Silicone elastomer cerebrospinal fluid shunt systems. Council on Scientific Affairs, American Medical Association

A 1995 resolution of the American Medical Association House of Delegates, introduced by the American Academy of Neurology, the American Association of Neurological Surgeons, and the Congress of Neurological Surgeons, asked the American Medical Association Council on Scientific Affairs to add the use of hardened silicone shunts to its study of the effects of silicone gel used in breast implants. On consideration of the important differences between the two materials, silicone elastomer ("hardened silicone") and silicone gel, the Council on Scientific Affairs elected to address the subject of silicone elastomer shunt systems separately. This report describes the different types of medical-grade silicone used in medical devices, the incidence of hydrocephalus and its causes and treatment, and the use of cerebrospinal fluid shunt systems made of silicone elastomer. Published case reports of possible immunological disease in patients who have had silicone elastomer cerebrospinal fluid shunt systems implanted are reviewed. The Council on Scientific Affairs concluded that the evidence presented does not support the occurrence of immune-mediated systemic reactions to implanted silicone elastomer cerebrospinal fluid shunt systems. The local granulomatous or inflammatory responses observed in some patients with silicone shunt systems have not been shown to be immunologically mediated; similar reactions have been described with other implanted foreign bodies.     

Effect of acid concentration on chromogen formation from hexoses in sulfuric acid-based reactions

Dynamic mechanical properties of Silastic HP-100 finger joint implants were studied. Sixteen sections of unimplanted and 14 sections of retrieved implants were analyzed with standard thermal analysis techniques. Results show that implantation does not alter the viscoelastic properties of Silastic HP-100 elastomers. The authors conclude that fracture of Silastic HP-100 implants cannot be attributed to changes in rheologic properties of the implanted elastomer.     

Biocompatibility of fixation materials in the brain

Recent clinical reports documenting passive intracranial translocation of microplates and microscrews have prompted concerns regarding brain biocompatibility and neurotoxicity of fixation hardware used in craniofacial surgery. Although the effects of commercially pure titanium. Vitallium (cobalt-chromium-molybdenum), stainless steel, and various alloys have been well assessed in bone and soft tissues, there are no comprehensive studies of these materials in the brain. To investigate this, the biocompatibility of titanium, vitallium, and 316L stainless steel was evaluated in the rabbit brain and compared with silicone elastomer shunt tubing, a material that is used commonly as a neurosurgical implant material with well-established brain biocompatibility. Forty-eight juvenile New Zealand White rabbits were randomly assigned to one of three groups and underwent placement of either commercially pure titanium microscrews, vitallium microscrews, or 316L monofilament stainless steel wire into the parietal region. Silicone elastomer strips of similar size were implanted in the contralateral hemisphere of each rabbit. Animals were assessed daily for signs of neurotoxicity. Rabbits in each group were sacrificed at 2, 4, 8, and 26 weeks following implantation. Brains were sectioned at the implantation site and were examined by means of standard hematoxylin and eosin stains and with immunohistochemical markers sensitive to inflammatory changes in the brain. None of the animals showed any behavioral changes or neurologic deficits suggestive of either systemic or localized toxicity from the implant materials. Silicone clastomer was found to cause the least amount of inflammation relative to other materials tested at all sacrifice points, suggesting that as a standard neurosurgical implant material, it is an appropriate control for studies of brain biocompatibility. At 2 weeks, titanium was found to cause the largest inflammatory response in surrounding brain parenchyma based on analysis of markers for microglial proliferation, gliosis, and leukocyte infiltration. At the 26-week endpoint of our study, the biocompatibility of titanium was nearly equal to the biocompatibility of vitallium based on all studied markers of inflammation. A progressive increase in the inflammatory response surrounding stainless steel implants was noted at 8 and 26 weeks. Relative to all materials studied, at 26 weeks the greatest leukocyte response was found with stainless steel implants. Our results indicate that at the 26-week end-point of our study, titanium and vitallium incited a similar inflammatory response in the rabbit brain that was greater than the response found with silicone elastomer, a standard neurosurgical implant material, but less than that found with stainless steel wire, which is commonly recommended as an alternative fixation material.     

