Silastic Silicone Rubber Research Articles

Silastic silicone rubber band migration: an unusual complication resolved by endoscopy

Silastic silicone rubber band migration: an unusual complication resolved by endoscopy

Balloon dilatation for treatment of resistant nasolacrimal duct obstruction

Purpose: Our purpose was to report our experience with balloon catheter dilatation for resistant nasolacrimal duct obstruction. Methods: Patients enrolled had symptoms of nasolacrimal duct obstruction and (1) had failed previous probing or (2) were more than 2 years old. Balloon dilatation was performed with a LacriCATH lacrimal catheter (Atrion Medical Products, Birmingham, Ala.). A subset of patients had Silastic silicone rubber (Dow Corning, Midland, Mich.) intubation after balloon dilatation. Success was determined by clinical examination a minimum of 6 weeks later. Results: Twenty-one lacrimal systems of 12 patients were treated (age range 4 months to 7 years). Of the patient subset treated with a LacriCATH lacrimal catheter alone, 9 of 18 systems demonstrated complete resolution of symptoms. Three of the 12 patients underwent balloon dilatation intraoperatively after attempts at Silastic silicone rubber intubation were unsuccessful. In two of these patients, who were younger, Silastic silicone rubber tubes passed easily after balloon treatment; however, in an older patient, age 5 years, intubation still could not be accomplished. Conclusion: Common clinical strategy for treatment of resistant nasolacrimal obstruction includes repeat probing, intubation of the nasolacrimal system with Silastic silicone rubber tubes, or dacryocystorhinostomy. Balloon catheter dilatation is an alternative or adjunct to consider. Factors that may affect the success of treatment include the age of the patient, the complexity of the nasolacrimal anatomy, and use of adjunctive systemic antibiotics and steroids.

Inhibition and augmentation of progesterone production during pregnancy: Effects on parturition in rhesus monkeys

OBJECTIVES: Uterine quiescence during mammalian pregnancy is attributed to progesterone. However. systemic progesterone levels remain elevated in primates before parturition. Epostane, a selective 3β-hydroxysteroid dehydrogenase inhibitor, and progesterone (with or without epostane) were administered to late pregnant rhesus monkeys to clarify the role of progesterone in primate parturition. STUDY DESIGN: On days 122 to 132 of gestation (term 167 days), 11 rhesus monkeys (Macaca mulatta) with timed pregnancies were divided into three treatment groups: (1) epostane alone (10 mg/kg subcutaneously), (2) epostane with progesterone subcutaneously in Silastic silicone rubber capsules, and (3) progesterone implants only with no surgical instrumentation. Maternal and fetal blood and amniotic fluid were sampled for progesterone, estrone, estradiol, cortisol, testosterone, androstenedione, dehydroepiandrosterone, dehydroepiandrosterone sulfate, and amniotic fluid was sampled for prostaglandins E 2 and F 2α. Uterine activity was monitored continuously by electromyography and intraamniotic pressure. Cervical status was assessed by a modified Bishop's score. Production of prostaglandins E 2 and F 2α by amnion was determined by tissue superfusion. The group of three noninstrumented monkeys, which received only progesterone Silastic silicone rubber implants subcutaneously at 146 to 148 days, were observed until spontaneous vaginal delivery. RESULTS: Epostane reduced maternal and fetal progesterone levels by 75% and 50%, respectively, followed by increased uterine activity and cervical ripening within 24 hours and vaginal delivery within 48 hours. Amniotic fluid progesterone decreased to undetectable levels. Progesterone implants prevented the epostane-induced decrease in maternal and fetal progesterone levels and the associated myometrial and cervical changes until the implants were removed. Alterations in other steroid hormones were consistent with inhibition of 3β-hydroxysteroid dehydrogenase. Amniotic prostaglandin E 2 production was increased sixfold by epostane ( p < 0.05) but did not reach the high levels normally seen at spontaneous parturition. Animals that received progesterone implants alone had markedly elevated circulating progesterone concentrations yet were delivered spontaneously at term (range 163 to 167 days). CONCLUSIONS: Progesterone withdrawal induces preterm labor and delivery (which can be blocked by progesterone substitution) but exogenous progesterone, even in substantial quantities, does not prevent parturition at term. (Am J Obstet Gynecol 1997;176:682-91.)

