Introduction:

Implants generally create unique environments in their immediate vicinity. This is because of the formation of collagen-rich structures termed ‘capsules’ or ‘capsule membranes’. Capsule formation is a natural phenomenon. It is an expression of the normal physiologic response to a foreign body. For correctly designed ‘clean’ implants in a sterile environment, this capsule is extremely thin. It forms early and does not thicken with time. The constituent collagen fibrils remain elastic and have no ability to cause severe compression of the implant through linear shrinkage. Capsules for faulty implants tend to be pathogenic. They are progressive. Their thickness increases and their permeability decreases with time, some vascularize, others undergo focal fibrosis and calcification. Later, they undergo partial resorption leaving lace-like structures unlike the starting membranous entities. Instances where they become dense tissue layers of several millimeters in thickness are commonplace.

Breast implant users generally fit in this category. Foam device coated users encounter the effects in their most extreme forms. After several years, foams implants create situations that have no parallel in prosthetic technology. Many subjects develop large, fluid-filled capsules with thick walls consisting of disorderly arrays of tissue and synthetic debris. Natural materials, sometimes denatured by the long dwell time in stagnant fluid environments, are intermingled with degraded foreign material and adulterated silicone oil globules.

Under these conditions, the tissue adjacent to foam-based implants is avascular, poorly irrigated and almost abiotic. It reflects ongoing tissue destruction processes driven by sustained effusion of effluents and bioactive substances released by the prosthetic system. Adventitious microorganisms found habitually in these sites accelerate the denaturation process. In principle, such an environment would not exist had the capsule not formed a closed environment around the implant, at least not during the first 4-7 years following insertion of the device. Such an environment is unlike other compartments of the body. Its composition is controlled by the deteriorating implants, its effluents and the presence or absence of viable micro-organisms within the capsule space.

The environment is not static. It behaves as a diffusion-controlled bioreactor where the various synthetic chemical entities, biological toxins and prosthetic impurities interact together to form secondary products most of which have potential for biological action. More disturbing, the presence of large amounts of oils within this environment, in combination with surface active agents such as degraded proteins, makes the area propitious for the formation of coacervates, agglomerates and other micellar entities which may acquire antigen-like properties (‘super antigens’). If suitable protein fragments are present, the superantigens may have potency for clinical impact.

Implants which form debris and reagent-rich environments such as foam-coated systems are well suited for these phenomena. Recent reports of T cell aberrations and lymphomas in long term implant users are particularly alarming. They support views which predicted risk of inducing atypia through improperly designed implant systems. Concurrent infections uncontrollable via conventional clinical management strategies are even more worrisome. Microbiological activity in such environments catabolizes and rearranges proteins into uncommon entities. The mixing of these modified proteins with adjuvants known to induce immune aberrations is even more disturbing. The collectivity of this information militates towards rigid avoidance of faulty implant systems which have no life-maintaining or functional purpose, in particular for devices known to degrade with time and which produce reactive debris and fine solid particles.

"Polyurethanes" are not a single uniform generic class of material; most are industrial products unsuited for clean applications. Their applications in medicine are limited to a few specially made products. They occupy the spectrum from ‘passable’ to extremely hazardous. Least of all, they are not equivalent or even comparable to one another. They constitute a broad range of substances with diverse and often unpredictable properties. Some have proven valuable in health care products, but even the best ones show poor prospects as long-term implants. Their performance has been disappointing and long term studies have revealed potentially severe and irresolvable limitations with obvious risk components.

The term "polyurethane" encompasses a large class of plastics, each endowed with unique properties. Close to 200 widely different polymers of that family have been commercialized. Only a few have been found suitable for medical applications. Although some are excellent for short term devices such as catheters and blood handling accessories, these materials are controversial as long-term implants. To further complicate matters, synthesis of the polymers and the conversion into finished devices are critical performance factors; minor changes in process conditions can lead to drastic variations in properties, in particular, their stability.

Unstable polyurethanes, unlike specifically designed biodegradable polymers such as those used for resorbable sutures, do not yield benign substances on degradation. Instead, generally deleterious products such as aromatic amines, amides, carbamates, glycols, acids, and substituted ureas, as well as embolizing microparticulates and surface active agents are formed. The rate of formation and the exact chemical nature of this debris is complex and depends on the structure of the polyurethane and its environment.

