Tubularized urethral replacement with unseeded matrices: what is the maximum distance for normal tissue regeneration?

PURPOSE: Complete urethral replacement using unseeded matrices has been proposed as a possible therapy in cases of congenital or acquired anomalies producing significant defects. Tissue regeneration involves fibrin deposition, re-epithelialization, and remodeling that are limited by the size of the defect. Scar formation occurs because of an inability of native cells to regenerate over the defect before fibrosis takes place. We investigated the maximum potential distance of normal native tissue regeneration over a range of distances using acellular matrices for tubular grafts as an experimental model. MATERIALS AND METHODS: Tubularized urethroplasties were performed in 12 male rabbits using acellular matrices of bladder submucosa at varying lengths (0.5, 1, 2, and 3 cm). Serial urethrography was performed at 1, 3, and 4 weeks. Animals were sacrificed at 1, 3, and 4 weeks and the grafts harvested. Urothelial and smooth muscle cell regeneration was documented histologically with H&E and Masson's trichrome stains. RESULTS: Urethrograms demonstrated normal urethral calibers in the 0.5 cm group at all time points. The evolution of a stricture was demonstrated in the 1, 2, and 3 cm grafts by 4 weeks. Histologically all grafts demonstrated ingrowth of urothelial cells from the anastomotic sites at 1 week. By 4 weeks, the 0.5 cm grafts had a normal transitional layer of epithelium surrounded by a layer of muscle within the wall of the urethral lumen. The 1, 2, and 3 cm grafts showed ingrowth and normal cellular regeneration only at the anastomotic edges with increased collagen deposition and fibrosis toward the center by 2 weeks, and dense fibrin deposition throughout the grafts by 4 weeks. CONCLUSIONS: The maximum defect distance suitable for normal tissue formation using acellular grafts that rely on the native cells for tissue regeneration appears to be 0.5 cm. The indications for the use of acellular matrices in tubularized grafts may therefore be limited by the size of the defect to be repaired.     

组织工程引导骨再生膜修复节段性骨缺损

目的　将组织工程技术和引导性骨再生技术相结合修复长骨节段性缺损。方法　兔 2 7只 ,动物模型均为桡骨 1 2cm节段性骨 骨膜缺损 ,分成 3组 ,A组 :利用体外构建的细胞 材料复合物膜修复 ;B组 :利用单纯的膜材料进行修复 ;C组 :断端不作任何处置作空白对照。分别观察 3、 6、 12周后进行X线观察和组织学观察。结果　A组的骨愈合优于B组 ,在 12周时已经完成骨缺损的修复 ,B组在术后 12周仍处于塑形改建之中 ;C组 12周形成典型的骨不连。结论　将组织工程的技术与引导性骨再生技术相结合 ,可以比单纯的引导性骨再生更好地修复长骨节段性缺损。     

骨髓基质干细胞联合血管束植入构筑血管化组织工程骨修复兔大段骨缺损

目的 研究兔骨髓基质干细胞(BMSCs)联合动静脉血管束植入异种脱蛋白松质骨(XDCB)构筑血管化组织工程骨修复兔桡骨中远段完全骨膜骨缺损的能力. 方法 从兔髂嵴捕骨髓培养制备兔BMSCs,将第5代BMSCs种植于多孔XDCB,并进行成骨诱导2周制备组织工程骨,手术中分离兔桡动、静脉血管束.动物模型为制备24只兔舣侧桡骨中远段完全骨膜骨缺损1.5 cm共48侧,分4组修复(n=12),A组为空白未治疗组,B组为单纯材料+血管束植入组(XDCB+VB),C组为组织工程骨组(XDCB+BMSCs),D组为组织工程骨+血管束植入组(XDCB+BMSCs+VB),符组交叉配对.分别于术后4、8、12周行X线片、大体解剖、组织切片、生物力学等检查,观察各组骨缺损修复效能及移植物血管化情况.结果 D组骨缺损修复效能(术后12周新骨面积比2.02%±0.16%)及血管化情况(术后12周血管面积比6.89%±0.32%)优于C组(1.50%±0.28%和3.17%±0.19%),而C组又优于B组(1.59%±0.19%和6.52%±0.23%),A组骨缺损未修复,各组结果差异有统计学意义(P<0.05).结论 BMSCs联合动静脉血管束植入构筑的血管化组织工程骨能促进成骨过程和新生骨的血管化,显著提高组织工程骨修复大段骨缺损的能力.     

