Alloplastic Implants

Implantation of synthetic material into the nose must be done with considerable trepidation. Early postoperative or long-term failure is a risk of any implant placed into the nose. In general, synthetic material, if used in the nose, should be reserved for the relatively immobile dorsum and should be considered the last resort after autologous and homologous implants have been considered. Costantino28 described four concepts to be cognizant of when planning alloplastic implantation: porosity, particle formation, elemental makeup, and location.

Implant materials have pores of varying sizes and can range from less than 20 ^m to several hundred ^m. Pores permit tissue ingrowth; the larger the pore, the more aggressive the ingrowth. Pores also permit influx of bacteria, which is not necessarily problematic if the pores are sufficiently large enough to allow ingress of macrophages (50 ^m) as well.29 Sufficiently large pores, > 100 ^m, will theoretically allow for bony and fibrous ingrowth, which would further stabilize the grafted implant.28 Solid silicone rubber implants, for example, lack pores and are therefore impenetrable to bacterial invasion and tissue growth. Stabilization is therefore dependent on capsule formation, and infection can occur at any time. Deformation of overlying tissue can be an unfortunate sequelae of silicone rubber implants as a consequence of thick capsule formation.

Particle formation is primarily a concern for implants placed in areas of mobility. Relatively inert particulate materials of 20 to 60 ^m can be phagocytized, but ingestion leads to macrophage demise and subsequent release of several inflammatory factors responsible for chronic inflammation. Particles > 60 ^m in diameter cannot be phagocytized. Immune complex formation may also be a factor contributing to significant immune reaction in the area.28

The ideal implant does not exist. New biomaterials continue to be developed and investigated to meet the rigid criteria necessary to satisfy the needs of a surgeon using implants. An implant should be completely inert, incapable of inducing inflammation or allergy, noncarcinogenic, resistant to mechanical strain, easily modified for shaping, and sterilizable. The most favorable materials are those that most closely resemble the human tissue adjacent to the proposed implant site.28 Silicone, for example, is close to carbon, one of the main constituents in the body, on the periodic table. Consequently, silicone has been used extensively as an implant because of its relative nonreactivity.

Location of implant placement is critical to success. Regardless of biocompatibility, those areas of the body that are susceptible to movement are at higher risk of implant failure. In the nose, the tip should be considered a mobile unit, and therefore should not undergo alloplastic implantation. The dorsum of the nose and premaxilla are fairly stable areas and are sites that are more appropriate for augmentation with an alloplast. Success even on the dorsum, however, can be difficult to achieve if an adequate amount of skin and soft tissue is not covering the implant, offering sufficient blood supply to the area.

Alloplastic implants for the nose fall into several groups: polymers, metallics, ceramics, and injectables. Polymers comprise the largest group. All these materials discussed have been used with varying success in the nose. We believe, however, that alloplastic implants should be considered the third choice behind autologous or homologous grafts.

0 0

Post a comment