Severe lower limb trauma with large-sized soft tissue defects and tibia bone exposure is frequently encountered at the emergency department, and further reconstruction remains a major challenge for surgeons [20]. In this situation, flap procedures were necessary for defect coverage and limb salvage. However, the local flap technique or ipsilateral free flap transplantation is often impossible due to extensive tissue defects and potential vascular damage. In this study, we introduced a modified recipient blood flow-preserved cross-leg anterolateral thigh flap procedure to reconstruct complex lower limb injuries. This method is an effective and safe alternative for patients with different sizes of tissue defects in the unilateral lower limb.
The cross-leg flap technique was applied to patients with lower limb injuries that had occurred a long time ago. Since Stark first introduced it in 1952, various cross-leg flap procedures have been reported, including pedicled flap procedures and free flap procedures [1, 21]. For small-sized tissue defects, the cross-leg pedicled flap procedure is preferred because it is relatively easy and safe to perform [22]. However, for large defects, the cross-leg free flap procedure is the optimal strategy [23, 24]. Cross-leg free flap surgery has been applied to lower limb reconstruction since 1979 [25]. In this procedure, the free flap was temporarily nourished by vessels of the uninjured lower limb and was separated from the intact leg after flap revascularization. Skilled microsurgical techniques are requisite for this procedure. With the increasing popularity of microsurgical techniques, free flap transplantation has gradually become an important method for salvaging severely traumatized lower limbs [23, 26, 27]. A favorable lower extremity salvage rate of 93% was reported in free flap transplantation [27]. Compared with an end-to-side fashion, an end-to-end anastomosis between recipient vessels and donor vessels is preferred in the free flap procedure, which obviates potential thrombosis caused by changes in blood flow at the anastomosis site. However, the major drawback of end-to-end anastomosis is sacrificing the recipient artery, which results in a considerable reduction in blood supply to the distal leg. In early-stage clinical studies of the cross-leg free flap technique, recipient arterial sacrifice was considered inevitable [28]. Nevertheless, in recent years, several innovative techniques have been reported to preserve the integrity of the recipient artery. In 2000, Topalan et al. introduced a latissimus dorsi free flap with a Y-shaped arterial pedicle in lower limb construction. This strategy not only provided blood supply to the flap but also preserved the blood flow of the recipient artery; it is called the flow-through technique [13, 29]. For the case without arterial bifurcation, Akyurek et al. introduced a two-stage method to restore the continuity of the recipient artery in 2002 [30]. In the first stage, an end-to-end anastomosis was performed between the thoracodorsal artery of the latissimus dorsi free flap and the uninjured recipient posterior tibial artery. After flap revascularization, the thoracodorsal artery was transected and rerouted to the distal end of the posterior tibial artery in the second stage. In 2016, Gencel et al. performed the cross-leg flow-through pedicled latissimus dorsi free flap procedure on 6 patients with high voltage electrical injuries [11]. In this small-sample clinical study, the thoracodorsal artery and circumflex scapular artery (or serratus branch) were prepared as T-shaped pedicles and further anastomosed to the contralateral posterior tibial artery. Adequate diameter and blood flow of the posterior tibial vascular system contribute to the survival of the flap. In 2020, Bali et al. conducted a study of 12 patients who underwent recipient blood flow-preserved cross-leg free flap procedures [12]. In Bali’s study, an anterolateral thigh fasciocutaneous flap was used in 8 patients to reconstruct small or medium defects, while a latissimus dorsi flap was used in 4 patients with large defects. In addition, the arterial pedicle was designed in a T-shaped fashion in the anterolateral thigh flap but not in the latissimus dorsi flap. Thus, the blood flow of the recipient posterior tibial artery was reestablished in the first stage of the anterolateral thigh flap procedure (flow-through technique) and in the second stage of the latissimus dorsi flap procedure (rerouting technique). To our knowledge, there are only a few studies of flow-through pedicled cross-leg free flap procedures for lower limb reconstruction, all of which involved fewer cases [11, 12, 29, 31–34]. In these studies, flaps were chosen based on the size and shape of the tissue defect. Generally, the anterolateral thigh flap is preferred for relatively small defects, while the latissimus dorsi flap is suitable for relatively large defects. Compared with the anterolateral thigh flap, the latissimus dorsi flap is relatively traumatic to harvest, and it is difficult to prepare a Y-shaped arterial pedicle. In addition, the surgical position needs to be changed during cross-leg latissimus dorsi flap transplantation. Therefore, the anterolateral thigh flap is ideal for complex lower limb reconstruction, but it is hindered in popularity due to limited defect coverage. Traditionally, the proximal part of the free flap is used to cover the vascular pedicle, which will lower the effective flap area for defect coverage. In the present study, we made two modifications as follows: (1) the lateral circumflex femoral arterial bifurcation was employed to design the Y-shaped arterial pedicle instead of the perforating arterial branches; (2) the vascular pedicle was wrapped by split-thickness skin instead of the proximal part of the flap. We performed this modified flow-through pedicled cross-leg free flap procedure on patients with different sizes of unilateral lower limb tissue defects. The main indication is severe trauma or a large stubborn ulcer in a lower limb, which requires free flap transplantation, but no suitable donor artery was available in the injured leg. The contraindications include pTA injury in the contralateral lower limb, coagulation disorders, or conditions in which patients are intolerant to surgery. Compared to previous techniques, our method has several advantages.
