Vein Grafts in Free Flap Reconstruction: Review of Indications and Institutional Pearls

Summary:

Vein grafts enable soft-tissue reconstruction in cases of insufficient pedicle length, a lack of nearby recipient vessels, and a wide zone of injury caused by trauma or radiation therapy. The purpose of this article is to provide a comprehensive review of vein grafts in free flap reconstruction focusing on the timing of arteriovenous loops, complications, and surgical technique. Vein graft indications, types of vein grafts, and location-specific considerations are also reviewed. Three reconstructive microsurgeons at high-volume centers were asked to offer institutional pearls on the order of anastomosis, selection of donor veins, and timing of arteriovenous loops. In terms of gap length, vessel gaps less than 10 cm may be reconstructed with an interposition or transposition vein graft. For longer gaps, surgeons should consider the use of arteriovenous loops, transposition arteriovenous loops, or flow-through flaps. Both one and two-stage arteriovenous loops are used, depending on patient comorbidities, potential exposure of critical structures, and surgeon preference. Although one-stage arteriovenous loops expedite the reconstructive process, two-stage arteriovenous loops require shorter operations and help identify patients at risk of flap failure. Although whether the use of vein grafts increases flap failure rates is controversial, complications are highest in lower extremity reconstruction, cases of a prolonged interval between stages in two-stage arteriovenous loops, and unplanned vein grafts.

In the past several decades, free flaps have become a reliable method for reconstructing complex defects. Although local vessels are ideal recipients, there are many scenarios when vein grafts become necessary. They are most commonly used in head and neck, lower extremity, and perineal reconstruction.^1–3 However, they are also frequently used in the breast, trunk, and upper extremity. With such a wide variety of grafts and staging strategies, many institutions have developed specific protocols and surgical techniques. The purpose of this article is to review the indications for vein grafts in the setting of free flap reconstruction, types of vein grafts, the timing of arteriovenous loops, complications, and surgical techniques.

INDICATIONS FOR VEIN GRAFTS

The most common indications for vein grafting are insufficient pedicle length or a paucity of recipient vessels.² For head and neck reconstruction, irradiation and prior neck dissection decrease the availability of local recipient vessels.⁴ In lower extremity reconstruction, atherosclerosis or a wide zone of injury limits the availability of local recipient vessels. Vein grafts also play a role in salvage situations after vessel thrombosis, intraoperative venous congestion, vessel injury, or as a means of supercharging a congested flap.^2,5 Conditions that frequently create a large field of injury and deplete local vessels include infection, trauma, and ablative oncologic surgery. Importantly, appropriate flap selection may circumvent the need for a vein graft. For example, choosing the latissimus flap with a distally based skin island for a scalp defect may allow the surgeon to reach the neck without a vein graft.

TYPES OF VEIN GRAFTS

There are four categories of vein grafts to consider. First, with an interposition vein graft, a donor vein is harvested and used as a conduit to connect the donor to the recipient artery or vein, which requires two separate anastomoses (Fig. 1). A transposition vein graft uses a branch of the recipient vein so that only one anastomosis with the pedicle vessel is required. The third option is an arteriovenous loop, in which a donor vein is used to bridge an arteriovenous gap. This method requires four anastomoses and can be performed in one or two stages. The final option is a transposition arteriovenous loop, in which a branch of the recipient vein is used as the loop, which requires three anastomoses (Fig. 2).

Fig. 1.

Interposition vein graft for lower extremity trauma. The vein graft is anastomosed end-to-side to the descending genicular artery proximally and the flap artery distally. (Illustrated by Megan Llewellyn, M.S.M.I., C.M.I.; copyright Duke University; with permission under a CC BY-ND 4.0 license.)

Fig. 2.

Transposition arteriovenous loop using the saphenous vein, which is anastomosed end-to-side to the common femoral artery. This arteriovenous loop can be used in the setting of an abdominal wall transplantation (Erdmann D, Atia A, Phillips BT, et al. Small bowel and abdominal wall transplantation: A novel technique for synchronous revascularization. Am J Transplant. 2019;19:2122–2126.). (Illustrated by Megan Llewellyn, M.S.M.I., C.M.I.; copyright Duke University; with permission under a CC BY-ND 4.0 license.)