The non-specific binding of immunoglobulins to silicone implant materials: the lack of a detectable silicone specific antibody

Recent studies have suggested that anti-silicone antibodies develop in patients implanted with silicone materials. The majority of these studies have utilized enzyme-linked immunosorbent assay (ELISA) methodology with a silicone material substrate as a means to detect the presence of the anti-silicone antibody. The current studies were undertaken to determine whether the binding of IgG to a silicone substrate was consistent with an antigen-specific antibody interaction or the result of non-specific hydrophobic interactions. While significant differences were detected in serum from silicone antibody "positive" and "negative" patients when the ELISA was conducted using a phosphate buffered saline (PBS)-0.05% Tween 20 (Tween) blocking system, the difference in the responses was attenuated when protein blocking systems were used or when incubation times were decreased. Furthermore, ELISA studies, using purified mouse and human IgG, demonstrated a concentration-dependent binding of IgG to silicone elastomer substrate which was also attenuated when a protein blocking system was used in lieu of Tween. In controlled animals studies in which female B6C3F1 mice were implanted with silicone gel or silicone elastomer for 180 days, no difference was observed between the implanted animals and the PBS control animals with respect to binding of IgG to the silicone substrate. Similar studies in female Fischer 344 rats implanted with silicone gel for 84 days also failed to demonstrate the presence of anti-silicone antibody. Collectively, the results suggest that the binding of IgG to silicone implant materials is non-specific in nature, consistent with the well-recognized interactions between hydrophobic molecules (IgGs) and hydrophobic surfaces (silicones) in an aqueous-based system.     

Observation on women with breast implants

The controversy over silicone breast implants continues. This review considers evidence on both sides of the issue. Clinical observations suggests consistent chronic fatigue, muscle pain, joint pain, lymphadenopathy, peripheral neuritis and bladder dysfunction syndrome. Epidemiologic studies of defined connective tissue diseases do not show an association, but some studies show a statistical increase in prevalence of symptoms. The author believes symptomatic women should consider having the breast implants removed and not replaced.     

Silicone breast implants: an oncologic perspective

In 1992, the FDA decided that silicone gel-filled breast implants would be available only through controlled clinical studies, despite the fact that they had been used for mammoplasty in millions of women around the world for more than 30 years. The safety of silicone breast implants had been called into question after several reports of a possible association between the implants and the subsequent development of connective tissue diseases. Such reports led to general public concern fueled by popular media attention and multiple class-action lawsuits against the product's manufacturers. It was in this climate that the FDA was forced to make its decision. This article reviews current scientific evidence on the safety of silicone gel-filled breast implants. Issues pertinent to oncology are highlighted. These include the possible carcinogenic effect of silicone gel, the safety of irradiating breasts with silicone implants, and the ability to mammographically image the implanted breast.     

Silicon analysis of breast and capsular tissue from patients with saline or silicone gel breast implants: II. Correlation with connective-tissue disease

The silicone breast implant controversy rages on. Recent work has demonstrated that normal or baseline breast tissue silicon levels in women who had had no prior exposure to any type of breast implant may be as high as 446 microg/gm of tissue. These data ranged from 4 to 446 microg/gm of tissue, with a median of 27.0 microg/gm of tissue. In addition, numerous other epidemiologic and rheumatologic studies have demonstrated no association between silicone breast implants and any connective-tissue diseases. Despite these reports, the use of silicone implants remains restricted. The present study measured breast and capsular tissue silicon levels from 23 breasts in 14 patients with saline implants, and from 42 breasts in 29 patients with silicone implants. No patient in the saline implant group presented with signs or symptoms of connective-tissue disease. Patients with silicone implants, however, were divided into three groups based on the presence or absence of signs or symptoms of connective-tissue disease: group I, no symptoms or signs; group II, + symptoms, no signs; and group III, + symptoms, + signs. Six patients in group III were diagnosed with a specific connective-tissue disease, including systemic lupus erythematosus, rheumatoid arthritis, or scleroderma. The most common indications for implant removal or exchange were capsular contracture and implant rupture, although 41 percent of patients with silicone implants expressed media-related concern over the implant issue. The most common symptoms described by patients in groups II and III were joint pain and stiffness, arm pain and numbness, and fatigue. In all groups, capsular tissue silicon levels were significantly greater than breast tissue levels. This finding may indicate that the capsule serves as a barrier to the distribution of silicone from the implant into adjacent breast tissue. Although breast tissue silicon levels in patients with silicone implants were not significantly greater than those in patients with saline implants (p = 0.48), capsular tissue levels in patients with silicone implants were, indeed, significantly greater than those in patients with saline implants (p < 0.001). However, no statistically significant differences in tissue silicon levels were observed with relation to the presence or absence of connective-tissue disease signs or symptoms in patients with silicone implants (groups I to III). Therefore, these data strengthen the conclusion that there is no association between tissue silicon levels and connective-tissue disease.     