First, meshed split-thickness skin was used to wrap the vascular pedicle. For anterolateral thigh flaps, a sufficient length of vascular pedicle can be harvested. Instead of flap coverage, we performed a free skin wrapping technique to protect the vascular pedicle. On the one hand, the obtained flap can be fully used for defect coverage, which means that the anterolateral thigh flap procedure is suitable for patients with large-sized tissue defects. Our study suggests that various defects ranging from 72 to 378 cm2 could be effectively covered by relevant-sized anterolateral thigh flaps. On the other hand, compared with flap coverage, skin wrapping is more convenient for postoperative blood flow observation and dressing change, and it is much easier to perform pedicle division in the second-stage procedure [12]. The free skin wrapping technique has been reported previously [35]. Serel et al. reported a case of an unhealed wound on the right foot that underwent a cross-leg anterolateral thigh perforator flap procedure in which split-thickness skin was used to wrap the vascular pedicle [35]. Together with our results, meshed split-thickness skin grafting is an effective and convenient method for vascular pedicle coverage.
Second, the lateral circumflex femoral arterial system is employed for the design of the Y-shaped arterial pedicle. The lateral circumflex femoral artery consistently gives off the transverse branch and descending branch. This arterial bifurcation is not difficult to dissect and prepare in a Y-shaped fashion. The anterolateral thigh free flap is widely used in posttraumatic reconstruction, including reconstruction of the upper limb, lower limb, and body trunk [15, 36, 37]. The anterolateral thigh flap can be harvested as a fasciocutaneous or musculocutaneous flap for the reconstruction of different injury types. Generally, a satisfactory survival rate and aesthetic outcome can be achieved by the anterolateral thigh flap procedure [36]. In addition, the anterolateral thigh flap is rich in its arterial perforator system, which is beneficial to flap survival on the one hand and can be designed as a single or bilobed style on the other hand. A bilobed flap is an optimal and practical choice to cover irregular tissue defects. In particular, when the defect width is large, a large-length single anterolateral thigh flap can be redesigned as a large-width bilobed flap. In our case series, both single and bilobed flap procedures produced good clinical results.
Third, anterolateral thigh flap harvest and cross-leg flap transplantation are performed in the same surgical position, which can shorten the first-stage operation time. Furthermore, the vascular pedicle is easily separated after flap revascularization, which shortens the second-stage operation time. After flap transplantation, parallel external fixation between the two legs is relatively comfortable.
One disadvantage is that the donor-site incision is relatively large; hence, direct suture could not be performed in some patients. In this situation, a second-stage skin grafting is necessary. Another disadvantage is that two anastomoses increase the risk of postoperative vascular occlusion. Skilled microsurgery techniques are necessary.
There are some limitations of our study. Postoperative parallel fixation of both lower limbs is necessary, and the fixation time is relatively long (4 weeks). Pressure ulcer prevention and physical therapy intervention should be carried out during the fixation period. In our procedure, the incision at the flap donor site was relatively large, requiring further skin grafting in some cases (27% in our study). This study has a retrospective design and a relatively small sample size, and a large-sample prospective study is needed in the future.