These authors measured the blood flow in different free flaps with transit-time flowmeter. According to the preliminary results, the venous outflow in a free fibular graft is surprisingly low, compared to the arterial inflow. In order to clarify the hemodynamics of a free bone-only fibular graft, they measured the flow in the artery and vein in the leg, just before ligating the pedicle vessels. In a second procedure, they performed a distal shunt between the artery and vein, and measured the effect on circulation.
Ten consecutive patients operated on for femoral head necrosis or nonunion of the femoral neck were included in the study. The mean age of patients was 34.5 years (range: 20 to 46 years) and the male to female ratio was 7:3. The fibular bone was dissected extraperiosteally and cut both proximally and distally. The distal fibular vessels were ligated and the bone was dissected free, so that it was in contact only with the proximal fibular vessels. Before ligating the pedicle, the flow in the peroneal artery and vein was measured using a transit-time flowmeter. An anastomosis was performed to the distal ends of the peroneal vessels, forming an arteriovenous shunt to the distal end of the fibula. The effect of the shunt on the flow was then measured.
The fibular grafts were, on average, 17.7 cm long. They all were bone-only grafts without septocutaneous portions. The arterial inflow was, on average, 6.4 ml/in (range: 10 to 3 ml/min) and the venous outflow was 2.3 ml/min (range: 1 to 5 ml/min). After opening of the distal arteriovenous shunt, the flow was 10.7 ml/min (4 to 22 ml/min) in the artery and 3.5 ml/min (1 to 7 ml/min) in the vein.
Venous outflow was three times smaller than arterial inflow in the free fibular bone-only graft. Obviously, a substantial portion of the venous outflow runs out from the medullary canal of the fibula. It is possible that the venous anastomosis of a bone-only graft is not mandatory for flap survival. The arteriovenous fistula seemed to increase the flow both in the artery and in the vein in the free fibular graft. Performing a shunt can be advantageous for flap survival in selected cases. An A-V shunt will increase the arterial inflow and may help to keep the microvascular anastomosis open.
