Computational fluid dynamics of flow through a free flap in reconstructive surgery

A computational fluid dynamics investigation into fluid flow through a simplified arterial network of a transverse rectus abdominis musculocutaneous (TRAM) free flap has been carried out. This paper focuses on the effect of anastomosis on the fluid flow and the subsequent wall shear stress distribution both inside the anastomotic region and also in the downstream network. The simplified model of the arterial network consists of an axial perforator and its connecting axial flap vessels. Two different anastomosis situations are considered in this paper: one in which the anastomosis forms a bump type stenosis and a convergent type stenosis. Both are typical examples of end-to-end type anastomosis performed in reconstructive surgery. Various degrees of stenosis have been investigated and have shown that as the degree of stenosis increases, the wall shear stress also increases. The increase in wall shear stress is not a favourable feature and can be a reason as to why free flap reconstructive surgery can fail. For the case of the bump stenosis with a large degree of stenosis separation bubbles formed just downstream of the anastomosis. This flow feature could lead to a ‘clogging’ effect and subsequently lead to partial necrosis of the flap. No separation bubbles were observed in the case of the convergent stenosis. It was found that the increase in wall shear stress was a local effect and further downstream the degree of stenosis did not influence the wall shear stress.