Versatile Sural Flap Supplied By A Dominant Peroneal Perforating Artery Through Neurocutaneous Vascular Axis:Anatomic Study And Clinical Application

Objective To explore the anatomical bases, individual flap planning and relevant theoretical foundations of free and pedicled sural flap supplied by a dominant peroneal perforating artery (DPPA, with a diameter≤1.0mm) arising from the posterolateral intermuscular septum through neurocutaneous vascular axis for repairing of defects located anywhere, and put forward technique suggestions and related clinical guidelines.Methods1-Applied anatomical research(1)20fresh legs were injected with the mixture of red latex and cardiografin. After CT scanning, direct dissection and virtual three-dimension research were performed to explore:①the distribution and anatomic classification of vascular networks of sural flap, the anatomic variation of the sural nerve and the relationship between them;②The anatomic distribution and classification of DPPAs and their clinical significances;③The value of computer aided three-dimension technique in the research of this flap.(2) Flap models were harvested from three fresh legs and DSA was performed through the simulated blood supply DPPA to observe both static and dynamic images of the flap’s vascular networks and then methylene blue injection and dissection to observe dyeing of different tissue layers which also help to understand the distribution of vascular networks for harvesting super-thin flap and adipofascial/cutaneoadipofascial flap.2. clinical research(1) Hemodynamic reach of the flapThe peak systolic flow velocities (PSFV) of the blood supply pedicles in36flaps were measured before and after operation and statistically compared. The phenomenon of crossing angiosomes supply of the flap was explained from a hemodynamic view and its clinical significances were discussed.(2) individual optimal flap planning and clinical applicationBased on the distribution and anatomic classification of the DPPA and vascular networks, three basic surgical methods (flap pedicled on the lowest DPPA for repairing defects near the ankle, flap pedicled on the different DPPA for that of the leg and free flap) were designed and combined individually with techniques of super-thin flap, cutaneoadipofascial flap, combined-tissue flap and double-leaf flap to repair different defects in142cases. We also developed a reverse method for flap innervation. The essential anatomic data observed during operation were recorded. In order to assess the clinical results and significances of the flap, a large number of relating papers were reviewed and the similar cases treated earlier in our center were studied retrospectively. Detailed techniques of flap planning and harvesting were described for our new methods.(3) Preoperative locating and assessment of DPPA137cases’preoperative CDFI data were compared with intraoperative findings. The causes of false negative and false positive were analyzed to improve examination techniques.90DPPAs in90cases chosen as the blood supply pedicles only with CDFI preoperatively were used to calculate the rate of accuracy of this method for flap planning by comparing with the actual design and harvesting of the flap. CTA was also used for locating and assessment of the peroneal perforators in52cases. The stacked imaging data of CTA were inputted into the platform of Mimics image processing software to gain more detailed and accurate surface3-D models for the surgeons to design flaps. We compared the advantages and disadvantages of CDFI with those of CTA as a way to locate and choose a suitable DPPA for optimal flap planning preoperatively and thus offered clinical suggestions.(4) The timing after injury for defects repairing using this flap and vascular monitoring after operation were discussed with literature and case reviews.Results1.anatomical researchThe average number of the DPPAs observed in each leg was3.3with the average diameter of1.53±0.40mm (1.00-3.02mm). They located in the second to ninth segments of the line from the fibular caput to the tip of lateral malleolus which was equally divided into nine segments, and71.2%of which located in the fifth to eighth segments. The largest DPPAs averaged1.87±0.48mm (1.30～3.02mm) and mostly located in the third to sixth (81%). The lowest DPPAs located from the sixth to ninth with an average diameter of1.37±0.27mm (1.00～1.92mm) and mostly, the seventh to ninth (65%).40%of the lowest DPPAs appeared in the eighth. According to their clinical significances and morphological characteristics, those perforators were classified into three types:Type ⅠType Ⅰ perforators had the longest pedicle (averaged5.8cm) and the average diameter of their root segments was the largest(1.68±0.43mm) comparing with other two types. They detoured before appearing at the location of posterolateral intermuscular septum and with many large branches to supply the neighboring muscles and fibula. There were31type Ⅰ perforators (47%of the total66DPPAs) and mostly located in the third, and the sixth to eighth segments. According to the number of cutaneo-fascial branches of intermuscular septum, they were classified into two subtypes:type Ⅰ a and type Ⅰ b.Type ⅡThe morphological characteristics of Type Ⅱ perforators were between type Ⅰ and Ⅲ. The average length of their pedicles and average diameter of their roots were respectively4.0cm and1.45±0.34mm.21type Ⅱ perforators were found during dissection located mostly in the second to ninth segments of the leg. They were relatively straight and with less and smaller branches than the type I vessels. Type IIIType Ⅲ DPPA was short, small, straight and the typical intermuscular septum perforator primarily supplying the skin and fascia. There were totally14Type Ⅱ DPPAs (21%) in this group located mostly in the seventh to