Mechanics of type IV tympanoplasty: experimental findings and surgical implications.

In a type IV tympanoplasty, the stapes footplate is directly exposed to incoming sound while the round window is "shielded," usually with a fascia graft. Postoperative hearing results are quite variable, with air-bone gaps ranging from 10 to 60 dB. A cadaveric human temporal bone preparation was developed to investigate the middle ear mechanics of this operation to identify causes of variable results and to test predictions of a recently described theoretic model of type IV tympanoplasty. The ear canal, tympanic membrane, malleus, and incus were removed so as to expose the stapes and round window to the sound stimulus. A "cavum minor" chamber (air space adjacent to the round window) was constructed around the round window niche. The round window could be isolated from sound by placing an acoustic shield over this chamber. The mechanical properties of the shield, cavum minor, annular ligament, and round window membrane were varied experimentally. Stapes velocity as determined by an optical motion sensor was used as a measure of hearing level. The largest stapes velocity occurred with a mobile stapes and round window, a stiff shield, and a well-aerated cavum minor. Partial fixation of the stapes or round window caused a decrease in stapes velocity. Acoustic shields of conchal cartilage or Silastic silicone rubber sheeting (approximately 1 mm thick) provided near-optimal shielding. A temporalis fascia shield resulted in a stapes velocity 10 to 20 dB less than that seen with a cartilage or Silastic silicone rubber shield at low frequencies. A cavum minor air space as small as 16 microL was sufficient for unrestricted stapes motion, provided the air was in contact with the round window membrane. These results qualitatively matched predictions of our model, but there were some quantitative differences. The clinical implications of our results are that in order to optimize postoperative hearing, the surgeon should 1) preserve normal stapes mobility, preferably by covering the footplate with a very thin split-thickness skin graft, not a fascia graft; 2) reinforce a fascia shield with cartilage or Silastic silicone rubber; 3) create conditions that promote aeration of the round window niche; and 4) preserve the mobility of the round window membrane.

Long-Term Follow-up of Recurrent Laryngeal Nerve Avulsion for the Treatment of Spastic Dysphonia

Long-term follow-up of 3 to 7 years is reported on 18 patients who had undergone recurrent laryngeal nerve avulsion (RLNA) for the treatment of adductor spastic dysphonia (SD). Data on neural regrowth after previous recurrent laryngeal nerve section (RLNS) are presented in 2 of these 18 patients. We introduced RLNA as a modification of standard RLNS to prevent neural regrowth to the hemiparalyzed larynx and subsequent recurrence of SD. We have treated a total of 22 patients with RLNA, and now report a 3- to 7-year follow-up on 18 of these 22 patients. Resolution of symptoms was determined by routine follow-up assessment, perceptual voice analysis, and patient self-assessment. Sixteen of 18, or 89%, had no recurrence of spasms at 3 years after RLNA as determined at routine follow-up. Two of the 16 later developed spasms after medialization laryngoplasty for treatment of weak voice persistent after the avulsion. This yielded a total of 14 of 18, or 78%, who were unanimously judged by four speech pathologists to have no recurrence of SD at the longer follow-up period of 3 to 7 years. Two of these 4 patients were judged by all four analysts to have frequent, short spasms. The other 2 were judged by two of four analysts to have seldom, short spasms. Three of 18 patients presented with recurrent SD after previous RLNS. At the time of subsequent RLNA, each patient had evidence of neural regrowth at the distal nerve stump as demonstrated by intraoperative electromyography and histologic evaluation of the distal nerve stump. One remained free of SD following RLNA, 1 was free of spasms at 4 years after revision avulsion but developed spasms after medialization laryngoplasty, and the final patient developed spasms 3.75 years after revision RLNA. Medialization laryngoplasty with Silastic silicone rubber was performed in 6 of 18, with correction of postoperative breathiness in all 6, but with recurrence of spasm in 3. Spasms resolved in 1 of these with downsizing of the implant. We conclude that RLNA represents a useful treatment in the management of SD in patients not tolerant of botulinum toxin injections.