Polyurethane foam breast implant technology began in the fifties with W.J. Pangman's investigations on breast reconstruction with alloplastic materials that were expected to be permanent and stablein situ . Pangman used uncharacterized early commercial foams with predictably poor results. His teachings are summarized in patents which describe composite polyurethane foam breast prostheses, including the ‘Ashley’ Natural-Y breast prosthesis. This product was implanted in small numbers between 1970 and 1978 following claims of favorable results. Later papers in medical journals describe failures, complications, in vitro degradation, and spallation of debris suggestive of gross material-tissue incompatibility of the foam at the tissue-foam interface.

The commercial survival of the product into the late eighties is creditable to excellent salesmanship on the part of promoters and to testimonials by a small number of unsophisticated scientists and surgeons. The polyurethane cover of these implants, termed "Microthane" by promoters, was in fact Scotfoam™, one of the first polyurethane foams sold in North America for general consumer and industrial applications. Some surgeons had investigated it as a tissue augmentation material in the 1950s, but its use was soon condemned by the clinical community because of hardening, degradation, and poor cosmetic results.

The composition of Scotfoam™ was never made public. Court documents suggest that even the manufacturer of the prosthesis was unaware of its nature until 1988, almost 20 years after it was sold for the first time. Patents, corporate records and laboratory analyses confirm its identity as a cross-linked polyesterurethane of variable composition made from diol-terminated polyadipate oligomers extended with impure toluene diisocyantes containing small amounts of amines and amine-isocyanates.

The substance was prepared in large commercial quantities using a continuous foaming reaction process. The foam was sold as large blocks and was converted into articles and sheet by local plastic converters.

In summary, the nature and the origin of the product is such that no one fluent with medicine, pharmacology or biomaterials would have recommended its use or perhaps even expected to find it as part of a long term implant. The reason is that there are obvious, well documented risks from implanting industrial materials that degrades to form toxic reactive entities directly into a disease-prone areas such as the female breast.

General Background on Commercial Foam Breast Implants:

Foam prostheses using Scotfoam™ and related polyurethanes have been manufactured commercially in various forms since the late-fifties. All are particularly injurious for a multiplicity of reasons. The mechanisms of injury are significantly different from conventional smooth wall and homogeneous (silicone elastomer) textured surface ‘gel-in-shell’ prostheses without polyurethane foam coating. The primary differences arise from the presence of frangible reactive debris which degrades over long periods of time and which produce significant quantities of soluble, aggressive chemical entities.

Another difference has to do with the ability of such surfaces to become finely porous and occlude large amounts of biological liquids. This unusual structure allows tissue ingrowth and deep penetration of biological fluids even after partial dissolution of the polyurethane foam. Fine channels created by the original foam structure are left within the adhesive coating and remain for the duration of the implants’ dwell time. Such channels are blind pockets ideally suited for storing chemically reactive toxins as well as viable micro-organisms. Once colonized, these channels are nearly perfect protected environments for denaturation of endogenous proteins (biochemical reactions) and proliferation of viable entities ideally suited for this environment. Eventually, the interface between the implants and the surrounding capsule degenerate into a layer of largely immobile, poorly irrigated, composite of tissue with synthetics and related debris. Still other problems relate to their difficulty in production.

It is nearly impossible to ensure standardization of the items and guarantee cleanliness during fabrication and fastening the surface coatings to the gel-filled elastomer cores. These basic problems are superposed on other mechanisms of injury deriving from the poor engineering of these devices, their susceptibility to mechanical failure and the inevitable dispersion of their content throughout large parts of the breast and the proximal lymphatic system.

Problems surrounding such devices were encountered early. The precursor to the ‘modern’ gel core foam-coated prostheses were foam core implants sometimes constructed with shells and supplemental bonded surface layers made of polyurethane. They did not incorporate silicone gel-filled or saline-filled interior compartments at that time but later versions did. This added another dimension to their risk and, in some instances, potentiated the damage imparted by the degrading foam which contacted tissue.

Not all early devices used the same foam types for the core or for the coating. Some incorporated ether-urethane compositions, in particular a product known as "Etheron". This substance was a polyethylene glycol "prepolymer" coupled with various isocyanates, in particular isomers of toluene diisocyanates. Most items, however, used a commercial polyester urethane based on polyadipate ester segments coupled with mixed toluene diisocyanate-isomers. This foam was marketed as Scotfoam™. This material was produced in large quantities primarily for the upholstery, clothing, automotive and aircraft industries. For practical purposes, all such foam products presented a similar porous, partly biogdegradable interface between the device and the capsule.

