Color Doppler ultrasonography targeted reconstruction using pedicled perforator flaps—a systematic review and meta-analysis

Background Flaps are increasingly popularized in reconstructive surgery and there is need to test and increase their reliability. Color Doppler ultrasound has been stated to be valuable in flap planning. The aim of this study was to conduct a systematic review and meta-analysis of the literature of Color Doppler ultrasound targeted pedicled perforator flaps and provide information on outcomes and complication rates. Method A systematic review and meta-analysis were conducted for articles published until April 2017 in PubMed and Embase. We aimed to include randomized clinical trials, meta-analysis, prospective studies, case-control studies, and cohort studies written in English. We included studies where CDU was used to identify the perforator(s) prior to surgery. We evaluated the quality of the included studies using checklists recommended by the Cochrane group. Results From the initial 219 studies, only 12 studies using Color Doppler targeted pedicled perforator flaps in 252 cases met the inclusion and exclusion criteria. Eleven of these were case series and one a prospective study. The incidence of major complications was 8% (21/252) and minor complications was 14%, comprising of mostly necrosis 8% (24/252) and venous congestion 8% (21/252). Conclusions The reconstructive success rate following pedicled perforator flap reconstruction targeted by CDU appears to be high and the procedure provides a wide scope of applications and margin of safety. It is evident that the risk of venous congestion is 11 times greater in the lower extremities than the truncus, a finding that needs further attention in future studies. Level of Evidence: Level IV, risk/prognostic study


Introduction
Knowledge about perforator anatomy has led to an increased use of pedicled perforator flaps for reconstruction throughout the body [1]. Pedicled perforator flaps allow the surgeon to relocate local tissue and facilitate a simple reorganization, which enables an optimal cosmetic and functional reconstructive outcome. They provide a fast and simple, single-stage solution and offer an alternative to microsurgery or skin graft [2].
Handheld Doppler and color Doppler ultrasonography (CDU) have been shown to be useful to identify perforators and aid in the planning of flap reconstructions [2].
CDU provides additional visual information about available soft tissue, vessel flow patterns, vessel course through the soft tissue as well as perforator size and location. However, the use of CDU is not widely reported for use in the planning of pedicled perforator flaps reconstruction [3].
The aim of this systematic review was to evaluate the existing literature regarding color Doppler ultrasonography used to identify perforators for pedicled perforator flap reconstruction and evaluate the associated risk of major and minor complications.

Methods
This systematic review was conducted according to the recommendations outlined in the Cochrane Handbook for reviews [4] and the PRISMA statement (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) [5].

Literature search
We performed a literature review regarding the use of CDU in the preoperative assessment and planning of pedicled perforator flap reconstruction in April 2017 in the PubMed and EMBASE databases, using the search string: ((CDU OR color doppler ultrasound OR color doppler ultrasonography OR ultrasound)) AND (perforator flap) AND (pedicled) The search yielded 71 studies. The retrieved articles were reviewed and their bibliographies were scanned for publications relevant for this review (Fig. 1).

Inclusion criteria
We planned to include randomized clinical trials, metaanalysis, prospective studies, case-control studies, and cohort studies written in English. We only included studies where CDU was used to identify the perforator(s) prior to surgery using pedicled perforator flaps for reconstruction of local defects.
We recorded demographics, etiology and location of the defect, the type of pedicled perforator flap used, size of the flap, and arc of rotation. We also recorded minor complications defined by conservative treatment or by use of local anesthesia and major complications defined by return to the operating theater in general anesthesia ( Table 1, Fig. 2).

Quality assessment of the studies
We evaluated the quality of the included studies using checklists recommended by the Cochrane group [6]. The Carmen Mogas checklist was used to evaluate the quality of case series and prospective chart reviews [7]. Six questions were not applicable and thus omitted ( Table 2).

Statistical analysis
We conducted a meta-analysis for outcomes of complications; any necrosis, venous congestion, and flap loss. We calculated proportions with a 95% confidence interval (CI) based on a random-effects model due to the heterogeneous nature of the studies [8]. The heterogeneity was investigated using chisquared and the I 2 statistics. All statistical analyses were conducted using Stata/IC 14.0 (StataCorp LP) and supervised by a statistician at Odense University Hospital.