RGD多肽表面修饰对HA-TCP生物陶瓷修复骨缺损的影响

目的：了解精氨酸-甘氨酸-天冬氨酸（Arg-Gly-Asp,RGD）多肽表面修饰对羟基磷灰石-磷酸三钙（hydroxyapatite-tricalciumphos phate,HA-TCP）修复节段性骨缺损的影响。方法：以骨髓基质干细胞（marrow stromal cells,MSCs）复合RGD多肽表面修饰的HA-TCP或单纯材料培养制备组织工程骨,选择60只新西兰白兔,制作15mm长的桡骨节段性骨缺损模型,实验根据植入不同的材料分为A、B、C和D组,A组：骨缺损区植入MSCs复合RGD多肽表面修饰的HA-TCP培养制备的组织工程骨;B组：骨缺损区植入MSCs复合HA-TCP培养制备的组织工程骨;C组：骨缺损区植入RGD多肽表面修饰的HA-TCP;D组：骨缺损区植入HA-TCP。术后4、8、16周取材,行X线检查、组织学观察、计算机图像分析和生物力学测定。结果：术后4、8、16周各组骨缺损区均有新骨生成,成骨量随时间的推移而增加。经X线、组织学和生物力学评估,成骨能力依次为：A〉B〉C〉D（P〈0.001,P〈0.05）,其中A组术后16周骨缺损完全修复,骨髓腔再通,生物力学性能接近正常骨。结论：RGD多肽表面修饰对以HA-TCP为支架材料组织工程骨的修复作用有明显优化作用。     

RGD多肽表面修饰生物陶瓷修复骨缺损BMP-2的表达

目的：了解精氨酸-甘氨酸-天冬氨酸（Arg-Gly-Asp,RGD）多肽表面修饰的羟基磷灰石-磷酸三钙（hydroxyapatite-tricalcium phosphate,HA-TCP）修复节段性骨缺损局部骨形态发生蛋白-2（bone morphogenetic protein-2,BMP-2）的表达。方法：以骨髓基质干细胞（marrow stromal cells,MSCs）复合RGD多肽表面修饰的HA-TCP或单纯材料培养制备组织工程骨,选择60只新西兰白兔,制作15mm长的桡骨节段性骨缺损模型,实验根据植入不同的材料分为A、B、C和D组,A组：骨缺损区植入MSCs复合RGD多肽表面修饰的HA-TCP培养制备的组织工程骨;B组：骨缺损区植入MSCs复合HA-TCP培养制备的组织工程骨;C组：骨缺损区植入RGD多肽表面修饰的HA-TCP;D组：骨缺损区植入HA-TCP。术后4周取材,行修复区局部BMP-2免疫组化分析。结果：术后4周各组骨缺损区均有新骨生成,修复区局部BMP-2表达水平依次为：A〉B〉C〉D（P〈0.001,P〈0.05）。结论：RGD多肽表面修饰对以HA-TCP为支架材料组织工程骨的修复作用有明显优化作用。     

Tissue-engineered constructs for urethral regeneration

Those who have urethral injury, long-distance urethral stricture, hypospadias, or epispadias need tissue for urethral repair. Tissue engineering is one of the solutions for urethroplasty. Three components essential for tissue engineering are cells, scaffolds, and bioactive factors. Several animal studies of tissue-engineered urethras have been conducted and progressed to human clinical trials by 1999. These studies have shown that the maximum distance for normal tissue regeneration in tubularized urethral replacement with unseeded matrices is 0.5 cm. Although autologous tissue-engineered tabularized urethras have been successful in clinical trials, this method could be an alternative treatment for urethral reconstruction.     

股前外侧穿支皮瓣修复足踝部软组织缺损

目的 探讨游离股前外侧穿支皮瓣修复足踝部皮肤软组织缺损的临床效果.方法对18例足踝部皮肤软组织缺损患者进行皮瓣移植,缺损面积9 cm×6 cm～26 cm×15 cm.受区彻底清创,切取股前外侧穿支皮瓣修复创面.结果 18例均获得随访,时间6～12个月.皮瓣全部成活（其中2例皮瓣术后发生血管危象,经手术探查处理后成活）,皮瓣色泽、弹性、厚度均为优良,供区及受区外观均满意.结论 股前外侧穿支皮瓣供区隐蔽,用于足踝部皮肤软组织缺损修复,临床效果良好.     