Safety of silver oxide-impregnated silastic tympanostomy tubes

Otorrhea occurs after the insertion of tympanostomy tubes in as many as 50% of ears. Although topical antibiotic solutions minimize otorrhea in the immediate postoperative period, recurrent otorrhea is sometimes a clinical problem. The antimicrobial effects of silver oxide when impregnated into a tympanostomy tube may decrease the incidence of recurrent otorrhea. This study demonstrates that silver oxide-impregnated silicone elastomer is well tolerated within the middle ear of gerbils when implanted for 1 year, and the tissue reaction is no more than silicon elastomer without silver oxide. When applied directly to the round window of guinea pigs, there was no evidence of ototoxicity of silver oxide as measured by electrocochleography (N-1 thresholds) and cytocochleography (hair cell counts). These animal studies indicate that silver oxide-impregnated silicone elastomeric tympanostomy tubes may be used safely in clinical trials to determine efficacy.     

Breast prostheses and their complications

In the past few years silicone breast implants have been a highly charged and controversial topic for psychologic, health and politico-legal reasons for patients and for surgical, medical and research concern for professionals. Both sides are interested in knowing about the complications encountered with these implants on one hand and to find the ideal device needed for mammary reconstruction on the other. Indeed silicone does not fulfill the characteristics initially expected for a synthetic soft-tissue substitute. The local cellular response leads to the formation of a capsule around the implant with frequently unsatisfying cosmetic results. The well described leakage occurring through the silicone envelope allows the silicone gel to diffuse to multiple anatomic areas in the body. Scientific works demonstrated that silicone gel acts as a potent immunologic adjuvant and can induce antibodies to silicone surface-associated antigens. Breast implanted women who present with systemic clinical symptoms can be included either in the group of well defined connective tissue diseases or in the atypical connective tissue disease-like syndrome. The largest epidemiologic studies have shown reassuring evidence against large hazards but have documented a low but statistically significant risk of connective-tissue diseases in women with silicone gel filled implants. Practitioners must manage these patients with the awareness that reliable objective tests to identify the useful problem are not yet available.     

A guide to safe corporotomy incisions in the presence of underlying inflatable penile cylinders: results of in vitro and in vivo studies

PURPOSE: Because iatrogenic injury to an underlying inflatable implant may be induced by electrocautery incision of the tunica during tunical release or cylinder reexploration, safe electrocautery guidelines are needed. MATERIALS AND METHODS: For the in vitro model silicone and polyurethane elastomer lined inflatable penile prosthetic cylinders were used, and cutting and coagulation electrocautery was applied directly on the device, on a tissue-implant interface, and at minimal, partial or full inflation with saline. For the in vivo study 10 patients with underlying inflatable prosthetic cylinders underwent tunical releases for treatment of secondary penile curvature (7) and reexploration for a malpositioned device (3) with a minimum 1 year of followup. RESULTS: In the in vitro study electrocautery injuries either did not occur when applied directly to silicone and polyurethane elastomer lined devices, occurred in both devices in the presence of a tissue-implant interface, occurred in polyurethane elastomer lined devices at a far less thermal energy setting than with silicone, occurred in both implants at lower wattages with increasing saline inflation or did not occur in 100% of polyurethane elastomer lined devices when coagulation electrocautery was less than 65 watts. In the in vivo study, by adhering to the aforementioned principles and using novel surgical techniques, no device malfunctions were created intraoperatively or observed within a mean followup of 22 months. CONCLUSIONS: Electrocautery can be used safely to create a tunical incision with any underlying inflatable cylinder. To avoid electrocautery injury, based on the clinical study results in polyurethane elastomer lined devices, one should deflate the cylinder before electrocautery, use coagulation current at 35 watts, apply the electrocautery only to the outer longitudinal tunical layer, bluntly dissect through the inner circular layer, and elevate the tunica, protect the device and incise the tissue under direct vision.     