Tissue/biomaterial interface characteristics of four elastomers. A transmission electron microscopical study

The tissue/biomaterial interface reactions of four elastomers--selected as candidates for scaffolding for tympanic membrane tissue in a total alloplastic middle ear prosthesis--were studied at the electron microscopical level after implantation in the rat middle ear. Time-dependent changes in the phagocyte/polymer interface suggested degradation of porous implants made of Estane polyether urethane, polypropylene oxide, and a poly(ethylene oxide hydantoin) and poly(tetramethylene terephthalate) segmented polyether polyester copolymer (HPOE/PBT copolymer), but not of dense Silastic silicone rubber implants. Silastic was always encapsulated in fibrous tissue. Contact between fibrous tissue and HPOE/PBT copolymer or Estane was established in the third month, but fibrous tissue was never seen close to polypropylene oxide. Bone made contact only with Estane and HPOE/PBT copolymer implants. The bone/copolymer interface showed an electron-dense layer morphologically similar to that seen between bone and hydroxyapatite ceramic, suggesting that with respect to bone HPOE/PBT copolymer behaves like a bioactive implant material. The electron-dense layer was absnet at the bone/Estane interface. Estane and especially HPOE/PBT copolymer seem to be suitable as alloplastic tympanic membrane because of their interface behavior with respect to fibrous tissue and bone.

Velour-lined silicone rubber as an artificial bladder material.

AbstractAn ideal material for an artifical urinary bladder has not yet been designed. In order to study the effects of long‐term exposure of urine to velour‐lined Silastic silicone rubber, seven 80% cystectomized sheep had their natural bladders replaced with a Dacron velour‐lined, Silastic prosthesis. Animals were sacrificed 1 week, 3, 6, 9, and 18 months postimplantation of their prosthesis.While the luminal surface of the prosthesis one week after implantation had small isolated patches of epithelium on it none of the remaining animals had any evidence of tissue growth on this surface. No stones or calcifications were found on the luminal surface of the prostheis in any of the animals except the 18‐month survivor who had microscopic evidence of early calcification.The convex (serosal) surface of all the artifical bladders was covered with a thick connective tissue layer. At 9 months a muscle layer was seen in this tissue and it was clear the prosthesis was acting as a scaffold around which regeneration of the natural bladder was taking place. At 18 months after implantation regeneration of the natural bladder was complete and the prosthesis remained as a functionless, crumpled, hard foreign body in the lumin of the new bladder.It appears that velour‐lined Silastic silicone rubber though not ideal may be an effective artificial bladder material as long as it remains functional.

Experiments with injectable plastic: Use of silicone and silastic rubber in animals and its clinical use in deformities of the head and neck

In summary, silicone fluid, solid RTV Silastic silicone rubber, and gel-like mixtures of the two were individually studied and found to provoke similar host-tissue responses in the liquid, solid, and gel states. The sole exception was a variable diminution in the residual amount of the fluid silicone injected. Each variation after injection showed physical properties quite similar to the bony and soft tissues present around the head and neck; that is, the RTV silicone rubber could blend quite easily with bony and hard muscle contours, the silicone-rubber-Silastic fluid mixtures were not dissimilar from muscle and glandular tissue, and the fluid silicone, after injection, blended extremely well with the soft subcutaneous areas. Since the Federal Food and Drug Administration has listed the injectable silicone fluid and RTV Silastic materials as drugs rather than prostheses, injection of these materials in humans has been halted in this clinic. This has seriously hampered the study and use in the clinical correction of deformities of the head and neck such as defects of the calvarium, forehead, and malar and mandibular regions, as well as the correction of extensive tissue deformities after hemiatrophy of the face, the removal of large deep tumors, severe surgical losses of tissue, and the correction of late enophthalmos. In view of the microscopic findings presented it is hoped that the F.D.A. will soon release this new drug to a more extensive clinical investigation.