股前外侧皮瓣修复伴有骨外露的四肢皮肤软组织缺损

目的探讨游离股前外侧皮瓣修复伴有骨外露的四肢皮肤软组织缺损的临床效果。方法对62例伴有骨外露的四肢皮肤软组织缺损患者进行皮瓣移植,缺损面积6 cm×4 cm~25 cm×15 cm。术前、术中彻底清创受区,切取股前外侧皮瓣修复创面,处理血管危象。结果 62例均获得随访,时间6~12个月。出现血管危象6例,经及时处理后皮瓣恢复血液循环5例,皮瓣坏死1例,成功率为98.39%。结论股前外侧皮瓣供区隐蔽,简便实用,可用于伴有骨外露的四肢皮肤软组织缺损修复。     

Uretroplastia con injerto de mucosa oral para la estenosis de uretra bulbar: resultados y factores predictivos asociados al éxito

Introduction and objectiveThe bulbar urethra is the location where urethral stricture is most commonly observed. The most successful method for long and recurrent urethral stenosis is graft urethroplasty. The most successful graft source is buccal mucosa, with advantages like easy adaptation to the corporeal bed, thick epithelium, thin lamina propria with rich vascular structure and easy ability to obtain the graft. In this study we aimed to retrospectively assess the outcomes and predictive factors affecting surgical success of our buccal mucosal graft urethroplasty surgery performed for bulbar urethra stenosis with moderate length.Material and methodIn this study, we monitored 51 patients with mean 4.4 cm bulbar urethral stricture length for mean 17 months follow-up. From operative and postoperative data, stenosis length, operation duration, Qmax, International Prostate Symptom Score, International Index of Erectile Function-Erectile Function and OF, success rates in total and in subgroups (age, according to DVIU, etiology, BMI and DM), follow-up duration, complications, re-stricture time and number were assessed.ResultsThe total success of the operations was 86.3%. In 17 months, the re-stricture rate was 13.7%. Oral and urethral complications were all minor. The complications with longest duration (6 months) were ejaculation, erection problems and urethral fístula. Mean time to re-stricture was 11 months. All re-stricture patients were relieved by one DVIU session each.ConclusionFor bulbar urethral stricture longer than 2 cm and with recurrence, the dorsal buccal mucosa graft replacement is a very successful method with low complication rates.     

背阔肌皮瓣游离移植修复下肢巨大软组织缺损

目的探讨背阔肌皮瓣游离移植修复足跟合并小腿或足底、足背巨大软组织缺损的临床效果。方法1998年3月~2005年5月,采用背阔肌皮瓣游离移植修复10例足跟合并小腿或足底、足背软组织缺损的巨大创面。其中男9例,女1例,年龄32~60岁。病程:2h~2个月。耕田机损伤5例,交通事故伤2例,毒蛇咬伤2例,电击伤1例。其中足跟后侧合并小腿后侧皮肤、腓肠肌及跟腱不同程度缺损8例,缺损范围21cm×12cm~35cm×15cm;足跟合并足底、足背和踝部皮肤软组织缺损2例,缺损分别为27cm×14cm和30cm×21cm。均合并骨外露,6例合并骨折,2例合并胫后血管及胫神经损伤,4例合并踝关节开放感染。切取背阔肌皮瓣25cm×14cm~33cm×24cm,其中1例背阔肌皮瓣达38cm×18cm。供区均采用大张中厚皮片移植覆盖。结果术后10例背阔肌皮瓣全部成活,无血管危象和感染发生,创面均期愈合。术后获随访3~24个月,其中5例皮瓣外形臃肿,影响穿鞋,二期行皮瓣修薄整形术;重建感觉的5例患者3例恢复保护性感觉,2例胫神经损伤患者足底痛、温觉恢复,足内在肌功能无明显恢复;5例桥接腓肠肌的背阔肌肌力恢复至级,踝关节功能部分恢复。无继发溃疡发生,所有患者均恢复负重与行走功能。3例供区植皮部分坏死,其中2例经换药后治愈,1例二期植皮修复,余供区植皮均成活。结论背阔肌皮瓣血运丰富,切取范围大,肌瓣可填塞死腔,抗感染能力强,是修复足跟合并邻近巨大皮肤软组织缺损和骨外露感染创面的一种理想皮瓣。     