Which type to use depends on gap size, availability of a nearby vein for transposition, and surgeon preference. Interposition vein grafts are typically used when the vessel gap is less than 10 cm, and an arteriovenous loop is used for larger gaps.⁶ Another option for large gaps is a flow-through flap, in which a second free flap is used to bridge the recipient vessels to the main defect-filling flap. Although there is added donor-site morbidity, using a radial forearm flap as a flow-through flap results in fewer incidents of flap compromise compared to a long interposition vein graft, defined as greater than 10 cm.⁷ A flow-through free fibula osteocutaneous flap can be used in the unique circumstance when an extremity defect requiring bone with or without soft tissue also necessitates arterial reconstruction.^8,9

DONOR VEINS

When planning reconstruction, selection of the donor vein depends on the length, appropriate size match, donor-site morbidity, and the ability to efficiently harvest the vein. The greater saphenous vein is often easiest to harvest for lower extremity reconstruction. In addition to wound healing complications, harvest can result in numbness/paresthesia in 33 to 41 percent of patients.^10–12 Transposition of the cephalic vein is a common option for head and neck and thoracic wall reconstruction because it provides good length and is outside the zone of irradiation.¹³ Other less common donor veins include the external jugular, basilic, lesser saphenous, and dorsal foot veins. When examining interposition vein grafting complications in head and neck reconstruction, the vein graft donor site was not associated with flap compromise or flap loss.^14,15

TIMING OF ARTERIOVENOUS LOOPS

Arteriovenous loops provide low-resistance, high-flow shunts that can be used for one- or two-stage free flaps. Unlike interposition vein grafts, the length of the arterial and venous limbs can be adjusted as needed. In one-stage reconstructions, the vein graft is harvested and the free flap is inset in the same operation (Fig. 3). In two-stage reconstructions, the vein graft is harvested and two anastomoses are performed to the recipient vessels in the first stage, and the free flap is transferred in the second stage (Fig. 4). Advantages of one-stage reconstructions include needing only one procedure and a shorter length of stay. Proponents argue that assessing the patency of the loop does not require a long period.¹⁶ The two-stage approach also has several advantages, including a shorter operative time for each procedure and the ability to potentially detect thrombosis by means of ultrasonography before flap transfer, especially in hypercoagulable patients. Proponents of the two-stage approach assert that by delaying flap transfer, the venous loop can dilate and may help prevent subsequent venous stasis and thrombus formation.¹⁷ However, too long of an interval between stages will increase the extent of local inflammation (perhaps thickening the vessel wall) or lead to too much dilation, thereby creating a caliber mismatch with the flap vessels at the subsequent procedure. A recent meta-analysis of arteriovenous loops reported an average interval of 8.8 days between stages.¹⁸ Another study reported an increased risk of flap thrombosis as the time interval between stages increased, suggesting that flap transfer should not be delayed beyond 10 days.³

Fig. 3.

(Left) One-stage arteriovenous loop for cranioplasty coverage because of a diminutive superficial temporal artery with poor flow. The saphenous vein is anastomosed to the facial artery and the external jugular vein. (Right) The loop was divided and a radial forearm flap was inset in a single stage. The radial artery is anastomosed to the radial end of the loop and a vena comitans was coupled to the venous end of the loop. The cephalic vein is coupled to the superficial temporal vein.

Fig. 4.

(Left) Two-stage arteriovenous loop for a chronic nonhealing back wound. The saphenous vein is anastomosed to the suprascapular artery and coupled to the external jugular vein. (Right) The loop was divided in the second stage and an anterolateral thigh flap with a pedicled vastus lateralis muscle flap was inset to reconstruct the defect.

