Uso do silicone e poliuretano na uretroplastia dorsal: estudo experimental em coelhos / The silicone and polyurethane used in dorsal on lay urethroplasty: experimental study in rabbits

AUTOR(ES)
DATA DE PUBLICAÇÃO

2008

RESUMO

BACKGROUND: Actually, the treatment of urethral stenosis employs biological grafts, usually autologous grafts. The success with synthetic biomaterials in others medical specialtys motivated the search of these materials in urethral reconstruction. The knowledge about the silicone mamarian prosthesis covered with polyurethane foam reduces capsular contracture in breast implants and because these polymers are already used in the urinary tract like catheters make the choice for these materials. METHODS: The resection of dorsal segment of anterior urethra of 20 male rabbits NZW was carried through. The urethral defect was treated with the on lay dorsal graft in urethra, compound a silicone not tabularized, coated with polyurethane foam in one face (Si-Pu). The control group (sham) was confectioned with 12 animals was submitted to longitudinal dorsal uretrotomy and suture, without any type of implantation (SG). The analyses intervals were 2, 4, 8 and 24 weeks after surgery. The circumference of urethra and surgical complications had been analyzed. Material for histological evaluation was stained with Massons thrichrome, hematoxylin and eosin and Picrosirius red. Intensity and characteristics of the inflammatory response, thickness of the urethra (oedema) and concentration of the collagen in the submucosa had been evaluated. Still, was performed microbiological analysis and research of implants incrustation with thermogravimetry. The findings had been compared with the data of three rabbits that had not suffered any intervention. RESULTS: The morfological analysis not founded fistula, obstruction, stenosis, cicatricial retraction, calcification and dehiscence. The graft was extruded after 4 weeks in 1/5 of the animals, in 2/5 after 8 weeks and after 24 weeks, 3/5 of the animals had failure of union with the surrounding tissue. Except for the interval of 8 weeks, It did not have urethral circumference reduction in the comparison between groups, Experimental (EG) and SG. Infection of the surgical place occurred in 11 of 12 animals of the GS and in 13 of 20 animals of EG. Staphylococcus DNAse-negative and Escherichia coli were the most frequent bacterium founded, and occurred in 9/32 and 5/32, respectively. The infection with Enterobacter cloacae was associated to lesser weight gain for the animals (P=0,02), fact not observed in infection with other bacteria. The Staphylococcus infection was associated to larger urethral circumference (P=0,006), when compared to sterile samples. The EG histological analysis showed early severe inflammatory process and substitution of smooth muscle fibers for collagen and regression of edema and inflammatory cells decrease laterly. Occurred delayed deposition of collagen and slight inflammation in the SG, however this process was constant. Was observed urothelial reepithelialization in both groups. The collagen concentration in urethral wall at surgical site was larger in EG with 24 weeks when compared to SG at same time (P<0.001). There was significantly less urethral wall oedema in SG at 2 weeks, at 4 weeks (P<0.001) and after 8 weeks (P<0,05) than EG at the same time. After 24 weeks no difference was verified in submucosa thickness between the groups. The descriptive thermogravimetric analysis showed graft incrustation with organic material, however without statistic significance in quantitative analysis of mass loss. The inorganic graft incrustation was negligible. CONCLUSIONS: The use of Si-Pu implants in urethra originated a fibrous collagen capsule that allows reepitelialization without local contracture, like a biological skeleton. Nevertheless, grafts extrusion limits their clinical employment

ASSUNTO(S)

rabbits poliuretanos uretra/cirurgia polyurethanes silicones coelhos urethra/ surgery silicones

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