Early implant fabrication techniques were amateurish and varied widely depending on the time of commercialization and the manufacturing plants involved. Interestingly, many were made by large medical product manufacturers using ‘custom’ production lines. Corporations such as Heyer Schulte, Polyplastic and American Heyer Schulte played a major role in the early promotion of the products. Commercially made items often varied from year-to-year or batch-to-batch. Some of the production technologies were early improvisations using manual processes and unskilled technicians.

Constituent materials were often commercial products intended for general industrial applications. Others were inappropriate and the assembly processes were transparently faulty. In most cases, they also incorporated mutually incompatible substances, in particular adhesives which degraded the foams. By the mid-sixties, the products were made in large numbers using semi-mechanized assembly line processes and significant quantities were being released into commerce. Advertisements contributed to widespread usage of some of these items. Major production levels were reached for at least three families of such products. Some were sold into the late-eighties and a few remain currently in commerce mainly through Latin American and European suppliers, some of which employ production equipment and staff which had been part of earlier U.S.-based enterprises.

The principal products are described below in their approximately chronological order. Paradoxically, systematic studies on these products never took place. In spite of morbidity anecdotally reported at conferences and in published articles, sales continued for nearly 25 years before medical concerns motivated discontinuation of this class of product in North America.

Early Monolithic Sponge "Block" Prostheses:

This prosthetic class included the earliest implanted foam items, typically, objects made of bulk foams such as Ivalon. This substance was a reaction product of polyvinyl alcohol and formaldehyde. It had been used for other medical applications in the fifties. It reappeared as pre-shaped breast prostheses sold commercially by at least one U.S.-based distributor. The product was derived from work at the Mayo Clinic in connection with cardiac repair materials. It was widely promoted and was the object of several early publications. Early morbidity surrounded its use and led to its discontinuation as a tissue reinforcing entity for vascular repair prior to the sixties. It is in a sub-category of its own. In a way, it led to the development of the polyurethane foam implants later used for breast augmentation.

The primary product of the time was termed ‘Etheron’. It used a prefabricated bulk foam technology. Large blocks were purchased from distributors and cut extemporaneously or molded into breast shape. This substance was chemically different from the Ivalon foam materials. It was based on an industrial foam used primarily by the automotive and aircraft industries. It was a common plastic foam product of the fifties with origins in World War II Germany.

The ‘Etheron’ prostheses were marketed under various names and significant numbers of these items were sold in the U.S., Europe and Canada. The material was also sold in bulk for intraoperative modification according to surgical needs. Some items were available as breast shapes. A typical product included the Robbins Etheron mammary implant. It appears that similar products based on Scotfoam™ (Scott Paper) were also marketed at various times or were used extemporaneously by some plastic surgeons in North America.

All of these products were primitive and had limited commercial appeal. They were difficult if not impossible to sterilize without gross chemical changes. Their clinical performance was extremely poor. Most early users encountered severe complications, adverse reactions, in particular infective sequelae, and surgeons eventually had to explant the items with significant peripheral tissue damage and deformity.

Implants from Assembled Foam Sponges:

These were surgical products distributed from the early-sixties. Some were sold as late as the early-seventies. They consisted of foam cores or combinations of foam and fluid-filled cores based largely on the technology outlined by W.J. Pangman and R. Franklyn, both surgeons from Los Angeles with early visibility in the emerging commerce of cosmetic breast augmentation. Their products are described in the literature of the time, in particular patents. Several types evolved into commercial versions. These were the Pangman-Wallace prostheses and the Polyplastic composite sponge implants, later manufactured by the Heyer Schulte Corporation. They were manufactured in several variations.

The most common version consisted of a foam core, usually Etheron or Estheron (Scotfoam™), coated with an overlay of room temperature vulcanizing silicone adhesive (RTV). This core was subsequently coated with a distinct and comparatively thin layer of polyesterurethane foam. The product was made in several sizes and was widely advertised. Ultimately, the technology became associated with the Heyer Schulte Corporation of Santa Barbara, California and the processes evolved into additional variants, some of which used gel-in-shell core configurations. All of these products used manual assembly processes and were impossible to manufacture without extremely elevated levels of chemical contaminants and microbiological burdens. Their multi-layered and enclosed configurations made sterilization particularly difficult and quality assurance largely irrelevant.

