Complex lower extremity defects from high-energy trauma can hardly be repaired by simple free flaps, which pose a reconstructive challenge to surgeons. An ideal reconstruction would result in reinstated function and aesthetic appearance. Several methods have been reported, however, cases of severe soft defects have not been reported. As listed in Table 1, high-energy trauma often leads to complications, such as refractory soft tissue defects, recurrent ulcers, skin necrosis, osteomyelitis, Achilles tendon exposure, exposed bones, and even extensive bone defects. Traditional free flap reconstruction failed to achieve satisfactory results because a single ALTF or PAPF failed to solve skin, soft tissue, and bone defects simultaneously. Moreover, the ETE method sacrifices the main artery, leaving little space for distal blood supply and subsequent vascular surgeries15. To solve the problem, a chimeric free flap based on the ETS anastomosis is an ideal option for complex reconstruction.
Bone defects should be given priority before soft tissue reconstruction, which often results from osteomyelitis, trauma, and congenital and acquired deformities16. Traditionally, the treatment is divided into non-vascularized and vascularized bones. Non-vascularized bones are allografts and autografts. Compared to allografts -- slower revascularization, autografts are ideal choices for less dead bone, no immune rejection, and less infection17. If the bone defects are longer (≥ 4cm), vascularized bone flaps would be chosen, such as the iliac and fibular flaps. Due to anatomical characteristics, the iliac flaps have thinner blood vessels, shorter pedicles, a maximum 10cm bone mass, and a higher proportion of cancellous bone, making them more suitable for oral and maxillofacial reconstruction18,19. By contrast, fibular flaps can provide more bone mass for structural support because the cortical bone to cancellous bone ratio is approximately 1:1. Considering that the collapse of the femoral head is significantly less in the implantation of a fibular flap than an iliac flap20. We also attached a video about reconstructing an 8cm tibia defect with a fibular flap to prove the ability of structural support, in which the affected limb demonstrated good load-bearing (Video 1). Therefore, when there is a requirement for weight-bearing reconstruction, the fibular flap is preferred.
In this report, we present that chimeric ALTF and PAPF can cover kinds of complex lower extremity defects (Table 2). Chimeric ALTF can provide a large area, thick fat, massive muscles, and a long vessel pedicle21, while chimeric PAPF can provide a smaller area but is sufficient for moderate skin defects, thin fat, muscles, a short vessel pedicle, and a maximum of 22cm bones22,23. All cases in this study achieved relatively reinstated function and aesthetic appearance. Other flaps, such as the latissimus dorsi flap, forearm perforator radial artery flap, an superficial circumflex iliac artery perforator flap, may require position changes, influence flexibility of upper extremities, and have small vessel diameter problems24,25. The flow-through technique has more requirements: the recipient sites have a vascular injury, and the donor sites require the removal of part of the main vessels along with entire perforator vessels26. Therefore, chimeric ALTF and PAPF are superior to other flaps for flexible reconstruction.
Successful microvascular free flap transfer is highly dependent on sufficient microvascular anastomoses. While ETE anastomosis is significantly successful for stable hemodynamic improvement, many studies have suggested that no significant differences exist in extremity perfusion and flap failure between ETS to ETE15,27,28. As presented in Table 2, the success rate after the first ETS flap was over 85%. This rate climbed to 88% after conservative treatment (n = 2) and over 96% after exploratory surgeries (n = 2). Based on the mature microsurgical technique, well-filled vessels, and no blood leakage were observed after vascular recanalization (Fig. 3C, 4E). Albertengo et al. reported that in ETE anastomosis, the intima, media, and outer membrane of arteries at the recipient site are completely severed, which would cause turbulence and thrombosis with the contraction of the middle smooth muscles. However, in ETS anastomosis, the contraction or spasm of smooth muscles will enlarge the opening because they were partially cut off29. Furthermore, researches indicate that the blood flow in free flaps depends on the specific tissue composition rather than the recipient artery flow rate, for example, a muscle flap has more sufficient blood flow than a fasciocutaneous flap30. Most cases in our study underwent computed tomography angiography after reconstruction demonstrating rich blood supply. As a result, we believe that ETS in chimeric free flaps can preserve distal perfusion without increasing complications.
It is worth noting that we designed retrograde flaps for some specialized defects because soft tissue defects around the knee account for a considerable proportion. The main reasons are trauma and complications of total knee arthroplasty. The skin around the tibial plateau is thin, surgical trauma is severe, and some patients require secondary reconstruction, in which cases, traditional free flaps provide limited solutions for bone, tendon, joint, and internal fixation exposure. During intraoperative anatomy, aTA often emerges from the intermuscular septum near the proximal 1/3 of the tibia. Because platform fractures often result in scars on both sides of the knee, and local blood vessels may be damaged, a local transfer of the medial gastrocnemius flap is not considered. Our group designed chimeric retrograde ALTF or PAPF for defects in the proximal 1/3 of the plateau area (Fig. 2). Chimeric ALTF or PAPF can provide a relatively large vessel diameter compared with other free flaps, which ensures relatively abundant blood perfusion under retrograde situations. The defects of the distal 2/3 of the tibia and the beyond are designed as chimeric antegrade free flaps, in which the reconstructed blood flow was always satisfactory. In this research, the complication rates of retrograde flaps and antegrade flaps were 16.67% and 28.57%. While the retrograde cases were fewer than the antegrade ones, the lower complication rate reveals that applying chimeric ALTF or PAPF based on arterial ETS anastomosis becomes a reliable choice.
All the surgeries were performed by the same group led by the same surgeon. Thus, the anastomotic technique depended on the expertise and training of surgeons. The surgical technique improved as cases accumulated, which may introduce bias. Our study is subject to the limitations inherent to retrospective, uncontrolled case reviews, including small sample size, lack of strict criteria for patient selection, and absence of prospective data collection, especially a final comprehensive strict functional assessment. All surgeries were performed at a single center. Further, prospective studies and data summarization are required to clarify the risks and prognosis in the future.