referring to the drawings , fig1 and 2 depict a preferred form of a shape retention tissue expander 100 which is composed of an outer envelope 101 having a generally hemispherical shape after complete inflation having a means for inflating and thus pressurizing the envelope . that inflation means is shown in the form of injection button 102 of conventional design having a self - sealing hollow dome 103 of , for example , biocompatible silicone elastomer mounted to a flat base 104 to permit inflation by addition of fluid such as isotonic saline solution into the interior region 200 of envelope 101 . a hypodermic needle is used to introduce fluid into the hollow region beneath dome 103 . it travels through the center 1005 of tube 105 which can be of a biocompatible silicone elastomer up to attachment point 106 by which tube 105 is sealed such as by means of a silicone adhesive to the surface of envelope 101 such that the center 1005 of tube 106 is in communication with the interior region 200 of envelope 101 . similarly , the second envelope 201 , which after inflation forms an annular resilient base surrounding the lower portion 112 of envelope 101 , also contains a separate injection button 107 having a hollow dome 108 attached to a flat base 109 such that fluid injected through dome 108 travels through the center of tube 110 up to attachment point 111 by which tube 110 passes through envelopes 101 and 201 and is in sealing communication with the interior region 202 of envelope 201 . one example of an injection button that can be used is found in u . s . pat . no . 4 , 190 , 040 to schulte ( issued feb . 26 , 1980 ). in alternative embodiments , one or both of the above remote inflation means could be mounted directly on the envelope and an injection button of the type described in u . s . pat . no . 4 , 428 , 364 to bartolo ( issued jan . 31 , 1984 ) could be used . interior region 202 of envelope 201 is shown as containing a fluid which is preferably an isotonic saline solution although other biocompatible fluids which will remain under pressure within each envelope , such as a silicone gel , could also be used . region 200 would also contain a fluid when inflated as shown in fig1 and 2 , but the fluid has been omitted from the figures for the purposes of clarity . envelopes 101 and 201 are preferably constructed of a biocompatible silicone elastomer such as one of the medical grade silicone elastomers commonly used in the manufacture of mammary implants or tissue expanders ( e . g ., those which are available from dow corning corporation , midland , mich . 48640 ), but could be manufactured of any other biocompatible elastomer material such as a polyurethane material . envelope 201 is employed to provide an annular resilient base for the lower portion 112 of the expander 100 , but need not have a circular cross - section as shown in fig2 . likewise , envelope 201 may be formed separate and apart from envelope 101 as shown in fig2 or may be integral with the lower portion 112 of envelope 101 . envelope 201 may also be affixed to the exterior rather than the interior of the lower portion 112 of envelope 101 . to insure that the lower portion of expander 100 remains opposite the tissue to be expanded so that the tapering upper portion of the hemispherical pocket is ultimately formed away from the body in the tissue being expanded , lower portion 112 can contain an external means such as fixation tabs 113 and 114 ( further containing corresponding opposing tabs -- not shown ) attached to the bottom of portion 112 for suturing or ingrowth to underlying tissue . similarly , the attachment means could take the form of a conventional polyester tissue ingrowth material or a backing situated across the bottom of lower portion 112 of expander 100 in place of fixation tabs . having described the tissue expander , the manner in which it can be used will now be described with reference to fig3 - 5 . in fig3 a sectional side view of deflated shape retention tissue expander 300 ( of the same type as that shown in fig1 and 2 ) having outer envelope 301 of biocompatible silicone elastomer and hollow interior region 302 has been implanted beneath the tissue 303 to be expanded ( e . g ., at the site where a female breast had been previously removed ) according to operative techniques familiar to those skilled in the art of implantation of tissue expanders . the lower portion of expander 300 containing inner envelope 304 of biocompatible silicone elastomer with hollow interior region 305 surrounds the lower portion of envelope 301 to form an annular base after inflation of envelope 304 is completed . fixation tabs 306 and 307 are sutured to underlying tissue 308 ( e . g ., fascia on the chest wall where expander 300 is being used in post mastectomy reconstructive surgery ). expander 300 contains an inflation button 309 having a self - sealing dome 310 and a flat base 311 which forms a hollow interior region 312 which is in sealing communication with interior region 302 of envelope 301 by means of the hollow center 313 of tube 314 . a metal needle stop 315 is fixed to base 311 to prevent a hypodermic needle from passing completely through button 309 . similarly , envelope 304 is inflated by means of injection button 316 having a self - sealing dome 317 and a flat base 318 which forms a hollow interior region 319 which is in sealing communication with interior region 305 of envelope 304 by means of the hollow center 321 of tube 320 . a metal needle stop 322 is fixed to base 319 to prevent a hypodermic needle from passing completely through button 316 . inflation buttons 309 and 316 are also implanted beneath tissue 303 at some distance from the expander 300 . tubes 314 and 320 may each contain check valves or disconnecting fittings along the tube of the type described in the radovan , et al . patent to enable one or both injection buttons to be removed if desired at some point after inflation of the expander 300 has begun . in practicing the method of this invention , syringe 400 is filled with isotonic saline and hypodermic needle 401 is passed through skin 303 and through dome 317 to accomplish the gradual inflation of envelope 304 with the saline solution over a period of several days to several weeks . during inflation , tissue 303 is stretched laterally in the direction of arrows 402 until the envelope 304 is pressurized to an adequate extent to form a resilient base which will resist forces by the surrounding tissue and any fibrous contractile tissue which may form around expander 300 . the same level of pressurization upon inflation as was described in my &# 39 ; 401 patent described above can be employed in this application to inflate the envelope forming the resilient base : at least about 5 grams per square centimeter . upon complete inflation , as shown in fig4 skin 303 has stretched laterally in the direction of arrows 402 and has also raised away from underlying tissue 308 to form a disk - shaped , generally flat pocket . upon complete inflation of envelope 304 , envelope 301 is inflated gradually over a period of several weeks in accordance with accepted tissue expansion techniques to avoid necrosis of the skin being expanded . as shown in fig5 syringe 400 is filled with isotonic saline solution to enter region 302 of envelope 301 until envelope 301 is fully inflated and develops a generally hemispherical pocket . upon full inflation , expander 300 is surgically removed and a conventional mammary prosthesis of a preselected size suited to match the size of the pocket developed is implanted in the pocket remaining upon removal of expander 303 to complete the method of the present invention . while the invention has been described with reference to post mastectomy reconstruction procedures , other modifications and variations of the expander and method of the present invention will become apparent to those skilled in the art upon an examination of the above specification and drawings . therefore , other variations of the present invention may be made which fall within the scope of the appended claims even though such variations were not specifically discussed above .
this invention relates to an implantable , inflatable dual chamber shape retention tissue expander having a resilient annular base and a generally hemispherical shape after inflation which is used to form a generally hemispherical pocket beneath the tissue to be expanded to , for example , provide an appropriately shaped pocket for the receipt of an implantable mammary prosthesis and to a method of using such a tissue expander .