Flap valve ureteral stent with an antireflux function: a review of 46 cases.

During a 2-year period, 46 patients with upper urinary obstructions (intrinsic obstruction and extrinsic compression) underwent treatment with a flap valve indwelling double-pigtail stent. Our subsequent analysis suggests that a flap valve at the lower end of a conventional ureteral stent can effectively prevent reflux in the upper urinary tract, and reduce discomfort and pain in the flank region during micturition.     

New bioabsorbable polylactide ureteral stent in the treatment of ureteral lesions: an experimental study

OBJECTIVE: To evaluate the suitability of a new biodegradable double-helical spiral self-reinforced poly-L,D-lactide copolymer (SR-PLA 96; L/D ratio 96/4) stent as a device for ureteral stenting in respect to changes in kidney function during the biodegradation process. MATERIALS AND METHODS: Sixteen dogs were used as experimental animals and were subdivided into two groups of eight. In Group A, both ureters were cut transversally, sutured, and stented. The right ureter was stented using an SR-PLA 96 stent, whereas a double-J C-Flex stent was used on the left side. Cystotomy was performed at 6 weeks to remove the double-J stents. In Group B, the right ureter of each dog was cut and stented in similar manner using an SR-PLA 96 stent, whereas the left ureters served as untreated controls, and cystotomy was not performed. Serum creatinine and nitrogen values were measured, urine was analyzed for signs of infection, and renal function was evaluated by urography and renography examinations preoperatively and at 6, 12, and 24 weeks postoperatively, at which time points, the dogs were euthanized and the ureters dissected to find persistent SR-PLA 96 particles and macroscopic local changes. There were no urinary tract infections found during the study. RESULTS: In the SR-PLA 96-stented ureters, obstructive hydronephrosis and stricture formation were observed in two cases (11%), with distal displacement of the SR-PLA 96 stent in another case (5.5%). In two additional renal units, a temporary prolongation in the kidney washout time was observed at 6-week renogram examinations. In the C-Flex-stented ureters, temporary changes in renography studies were observed in three cases (37.5%) at 6 weeks. Kidney washout times were protracted at 6 weeks in the pigtail-stented ureters in Group A as a sign of a pressure rise in the renal pelvis secondary to the direct connection between the renal pelvis and bladder, whereas pressure remained normal in SR-PLA 96-stented ureters. In Group B, renal function remained normal after ureteral repair in SR-PLA 96-stented ureters compared with the controls. CONCLUSIONS: The double-helical apical stent design offers some advantages over a double-J design. The risk of pressure-induced kidney damage is lowered, because there is no direct connection between the bladder and renal pelvis, and the risk of upper urinary tract infections is reduced. The biodegradation of the device necessitates the removal of the stent. These preliminary results suggest that a biodegradable SR-PLA 96 stent with more effective expansion capacity can be used for stenting after a ureteral repair.     

Interstitial laser coagulation and biodegradable self-expandable,self-reinforced poly-L-lactic and poly-L-glycolic copolymer spiral stent in the treatment of benign prostatic enlargement

BACKGROUND AND PURPOSE: Interstitial laser coagulation of the prostate (ILCP) induces necrosis, edema, and an increased risk of postoperative urinary retention. The object here was to evaluate the efficacy, safety, and utility of a new self-expandable self-reinforced (SR) PLGA copolymer(lactic:glycolic ratio 80/20) spiral stent inserted after ILCP to promote voiding. The SR-PLGA stent has a degradation time of 2 to 2.5 months. PATIENTS AND METHODS: Fifty men with a mean age of 70.5 years (range 52-85 years), suffering from lower urinary tract symptoms secondary to benign prostatic enlargement underwent ILCP. A suprapubic catheter was inserted, ILCP performed, and an SR-PLGA 80/20 spiral stent inserted on completion of the operation. The suprapubic catheter was removed when voiding commenced. As prophylactic antibiotic, ciprofloxacin was used in a single dose before ILCP, followed by trimethoprim or nitrofurantoin for 2 weeks. RESULTS: All except three patients started to void on the first postoperative day. In two of the three cases, the stent had moved proximally and had to be relocated, whereafter voiding succeeded. The mean maximum and average flow rates increased, while DAN-PSS-1 symptom score and post voiding residual urine volume decreased statistically significantly. At 2 months, the stent was still intact in the urethra in all except three patients. At 4 months, it had been degraded into small fragments, and at 6 months, it had been completely eliminated. The only exceptions were three patients with an uncalcified piece of the stent in the bladder. Half of the patients had irritative symptoms caused at least partly by ILCP itself; 10% had asymptomatic urinary infection postoperatively. CONCLUSIONS: The self-expandable SR-PLGA copolymer stent is safe and highly biocompatible. It ensures voiding in the case of temporary obstruction caused by prostatic edema. The degradation time is long enough in all patients to cover the need for postprocedure urinary drainage.     