In this same meta-analysis, rates of major complications (23.5 percent) and flap failure (23.7 percent) for two-stage procedures were significantly higher than rates of major complications (15.7 percent) and flap failure (4.2 percent) for one-stage procedures.¹⁸ However, there were significantly more two-stage procedures for lower extremity reconstruction, which is known to be a high-risk location even without an arteriovenous loop.^19,20 Conversely, in a single-institution comparative study, there were no differences in complications or flap failure between one-stage and two-stage arteriovenous loops when considering all cases and when just examining lower extremity reconstruction.³ This result was in spite of patients with two-stage reconstructions being older, having a higher rate of peripheral vascular disease, and including a higher proportion of lower extremity reconstructions. The authors suggest that the higher complication rate in two-stage reconstructions in the meta-analysis by Knackstedt et al. is attributable to the wide range of loop-flap time intervals and selection bias given that four of the included studies preferentially resorted to two-stages in high-risk cases.¹⁸ Finally, in an abstract examining 54 free flaps requiring vein grafts, all of the 11 flap failures occurred in one-stage procedures and all nine of the two-stage arteriovenous loops that received flaps survived, suggesting that staging the reconstruction helps identify patients who might have developed flap compromise during a one-stage procedure.²¹ In patients undergoing a two-stage arteriovenous loop, thrombectomy was performed in 11 to 14 percent of patients before the second stage and aborted after a failed first stage in 11 to 19 percent.^3,17,21 An alternative interpretation may be that the vein grafts were used because of unanticipated changes in the nature of the original operation, including compromised vessels. Despite conflicting data, both staging strategies can be safely used, depending on patient comorbidities, ability to provide soft-tissue coverage, location of the reconstruction, and surgeon experience and preference.

VEIN GRAFTS BY LOCATION

Head and Neck

Reconstruction after ablative surgery for squamous cell carcinoma is the most common indication for vein grafting in the head and neck.²² When arteriovenous loops are used, a one-stage approach is more common than a two-stage approach (Fig. 5).¹⁸ The most common flaps used for head and neck reconstruction are the fibula, rectus abdominis, latissimus dorsi, radial forearm, and anterolateral thigh flaps.^6,7,13,22,23 The facial, superior thyroid, external carotid, superficial temporal, and transverse cervical arteries are the most common recipient arteries, and the internal jugular, facial, superficial temporal, and external jugular veins are the most common recipient veins.^4,6,14 Although some studies show increased flap failure rates when vein grafts are used for head and neck reconstruction,^14,23 others show that interposition vein grafts are not associated with decreased flap survival.²²

Fig. 5.

Arteriovenous loop for reconstruction of a scalp defect. The vein graft is anastomosed to the facial vessels. (Illustrated by Megan Llewellyn, M.S.M.I., C.M.I.; copyright Duke University; with permission under a CC BY-ND 4.0 license.)

Lower Extremity

Lower extremity free flap reconstruction is inherently higher risk compared to other locations.³ When an arteriovenous loop is used in the lower extremity, rates of failure are higher for both one-stage and two-stage reconstructions.³ The latissimus dorsi and anterolateral thigh are the most common free flap choices for soft-tissue reconstruction, and the fibular flap is most commonly used for bony reconstruction.^3,24 The greater saphenous vein is the most common donor vein.^3,24 In a large cohort study of all two-stage arteriovenous loop reconstructions, 81 percent were performed in the lower extremity, compared with 49 percent of one-stage reconstructions.³ Likewise, in a recent meta-analysis, there was a significantly higher number of lower extremity cases using a two-stage approach.¹⁸ One way to enhance the success of lower extremity arteriovenous loops is preoperative planning. In a study including 15 planned arteriovenous loops, 11 of which were in the lower extremity, the success rate was 93 percent, with no differences between flaps with and without vein grafts. Conversely, one of two flaps that required unplanned vein grafting intraoperatively failed.²⁵ Despite a small sample size, the study reminds surgeons to plan for a potential vein graft.

