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Liquid Injectable Silicone


Summary and Key Features

  • Two forms of highly purified injectable liquid silicone (Silikon-1000 and Adatosil-5000) are US Food and Drug Administration (FDA) approved for intraocular tamponade of retinal detachment.

  • Both products may be legally injected off-label for skin augmentation, according to the 1997 FDA Modernization Act.

  • Industrial liquid silicone, including “medical-grade” industrial liquid silicone, may contain contaminants that cause granulomatous reactions.

  • Industrial-grade liquid silicone should never be injected into the human body.

  • Three rules should always be followed when using liquid injectable silicone (LIS) for skin augmentation, as follows:

    • Rule 1: Inject only FDA-approved highly purified liquid silicone.

    • Rule 2: Use only the microdroplet technique.

    • Rule 3: Inject limited amounts of volume at monthly intervals or longer.

  • There is much evidence supporting the safety and efficacy of LIS for human immunodeficient virus-associated lipoatrophy. However, late-appearing granulomatous reactions are not infrequent (> 5%), may be managed with intralesional injections of 5-fluorouracil and triamcinolone, but tend to recur.

  • With proper protocol, serious adverse events are rare and are usually treatable.

  • Given the availability of newer longer-lasting volumizing hyaluronic acid fillers, they can be considered as an alternative for the management of HIV-associated facial lipoatrophy, although they are more expensive. Use of LIS can be considered in disease states where cost benefits outweigh the risk of adverse events.

  • Use of small-volume microdroplet LIS in the treatment of acne scarring may be less likely to lead to the development of delayed reactions with persistent lumps.

Introduction

Physicians and patients continue to strive for the “ideal filler,” which would offer consistent, sustained results that remain natural and free of complications over time and that would be biocompatible, safe, cost-effective, and versatile. When injected properly, highly purified liquid injectable silicone (HPLIS) meets the majority of these criteria. However, as with any permanent filler, late-appearing lumps, bumps, and granulomatous reactions may occur. Use of injectable silicone has historically been met with controversy. However, when modern HPLIS was properly injected in small amounts using the microdroplet technique with repeat treatments spaced at least a month apart, physicians have achieved optimal and enduring correction of scars, rhytides, and facial atrophy.

HPLIS may be much less forgiving than temporary fillers and is a potential liability when it is injected incorrectly, results in undesired augmentation, or serves as a nidus for inflammation and infection. Therefore, to achieve good outcomes, experience and precise technique are imperative. Physicians should use HPLIS only after extensive training in proper technique and patient selection. Candidates for treatment should have clear treatment objectives and understand that multiple treatment sessions may be required to achieve optimal correction and that late-appearing (months to many years) inflammatory and granulomatous reactions clinically appearing as nodules or firmness occur more frequently then with most hyaluronic acid fillers.

Patients who desire immediate correction or are uncertain of their treatment goals or are risk-adverse are better treated with temporary fillers rather than HPLIS.

Basic Science

Silicon (Si) is a relatively inert element that is essential to humans in small amounts and is second only to oxygen as the most abundant element of the Earth's crust. “Silicone” describes a group of synthetic polymers containing elemental silicon. Polymers in the silicone family may exist in solid, liquid, and gel states, with various chemical, physical, and thermal properties. Silicone polymers also vary with regard to purity, sterility, and biocompatibility. Although various silicone polymers are used for medical use, polydimethylsiloxane is the liquid injectable silicone (LIS) used for soft tissue augmentation. The molecular structure of this colorless, odorless, nonvolatile oil consists of repeating dimethylsiloxane units with terminal trimethylsiloxane ends.

The viscosity of a given liquid silicone product is dependent upon the mean number and chain length of the dimethylsiloxane subunits within the polymer, with longer chain molecules conferring a higher viscosity. Viscosity is measured in centistokes (cs), where 1 cs equals the viscosity of water. Current HPLIS is either 1000 cs (similar to the viscosity of honey) or 5000 cs.

Silicones have not been found to be carcinogenic and have demonstrated “an enviable record of safety,” according to a 1998 National Science Panel investigating silicone implants, reported by Diamond et al. HPLIS is not altered in vivo, although small amounts may be phagocytized and enter the reticuloendothelial system.

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