Invited Discussion

The venous flow-through flap (VFTF) is an underutilized resource for thin vascular coverage of soft tissue defects of the hand and other areas that suffer from bulky tissue transfer. It has several advantages over conventional reconstructive options, such as the flag,[1] kite,[2] island,[3] and cross-finger flaps.[4] [5] [6] VFTFs have the ability of covering larger defects, defects at the ulnar aspect of the fifth finger, and radial aspect of the index finger or thumb. When a digit sustains soft-tissue loss in crush-avulsion injury or amputation, the flow-through vein can be interposed between digital arteries, allowing the VFTF to both resurface and revascularize. The VFTF is transplanted as free tissue in a single stage, avoiding secondary surgical procedures and the dependent arm positioning associated with the pedicled groin flap. VFTFs from the forearm have other advantages over free-tissue transfers: there is little donor morbidity, no artery is sacrificed, and the length, branching pattern, and diameter of the vascular pedicle can be selected from veins visible during a preoperative design phase. Disadvantages of the VFTF include the need for microsurgical expertise, an assistant, and longer initial hospital stay if intravenous anticoagulation is used.

The concept of perfusing tissue through its subcutaneous venous plexus was first described and studied by Nakayama and colleagues.[7] Since then, a number of experimental[8] [9] [10] [11] and clinical[12] [13] [14] [15] [16] studies have drawn attention to recurrent themes regarding the use of these unconventional flaps. First, arterialized VFTFs, those interposed between an artery and a vein (A-V-V) or two arteries (A-V-A), are more reliable than purely venous flaps, those interposed between two veins (V-V-V). Second, the natural evolution of the flap includes congestion over the first few days, with varying degrees of ecchymosis by the fifth day. This usually resolves between the second and third weeks, presumably after peripheral arterialization occurs. Third, small VFTFs are usually reliable, but larger VFTFs are susceptible to partial necrosis, thus limiting flap application beyond hand defects.

DeLorenzi and colleagues present one of the largest published experiences with arterialized VFTFs. The data presented contribute to the current state of knowledge in the clinical use of VFTFs. The authors reaffirm our understanding that these flaps are reliable and that early congestion gives way to normal capillary refill after 2 to 3 weeks. Furthermore, they present new information regarding flap survival. They introduce patient age as another factor which may affect flap survival, and present evidence that the condition of the recipient bed may not affect flap survival. However, in contrast to the literature, the authors claim that there is no need for multiple out-flow vessels in arterialized VFTFs. This point should be clarified. Tsai et al.[17] recommended multiple inflow and outflow vein repair when reconstructing dorsal skin defects in replanted digits. This was based on clinical observation related to purely venous VFTFs (V-V-V), not arterialized VFTFs. Woo and colleagues[18] recommended multiple outflow vein repairs based on clinical observation, to decrease partial necrosis in larger arterialized VFTFs. This was followed by a formal recommendation to repair at least two or more efferent veins in larger VFTFs, based on an experimental study in canines, which showed that when the arterialized VFTF is designed to contain a venous plexus at its center, and is drained by two or more efferent veins, the survival patterns between larger arterialized VFTFs and conventional flaps were not statistically different.[19]

Unfortunately, the authors do not report the size of the VFTFs in this series, and the reader cannot therefore determine if increasing flap size correlates with decreasing survival on a percent basis. When designing larger VFTFs, we follow the recommendations of Woo et al.[18] and attempt to place the venous plexus over the entire area of the flap, in order to decrease areas that are remote from functioning veins (Fig. [1]). This usually requires multiple outflow vein repair to decrease blind-ending channels. In our experience, VFTFs can reliably cover bone or tendon. However, some portion of the wound bed, usually the periphery, needs to be available, so that arterialization can occur by the second week. Infection which affects the entire wound bed is the only strict contraindication to the transplantation of VFTFs.

It is a pleasure to review work from other groups investigating the clinical use of VFTFs. Techniques such as delay[20] or expansion,[21] pre-conditioning the VFTF by initiating angiogenesis, have led to increased flap survival in the animal model. Hopefully, on-going interest in these flaps will lead to application of such techniques in the clinical arena, resulting in VFTFs which display less congestion and are ultimately reliable regardless of size.

REFERENCES

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