Foam-Coated Gel and Saline Core Implants:

The most widely encountered products of this kind are credited to the Heyer Schulte Corporation. Several versions were described in promotional brochures and appeared in plastic surgery journals. Most were marketed under the names of surgeons deemed to have ‘designed’ the items. They were later marketed under formal catalogue codes. Some were sold through commercial surgical supply distributors such as Weck Instruments (later purchased by Squibb), Codman & Shurtleff (associated with Johnson & Johnson) and V. Mueller which later became part of the Baxter group.

The items included products such as the ‘Tabari’ and ‘Capozzi’ foam-coated prostheses as well as the Ashley Natural-Y gel core mammary prostheses. These were widely distributed by surgical supply firms as well as by independent marketing agencies, such as Mark-M and Markham Medical. More complex composite variants such as the Jobe mammary implants, a combination inflatable saline core/bulk foam/foam coated implant and other variations of gel-filled devices such as the Pennisi-Capozzi implant series, were also made in production quantities.

The Ashley variant was the most widely used. It was made in several different versions, some of which consisted of a thin foam layer superposed on a thick shelled conventional gel core implant similar to the Dow Corning "Cronin Technique" style devices which were already heavily used. The foam layer measuring approximately 1-3 mm, was bonded to the core with conventional peracetic acid-catalyzed RTV silicone adhesive. Others were made by casting a semi-solid block of "thick gel" and dipping or "painting" this uncontained mass of gel with a thicker layer of RTV and then adding the supplemental layer of polyurethane foam as previously done for the earlier types of composite implants. The design of the cores for such prostheses evidently varied through the years and depended on the facility which manufactured the products. These items remained in production until the early-nineties.

Commercial, financial, product liability and administrative difficulties were encountered by the promoters from about 1976 and production was interrupted on several occasions, leading to changes in composition, design and production techniques. Eventually the classical Ashley designs with an internal support structure simulating the Ligament of Cooper (a trilobal septum made of sponge) were abandoned circa 1990 following unfavorable publications claiming injuries, disintegration of the product and adverse tissue reactions followed by mandatory explantation.

Foam Prostheses of the Eighties:

Paradoxically, the Ashley designs evolved into another series of devices based on the same technology but incorporating simplifications for faster, less costly production. The most widely used was a modified Ashley-style incorporating a somewhat differently formulated elastomer shell and a non-standard gel combination. It had the similar RTV bonded foam coating. It encountered clinical difficulty and adverse publicity almost from its beginning. It is credited to the Aesthetech and the Natural-Y Corporations, two interconnected firms believed to have been founded by H. Markham, a former employee of Weck Surgical and former staff members from Cox Uphoff Corporation and their associates.

This facility was established in the early-eighties in Paso Robles, California. It was located in an airport building. The original Ashley design was modified and simplified; this afforded significant cost reductions and made the assembly less dependent on skilled manual workers. The corporation released variations such as the Vogue and Meme implants.

Concurrently, another variation of the Meme appeared. It is associated with the earlier design and a patent credited to J. Cavon (termed the "Meme-Cavon" implant). This was a family of gel core implants mostly with round shapes intended for cosmetic augmentation. The gel containment shells were extremely thin, or in some cases non-existent. They used the same polyesterurethane coating technologies as before. The Cavon variants were designed to disintegrate and scatter the filling material throughout the breast tissue several months after implantation. This was claimed to enhance the cosmetic desirability of the product and greatly diminish the risk of capsule contracture.

The Meme ME:

The Meme implants were made in multiple forms. Early versions were thin wall products similar to the Vogue but assembled without a supporting internal structure such as found in the Ashley, the successor Optimam and the Vogue variants. Meme designs appear to have been motivated primarily by cost containment consideration and a wish to develop the cosmetic augmentation market. Very early models of this implant are rare and are believed to have been made according to processes similar to those used by the breast implant industry in general. Typically, a separate shell would be formed on a mandril, removed, patched and filled with gel precursors. This superficially conventional prosthesis would then be coated with polyurethane foam using RTV-based adhesives according to the earlier process. It shared the same problems of all other foam implants, including elevated risk of surviving micro-organisms deeply embedded within the surface structure and adhesive layers.

However, in the late-seventies, a patent aiming to produce implants without shells for the purpose of creating a "contracture-resistant" prosthesis appeared; Iit was credited to J. Cavon, a Newport Beach, California surgeon. This was not new. The concept had already been used on some variations of the Ashley. However, in this case, a new element was introduced. Accordingly, a device was to be made with a temporary, resorbable or frangible shell designed to break or disappear sometime after surgical implantation. Thus, the shell would somehow disintegrate to release the semi-liquid silicone gel core filling within a tissue capsule which was expected to form around the temporary shell. This process was tantamount to silicone oil-gel injections which were popular in the late-forties, fifties and sixties. Its primary appeal was that the procedure would be performed in a single surgical session. It was claimed to confer a lasting contracture-resistant cosmetic result to the subject.