Upper Extremity

Avulsion and crush injuries create a significant zone of injury that may result in segmental vessel defects. One option is to use interposition vein grafts to repair both venous and arterial gaps. Although the success rate of interposition vein grafting for fingertip replantations is acceptable at 80.8 percent, it is lower than the survival rate of 93.1 percent in the simple end-to-end anastomosis group.²⁶ Another method of repairing vessel gaps during replantation is transposition vein grafting. In a single-institution study on thumb replantation, the authors report transposing the vein on the dorsal radial side of the index finger so that only one anastomosis is performed. To repair the arterial gap, the deep inferior epigastric artery is used as a conduit for better size match compared to a vein graft. Five of the six patients requiring an arterial conduit had successful replantations, and two of the four patients requiring a venous transposition had successful replantations.²⁷

Perineum

A growing use for vein grafts in transgender surgery is phalloplasty. In one study including vein grafts for 23 phalloplasties, the authors anticipated needing a longer pedicle, and transposition arteriovenous loops were planned. The complication rate in their cohort was significantly higher when the vein graft was unplanned, suggesting that a contingency plan should be discussed preoperatively for cases with potential for inadequate recipient vessels or pedicle length.²

Breast

Although the internal mammary vessels are the most common recipient vessels in autologous breast reconstruction, they are not usable in up to 20 percent of patients.^28,29 In a study of breast reconstruction using vein grafts, 70 percent of cases used cephalic vein transposition for salvage after venous thrombosis and 71 percent used interposition vein grafts to supercharge venous drainage (Fig. 6). However, in the setting of venous congestion, there was no difference in salvage rates between a cephalic vein transposition and an interposition vein graft.⁵ The lumbar artery perforator flap represents an alternative to abdominally based free flaps. Because of the short pedicle length or size discrepancy between the lumbar artery and internal mammary vessels, this flap often requires interposition grafts. Most commonly, the deep inferior epigastric artery and vein are used as interposition arteriovenous grafts to the internal mammary vessels.³⁰ Composite grafts have also been used for the transverse upper gracilis, superior gluteal artery perforator, superficial inferior epigastric artery, and lateral thigh flaps.^31,32 Other options for interposition grafts include the superficial inferior epigastric vein, the superficial circumflex iliac vein, the lateral thoracic vessels, and the thoracodorsal vessels.^30,32,33

Fig. 6.

Transposition vein graft for breast reconstruction. The cephalic vein is transposed into the chest before free flap transfer because of a diminutive internal mammary vein. (Illustrated by Megan Llewellyn, M.S.M.I., C.M.I.; copyright Duke University; with permission under a CC BY-ND 4.0 license.)

COMPLICATIONS

When using a vein graft, there is a risk of flap failure and loop thrombosis. Whether the use of vein grafts or staging an arteriovenous loop is associated with increased flap failure rates is controversial.^{3,14,18,22,34} Outcomes depend on many factors, including location, loop-flap interval, ischemic time, and surgeon experience. In addition, irradiation, tobacco use, prior neck dissection, and prior free flaps increase flap loss.^4,6,7,14,15 For interposition vein grafts, increasing length of the graft increases the risk of failure such that an arteriovenous loop or flow-through flap should be considered when the vessel gap exceeds 10 cm.⁷ In terms of flap choice, a single-institution study showed that anterolateral thigh flaps in conjunction with arteriovenous loops suffer higher thrombosis and flap failure rates. The authors suggest that increased flow resistance through the small-caliber perforators compared with the low-resistance of the vein graft may be to blame.³ To decrease thrombosis risk, many institutions have anticoagulation protocols. In a meta-analysis of arteriovenous loops, the authors found that most surgeons infuse heparin at the time of arteriovenous loop creation and continue to use intravenous heparin in between stages, whereas others are also proponents of dextran.^18,35–39 However, more recently, surgeons have advocated for giving low-molecular-weight heparin or subcutaneous heparin postoperatively and initiate intravenous heparin only if there were intraoperative concerns for thrombosis.^2,3 Overall, when embarking on a complex free flap, surgeons should avoid long interposition vein grafts, expedite the loop-flap interval, and plan for the potential need to use vein grafts.

INSTITUTIONAL PEARLS

Commentary on Order of Anastomosis

Duke University: Brett T. Phillips, M.D., M.B.A.