A biomechanical study of flexible penile implants

The prostheses used are silicone elastomer flexible penile implants. They are not hard, but flexible and capable of being elongated without traction. These implants have the advantage of resisting axial pressure which facilitates intromission, even in the absence of erection. Their flexibility also allows the penis to hang when the patient is standing. For the penis to hang normally, it must be sufficiently long (hence the value of cavernopubic release) and the intracavernous cavity must be longer than the prosthesis. The prosthesis does not alter the cavernous artery, but markedly flattens the venous plexus (lakes and efferent veins).     

Comparison between lung and liver lipid peroxidation and mortality after zymosan peritonitis in the rat

The author presents a 3-year study of 10 cases of revisional arthroplasty utilizing the Biomet Total Toe System. The procedure is performed to eliminate pain and restore function in cases of metatarsophalangeal joint silicone elastomer implant failure. The surgeon should be familiar with the Total Toe System before attempting revision.     

Diagnosing breast implant rupture with MR imaging, US, and mammography

A total of 135 symptomatic women with 262 breast implants were examined with magnetic resonance (MR) imaging performed with a body coil, ultrasound (US), or both to determine imaging features of implant rupture. Surgical proof was available for 33 women with 62 implants; 24 were ruptured and 38 were intact. Complicated internal structure was the most reliable predictor of implant rupture: Diffuse low-level echoes were seen on sonograms in 56% of ruptured implants; internal membranes (which correspond to the collapsed implant shell) were seen on MR images in 58% of ruptured implants. Fluid droplets were seen within the silicone in 26% of ruptured implants on MR images. Irregular implant contour can be a sign of rupture but is unreliable. Fluid collections around silicone implants are not a sign of rupture. At present, neither US nor conventional MR imaging with a body coil is sufficiently reliable to advocate routine screening of asymptomatic women with breast implants. Evaluation with MR imaging performed with a surface coil is more reliable.     

High implant fracture incidence with Sutter silicone metacarpophalangeal joint arthroplasty

We performed a retrospective review of Sutter silicone metacarpophalangeal (MP) joint arthroplasties in 34 patients (42 hands, 168 implants) with rheumatoid arthritis. Patients were evaluated at an average of 27 months (minimum follow-up period, 12 months). Twenty percent of the implants were shown to be definitely fractured on final follow-up examination, and 45% followed for more than 3 years were definitely fractured. At the final follow-up examination, the average ulnar drift in intact implants was 11 degrees and in the fractured implants, 23 degrees. However, there was no correlation between implant fracture and patient satisfaction. Eighty percent of patients said they would undergo the procedure again. Because of a significantly higher implant fracture incidence at a relatively shorter follow-up period than that of most studies of silicone MP implants of the Swanson design, we have abandoned the use of the Sutter implant.     

Carpal bone titanium implant arthroplasty. 10 years' experience

In 1984, in an effort to address the silicone wear particle problem, titanium implants were developed for the scaphoid, lunate, and trapeziometacarpal joint. The design of these implants closely resembled their silicone counterparts, though some modifications were made to accommodate the properties of unalloyed titanium and enhance their stability. Carpal bone implants act as articulating spacers to help maintain the relationship of adjacent carpal bones after local resection procedures. Their use allows carpal stabilization procedures and provides functional mobility with good strength and pain relief. Their surgical application began in 1985. The 10-year clinical experience seems very promising to date.     