This technology was credited to Joseph Cavon, a Los Angeles-based plastic surgeon. It appears that such devices were initially manufactured under contract by the Cox Uphoff Corporation. Later, staff from Cox Uphoff formed a competing corporation, the Aesthetech Surgical Specialties Corporation of Paso Robles, California. They produced such devices and later introduced subtle variations known formally as the Meme ME. These products although not formerly made of resorbable shell materials, still fulfilled the Cavon requirements and had the ability to rupture, disintegrate or "disappear" shortly after implantation.

Thus, the process used by Aesthetech which consisted of coating a pre-vulcanized (cured) uncontained gel core with solvent-diluted RTV yielded easily broken and frangible shells. Such implants have been habitually recovered with frank ruptures, partial disappearance of the shell and gross infiltration of the gel into the surrounding tissue.

The shell making and foam coating processes were essentially analogous to that used in early Ashley Natural-Y devices produced by predecessor plants. It amounted to casting a similar semi-solid shape of gel and subsequently coating this gel "lump" with a much thinner layer of RTV than the Ashley. In effect, it was more like a "paint layer". Because of the presence of solvent in this "RTV paint", the produced "shell" had a very large amount of diluent and for practical purposes, was porous in addition to being extremely weak. Furthermore, the solvent in the paint consisting generally of toluene or chloroethanes, rapidly absorbed into the gel core and much of it remained tenaciously bound despite strong heating.

The process required repeated handling and further enhanced the bioburden of the items. The oily and tacky surface afforded further protection for hardy micro-organisms encountered in the uncontrolled production environment. Sterilization deemed to have sufficient lethality to ensure medical suitability was so aggressive that in effect it destroyed the product. Therefore, virtually all such products which survived the sterilization process mechanically would have had a high probability of non-sterility.

The addition of a polyurethane foam coating and its adhesive initially contributed to reenforcing this weak structure so that it withstood the rigors of packaging and surgical handling. Upon implantation, the polyurethane foam would disintegrate within the tissue by design and the large mass of solvent and solvent impurities containing silicone gel was then released into the capsule pocket. This effect was evidently sought by the promoter. In retrospect, it appears that this rupture process, followed by disintegration and partial absorption of the silicone gel mass by the surrounding tissue, is what accounted for the apparently reduced incidence of contracture.

Outwardly these devices looked like gel-in-shell prostheses except that there was no shell patch and the tactile characteristics of the bare shells were widely different from the expected properties for these elastomers. Their life cycle in vivo was extremely brief with frequent intrasurgical ruptures and inevitable multi-site rupture-dissolution and disintegration taking place within the order of 2-3 years at best. In many cases, disintegration took place even earlier and left little more than fragments of shell to be recovered intermingled with tissue and a mass of partly-liquified gel. Later versions included and added a ‘cosmetic’ patch to make the items resemble conventional gel-in-shell prostheses.

On explantation, after several years in vivo, the patch of the late-ME implants was generally retrieved as a recognizable structure. The function of this patch and the reasons for its use appear related to litigation surrounding alleged infringement of the Cavon patent. Thus, the Meme ME appears to have been modified with a ‘glued’ patch to resemble conventionally assembled prostheses. This was later supplemented by marginally increasing the thickness of the ‘shell’ coating to create the illusion of a device assembled through a conventional patched shell with separate gel filling.

In the early-eighties, litigation ensued between the inventor of the process and the promoters who were using the ‘shell-free’ technology to manufacture the Memes. Ultimately this technology was abandoned and the Meme ME was discontinued amidst reports of adverse reactions, shell failures and problems with lasting health consequences.

The Meme ME was replaced by the Meme MP, a conventional gel-in-shell type device with an inordinately thin shell wall, filled conventionally through a perforation at the center of the patch. It may have been the intention to retain the frangibility of the shell for ‘control’ of contracture. Production of this variant lasted from about 1984 to 1989. Following regulatory difficulties at the Paso Robles, California plant manufacturing the Meme MP, the production line was terminated circa 1989 and a new production line was created at the Racine, Wisconsin facility. However, variations in design were introduced almost from the outset.

