Chapter 14

Core Messages

■The advent of porous orbital implants has greatly advanced the field of anophthalmic surgery.

■Thedevelopmentof hydroxyapatite(HA)implants initiated a new generation of porous implants. Porous polyethylene and aluminum oxide are now commonly used alternatives.

■Orbital implants are available in spherical, mounded, egg, and conical shapes.

■Implant material selection is determined by several factors, including patient age and medical history, cost, availability, and surgeon preference.

■A variety of techniques may be utilized to determine the appropriate implant size.Adults undergoing enucleation surgery most frequently require a 20to 22-mm sphere, whereas 18to 20-mm spherical implants may be adequate for evisceration procedures.

■Patients younger than 5 years old typically receive a nonporous implant as this facilitates replacement with a larger porous implant later in childhood or adolescence. Older pediatric patients may do well with porous implants. Appropriate implant size

selection depends on the age and development of the patient.

■Surgeons who use porous polyethylene as their implant of choice commonly do not use an implant-wrapping material. Wrapping HA and aluminum oxide implants facilitates implant insertion and rectus muscle attachment to the implant.

■Several implant-wrapping materials are commercially available. Polyglactin 910 (Vicryl®) is simple to use, is readily available, and may permit earlier implant fibrovascularization than other available materials.

■Porous implants can be coupled to the overlying artificial eye with a titanium peg system. These coupling systems may allow for greater prosthesis motility. Implant peg use has declined due to the high incidence of postpegging complications (increased discharge, recurrent pyogenic granulomas, implant exposure around the peg, implant infection, tissue overgrowth, clicking).

14.1Introduction

The introduction of coralline HA orbital implants in the midto late 1980s following enucleation, evisceration, or as a secondary orbital implant introduced a new era of anophthalmic socket surgery. Over the past three decades, several other porous implant materials have been introduced as alternatives (e.g., synthetic HA, porous polyethylene, aluminum oxide). A variety of orbital implant

wraps have also entered the market over this same period. Implant wraps facilitate entry of the implant (decrease tissue drag), allow extraocular muscle attachment, and may provide a barrier function over the spiculated porous implant surface. There is some debate whether covering the anterior surface of the implant with an avascular material is helpful in preventing implant exposure, and some investigators have questioned whether an implant wrap is advantageous.

Direct coupling of porous implants to the overlying prosthetic eye has evolved from a simple polycarbonate peg to a titanium peg-and-sleeve system and more recently to a magnetic peg-and-sleeve system. The con-

14 cept of pegging, however, is controversial, as it is associated with an increased risk of complications. An assortment of implant designs have also been developed, and there has been increasing attention to socket volume restoration.

Minimizing orbital dissection to limit disruption of socket anatomy is another recognized factor one should consider during anophthalmic socket surgery. Successful anophthalmic surgery is achieved when the anophthalmic patient obtains a painless, noninflamed eye socket with adequate volume restoration and an artificial eye that looks and moves almost as naturally as a normal eye. Current controversies in implant selection, wrapping, and pegging are reviewed in this chapter.

14.2Porous Orbital Implants

In an e ort to design a biocompatible, integrated orbital implant, Perry (1985) introduced coralline (sea coral) HA spheres [100]. HA had been used for more than 10 years as a bone substitute in orthopedic surgery; however, the BioEye (Integrated Orbital Implants, San Diego, CA) did not receive US Food and Drug Administration (FDA) approval until 1989. The HA orbital implant represented a new generation of buried, integrated spheres with a regular system of interconnecting pores that allowed host fibrovascular ingrowth (Fig. 14.1a–c) [27, 100]. Implant fibrovascularization potentially reduced the risk of migration, extrusion, and infection [96]. The HA implant also allowed secure attachment of the extraocular muscles, which was felt to lead to improved implant motility and perhaps more rapid fibrovascular ingrowth [27, 100]. By drilling into the HA implant, inserting a peg–sleeve system, and coupling

the peg to the overlying prosthetic eye,an improved range of prosthetic movement as well as fine darting eye movements (commonly seen during close conversational speech) often resulted. This allowed a more lifelike quality to the artificial eye. In addition, it was postulated the peg may help support the weight of the prosthesis, which in turn would help decrease the risk of progressive lower lid laxity and malposition associated with long-term prosthesis wear.

Although HA implants represented a significant advance in anophthalmic surgery, experience with HA over the last two decades has expanded our understanding of the limitations of HA. Reported complications are not uncommon and include implant exposure, conjunctival thinning, socket discharge, pyogenic granuloma formation, implant infection, and persistent pain or discomfort [23, 33, 52, 74, 96, 98, 104, 108, 120]. Implant exposure problems continue to deter some surgeons from using HA implants, but this complication largely appears to be related more to surgical implantation and wound closure techniques (including implant wrap selection) and host factors than properties related to HA spherical implants [60, 96, 116, 120].