手背软组织缺损皮瓣修复的临床选择

目的探讨利用三种游离皮瓣及带前臂皮神经营养血管岛状皮瓣修复手背软组织缺损的临床效果。方法采用小腿外侧皮支皮瓣、足背皮瓣、股前外侧皮瓣及带前臂内、外、背侧皮神经营养血管岛状皮瓣,选择性修复手背软组织缺损225例。结果本组174例三种游离皮瓣中170例成活．4例出现血管危象,经及时探查1例皮瓣全部坏死,3例部分坏死：51例前臂皮神经皮瓣．除6例远端部分坏死外,余全部成活。随访6个月～8年．皮瓣质地好,色泽正常,手外形与功能改善满意,痛、深触觉逐渐恢复正常。结论选择性游离皮瓣修复效果普遍优于前臂皮神经营养血管的岛状皮瓣,适于临床开展。     

微创Ilizarov外固定架治疗胫骨感染性骨不连

目的评价Ilizarov外固定架下采用骨延长技术治疗胫骨感染性骨不连的临床结果及功能情况。方法22例胫骨感染性骨不连患者感染端进行清创后骨缺损的长度为4．1～12．6（6．72±2．42）cm。其中21例为小面积软组织缺损者,采用局部皮瓣转移覆盖,1例大面积软组织缺损者（8cm×5cm）,采用腓肠肌皮瓣转移术覆盖创面,22例均采用Ilizarov外固定架进行骨延长治疗。结果22例均获得随访,时间12～24（17．64±3．84）个月。骨不连均获得愈合,愈合时间7～19（9．86±3．01）个月,感染均得到控制。10例在延长过程中有局部针道渗液,治疗后愈合。牵引成骨的长度为4．1～12．6（6．72±2．42）cm。根据Paley骨折愈合评分标准：优13例,良7例,中2例。结论对于胫骨感染性骨不连,使用Ilizarov外固定架进行骨延长治疗临床结果及功能恢复满意。     

自体骨髓间充质干细胞复合胶原膜修复兔膝关节全层软骨缺损的实验研究

目的研究自体骨髓间充质干细胞(m esenchym a l stem ce lls,M SC s)复合胶原膜(m ed ica l co llagenm em brane of gu ided tissue regeneration,M CM G)对兔膝关节局部全层软骨缺损的修复作用。方法实验动物选用健康的新西兰大白兔27只,3~4月龄,体重2.1~3.4 kg,每只抽取自体骨髓3~4 m l,体外分离培养后以5.5×108/m l密度种植于M CM G支架上体外培养48 h,制成M SC s/M CM G复合物,将以上27只实验动物手术制成双膝关节、股骨内髁负重区及滑车全层软骨缺损模型后,随机分成A、B、C 3组,每组各9只。A组双侧股骨内髁负重区、滑车软骨缺损处植入M CM G/M SC s复合物;B组植入单纯M CM G;C组不作任何植入,为空白组,分别于术后4、8和12周各处死3只,取材进行大体、组织学及免疫组织化学染色观察,根据关节软骨组织学半定量评分标准进行评分。结果A组术后4周即可重建关节骨软骨缺损;修复软骨在观察期内逐渐变厚,在12周内始终保持关节面及软骨下骨结构完整,为透明软骨样修复,表面光整,与周围软骨色泽相近;而B组和C组12周时仍为纤维软骨样修复,色泽浅黄,呈虫蚀样改变,仍有空洞。A组糖胺多糖及Ⅱ型胶原表达呈阳性,B、C组则明显减少。术后4、8和12周各组组织学半定量评分及术后12周大体结果显示:股骨内髁负重区与滑车修复对比差异无统计学意义(P>0.05),A组明显优于B组和C组(P<0.05);B组优于C组(P<0.05)。结论自体M SC s复合M CM G在体内环境下可形成透明软骨修复兔膝关节全层软骨缺损。M CM G符合组织工程软骨基质材料的基本要求,有望成为一种理想的用于关节全层软骨缺损修复的软骨组织工程载体材料。     