Explanted products originating from the Paso Robles Surgitek plant during the period 1984-89 are easily differentiated from the earlier and later foam-coated Meme variants. Their main identification features include the thin shell, the brittle gel and the fine fabric disc reinforcement of about 4-6 mm embedded within the gel fill hole located on center of the posterior shell patch. Many are ruptured and a large number spallate the adhesive which failed to bond to the shell surface because of vagaries in the foam coating process and the handling of the adhesives. This silicone elastomeric debris is in fine particles and further complicates the pathology of the surrounding tissue.

The items issuing from the Wisconsin plant were of substantially different design. The shell was a conventional gel-in-shell implant similar to the conventional Surgitek round, low profile mammary prostheses sold as Series 15000 or Series 13000. The identity of the shell was masked by the same foam coating used on prior products but the tactile characteristics of the device were markedly different from the Paso Robles products. Grossly visible and palpable differences were also present. The devices had no fabric reinforced gel fill hole (Dacron taffeta disk) at the patch center. Instead, the gel fill hole was on the rim of the patch as opposed to the center as it was normally found on the 15000 Series. Adhesive and foam coating used essentially the same process as before and the devices were also subject to elevated and erratic bioburden. Correspondingly, the outcome of conventional sterilization on such products would have been unpredictable.

Injury Mechanisms for Foam-Coated Implants:

Foam implants were widely used in the 1980-91 period; they became a significant part of the volume of commerce in breast augmentation products and drastically affected the sales of contemporary conventional products. However, the devices were not of consistent composition and quality. Several suppliers and numerous processes were used to manufacture the various prostheses which were sold during that period. In the latter years of production, the manufacturing site was also changed several times.

The manufacturer was reprimanded by the Food and Drug Administration in 1988-89 for deviant manufacturing practices including major shortcomings in the hygiene of the production line. In one instance, an FDA inspector notes production staff blowing into shells to verify the absence of perforations. Items manufactured after 1989 were significantly different in design and production methodology from earlier versions. Production records in the 1980-91 period are frequently sparse and credibility gaps are evident. There are therefore lingering uncertainties in composition, predictability and safety of products issuing from these production facilities.

Technical, ethical and clinical problems surround these implants and their marketing. The most obvious is that the foam coating itself was incompatible with long term medical implantation and was never intended for that purpose by its manufacturers. Its chemical constitution made it a likely candidate for the production of toxic substances and the manufacturing process failed to control the level of impurity of this material at time of release. Furthermore, the material deteriorated on the shelf because of large amounts of reactive by-products This led to a gradually increasing level of contamination with time, thus making the performance and characteristics of the product dependent on the delay between manufacturing and clinical use.

The most obvious feature of the product under clinical use was the rapid loss of adhesion and detachment of the foam from the adhesive coated core in-vivo. Once detached, the material broke up further leaving microscopic debris which remained in patients' tissues for a variable period of time during which cytotoxic metabolites appeared in breast milk, blood and urine. Fragments of adhesive remained as initiating centers for foreign body reactions and inflammatory activity which further complicated the prosthetic environment.

Interaction of Foam and Tissue:

The fate of the very fine foam fragments over the long term is still the object of kinetic studies. What is known is that the very fine debris is long-lasting. Depending on the dwell time of the prosthesis, residual foam and adhesive material can vary from a fractional percent to as much as 80 percent of the original mass of foam into proximal tissue. The amount of foam debris lodged into tissue diminishes with time.

Conversely, the fragmentation and dispersal of the silicone-based adhesive is a slower process but increases gradually with dwell time. The polyurethane resorption rate is strongly affected by the simultaneous presence of silicone oils and gel which act as protective coatings that delay exposure of the foam and retard degradation of the foam. The adhesive layer used to bond the foam to the shell is also vulnerable to biodegradation but by a different process. Its terminal condition consists of very fine fibrosis-inducing fragments which are readily carried away from the implant site and which elicit macrophage activity. In summary, the surgical retrieval of spallated debris from coatings of this kind is a long and uncertain task with attendant risks which increase, in particular with the use of Bovie and thermal cautery.

Electrosurgery Surrounding Foam Prostheses:

The use of electrosurgical procedures such as electro-dissection and electrocautery, two procedures believed essential for the safe removal of breast prostheses with mature capsules, lead to the formation of significant amounts of injurious substances. The pyrolysis of polyurethane debris and silicone-based material results in toxic, mutagenic and immunogenic substances such as amine-oxides, amines, carbamates, silica, as well as other combustion products suspected of adverse bioactive effects.