The introduction of HA as an orbital implant significantly raised the costs associated with enucleation, evisceration, and secondary orbital implant procedures. The Bio-Eye HA implant currently costs US $695, whereas more traditional silicone or polymethylmethacrylate (PMMA) spherical implants cost less than US $25. Additional expenses associated with HA placement may include an implant wrap material, assessment of implant vascularization with a confirmatory magnetic resonance (MR) imaging study, a secondary drilling procedure with peg–sleeve placement, and prosthesis modification. In the search for porous orbital implants with a reduced complication profile and diminished surgical and postoperative costs, numerous alternative implant materials have been introduced around the world.

Synthetic HA implants developed by FCI (Issy-Les- Moulineaux, Cedex, France) are currently in their third generation (FCI3). The FCI3 implant has an identical chemical composition to that of the Bio-Eye, although scanning electron microscopy (SEM) has revealed decreased pore uniformity and interconnectivity and the presence of blind pouches [87]. Central implant fibrovascularization in a rabbit model still appears to occur in a similar manner in both the Bio-Eye and FCI3 implants [63]. The synthetic FCI3 implant has gained in popularity in many parts of the world over the past 10 years; however, it is not yet available in the United States as a result of patent restrictions. The problems and complications associated with the synthetic FCI3 implant are similar to that of the Bio-Eye [49]. It is less expensive than the Bio-Eye (approximately US $450), which appears to be its only real advantage.

Other forms of HA implants in use around the world include the Chinese HA and the Brazilian HA [57, 64]. Although less expensive than the Bio-Eye, these implants have impurities or a poor porous structure that is problematic. Other implant designs continue to appear, some of which seem to o er few advantages [51], while others have only been in use for a short time, and their advantages or disadvantages are not yet apparent [78].

Synthetic porous polyethylene (MEDPOR®, Porex Surgical, Fairburn, GA, USA) implants (a porous type of plastic) were introduced over a decade ago for use in the orbit and have been widely accepted as an alternative to the Bio-Eye HA [4, 9, 71, 92, 105]. Porous polyethylene implants, although less biocompatible than HA, are typically well tolerated by orbital soft tissue [88]. They have a smoother surface than HA implants, which permits easier implantation and potentially less irritation of the overlying conjunctiva following placement (Fig. 14.2a, b). These implants have a high tensile strength yet are malleable, which allows sculpting of the anterior surface of the implant. They may be used with or without a wrapping material, and

a

b

Fig. 14.2 (a) The pores within a porous polyethylene implant are more like channels than pores. (b) Scanning electron microscopy illustrating the numerous channels within the porous polyethylene implant (222 × 101)

the extraocular muscles can be sutured directly onto the implant, although many surgeons find this challenging without predrilled holes. Porous polyethylene implants are available in spherical, egg, conical, and mounded shapes

14 (MEDPOR Quad implant) [4, 71, 86, 92, 105]. The anterior surface can also be manufactured with a smooth, nonporous surface to prevent abrasion of the overlying tissue (e.g., MEDPOR smooth surface tunnel implant, SST™) while retaining a larger pore size posteriorly to potentially facilitate fibrovascular ingrowth. Despite these numerous modifications,significant complications may still occur,including implant exposure and implant infection, potentially requiring explantation [2, 16, 92]. The traditional MEDPOR sphere implant costs approximately US $200 less than the Bio-Eye HA sphere. The newer-generation porous polyethylene implant designs are more expensive. The MEDPOR Quad implant is US $520, and the MEDPOR SST is US $650.

Aluminum oxide (Al2O3,alumina,Bioceramic implant) is a ceramic implant biomaterial that has been used in orthopedic surgery and dentistry for more than 30 years. Spherical and egg-shaped Bioceramic Orbital Implants (FCI Ophthalmics, marshfield Hills, MA, USA) were approved for use in the United States by the FDA in April 2000 and for use in Canada by Health and Welfare Canada in February 2001. Aluminum oxide is a porous, inert substance and has been suggested as a standard reference material in studies of implant biocompatibility [15, 18]. These implants permit host fibrovascular ingrowth similar to the Bio-Eye [18, 62]. Human fibroblasts and osteoblasts proliferate more rapidly on aluminum oxide than HA, suggesting it is a more biocompatible substance than HA [15, 16, 18]. The Bioceramic implant is lightweight, has a uniform pore structure, and has excellent pore interconnectivity (Fig. 14.3a, b) [87]. The microcrystalline structure is smoother than the rough-surfaced Bio-Eye (Fig. 14.3c).