Biocompatibility and implantation properties of 2 differently braided, biodegradable, self-reinforced polylactic acid urethral stents: an experimental study in the rabbit

PURPOSE: Biodegradable urethral stents have been in clinical use for more than 10 years. To solve the problems connected with the helical spiral configuration of the stents used to date we developed a new tubular mesh configuration and evaluated the biocompatibility properties and degradation time of 2 differently braided stents in the rabbit urethra. MATERIALS AND METHODS: The biodegradable, self-expanding stents were made of self-reinforced polylactic acid polymer blended with BaSO4 (Alfa Chem, Kings Point, New York). Two braiding patterns, namely a diamond 1/1 and a regular 2/2 + 1 (Prodesco, Perkasie, Pennsylvania), were used to produce a tubular mesh configuration. Stainless steel stents with 1/1 braiding served as controls. The stents were inserted into the posterior urethra of 36 male rabbits. The animals were sacrificed after 1 week, 1 month, 6 months or 12 months. Light microscopy and scanning electron microscopy analyses were done. RESULTS: Tissue reactions to operative trauma were seen in all specimens at week 1. The changes gradually abated in the biodegradable stent groups, whereas chronic inflammatory changes and fibrosis were increasingly seen with metallic stents after 6 months. Epithelial hyperplasia increased with time for all stent types and materials. As expected, stent fragmentation started at 6 months. CONCLUSIONS: Biodegradable polymers are suitable materials for braided urethral stents. However, the braided configuration of the stent with a decreased mass of material does not prevent the development of epithelial hyperplasia. The biodegradable, self-expanding, braided stents functioned well in the rabbit urethra and are suitable for clinical studies.     

携带缓释药物的生物可降解输尿管支架体内外降解特性研究

目的 观察携带缓释药物的生物可降解输尿管支架的体内外降解特性,比较输尿管裸支架与输尿管药物支架的生物相容性等差异.方法 将输尿管裸支架与输尿管药物支架分别浸泡于新鲜人体尿液中,观察体外支架降解.将两种输尿管支架分别包埋于18只Wistar大鼠脊柱两侧肌肉内.通过组织切片染色、扫描电镜、相对分子质量测定及质量变化分析体内生物可降解特性差异.结果 输尿管药物支架体外人体尿液浸泡10周时,支架失重率已达35%.切片染色发现组织反应较轻,纤维增生不明显.扫描电镜支架表面失去原有形态,出现大块状脱落物.12周时,降解为细小泥沙样颗粒输尿管裸支架组纤维膜厚(21.24±3.27)μm,输尿管药物支架组纤维膜厚(10.75±3.69)μm,两组比较差异有统计学意义(P＜0.01).结论 与输尿管裸支架比较,输尿管药物支架的降解特性相似,但炎症反应轻,包裹纤维膜厚度更薄,具有良好的组织相容性.     