Foam Residuals:

Foam debris cannot be removed exhaustively without elaborate extracapsular capsulectomy procedures. Predictably, loss of tissue and contamination of the surgical site is more severe for these patients and adds to the risks of these implants. These factors contribute to the creation of an environment which is propitious for aberrant biochemical and biophysical processes. It also makes the sites well suited for tenacious infections. In combination with shell rupture and gel leakage and/or extravasation, these phenomena also pose major radiological interpretation difficulties.

Uniform clinical management protocols for patients with this history profile have not yet been developed. Patients with a history of infection are potentially even more complex. The ability of the prosthetic sites to harbor and protect colonies of atypical micro-organisms is another dimension in the complex impact of these devices. A priori, an environment supportive of encapsulated infection, is well suited for secondary phenomena. Studies on prevalence of T cell lymphoma and immunological aberrations suggest long term impact of protected infections, in particular with common nosocomial infective vectors (staphylococci).

Consequently, the foam implants present additional risks and costs arising from necessary human experimentation aimed at developing clinical management strategies for post-explantation complications. Marginal or unsuitable procedures used for treatment of symptoms or attempted removal of unwanted devices compound adverse effects from prostheses. Infective sequelae affect a significant number of patients and are particularly tenacious for users of foam technology implants.

Special Gel Compositions in Foam Implants:

Silicone gels used in plastic surgery products are proprietary formulae which can vary in composition from brand to brand and even within items of the same type. All are multi-component mixtures with potential for migration and adverse reaction. Their biocompatibility characteristics are much worse than that of "medical" silicone oils typically used to lubricate syringe barrels or "solid" silicone rubbers included in many other classes of medical implants.

The type of gel used in products associated with the Natural-Y technology differs grossly from many other contemporary types of prosthetic filling material. There is no satisfactory explanation for this observation. Possibilities include errors in formulation, contamination of the batches, incorrect vulcanization or possibly deviations from recorded formulae. Many items from these production series are noted to have gels that are "brittle" and decant spontaneously to very fluid oils and comparatively coherent "lumps". The toxicological implications of such deviations are not researched. Regrettably, the biocompatibility testing on gels was always conducted on ‘standard’ gel formulae.

The uptake of gel-derived components by tissues can contribute to fibrosis and affect the healing of the implant site. It can further harden the nidus of colonization by active microorganisms. Residues from damaged gel prostheses can disperse into mobile bioabsorbable entities if there is a long delay between rupture and removal. Hyperplasia, adhesions and/or periprosthetic contracture generally worsen in the presence of oil contamination originating from leaky prostheses. Burst prostheses left in-situ for long periods correlate with systemic adverse effects in many patients.

Prolonged use of leaky devices increases the risk of systemic diseases in proportion to the time that the devices are worn and the rate of ingress of foreign material into tissue. The presence of foam debris and adhesive fragments exacerbate these effects. They stimulate phagocytotic activity in the area. All of these factors appear to be at their optimum for adverse reactions from foam prostheses. This may explain the rapid deterioration of some patients who have a history of multiple implants and where the last implant is a foam device.

Use of "Outdated" Foam Implants- A Special Chemical Risk:

Foam develops large quantities of degraded residuals upon standing. This adds to substances already present as a result of the manufacturing process. Acids from the foam adhesive attacks the foam and creates water-soluble derivatives. Foam is thermally and photochemically reactive; this creates other families of contaminants with concentrations that rise with handling and storage. 

Foam implants effuse oil from the gel core during the storage period. The foam progressively absorbs oil, reaching levels sometimes in excess of 30% of the foam’s dry weight. During the post-implantation period the foam dissolves quickly leaving behind an inflammatory, finely dispersed adulterated silicone oil in the immature capsule. The use of a foam implant about 3 years after its release from production amounts to injecting a bolus of impure silicone oil of about 2-3 gm.

Contamination of the space between the capsules and the implants by viable micro-organisms compounds the problems of implant compatibility. For foam implants with deep microscopic channels with ongoing resorption of polyurethane spicules, the process is even more hazardous and virtually impossible to control with antibiotics. For most implants with protected intracapsular colonization, severe contracture usually takes place and unaesthetic displacement of the devices may follow. Such infections can be credited mostly to common micro-organisms from the skin which frequently enter and populate the intracapsular space; some of these organisms are occasionally revealed in post-surgical workup when patients infect grossly and require additional surgical interventions.