Discussion
Venous congestion was the most common complication in this series, which coincides with previous reports using pedicled perforator flaps for reconstruction [3,20]. The risk of venous congestion was significantly higher in the lower extremities (11%) than in the torso (1%), as described previously (Fig. 3)  [3]. We do not know the reason for the different complication rates between the torso and lower limbs. We speculate if it may be due to the following:

1) A difference in arterial flow and venous return
2) A greater vascular pressure in the extremities compared to the central body 3) A greater risk of twisting of the veins at the site of fascial penetration in the limbs 4) A need for a greater arc of rotation, which was close to 180°in many of the described flaps.
The complication rate seems to increase along with an increasing arc of rotation compromising the vascular flow [3,21]. It seems that the risk of complications is higher in areas where the amount of soft tissue is less abundant, like the distal part of the extremities. This translates to a shorter pedicle and restricted rotation, more prone to twisting and calls for greater dissection of the vessels or a different flap design for compensation (Fig. 5). This is where CDU may be helpful for designing the flap enabling precise planning based on the best-suited perforator, adjacent to the defect and with the best possible course through the subcutaneous tissue   (Fig. 4). The use of bi-or multi-lobar flaps might be another solution which can reduce the arc of rotation from 180 to 90°or less [3] (Fig. 5).
The overall major complication rate was 8% in this review, which was lower than the 14% described by Andrea Sisti et al.   [20]. However, we cannot use these results to conclude that the use of CDU is associated with an overall lower complication rate although it may show a trend. Interestingly, most of the included studies were small studies including 20 patients or less. Thus, the complication rates in this review, major 8% and minor 14%, have to be considered in the context of a learning curve setup. Better results should be expected once the learning curve is surpassed [11]. The summed major complication rate of the five smallest studies in this review was 16% compared to 8% overall, which is in accordance with Jiga et al. and Panse et al., who found that the overall outcome can be expected to improve while the complication rate decrease over time [22,23].
The use of CDU for detection of perforators is observer dependent, which can be exemplified by two studies using CDU for detection of perforators for the harvest of the radial forearm flap. CDU was found to be extremely useful for detecting perforators for the radial forearm flap in one of these studies, yet the other study described difficulties using CDU to identify the perforators, because the signal from the radial artery shielded visualization of the perforators [18,24]. It is therefore important to facilitate the correct use of CDU, which enables the surgeon to plan and design the pedicled perforator flap for reconstruction using the best available tissue adjacent to the defect, allowing for the least possible arc of  rotation and least possible risk of complications, thus securing a successful reconstruction (Fig. 5).
The handheld Doppler is still an important tool for identification of perforators. However, CDU may have some advantages to the handheld Doppler. CDU has been found to be more precise and reliable than the handheld Doppler in the detection of perforating arteries of the anterolateral thigh [25,26]. The CDU was able to visualize the perforator passage through the fascia, which the handheld Doppler could not. In another study comparing CDU and the handheld Doppler for the detection of the second dorsal metacarpal perforators, CDU identified more cutaneous perforators than the handheld Doppler. Furthermore, in some instances, the handheld Doppler mistook feeding vessels falsely as being perforators [27].
This systematic review revealed that the literature describing color Doppler ultrasonography used to identify perforators for pedicled perforator flap reconstruction of local defects is limited and the findings have some apparent limitations: first of all, the low level of evidence of the included studies. There was just one prospective study and 11 retrospective chart reviews. Secondly, several of the included studies were small case studies. On the other hand, the diversity of flaps and rate of successful reconstructions reported in this review seems to indicate that pedicled perforator flaps are a reliable alternative to other reconstructive options. Correct use of CDU enables the surgeon to target the perforator and plan a pedicled perforator flap for local reconstruction using the available tissue adjacent to the defect with the shortest possible arc of rotation or transposition to minimize the risk complications.

Conclusion
The study revealed an 11 times greater risk of venous congestion when pedicled perforator flaps were raised in the extremities compared to the trunk. There is a learning curve associated with the identification of perforators using CDU. Furthermore, we need to adapt and individualize the flap design with regard to shape and size according to tissue availability and knowledge of perforator whereabouts and course. CDU can be used as a tool to identify perforators for pedicled perforator flap reconstruction; however, the literature related to this subject is limited.