Expansion and fixation properties of a new braided biodegradable urethral stent: an experimental study in the rabbit

PURPOSE: Biodegradable spiral urethral stents have been used with favorable results combined with thermal treatments of the prostate and for recurrent urethral strictures but the configuration of the helical spiral is not ideal. We developed a new tubular mesh configuration for the biodegradable urethral stent and evaluated its expansion and locking properties in the rabbit urethra. MATERIALS AND METHODS: The stents were made of self-reinforced polylactic acid polymer (Bionx Implants, Ltd., Tampere, Finland) blended with BaSO (Alfa Chem, New York, New York) to achieve radiopacity. Two braiding patterns, that is 1 over 1 and 2 over 2 + 1, were used to produce a tubular mesh structure. Stainless steel stents (pattern 1 over 1) served as controls. The stents were inserted into the posterior urethra of 27 male rabbits. The animals were sacrificed after 1 week, 1 and 6 months, respectively. X-rays were done immediately after stent insertion and at sacrifice. Longitudinal movement and expansion were assessed on the x-rays.(4) RESULTS: All stents maintained position in the urethra without fixation. Macroscopic disorientation of the structure of the 2 over 2 + 1 braided self-reinforced polylactic acid polymer stents began before 1 month, while 1 over 1 braided stents retained their construction. At 6 months 3 of 6 biodegradable stents were degraded. Average longitudinal movement was 2 mm. (range 1 to 3) in the 1 over 1 self-reinforced polylactic acid polymer group, 2 mm. (range 0 to 7) in the 2 over 2 + 1 polylactic acid group and 3 mm. (range 3 to 3) in controls at 1 month. CONCLUSIONS: Biodegradable polymers are suitable materials for braided urethral stents. The expansion properties of the 2 braiding models tested in this study sufficed to fix the stents in situ in the prostatic urethra. However, the 1 over 1 braiding pattern was superior to the 2 over 2 + 1 pattern, in that it retained its macroscopic construction until the degradation of single self-reinforced polylactic acid polymer fibers.     

The morphological, in situ effects of a self-reinforced bioabsorbable polylactide (SR-PLA 96) ureteric stent; an experimental study

PURPOSE: The present study was done to evaluate the biocompatibility of a new biodegradable double helical spiral self-reinforced poly-L, D-lactide copolymer (L/D ratio 96/4, SR-PLA96) ureteric stent. MATERIALS AND METHODS: In sixteen dogs, the right ureter was cut transversally, sutured and stented with a 50 mm. long SR-PLA 96 stent. In eight dogs, left ureter was similarly operated and stented with a double-J pigtail stent (C-Flex, Cook Urological Inc.), while eight remaining ureters served as plain controls. Urine was analyzed for signs of infection. The dogs were terminated at 6, 12 and 24 weeks postoperatively and the ureters dissected to find persistent SR-PLA 96 particles or local ureteric changes. Histologic samples were taken at three levels of dissected ureters in contact with the stent. RESULTS: C-Flex and SR-PLA 96 materials were well tolerated. Both of these induced only minimal ureteral wall edema, epithelial hyperplasia, epithelial destruction and inflammatory cell reaction. In SR-PLA 96 stented ureters the tissue reaction subsided after the degradation of the device. CONCLUSIONS: SR-PLA 96 spiral stent is regarded highly compatible and SR-PLA 96 might be a suitable material for a partial ureteric stent. Biodegradation of a SR-PLA 96 stent makes stent removal unnecessary.     

A new biodegradable braided self-expandable PLGA prostatic stent: an experimental study in the rabbit

PURPOSE: The biodegradable PLGA (a copolymer of L-lactide and glycolide) urethral stent with a spiral configuration has been used clinically for the prevention of postoperative urinary retention after different types of thermal therapy for benign prostatic hyperplasia. A new braiding pattern for this stent has recently been developed by our group. The aim here was to investigate the in situ degradation and biocompatibility of the new braided stent in the rabbit urethra. MATERIALS AND METHODS: PLGA stents with a one-over-one braiding pattern and steel stents served as controls that were inserted into the posterior urethras of 24 male rabbits using a special delivery instrument. The animals were sacrificed after 1 week, 1 month, 2 months, or 4 months, and light microscopy and histologic analyses were performed. RESULTS: The delivery instrument worked well and cystoscopy was not needed in the insertion process. The braided PLGA stents degraded smoothly in 1 to 2 months. The metallic stents induced more epithelial hyperplasia and epithelial changes than the biodegradable stents at all time points analyzed. These differences increased during follow-up. CONCLUSION: The degradation process was well controlled and the biodegradable stents were more biocompatible than the metallic stents. The new stent can be inserted into the posterior urethra without cystoscopic aid.     