More serious situations develop when the colonization is from more aggressive nosocomial entities such as staphylococcus aureus. If the population of micro-organisms is large enough, significant amounts of toxins may be produced from the natural metabolism of the organisms. The capsule further reduces mobility and fluid exchange thus making clearance of the site a very slow process. Accumulation of deleterious microbiological metabolites is therefore inevitable as the implants age within their capsule.

In most cases, low activity, atypical organisms are involved. Cultures and diagnostic stain studies are not sufficiently detailed and prolonged to confirm the presence of unfamiliar, slow-growing micro-organisms. Such contamination is often introduced during surgery and would otherwise be adequately controlled by intra and post-operative antibiotics but a closed semipermeable capsule and the nature of the prostheses with their hydrophobic surface contaminants (silicone oils) ensures long term survival by protecting the colonies and in some cases, allowing the organisms to lodge within surface porosity, in particular for foam covered products. This problem is particularly notable for textured surface devices and devices incorporating "flaws" either by design such as complex leaf valves in multi-lumen prostheses or assembly defects leaving spaces between parts.

Capsule formation protects viable entities from natural body defenses and post-surgical antibiotics. This leads to progressive fibrosis over a brief period of time. Focal colonization of capsules can produce even more spectacular contracture anomalies. In some cases, gross malformation and irregularities that are outwardly obvious result. Secondary fibrosis of capsules with formation of contractile ‘bands’ as a result of low grade chronic intracapsular infection is well documented in plastic surgery literature. Typical reports include "The Fate of Breast Implants with Infections Around Them"; E.H. Courtiss, R.M. Goldwyn and G.W. Anastasi, Plastic Reconstructive Surgery, 63 (6) 812-816, 1979; "Acceleration of Capsule Formation around Silicone Implants by Infection in a Guinea Pig Model"; N. Kossovsky, J.P. Heggers, R.W. Parsons, M.C. Robson, Plastic Reconstructive Surgery, 73 (1) 91-97, 1984).

The micro-organisms receive additional nutrients from leakage of blood and plasma into the intracapsular space. Closed compression capsulotomies, or frequently prescribed "implant movement exercises", often lead to rupture of small blood vessels and intracapsular bleeding. This may occur early, in particular if the patient complies with recommendations from plastic surgeons for preventing "contracture". Additional complications result from major blood infiltration leading to outwardly visible or palpable hematomas and seromas contiguous to the prosthetic space.

Such events are common. In severe cases, they can be life threatening; it may become necessary to have the devices removed, the area debrided, disinfected and the hematomas evacuated. Infected hematomas/seromas are often discovered by surgeons who describe "malodorous and serosanguinous exudates" surrounding grossly infected prostheses. The role of capsules in stabilizing and protecting such infections is predictable although not well researched.

Textured surface implants appear significantly more prone to these problems; their capsules are more porous and generally thicker. They would therefore be expected to be a superior environment for proliferation of colonies and would allow significant populations of micro-organisms with a major output of metabolic toxins. They would constitute nearly ideal sites for clustered seromas and hematomas with secondary colonization.

In addition, these environments become more propitious for reactions of this kind with added prosthetic contaminants such as oils and plastic debris. The warm, nutrient-rich media already ideal for bacterial and fungal cultures are even better suited for protein denaturation and microbiologically-driven bioreactor activity. The presence of coacervating agents and surface active entities allows the reassembly of small, normally inert molecular debris to larger micelles with potential for sensitization of the host.

Such phenomena should be cause for concern. Mixtures of this kind have potential to create entities that function as ‘super antigens’, in particular with prosthetic oils. The silicone/oil impurities in the intracapsular mixture, the denatured tissue and plasma proteins, supplemented by microbiological proteins, become a nearly optimized sensitizing agent. It contains the silicone analog of Freund Complete Adjuvant (FCA) in addition to immunologically altered autogenous tissue and microbiological waste.

Mixtures involving FCA analogs and degraded proteinaceous matter from the host are expected to stimulate formation of antibodies directed against the micelles consisting of fragments of altered autogenous tissue.

The key role of microbiological debris in such mixtures was recognized by early workers in immunochemistry and there is current evidence validating the early data in the context of chronically infected, silicone-oil contaminated prosthetic sites. It may explain the prevalence of atypical autoimmune diseases in patients bearing prostheses with large amounts of oily or particulate debris. Phenomena of this kind also provide possible explanations for the occurrence of T cell lymphomas in sensitive patients.