胸脐双动脉蒂超薄皮瓣修复手及手指近端软组织缺损

目的探讨双侧胸脐皮瓣修复手掌、背侧皮肤,以及手指近端软组织缺损的方法及疗效. 方法 1992年8月～2000年6月共收治手部软组织缺损20例,其中男9例,女11例,年龄17～35岁.致伤原因:挤压伤4例,机器碾轧伤5例,撕脱伤7例,梳棉机伤2例,热轧伤2例.受伤至手术时间3～11小时,创面软组织缺损范围8 cm× 12 cm～10 cm×20 cm.同时设计切取两侧腹壁下动脉脐旁穿支所支配区域的两块皮瓣,将其制成超薄皮瓣,一块皮瓣修复掌屈侧缺损,另一块修复掌背侧创面,并将覆盖于手指近端缺损的皮瓣设计成分叶皮瓣. 结果 19例获随访 8～12个月,平均9.8个月,所有皮瓣均全部成活,皮瓣修复处的色泽基本正常,两点辨别觉恢复较满意,外观不臃肿. 结论双侧胸脐皮瓣能很好地修复全手掌及手指近端软组织缺损,术中无需吻合血管,手术简便,易于推广.     

股前外侧皮瓣修复四肢软组织缺损22例

目的探讨应用股前外侧皮瓣修复四肢软组织缺损的临床效果。方法对22例四肢软组织缺损患者采用股前外侧皮瓣进行修复。缺损面积8 cm×10 cm～12 cm×24 cm;皮瓣切取面积10 cm×12 cm-14 cm×26 cm。结果 22例皮瓣全部成活,经6～20个月随访,3个月后恢复感觉。10例二期修复,皮瓣外观及感觉良好。结论选用股前外侧皮瓣修复四肢软组织缺损临床效果较佳。     

应用携带肌肉的小腿内侧皮瓣修复足部软组织缺损

目的探讨应用携带肌肉的小腿内侧皮瓣修复足部软组织缺损的临床效果。方法采用携带肌肉的小腿内侧皮瓣修复足部软组织缺损9例,缺损面积：6cm×8cm～8cm×18cm。供区均选用同侧小腿。皮瓣切取面积：7cm×9cm～10cm×20cm。结果9例皮瓣均一期成活。获随访7例,时间4～13个月,皮瓣质地柔软,供区植皮处无明显瘢痕挛缩,外观及功能均满意。结论该类皮瓣成活率高,操作简单,切取方便,血供可靠,抗感染能力强,是修复足部软组织缺损较理想皮瓣。     

Autogenous venous graft with one-stage prepared Schwann cells as a conduit for repair of long segmental nerve defects

The use of autogenous venous graft with intraluminal injection of Schwann cells to enhance nerve regeneration of long segmental nerve defects was evaluated in a rabbit tibial nerve-repair model. Schwann cells were isolated from the excised rabbit tibial nerve by using the polylysine differential adhesion method. The cultured cells were identified by immunocytochemical labeling for S-100 protein. Tibial nerve defects in 4-cm segments were created in 24 animals, which were then divided into three groups. In Group 1, the tibial nerve defect was repaired with interposition vein graft alone; in Group 2, the nerve defect was repaired with a vein graft with intraluminal injection of Schwann-cell suspension; in Group 3, the nerve defect was repaired by autogenous nerve graft alone. At 2 months postoperatively, electrophysiologic evaluation showed that an evoked muscle action potential was recorded for the animals in Group 2, with vein grafting plus Schwann cells, and for those in Group 3, with autogenous nerve grafting, but not for those in Group 1, where vein grafting alone was used. The average motor nerve conduction velocity in the group with vein grafting and Schwann cells was 3.4 +/- 1.5 m/sec, which was slower than the nerve grafting group (7.8 +/- 1.8 m/sec). Histologic analysis confirmed there was formation of new nerve fascicles with myelination in the vein graft filled with Schwann cells. No nerve regrowth was found in the vein grafts without Schwann cells. These results suggested that isolated Schwann cells are able to survive in a vein graft, and that the vein graft with intraluminal seeded Schwann cells could be an alternative for repairing injured nerves with long gaps.     

