ALT flap has been widely used to reconstruct various complex soft-tissue defects due to its advantages of considerable harvesting area, long vascular pedicle, concealed donor site, and large vessel diameter [1, 3]. There were numerous studies focusing on the application of the ALT flap in reconstruction of soft tissue defects [3]. However, many complications of the ALT flap donor site still needed further research and resolution. Patients with a width of donor site defect more than 6 cm who underwent the primary closure may suffer from wound dehiscence and skin necrosis [6]. Skin graft was a common method to solve the donor site defect, but this method was associated with a secondary donor site and low aesthetic [12]. In the present study, we used the KDPIF to reconstruct the ALT flap donor site defect with a width of more than 6 cm in 12 patients. The efficiency of KDPIF was assessed by the aesthetics and complications in the donor site.
As an emerging reconstructive technique, KDPIF was first introduced by Behan in 2003 [8]. There were four types of KDPIF that were described in the previous study with Type I ( a standard flap design with direct closure of defects), Type IIA (type I combined with the additional division of the deep fascia), Type IIB (a skin graft is required to cover the secondary defect), Type III (double keystone flaps like a butterfly wing), and Type IV (rotational reconstruction) [8]. Furthermore, another modified keystone flap mentioned by Moncrieff et al. was named SMU (Sydney Melanoma Unit) - modification KDPIF [13]. A skin bridge along the greater arc of the KDPIF was maintained in patients with the SMU-modification KDPIF, which allows additional vascularity, preserves subdermal lymphatics, and promotes wound healing [13, 14]. In this study, 12 patients received the treatment of KDPIF (type IIA = 8 cases; SMU-modification KDPIF = 4 cases) for the ALT flap donor site defects (the mean width was 8.1 cm; range from 7 to 10 cm).
During the operation of KDPIF, the soft tissue defect in the donor site can be transferred from an area without surrounding tissue laxity to an area with sufficient laxity, and this method follows the principle of recruitment of laxity [9]. The skin tension can be redistributed from the donor site to both ends of KDPIF via the V-Y advancement [15]. Furthermore, The V-Y advancement flap from the corner of the KDPIF to the center provides an additional laxity for the horizontal axis movement of KDPIF into the donor site defect [8]. In this way, the donor site defect can be covered with local skin (replace like-with-like) without the need for harvesting free flap and vascular anastomosis, which not only reduces the incidence of vascular crisis, but also avoids the difference of skin color caused by free flap or skin graft. In the flap size designing, the original design of KDPIF was based on the 1:1 ratio between the width of the KDPIF and the elliptical defect [8]. However, due to there were many strong skeletal muscles and insufficient laxity in the thigh, this ratio was modestly increased (with adjustment for age and BMI) to ensure a lower skin tension. Furthermore, the deep fascia in the flap margin was divided to increase the flap movement to close the ALT flap donor site in all patients. In our follow-up, no one case presented the wound dehiscence, which indicated that the KDPIF was associated with satisfactory work to bear the skin tension. Hence, we recommended that the blunt dissection of deep fascia around the flap should be created when patients with the donor site defect were repaired using the KDPIF, so as to increase the movement of the KDPIF and disperse the skin tension, which can better prevent the risk of wound dehiscence caused by excessive skin tension in the thigh. Furthermore, the dissociation of deep fascia should be performed according to the patient’s age, BMI, and intraoperative skin tension assessment. For patients with low skin tension, the conventional dissociation (the deep fascia around the KDPIF) can be divided; for patients with high skin tension, the dissociation area should be gradually increased to prevent the high skin tension in the sutured area (Fig 2).
Additionally, the KDPIF was also associated with an extremely high survival rate, which was related to the fact that the flap was based on a multi-perforator-based advancement [16]. There were multiple hot spots of the perforator in thigh skin, which provides a reliable blood circulation for KDPIF even when the large keystone flap was designed. Furthermore, during the blunt dissection of the deep fascia around the flap, the central position of the flap (where the center of the flap was located near the hot spots of the perforator) was not divided, and the vascular pedicle was not dissected and anastomosed, so as to ensure the integrity of perforators and contribute to a high survival rate of the flap [7, 16-18]. In addition, by the blunt dissociation of the peripheral deep fascia, an unequal distribution of skin tension around the flap can be created with a considerable tension in the periphery of the flap and less skin tension in the central area [7]. The blood circulation was preserved in the area of low skin tension (the central area of the flap) where the vascular pedicle was not dissected, which may contribute to the reliable blood circulation of KDPIF. In this study, none of the patients developed wound dehiscence or vascular based flap necrosis.
With the continuous development of microsurgical techniques, aesthetics has become an important goal for patients and surgeons. It is our experience that patients are more receptive to linear scars compared to sheet scars (Fig 4). Furthermore, the local flap advancement in the reconstruction of soft-tissue defects can readily achieve an ideal reconstructive goal (replace like-with-like) and avoid large areas of pigmentation and skin color differences, which may be caused by skin graft [19]. In the present study, we performed VSS score and SCAR score for 12 patients with ASS core (mean, 6.7; range, 5-8) and SCAR core (mean, 7.3; range, 6-9), and all patients were satisfied with the appearance of the donor site. Furthermore, the skin morbidity in the donor area may significantly impact the aesthetics of the donor area and the patient’s rehabilitation. In our observation, patients who underwent the skin graft to repair the ALT flap donor site more likely to present the morbidity in initial or secondary donor site. However, the primary closure of the ALT flap donor site that was managed using KDPIF was associated with lower donor site morbidity and higher aesthetics compared with a skin graft. In this present study, there were just two cases exposed to the modest skin infection and controlled by the treatment of wound dressing change and oral antibiotics.
Another great advantage of the KDPIF is that it is easy to operate. The procedure does not require superb microsurgical techniques and microsurgical equipment. And it is easily performed in a variety of levels of medical institutions. As long as the surgeon strictly grasps the operative indications and the design scheme of the flap, and carefully separates the deep fascia around the flap during the operation, a high success rate of the operation can be achieved. In addition, the donor defect of the ALT flap was usually elliptical, which was in line with the design principles of KDPIF. In conclusion, this study demonstrated that using the KDPIF to close the ALT flap donor site primarily is an effective and alternative treatment including the advantages of high survival rate, low morbidity, good aesthetics and simple operation.