DISCUSSION
Elevating thin flaps has long been a goal of reconstructive surgeons. Thin flaps have numerous advantages for reconstruction, and there is no doubt that they are superior to thick flaps in terms of meticulously mimicking natural contours. Thin flaps are required for aesthetically significant areas, such as in facial and hand reconstruction. In order to cover the surface with a pliable and thin flap in an aesthetically pleasing manner, fascial free flaps with a skin graft were traditionally used [
5,
6]. In addition to aesthetic considerations, thin flaps are frequently required for functional reasons. In head and neck reconstruction, protection after resurfacing is the main goal of surgery. Thus, establishing a well-vascularized tissue bed that can tolerate future radiation therapy, thereby preventing fistula formation, is critical in reconstructive operations [
1]. However, bulky flaps in the head, hand, and neck region may cause critical problems. Bulky flaps may interfere with smooth swallowing and cause airway obstruction [
1]. In extremity reconstruction, reconstructive surgeons may frequently experience mechanical injuries in reconstructed tissue because of excessive bulk, which may cause shearing or abnormal contact. Moreover, bulky flaps on the foot dorsum or toes can make it difficult for patients to wear shoes, potentially affecting foot function [
7].
For those reasons, reconstructive surgeons have made many efforts to achieve thin and durable flaps. Debulking procedures have been performed as a classical method to control the thickness of the flap. Direct excision of the fatty layer or liposuction is widely used as a debulking method. Secondary debulking procedures after lower extremity flap coverage have been reported to be performed in 17% to 52% of cases [
7-
9]. In face reconstruction, complicated contour and color matching is also difficult to obtain, meaning that additional revisional procedures are often required in order to achieve an acceptable contour [
10]. However, secondary debulking procedures have some pitfalls. First, they cause additional costs, and are not covered by the national health insurance system in South Korea. Circulation issues are another problem of debulking procedures. Direct excision largely depends on the dermal-subdermal plexus, and several stages are required to ensure the viability of the skin [
11].
In order to control the thickness of the flap, we advocate suprafacial elevation. As described above, the goal of this technique is to elevate the flap over the superficial fascia, preserving not only the deep fascia, but also the deep fat layer below the superficial fascia. By elevating the flap in a way that preserves the superficial fascia, we were able to achieve a very thin flap and increase pliability at the same time.
Combined with super-microsurgery techniques, we can maximize the utility of supra-superficial fascial flaps. We perform perforator-to-perforator techniques unless a long pedicle is required, to minimize recipient vessel morbidity by preserving the large vessel to the distal area. Not using the main vessel as a donor vessel is advantageous in cases of extreme calcification and atherosclerosis. Theoretically, in such cases, the perforator level is less affected than large vessels. When elevating an ALT free flap, the lateral circumflex femoral artery, including its descending branch is not atherosclerosis-resistant [
12]. As a result, in severe cases of atherosclerosis, especially in diabetic foot patients, we cannot guarantee the patency of the donor vessel, even if we use the larger branch as a donor.
Theoretically, it was considered that not including the fascia would decrease flap perfusion. However, partial necrosis does not generally occur in flaps after suprafascial elevation. The interconnections between direct and indirect linking vessels create interperforator flow [
13]. Suprafascial flap viability is explained by the perforasome theory [
14]. A supra-superficial fascial flap might not include a direct linking vessel located at the subcutaneous layer and suprafascial plexus. However, as we can also conclude from our results, partial necrosis of supra-superficial fascial flaps due to impaired circulation does not occur to a greater extent than in formal suprafascial flaps and fasciocutaneous flaps. Large thin flaps can survive without direct linking vessels [
4,
15,
16].
One case of total loss of the flap in our study was reported. However, we do not think that this result indicates an inherent risk associated with technique of flap elevation over the superficial fascia. The reason for necrosis was a delayed infection postoperatively. The patient had flap coverage because of an unstable scar with underlying chronic osteomyelitis, and had diabetes and poor nutritional status. Preoperative nutritional status has been described as an accurate predictor of postoperative outcomes [
17]. Prealbumin is a visceral protein that is commonly used to evaluate nutritional status [
18], and the patient had a low prealbumin level at admission.