Apatite-coated silk fibroin scaffolds to healing mandibular border defects in canines

Tissue engineering has become a new approach for repairing bony defects. Highly porous osteoconductive scaffolds perform the important role for the success of bone regeneration. By biomimetic strategy, apatite-coated porous biomaterial based on silk fibroin scaffolds (SS) might provide an enhanced osteogenic environment for bone-related outcomes. To assess the effects of apatite-coated silk fibroin (mSS) biomaterials for bone healing as a tissue engineered bony scaffold, we explored a tissue engineered bony graft using mSS seeded with osteogenically induced autologous bone marrow stromal cells (bMSCs) to repair inferior mandibular border defects in a canine model. The results were compared with those treated with bMSCs/SS constructs, mSS alone, SS alone, autologous mandibular grafts and untreated blank defects. According to radiographic and histological examination, new bone formation was observed from 4 weeks post-operation, and the defect site was completely repaired after 12 months for the bMSCs/mSS group. In the bMSCs/SS group, new bone formation was observed with more residual silk scaffold remaining at the center of the defect compared with the bMSCs/mSS group. The engineered bone with bMSCs/mSS achieved satisfactory bone mineral densities (BMD) at 12 months post-operation close to those of normal mandible (p > 0.05). The quantities of newly formed bone area for the bMSCs/mSS group was higher than the bMSCs/SS group (p < 0.01), but no significant differences were found when compared with the autograft group (p > 0.05). In contrast, bony defects remained in the center with undegraded silk fibroin scaffold and fibrous connective tissue, and new bone only formed at the periphery in the groups treated with mSS or SS alone. The results suggested that apatite-coated silk fibroin scaffolds combined with bMSCs could be successfully used to repair mandibular critical size border defects and the premineralization of these porous silk fibroin protein scaffolds provided an increased osteoconductive environment for bMSCs to regenerate sufficient new bone tissue.     

自体骨膜延迟游离移植修复成年后关节软骨缺损的实验研究

目的：研究年龄对自体骨膜游离移植修复关节软骨缺损的影响,探讨延迟游离移植能否提高成年后骨膜修复软骨能力。方法：选中国白兔,成年兔20只,幼兔10只,分3组。A组：成年兔左膝骨膜直接游离移植组;B组：成年兔右膝骨膜延迟游离移植组;C组：幼兔骨膜直接游离移植组,取骨膜或骨膜新生组织、行光镜、电镜组织学观察比较。结果：移植前B、C组骨膜厚度、细胞计数及细胞活跃程度均优于A组（均为P＜0．01）,移植后12周3组关节软骨缺损获得不同程度修复,C组优于A组（P＜0．01）及B组（P＜0．05）,B组优于A组（P＜0．01）。结论：自体骨膜局部剥离、原位激活,体内培养、延迟游离移植可提高成年骨膜成软骨能力,更好地修复成年后关节软骨缺损。     

Experimental defect in rabbit urethra repaired with acellular aortic matrix

Urethral reconstruction following failed hypospadias repair or post-traumatic chronic stricture requires adequate amounts of tissue. Many surgical techniques utilizing different types of biological tissues have been attempted: (a) vascularized skin flaps from the prepuce, scrotum or penile shaft; (b) full-thickness free skin grafts; (c) vesical or buccal mucosa grafts; (d) ureter; artery; vein and appendix tissue. More recently, biodegradable polymers have also been used as delivery vehicles of urothelial cells in animals. It has been demonstrated that the implant of an acellular tissue matrix in the bladder can guide the regeneration of urothelium, blood vessels, smooth muscle and nerves. The aim of this study was to create an experimental model of urethral defect, and then repair it by implanting homologous acellular aortic grafts as urethral substitutes. An acellular matrix was obtained by detergent enzymatic treatment of rabbit thoracic aorta. The growth of urethral epithelium was verified in vitro, and homologous acellular vessels were then implanted in rabbits, bridging a previous surgical urethral defect. The outcome of reconstructive surgery was evaluated histologically at 10 days, 3 weeks, 3 and 12 months. As the time after surgery increased, the neourothelium became less thick, signs of inflammatory response disappeared, and the orientation of collagen fibrils and smooth muscle fascicles resembled that of a normal urethra. The implants displayed abundant vascularization, and the luminal surface started to become irregular. Acellular blood vessels may represent a promising approach to urethral defect therapy for different reasons: (a) unlimited availability, (b) readily obtainable in different lengths and gauges, (c) the potential for being organized as tissue bank, and (d) that just one simple surgical procedure is needed. Nevertheless, before this technique can be applied in humans, it must be tested in more species and animals. Received: 25 March 1999 / Accepted: 25 June 1999