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expander. Expanders can be replaced with various permanent implants. Some surgeons report advantages to augmentation patients in the use of permanent gel-saline or saline expanders with the inflation ports left in place (Berrino et al., 1998a). Inflatable implants usually are saline filled, but rarely they contain gel with provision for changing size by the addition of saline to the gel-filled lumen. Expanders contain saline in a single lumen or sometimes an expandable saline lumen inside a gel lumen. Some expanders are directionally expandable through shell modification or pig-gyback-bonded separate expanders (Hester and Bostwick, 1990).

Historically, single-lumen, gel-filled implants (that include polyure-thane-coated implants) have been the most commonly used, approximating 60-80% of devices implanted (Middleton, 1997; Zones, 1992). However, since the 1992 FDA moratorium on gel-filled implants, single-lumen saline implants, that historically comprised 5% of implants (Gabriel et al., 1994; Zones, 1992), have almost completely replaced gel implants (see Chapter 1). Saline as the filler for implants was originally considered, but discarded by Cronin in the early 1960s, presumably because gel implants ''remained normally expanded even when torn" (Cronin and Gerow, 1963) and "it seemed unlikely that leakage could be avoided for life" (Cronin, 1983a). Saline-filled implants were reported in France in 1965 (Arion, 1965) and in the United States in 1969 (Tabari, 1969—initially filled with dextran 6%). Saline implants were made earlier (1965) in New York City according to some observers (R.A. Ersek, personal communication, June 10, 1998). Their lesser popularity has been ascribed to a number of factors. These include: high deflation rates (since corrected) and leaky valves (Capozzi, 1986; Lantieri et al., 1997; Peters, 1997); a weight said to be up to 8% heavier than a comparable-volume gel implant (Barney, 1974); a fluid wave ("slosh effect") with sounds that can be heard by the patient (Asplund, 1984); and thin consistency and wrinkling that is visible through the skin and/or palpable (Gylbert et al., 1990a; Melmed, 1998; Slavin and Goldwyn, 1995). These undesirable features are alleviated to a large extent by the more tissue-like consistency of gel and its lower tendency to shift with different patient positions. Placement of the saline implant deep to the muscles of the chest and slight overfilling also minimize some of these problems (Nicolle, 1996). They must also be balanced against the problems of gel, such as gel fluid diffusion through the shell into the tissues; axillary adenopathy secondary to silicone; release of gel on implant rupture, which can be removed only incompletely by surgery and includes the possibility of gel migration and granuloma formation; higher incidences of contracture; and greater radiopacity of gel.

Standard double-lumen implants have two shells either connected or patched together or floating freely one in the other. The inner lumen is gel filled and the outer saline filled. In the case of reverse double lumen