Biocompatibility properties of a new braided biodegradable urethral stent: a comparison with a biodegradable spiral and a braided metallic stent in the rabbit urethra

OBJECTIVE: To compare the biocompatibility properties of a new braided biodegradable self-reinforced poly-L-lactic acid (SR-PLLA) urethral stent to the former spiral biodegradable SR-PLLA stent and the stainless steel stent in a rabbit model. MATERIALS AND METHODS: In all, 54 male New Zealand White rabbits were anaesthetized and stents inserted into the prostatic urethra, three of each kind for each sample time. The rabbits were killed after 1, 3, 6, 9, 12 or 15 months and light microscopy and scanning electron microscopy used to analyse the effects. RESULTS: The disintegration of the braided SR-PLLA stent was more closely controlled than that of the spiral SR-PLLA stent. The metallic stent induced epithelial hyperplasia and polyposis earlier than the biodegradable stents, and in these rabbits the polyposis disappeared after the disintegration process. There were no differences in the histological analyses between the biodegradable stents, whereas the metallic stents caused the strongest inflammatory reactions. CONCLUSIONS: The braided SR-PLLA urethral stent functioned well in the rabbit urethra and clinical studies are already planned.     

Effect of self-reinforced polyglycolide membrane on osteogenesis: an experimental study in rats

This study is part of a series of studies evaluating self-reinforced polyglycolide (SR-PGA) membranes. The aim of this study was to evaluate the effect of SR-PGA membrane on osteogenesis in order to assess its use in tissue engineering and bone regeneration. SR-PGA membranes (15×20 mm) were implanted over the femoral diaphyseal bone of 27 Wistar rats (over the periosteum). Each membrane was stabilized using a Dexon suture cerclage. Rats were followed-up for 1, 2, 3, 6, 8, 15 and 30 weeks. Histology and microradiography were used to evaluate bone formation. The membranes were excised and tested for their tensile strength properties, the results of which are published in a separate report. Bone formation periosteally was seen in 21/27 cases (77.8%, confidence interval 57.7–91.4). It occurred in all cases at 1, 2 and 3 weeks. At 6 weeks, it was seen in three out of four cases but at 8 weeks, only in one out of three cases. Bone formation seen as thickened cortex was detected at 15 weeks in all of the three cases and at 30 weeks in three out of six cases. Hence, bone formation was seen in most of the cases when SR-PGA membranes were applied around rats’ femora. They can be recommended for use in bone tissue engineering and regeneration. Received: 31 January 2000 / Accepted: 2 August 2000     

The ileopsoas tunnel,a new antireflux technique for ureteroileal reimplantation: an experimental study in dogs

A new antirefluxing ureteroileal anastomosis is described in which the implantedureter is placed between the ileal segment and psoas muscle. The procedure was studied in eight experimental dogs, which were observed for 20 weeks. Radiologic and bacteriologic examinations, necropsy assessment and histopathologic results provided evidence that this ileo-psoas tunnel technique allows a unidirectional, non-obstructed flow of urine. The technique could be applied when ileal replacement of the ureter is necessary or in association with continent bladder replacement.     

Rabbit muscle and urethral in situ biocompatibility properties of the self-reinforced L-lactide-glycolic acid copolymer 80: 20 spiral stent