Proximal interphalangeal joint silicone replacement arthroplasty: clinical results using an anterior approach

Sixty-nine proximal interphalangeal joint silicone arthroplasties in 36 patients inserted through an anterior approach were reviewed. Average followup time was 3.4 years. The average extension deficit was slightly improved from 17 degrees to 8 degrees, but the total active motion (active flexion minus active extension) did not significantly increase (44 degrees to 46 degrees). Coronal plane deformities were not successfully corrected. Pain relief was obtained in 67 of 69 digits. There were 12 digits with complications, and five implants fractured. The anterior approach allows preservation of the central slip insertion and initiation of immediate active and passive joint motion. With proper indications, careful surgical technique, and a supervised therapy protocol, proximal interphalangeal joint silicone arthroplasty is a useful operation for pain relief and functional gain.     

The use of grommets for flexible hinge toe implants. A case report

The postmortem examination of bilateral first metatarsophalangeal flexible hinge toe implants in a 66-year-old woman with rheumatoid arthritis is reported. The prosthesis had been inserted with grommets in 1 joint and without grommets in the other 2.5 years before her death. The implants were removed, and the bone/implant interfaces were examined microscopically by hematoxylin eosin stains and an electron probe microanalyzer. Surfaces of the implants were examined by scanning electron microscopy. Silicone particles within the fibrous tissue at the bone/implant interface, and a tear and significant scuffing of the implant surface, were detected in the joint without grommets. Such changes were not detected in the joint with grommets. These findings suggest that grommets may improve implant durability and preventing silicone synovitis.     

In vivo and in vitro responses to poly(ethylene terephthalate-co-diethylene glycol terephthalate) and polyethylene oxide blends

Although biocompatible polymeric compounds are generally nontoxic, nonimmunogenic, and chemically inert, implants made from these materials may trigger acute and chronic inflammatory responses. These inflammatory reactions may induce degeneration of implanted biopolymer. Interactions between implanted biomaterial and inflammatory cells are mediated by many cellular events involving cellular adhesion and activation. We studied the inflammatory responses in vivo and in vitro to samples of biopolymers composed of poly(ethylene terephthalate-co-diethylene glycol terephthalate) plus 0, 5, 25% of polyethylene oxide. We observed that these biopolymers did not induce inflammatory responses when implanted in the peritoneal cavity of mice for 28 days. However we observed deposition of hyaluronic acid at the surface of implanted biomaterial, suggesting that tolerance to biomaterial occurred after surgical implantation. No significant adhesion of inflammatory cells such as mononuclear phagocytes and peripheral leukocytes were observed in vitro, when poly(ethylene terephthalate-co-diethylene glycol terephthalate) blends were used as substratum to cellular adhesion. These results suggest that blends composed of poly(ethylene terephthalate-co-diethylene glycol terephthalate) induce low inflammatory cell adhesion, since no rejection of biopolymer was observed when implanted in experimental animal models.     

Follicular lymphoma adjacent to foreign body granulomatous inflammation and fibrosis surrounding silicone breast prosthesis

Silicone lymphadenopathy has been associated with fracture and/or erosive breakdown of silastic implants in joint replacements and is also known to occur with cosmetic and reconstructive breast implant surgery. In the orthopedic literature rare malignant lymphomas have been reported in association with silicone granulomas in lymph nodes; whether silicone is a causative agent remains controversial. We report a single case of a 56-year-old woman who had painful capsular contractures and a 2-cm palpable nodule medial to her silicone mammary implant. Histologically the mass comprised an extra nodal follicular mixed lymphoma with surrounding granulomatous response to polarizable foreign body material. Paraffin immunophenotyping, bcl-2 protein staining, and gene rearrangement analysis verified this diagnosis.     

Polydimethylsiloxane pellets for sustained delivery of morphine in mice

A new dosage form was designed whereby a polymeric silicone elastomer provided sustained delivery of morphine to mice over 11 days. These pellets, which can be made easily and inexpensively with a standard tablet mold, gradually released morphine sulfate into the implanted mice. Maximal morphine-induced physical dependence, measured by jumping during naloxone-induced withdrawal, was observed 3--5 days after implantation. At this time, slightly less than 50% of the morphine sulfate had been released. Drug release continued through Day 11 and was accompanied by a physical dependence of decreased magnitude compared to that observed on Day 3 or 5.