Industrial chemists working for the Corning Glass Company were the first to synthesize polymethylsiloxane and recognize its potential properties. In 1962, Corning introduced the first medical-grade injectable silicone (360 grade), which was intended for coating of medical devices. Although this represented a much purified form of the previous industrial silicones, it was not until 1965 that an injectable medical-grade silicone was available from Dow Corning, referred to as MDX4-4011. Because of the reported problems associated with silicone injection, in 1964, the Food and Drug Administration (FDA) classified silicone when injected as a “new drug.” To permit continued application, Corning filed for a “notice of claimed investigational exemption” so their 360 silicone medical-grade fluid could be used. Rees and Ashley1
injected over 1300 patients, but only 408 were followed-up on; they reported only one single complication. The continued reporting of complications and lack of quality clinical data led to the criminalization of the procedure in 1975 and suspension of the drug by the FDA in 1976. Undeterred, in 1977, Corning submitted an amended exemption and received FDA approval for a new study in 1979. This newer silicone was designated an “investigational device.” Conscious of the continued reported complications associated with liquid injectable silicone, the FDA requested interim clinical data in 1990; Corning had virtually no data. By 1992, the FDA investigational license had become invalid. What eclipsed the concerns surrounding the use of liquid injectable silicones was the issue of breast implants culminating in a $4-billion class action lawsuit against Corning. In 1992, because of the lack of data surrounding the use of liquid injectable silicone, the FDA banned its use outside of approved investigational studies.
The physical properties of silicone make it an ideal biomaterial.2,3
It is chemically inert, noncarcinogenic, capable of sterilization, not physically modified by soft tissue, noninflammatory, capable of resisting mechanical strains, and produces no state of allergy or hypersensitivity.4–6
Silicone-gel-filled breast implants became available in 1962 and were implanted in 1–2 million women. Thirty years later, anecdotal reports claimed that leakage from these implants could cause immune-related or connective tissue disorders such as systemic lupus erythematosus, scleroderma, rheumatoid arthritis, or polymyositis. Patient complaints included chronic fatigue, muscle pain, joint pain, and swollen lymph nodes. Though this received unprecedented public and medical attention, epidemiological studies in the United States concluded there was insufficient scientific evidence to correlate silicone breast implants with connective tissue disease. The U.K. Department of Health arranged for their own medical devices agency and an independent expert advisory group to assess the literature for those alleged disorders. A total of 270 papers were reviewed, and no scientific evidence was found linking silicone-gel-filled breast implants with any risk of connective tissue disease or evidence of systemic pro-inflammatory effects.7
Furthermore, there are substantial differences pertaining to potential risks between silicone breast implants and medical-grade liquid injectable silicone. Breast implants are contained within a capsule, with the potential for initiating tissue response itself. The large volume of liquid silicone contained within these units by comparison to the small volumes advised in the applications around liquid injectable silicone can be seen to promote greater safety potential.
From the late 1950s to the 1970s, thousands of women worldwide received unauthorized cosmetic silicone injections to enlarge breasts and contour various body parts. Between 750 and 2000 ml per patient was injected. These massive amounts of unknown, impure, or adulterated fluid silicone caused major infections, tissue necrosis, and, in some, the loss of breasts. In a few reported instances, intravascular injections were followed by death. This procedure, which was never approved and is now discredited, persists, as do the complications.
The first silicone fluid injection for treatment of complicated retinal detachment was approved in the United States in 1994. Injected silicone acts as a tamponade to hold the retina in place mechanically until natural attachment occurs. Vitreal-retinal surgeons rate the procedure as 60–75% successful and as the standard care for this problem that can cause blindness. The viscosity of silicone oil used in the eye is 5000 cSt, 15 times more viscous than the fluid injected for soft tissue defects. It requires a power injector, a 19-gauge needle, and special tubing and syringes to inject the 4.5–6.0 ml of silicone needed for this procedure.
Silicone also has a long history of use as facial soft tissue filler for treatment of wrinkles and facial atrophy.1,5
Liquid injectable silicone is considered by many to be a unique soft tissue augmenting agent that may be utilized effectively for the correction of specific cutaneous and subcutaneous atrophies. Orentreich and Leone6
found that liquid silicone is a safe and effective method for treating human-immunodeficiency-virus-associated facial lipoatrophy and compares favorably with other methods of tissue augmentation. Zappi and coworkers2
examined 35 skin biopsies by light microscopy. These biopsies were obtained from target areas where liquid silicone had been injected in 25 patients between 1 and 23 years prior for the correction of depressed scars on the face. The microscopic study revealed in 100% of the cases the continued presence, in significant amounts, of the silicone previously injected into the target areas, where it failed to elicit any significant adverse reaction. Although historical complications have occurred, resulting likely from the presence of adulterants and impurities,1,5
modern purified silicone products approved by the FDA for injection into the human body may be employed with minimal complications when strict protocol is followed.