The occurrence of partial necrosis is another issue. Predicting whether a flap will completely survive prior to surgery is of vital interest to reconstructive surgeons. In our results, three of the patients who experienced partial necrosis showed peripheral vascular disease on preoperative CT angiography. Suh et al. [
19] previously reported peripheral arterial disease to be a factor significantly related to flap loss. All patients with partial necrosis of the flap had at least one underlying comorbidity, and peripheral vascular disease was significantly related to partial necrosis (odds ratio=31.5, P=0.013). We presume that the comorbidities contributed to the flap necrosis, not the surgical technique of flap elevation (
Table 4). Furthermore, no cases of partial necrosis resulted in bone exposure or implant exposure requiring additional flap coverage. When planning a reconstruction with a superficial fascia–preserving flap, some modalities can be used to anticipate the proportion of necrosis and to prepare or modify the plan. Indocyanine green and fluorescence images can precisely predict tissue viability [
20]. With precise planning using CT angiography and color Doppler imaging, we are confident that surgeons can minimize flap morbidity.
A defatting procedure during flap elevation is another option for controlling flap thickness without a secondary revisionary procedure. However, immediate debulking during flap elevation cannot be done while distinguishing the exact anatomical plane, which can result in subdermal or subcutaneous vessel connection [
21,
22]. Immediate debulking is more dangerous than identifying and elevating the exact plane of the superficial fascia, preserving the subdermal plexus. As our study shows, elevating flaps thinner than 5 mm above the superficial fascia can reduce the defatting procedure rate, thereby avoiding the risk of damaging the subdermal plexus.
Delayed wound healing at the donor site is a significant issue in achieving an ultimately successful reconstruction. Many factors can impede wound healing. In the elevation of radial forearm flaps, by preserving the deep fascia of the forearm, less tendon exposure was reported [
23]. In our study, an extremely low percentage of donor site graft loss was noted. We presume that by leaving the deep fat layer at the donor site, the viability of the skin graft was maximized.
Sensory impairment at the donor site after free flap elevation is one of the most frequently reported morbidities, and abnormal sensation at the donor site is among the most common subjective complaints from patients [
14,
24]. Elevating ALT free flaps over the superficial fascia was reported to lead to fewer cases of abnormal sensation than in cases of subfascial ALT free flaps due to preservation of the fascial layer [
14]. The medial branch of the lateral cutaneous femoral nerve is often sacrificed during ALT flap harvesting [
25]. Moreover, it is still possible for an anterolateral flap elevated over the superficial fascia to utilize the sensory nerve for a sensate flap, which is an inherent advantage of the ALT free flap [
16,
26]. The sensory nerve utilized in sensate ALT free flaps is the lateral femoral cutaneous nerve, which runs at the deep fat layer [
14]. Surgeons can isolate and dissect the nerve during supra-superficial fascial elevation, even if the nerve is located beneath the superficial fascia. Seth and Iorio [
16] reported using a sensitized ALT free flap that was elevated above the superficial fascia.
Groin flaps lost their popularity because of frequent donor site morbidity. They were introduced as a good flap option with well-concealed donor site scar, but lost favor because of their bulky nature and frequent donor site–related complications, such as wound dehiscence and lymphorrhea [
3]. Traditional groin flaps included parts of the deep fascial structure. Because the lymphatic system is located in a deep fat layer, which is underneath the superficial fascia, including the tissues beneath the superficial fascia results in lymphorrhea and delayed wound healing. In a modified version of SCIP flap elevation, in which the elevation is performed above the superficial fascia, the donor site–related problems were reduced dramatically [
3]. There were no cases of wound dehiscence or delayed healing in our group of SCIP cases, precisely corresponding with previous reports.
The elevation time of suprafascial thin flaps compared to flaps elevated in the subfascial plane is controversial. Chen et al. [
14] reported no significant difference in elevation time between suprafascial and subfascial ALT flaps. Some studies reported that thinning flaps or elevating thin flaps was more time-consuming [
27]. Of course, elevating a free flap while preserving the superficial fascia has a steep learning curve. However, a study by Seth and Iorio [
16] reported a shorter operating time in superficial fascia–preserving elevation than in formal suprafascial flap elevation for ALT perforator flaps. In our results, the operating time in both the ALT and SCIP groups was comparable with previous studies [
16].