PURPOSE: A new type of self-reinforced L-lactide-glycolic acid copolymer, molar ratio 80:20, stent was developed. We evaluated the tissue biocompatibility properties of the new material. MATERIALS AND METHODS: Rods made of self-reinforced L-lactide-glycolic acid copolymer were inserted into rabbit dorsal muscles and rods of latex or polyvinylchloride and silicone served as positive and negative controls, respectively. Urethral stents of self-reinforced L-lactide-glycolic acid copolymer and steel were inserted in situ via cystoscopy into the rabbit prostatic urethra. The animals were sacrificed after 2 weeks, 1, 2 and 3 months, respectively. In situ histological analysis was done. Tissue reactions around the implantation types were analyzed histologically and scored semiquantitatively. In addition, macroscopic analysis was done of the urethral in situ stents. RESULTS: In rabbit muscle implantation test tissue reaction to the self-reinforced L-lactide-glycolic acid copolymer stent resembled that of negative control silicone. Less than moderate chronic inflammatory changes gradually subsided after 2 weeks. Foreign materials in the tissue and the reaction to these materials began to disappear after 1 month and at 3 months were completely absent. All rabbits fitted with the stent voided normally postoperatively. Self-reinforced L-lactide-glycolic acid copolymer stents were soft, partially fragmented and easily disintegrated when touched at 2 months, and were almost completely degraded at 3 months. The material did not encroach into the urethral wall macroscopically or microscopically. No calcification on the self-reinforced L-lactide-glycolic acid copolymer stents or bladder stone formation was seen. CONCLUSIONS: The new self-reinforced L-lactide-glycolic acid copolymer 80:20 material is safe, highly biocompatible and suited for future clinical use. It is most appropriate for preventing postoperative urinary retention after most minimally invasive thermal treatments for benign prostatic hyperplasia.     

Mechanism of ureteral stent flow: a comparative in vivo study.

BACKGROUND AND OBJECTIVES: The flow characteristics of ureteral stents have yet to be clearly defined. In this study, flow mechanics were studied in several silicone-based stents including 4.8F, 7F, and 10.3F pigtail; 7F Tower; and a prototype mesh stent. MATERIALS AND METHODS: Forty-five female Yucatan minipigs underwent bilateral laparoscopic occlusion of their renal vessels to stop urine production. A nephrostomy tract was established by retrograde puncture. A stent was placed in the ureter, and three measurements were taken with flow from a bag of irrigant 20 cm above the kidney: stent occluded with a guidewire (extraluminal flow), stent unobstructed (total flow), and laparoscopically placed extraureteral ligature (luminal flow). RESULTS: Luminal flow and, to a lesser extent, total flow appeared to increase as the internal and external diameters of the stent increased. The Tower stent, which had no sideholes, had much lower flow rates in all categories, while the prototype mesh stent showed greater total flow compared with the other stents. Extraluminal flow did not increase with stent size greater than 7F. CONCLUSIONS: Luminal flow, but not extraluminal flow, increased with an increase in the internal diameter of the stent. In general, the least favorable flow occurred with a Tower stent, which had the smallest internal diameter. The greatest flow was seen with the prototype mesh stent.     

A double-blind, randomized, placebo-controlled pilot study to investigate the effects of finasteride combined with a biodegradable self-reinforced poly L-lactic acid spiral stent in patients with urinary retention caused by bladder outlet obstruction from benign prostatic hyperplasia.

OBJECTIVE: To assess whether patients in acute urinary retention from benign prostatic enlargement can be treated with a combined therapy comprising finasteride and a bioabsorbable self-reinforced poly L-lactic acid (SR-PLLA) urethral stent. PATIENTS AND METHODS: Fifty-five patients in acute urinary retention were treated as outpatients; they had a suprapubic catheter inserted and the SR-PLLA stent placed cystoscopically. After 2 weeks the patients were randomized to receive either finasteride 5 mg daily or placebo. They were assessed at baseline and at 6, 12 and 18 months for maximum urinary flow rate, prostate volume and serum prostate-specific antigen (PSA). RESULTS: Nineteen patients completed the study while 36 discontinued. There was a statistically significant increase in the mean maximum flow rate, and a statistically significant decrease in the prostatic volume and serum PSA in the finasteride group. The same number of patients discontinued in both groups; the major reason for discontinuation was insufficient therapeutic response. CONCLUSIONS: The major problems were discontinuation of treatment because the response to therapy was insufficient, and uncontrolled breakdown of the spiral stent. To solve these problems, new configurations of bioabsorbable stents are needed.