Mehrotra et al. were the first to describe a perforator-plus flap in detail [11]. The DPAPF flap is similar to the distally pedicled sural fasciocutaneous flap in some features. However, the unique characteristics of the DPAPF flap are as follows: 1) a sizable perforator from the peroneal artery is located at the pivot point, and the flap receives dual blood supply and venous outflow; and 2) the role of the perforator is dominant [11, 12]. However, the reliability of these flaps remains the main concern. The highest necrosis (including complete and partial) rate of the distally based sural flap was 35.7% (25/70) [10]. In the last decade, various necrosis rates of the distally based sural flap in studies with relative large sample sizes (n ≥ 40) were reported to be 3.9% (2/51) by Asʼadi et al. [13], 8.3% (13/156) by Gill et al. [4], 8.8% (9/102) by Dhamangaonkar et al. [14], 11.8% (9/76) by Herlin et al. [15], 17.2% (15/87) by Raza et al. [16], 20.5%(9/44) by Dai et al. [17], 22.3%(33/148) by Schmidt et al. [18], 30.6%(36/85) by Perumal et al. [19]. In the present study, the sample size was relatively large and there were no cases of complete necrosis of the flap. The partial necrosis rate was 16.1% (9/56), and only one (1.7%) remnant defect was covered with a local flap. Forty-seven (83.9%) flaps completely survived within one stage, while the other eight (14.3%) defects were reconstructed using the DPAPF flaps with simple skin grafting or suturing in the second stage. The results suggest that the DPAPF flaps are relatively reliable for reconstructing the defects in the distal forefoot. Once partial necrosis of the flap occurred, the remnant defects in most cases were covered successfully with a simple procedure. The DPAPF flap is particularly suited for the reconstruction of the defects over the distal forefoot for physicians who are not experienced with using free flaps or patients who are not eligible for undergoing reconstruction with a free flap [20, 21].
Forefoot is defined as the area beyond the tarsometatarsal joint, and it is of great importance in ambulation; however, performing vascularization of this area is frequently challenging [5]. The distal forefoot—the forefoot beyond the midpoint of the metatarsal bones—includes the weight-bearing area. The defects over the distal forefoot are more distal than those over other parts of the foot. Covering the soft tissue defects in this region is difficult. Some authors considered that the defects of the middle foot or the distal foot were covered restrictedly by the distally based sural flaps [22, 23]. However, the defects in the region were successfully managed with the distally based sural flap in small simple sizes [2, 3, 6, 24, 25]. The cross-leg flap for that reconstruction of the defects over the distal forefoot is another safe alternative [26, 27]. However, the patients who receive the cross-leg flap have require addition nursing care and face difficulties in daily activities, which results in unavoidable reoperations. This will result in increased hospitalization costs, time to recovery, and psychological burden on the patients. Most of the pedicled or local flaps are difficult. This will result in increased hospitalization costs, time to recovery, and psychological burden on the patients. Most of the pedicled or local flaps are difficult to satisfy the requirements of regional repair because of confined dimensions and the rotating arc [5]. Free tissue transfer is an efficient way to reconstruct the defects of the distal forefoot, and it can be used to reconstruct larger defects as well [28]. However, the procedure has some disadvantages, such as time limitation, requirement of additional equipment, increased technical complexity, sacrifice of the main vessel, trained microsurgeons and teams, postoperative monitoring requirements, and the need for a relatively longer learning curve [6, 20].
Some authors have reported the repair of defects over the distal forefoot using the distally based sural island flap, with the pivot point being 5–7 cm above the lateral malleolus [6, 29, 30]. However, other authors consider that the defects in the region should be covered with flaps with lower pivot points [13, 21]. The higher the pivot point is, the longer is the flap needed. In the present study, only three pediatric flaps were designed with the pivot points under 5 cm above the tip of the lateral malleolus. Seven flaps were designed with the pivot point above 7 cm from the tip of the lateral malleolus, while the pivot points of other flaps lay between 5 cm and 7 cm. Fixing the ankle in dorsiflexion with a Kirschner wire was the key point in this approach because it reduced the distance from the pivot point to the recipient area, which subsequently reduced the length of the fascial pedicle. Because the shape of the skin island was not changed, the total length of the DPAPF flap was also shortened as much as the length of the fascial pedicle.
The potential risk factors for necrosis of the DPAPF flaps, including patient and flap factors, were analyzed. The constitute ratios of the patient factors and continuous variables of the DPAPF flaps were comparable between the survival flaps and partial necrosis flaps (p > 0.05). It remains controversial if the age, smoking status, and history of DM and peripheral arterial disease (PAD) affect the survival of the flap [2, 10, 20, 31, 32]. Some authors reported that smoking was the strongest association with flap failure [20, 31]. In the present study, the patients were advised smoking cessation since admission to the hospital. Based on our experience, we suggest that the DPAPF flap is not suitable for defects arising due to severe DM or PAD.
