Effect of torsion on microvenous anastomotic patency in a rat model and early thrombolytic phenomenon.

Torsion at the microanastomosis site is a basic fault and should be avoided. In this study, we investigate the effects of different degrees of microvenous torsion on patency and its physical changes on anastomoses in a rat model. One hundred anastomoses were performed at different degrees of torsion, using femoral veins of Sprague-Dawley rats. Anastomoses were performed at 0 degrees, 45 degrees, 90 degrees, 135 degrees, and 180 degrees of torsion randomly. Patency tests immediately, 1 h, and 1 week after the anastomoses were checked, using the refill test. Measurements of external diameter were recorded at three points: one at the anastomosis site, and the others 2 mm proximal and distal to the anastomotic site. Finally, histopathologic and scanning electron microscopy studies were performed. Subsequently, because of the peculiar phenomenon of early recannulation of the thrombosed vessels, 20 vessels were also explored on the first and the third days postoperatively. The data demonstrate that torsion at 180 degrees, compared with 0 degrees, 45 degrees, and 90 degrees, impaired patency significantly (P < 0.005). In the subsequent study of 20 veins that were thrombosed on the first day, all became patent on the third day and remained so. In conclusion, rotation of a microvenous anastomosis begins to affect the patency rate at 90 degrees of torsion, and at 180 degrees has a patency rate of only 25%. However, all become patent again from the third day onwards. Thrombosis of rat femoral veins without chronic obstruction results in rapid lysis of thrombus and transient proliferative changes.