RE, Wardrop RW, Wolford LM. Hydroxylapatite as a bone graft substitute in orthognathic surgery: histologic and histometric findings. J Oral Maxillofac Surg 1988; 46:661-71. 12. van Blitterswijk CA. Grote JJ. Biocompatibility of clinically applied hy droxylapatite ceramic. Ann Otol Rhinal Laryngol 1990; 99 (no. 2, pt. 2, suppl144). 13. Patka P, Hollander, WD, Otter GO, et al. Scintigraphic studies to eval uate stability of ceramics (hydroxyapatite) in bone replacement. J Nucl Med 1985; 26:263-71. 14. Frost WA. What is the best method of dealing with a lost eye? Br Med J 1887; 1:1153-4. 15. Wood CA, ed. The American Encyclopedia and Dictionary of Oph thalmology. vol. VI: Dioptric System to Exophthalmos, Chicago, Cleveland Press, 1915; 4418-56. 16. Culler AM. Basic principles of anatomy and physiology of the orbit and relation to implant surgery. Trans Am Acad Ophthalmol Otolaryngol 1952; 56:17-20. 17. Ruedemann AD. Plastic eye implant. Am J Ophthalmol1946; 29:947 52. 18. Cutler NL. A basket type implant for use after enucleation. Arch Ophthalmol1946; 35:71-83. 19. Piecuch JF. Extraskeletal implantation of a porous hydroxyapatite ce ramic. J Dent Res 1982; 61:1458-60. 20. Klawitter JJ. A Basic Investigation of Bone Growth into a Porous Ce ramic Material. [Thesis], Clemson, SC: Clemson University, 1970. 21. White EW, Weber JN, Roy, OM, et al. Replamineform porous bio materials for hard tissue implantation applications. J Biomed Mater Res 1975; 9:23-7. 22. Grenga TE, Zin JE, Bauer TW. The rate of vascularization of coralline hydroxyapatite. Plast Reconstr Surg 1989; 84:245-9. 23. Holmes RE. Bone regeneration within a coralline hydroxyapatite im plant. Plast Reconstr Surg 1979; 63:626-33. 24. Holmes RE, Hagler HK. Porous hydroxylapatite as a bone graft sub stitute in mandibular contour augmentation: a histometric study. J Oral Maxillofac Surg 1987; 45:421-9. 25. Reznick JB, Gilmore WC. Host response to infection of a subperiosteal hydroxylapatite implant. Oral Surg Oral Med Oral Pathol 1989; 67: 665-72. 26. Butts TE, Peterson LJ, Allen CM. Early soft tissue ingrowth into porous block hydroxyapatite. J Oral Maxillofac Surg 1989; 47:475-9. 27. Zide MF, Kent JN, Machado L. Hydroxylapatite cranioplasty directly over dura. J Oral Maxillofac Surg 1987; 45:481-6. 28. Block MS. Kent JN. Correction of vertical orbital dystopia with a hy droxylapatite orbital floor graft. J Oral Maxillofac Surg 1988; 46:420
5. 29. Pratt SG. Evisceration techniques. Adv Ophthal Plast Reconstr Surg 1988; 7:247-53.
377