Partial necrosis rates of reverse sural artery flaps were reported to increase significantly when the flaps had an LWR of 5:1 or greater, skin island width ≥ 8 cm, or the top edge of the flap was located in the 9th zone [7]. In the current study, the proportions of the aforementioned first two unfavorable conditions were 82.1% and 76.8%, respectively. However, compared with the survival flaps, the constitute ratios of the first two indicators were not significantly different in the partial necrosis flaps (p > 0.05). The top edge of the flap was a relevant factor that was associated with partial necrosis. In the present study, the top edge of all the flaps was located in the 8th zone (66.1%) or the 9th zone (33.9%). The partial necrosis rate of the DPAPF flaps located in the 8th zone (5.4%) was significantly lower than that of the flaps located in the 9th zone (36.8%) (p < 0.05). These findings suggest the following: (1) nearly a third of the DPAPF flaps with the top edge in the 9th zone, and the proportion of two other unfavorable conditions also is higher, the outcome of the DPAPF flaps for repairing the defects over the distal forefoot is acceptable; (2) when utilizing DPAPF flaps for repairing the defects over the distal forefoot, the location of the top edge in the 9th zone was the most relevant factor associated with flap failure; and (3) the DPAPF flaps with the top edge in the 8th zone were safer and more reliable in repairing the defects of the distal forefoot. The total length of the DPAPF flap was reduced with ankle fixation in dorsiflexion, which reduced the number of flaps with the top edge in the 9th zone. Therefore, this procedure can prevent complications of the flaps to some extent.
The upper boundary of the reverse sural fasciocutaneous flaps is controversial [4, 15]. Chen et al. suggested that the proximity limitation of the flap should not be beyond 6 cm from the popliteal crease [2]. Some authors have reported the highest location of the flap being 1–2 cm or 1.5-4 cm away from the popliteal crease [25, 33]. However, other authors have reported using flaps with the proximal border near the popliteal crease in repairing the defects of the forefoot [14, 34]. Mojallal et al. reported that including the sural nerve did not enhance the perfusion of the sural flap; however, it increased the arc of rotation, and the distance of “Surgical Unsafe Zone” from the popliteal crease was 4.6 cm [35]. A limitation of this conclusion was that the study included fresh adult cadaver legs. In another previous study, the posterior aspect of the calf was divided into nine zones (zones 1–9) to accurately assess the proximity limitation of the DPAPF flap [7]. In the present study, the upper boundary of a DPAPF flap was located at popliteal crease, and the flap survived completely. On the posterior calf, an average of 3.2 true anastomoses connect the perforators without change in the caliber, which are parallel to the sural nerve [36]. This could explain why the DPAPF flaps can survive longer and more reliably. However, the proportion of partially necrotic DPAPF flaps was significantly more in the 9th zone. Venous supercharging [15, 37], ligating the short saphenous vein distally in the pedicle [38], or delay technology [32, 39, 40] are the common methods used to improve the success rate of the flaps. It is definitely worth exploring how to improve the success rate of the DPAPF flaps under such conditions and identifying the best solution following analyses and comparisons.
The external fixation device is a device that prevents complications of distally based sural flaps and facilitates postoperative care [10, 41]. However, it requires an additional nail for external fixation nursing care during the postoperative fixation period. The external fixation device is more expensive in our country. Fixing the ankle with external fixation increases the financial burden on the patients. Pallua et al. introduced the concept of reconstructing the defects in the distal forefoot using pedicle flaps and fixing the feet using a cast [5]. We did not use this approach because of difficulties in changing the dressings and the high risk of pressure sores of the heel. In the present study, the ankle was fixed in dorsiflexion using a Kirschner wire, which is cheaper and requires a more convenient dressing and nursing care. There was no case of infection of the ankle or nail. After three weeks of the operation, the Kirschner wire was pulled out after confirming the stability of the flaps. The period of ankle fixation was short; therefore, the function of the ankle was not affected.
The mean duration of DPAPF flap elevation was approximately 30 minutes, which highlights that the flap can be elevated easily and quickly, and the defects over the distal forefoot can be covered without microsurgical techniques and sacrificing major arteries of the lower extremities. The disadvantage was that the donor sites were closed by resurfacing with a skin graft, which may be related to the relatively larger dimensions of the defects. Most of the patients in this study were satisfied with flap appearance. In the present study, although a follow-up of eight weeks or three months was enough [8, 17], we evaluated the reconstruction outcomes of the DPAPF flaps over more than 6 months of follow-up. The reconstruction outcomes were very satisfactory with only 2/48 cases having evaluated fair outcomes.
To the best of our knowledge, this is the first study to introduce the reconstruction of the defects over the distal forefoot with DPAPF flaps with the largest number of patients. A randomized controlled trial was not possible because this study was a retrospective review, which is a major limitation of the study. Another limitation is that only 56 cases were included in the study. Further studies with larger same sizes are required to improve the success rate of DPAPF flaps in the reconstruction of defects over the distal forefoot.