When vein grafts are required, I routinely harvest one long vein graft that measures enough for extension of both the flap artery and vein. The graft is then oriented in an arteriovenous loop configuration with the apex of the loop near the flap pedicle. I do not cut the loop before the anastomoses to the recipient vessels. Once the recipient vein and artery are connected to the vein grafts, the arteriovenous loop apex is cut to match the vessel lengths appropriately and accommodate for any length mismatch. The flap vein is then connected to the vein graft followed by the flap artery to vein graft. Before tying down the last arterial suture, the recipient vein clamp is released, and then the arterial clamp is released, and flow is assessed. By waiting on tying the last stitch, you confirm flow through the recipient artery and vein graft anastomosis and evacuate any air or debris in the vein graft. This completes the microanastomotic sequence.

Commentary on Donor Vein Selection

M. D. Anderson Cancer Center: Edward Chang, M.D.

The use of interposition vein grafts is often unavoidable in complex microvascular reconstruction, particularly in the setting of prior surgery, radiation therapy, or previous free flaps. Prior studies have demonstrated an increased risk of complications and flap loss in these circumstances; however, vein grafts were most commonly used in already more difficult circumstances.⁹ Therefore, attributing the increased risks of complications to the vein grafts itself is likely a simplification of the reality that complications and flap losses are multifactorial. An important consideration is proper flap selection and pedicle dissection to maximize the available length of the pedicle. When grafts are needed, the greater saphenous vein represents a readily accessible donor site but is thick-walled and does not dilate readily. Given the thicker wall, it is often more suitable for an arterial graft than for a venous anastomosis, whereas the cephalic vein is more pliable for the venous anastomosis. However, the greater saphenous vein provides length and caliber and is ideal for a long arteriovenous loop or when a long graft is needed. In general, sacrificing the pedicle of another free flap for a graft is ill-advised in the setting that that flap is needed. Other considerations that are less well-described but used frequently by the author is the use of the second vena comitans as a vein graft, or the use of flow-through flaps. It is our practice to perform one venous anastomosis, which should be sufficient for most flaps. Although considerable debate exists regarding the benefit of double venous anastomoses, the second vena comitans is readily accessible and often of suitable length, caliber, and quality to serve as a graft without incurring additional donor-site morbidity. Care must be taken not to injure the pedicle during the dissection, and any communicating branches should be ligated to the dominant vena comitans. In the setting that multiple flaps are needed, many flaps typically have large branches that can be used, such as the vastus intermedius branch of the lateral descending circumflex femoral vessels for the anterolateral thigh flap, or a large soleus branch from the peroneal vessels for the fibula flap.

Commentary on One- or Two-Stage Arteriovenous Loops

Memorial Sloan Kettering Cancer Center: Evan Matros, M.D., M.M.Sc., M.P.H.

In deciding whether to perform immediate interposition or a one-stage arteriovenous loop versus a two-stage arteriovenous loop, the following strategy can be considered. When vascular embarrassment arises unexpectedly during a flap transfer, immediate interposition vein grafting or a one-stage arteriovenous loop is preferred because the flap may already be elevated or ligated from its source. Moreover, for cases in anatomical areas such as the head and neck where critical structures are exposed, the defect cannot be safely left open to allow for a two-stage arteriovenous loop. However, there are situations where two-stage arteriovenous loops provide a trial window to improve the safety of flap transfer, including (1) when a potential defect is in a known area of depleted recipient vessels or (2) the planned defect will leave a critical structure exposed with no option for temporizing coverage (i.e., brain, spine). One example is a patient with previous neck dissection and radiation therapy who is undergoing a skull base resection for recurrence. A two-stage arteriovenous loop is a good option, as there are no back-up options if the flap is unsuccessful. At some point, this patient may not be a surgical candidate if the failure of the reconstruction is prohibitive with no back-up options available for coverage. A failed first stage would create minimal morbidity, avoid extreme circumstances, and declare the patient unresectable.

CONCLUSIONS

Vein grafts are an important tool when faced with challenging reconstructions. Plastic surgeons should be familiar with the surgical technique and indications for interposition vein grafts, transposition vein grafts, arteriovenous loops, and flow-through flaps. Which type of vein graft to use depends on the size of vascular gap and defect location.