In situ saphenous vein bypass: 1962 to 1987.

The historical development of in situ saphenous vein bypass has been traced over the past quarter century. The principal advantage of the in situ vein graft over the conventional reversed vein graft is the increase in flow that occurs in a tapered channel. Both the advantages of this hemodynamic observation in the in situ graft and its disadvantages in the reversed graft are accentuated in longer bypasses as the discrepancy in proximal and distal vein diameter increases. Furthermore, there is new evidence that unusual shear and stress tend to occur at sites of severe vein-artery discrepancy, such as seen in reversed vein grafts but less so in the in situ graft. Experience with the in situ graft has shown that another important advantage is that there is less chance of trauma to the vein from overdistention and rotation, which is inherent in the operation since the vein is not removed from its bed. On the other hand, the overly traumatic disruption of venous valves required in the in situ operation can cause subendothelial damage with resultant fibrosis of the vein. Although it has been demonstrated that equally good results with reversed as with in situ grafts can be obtained by careful attention to detail, this is true only for grafts carried to the popliteal level. The advantages of increased flow and less shear damage because of tapering, physiologic distention under arterial pressure, and finally, decreased handling and manipulation of the vein have become increasingly important as bypass is carried distal to the knee. I believe that the evidence to date indicates that the in situ operation has strong superiority over the conventional reversed graft for reconstructive operations on the lower extremity extending below the knee.