ninth segments with an average length of2.2cm and root diameter of1.29±0.20mm.Subdermal and deep fascial vascular plexus mainly constituted the flap’s blood supply networks and they were connected by skin arteries. Three obvious longitudinal vascular chains were observed on the deep fascia:①the internal chain (the neurocutaneous vascular axis of the sural nerve and the medial cutaneous nerve of calf);②the medial chain (the nerocutaneous vascular axis of the sural communicating nerve);③the lateral chain (the neurocutaneous vascular axis of the lateral cutaneous nerve of calf and the vascular chain of the posterolateral intermuscular septum). In the20legs,14sural nerves originated from the union of the lateral and medial cutaneous nerve of calf,4just from one of them and2from both of them without combining. The deep fascial vascular network varied with the anatomic variation of the sural nerve and could be classified into three types according to the optimal axis for mapping a large flap obtained by direct observation and measuring:Type Ⅰ (medial type)The axis divided the space between the internal and lateral vascular chain and found in14legs (60%).Type Ⅱ (internal type)The axis was leaning to the internal vascular chain. This type was found in5legs (25%).Type Ⅲ (lateral type)The axis was leaning to the lateral vascular chain and was found in3legs (15%).On the platform of Mimics image processing software (version:10.01), the artery, bone, muscle, fascia and skin could be showed separately or combined in vivid colors, and viewed at different angles. All DPPAs could be recognized in3D images, but only in12of the legs, the terminal branches of the DPPA were seen. The morphological characteristics of DPPAs could be demonstrated or measured from different angles of view, and the anatomic types decided. The vascular networks of the deep fascia and skin didn’t present in any of the images.The DSA of the flap models demonstrated the three vascular chains of the deep fascia described in direct anatomic dissection, and the most probable vascular circuit was:DPPA→vascular chains of deep fascia→superficial veins→comitant veins of DPPA. The dyeing maps of methylene blue proved that the optimal flap designing axes differed in accord with the different types of vascular networks of deep fascia. The dyeing areas and color depth of different layers of the flaps showed that the deep fascial and subdermal vascular plexuses were the most important blood supply networks. There were only interspersal dyeing dots or small areas observed on the layer of subcutaneous fat.2. Clinical researchThe mean PSFV of the pedicles of all38flaps were24.68±15.15cm/s preoperatively and38.65±16.96cm/s postoperatively. The preoperative and postoperative mean PSFV in the group of free flap were14.19±6.28cm/s and32.69±15.86cm/s respectively, and29.52±15.65cm/s and41.40±17.04cm/s in the pedicled group. By paired t-test, the postoperative PSFV was significantly higher than the preoperative PSFV (P<0.0001).Of the90DPPAs selected just with CDFI as the blood supply vessels for flap planning,9were false-positive and12were not the optimal ones, so the rate of accuracy was77.8%. What should be demonstrated was that if just consider the pedicled flaps based on the lowest DPPA, the rate of accuracy was91.2%. The intermuscular septum segment and the terminal branches of DPPA as well as how those branches passed through the deep fascia could be seen in ultrasound images, but it’s hard for CDFI to detect and show the full-length of those long perforators such as type Ⅰ DPPA and thus false results could occur.52patients (103legs) underwent CTA examination to locate and assess DPPA for flap planning preoperatively, and averaged2.3DPPAs as well as the neighboring anatomic structures could be shown in each leg. Most of the DPPAs seen in CTA images were type Ⅰ or type Ⅱ vessels, and except3 legs we didn’t found any DPPA shown in the eighth to ninth segments. In94legs using both CTA and CDFI for flap mapping preoperatively, there were63branches of peroneal artery shown in CTA images could only be differentiated from the pure nutrient branches of bone and muscle with the help of CDFI. In those patients if we could choose a DPPA as the blood supply vessel for free flap designing in CTA images with or without the help of CDFI, the accuracy rate was100%. CTA data could be inputted into the platform of Mimics image processing software for the surgeon to reconstruct different anatomic structures separately or combinedly to gain more detailed and accurate3-D images or even design and harvest flap in virtual environments.Of the total142cases of clinical operation, the blood supply DPPAs were located above the lateral malleolus in the range5.0-14cm (the diameters of the DPPAs averaged1.02±0.23mm, ranged1.00～1.62mm) which included49type Ⅲ,12type Ⅰ and7type Ⅱ vessels in the group of propeller flaps based on the lowest DPPA for repairing defects near the ankle (68cases), and in the range12～21cm (diameters averaged1.39±0.43mm, ranged1.00～2.10mm) which included17type Ⅰ,10type Ⅱ, and4type Ⅲ vessels in the group of pedicled flaps based on the DPPAs from different leg segments for defects of the leg, and in the range14～25cm (the second to sixth segments, and diameters averaged1.52±0.73mm, ranged1.10~2.30mm) which included35type Ⅰ,7type Ⅱ, and1type Ⅲvessels in the group of free flaps. Each DPPA had two comitant veins which could syncretize into one and were larger than the artery (1.2～2.3times in diameter).112cases’anatomic types of sural nerve could be decided in the operating field. There were96sural nerves of union type, and the sural communication nerve was superficial and larger than the medial cutaneous nerve of calf in most cases. There were16sural nerves of non-union type, and in5of which, the sural nerve was formed just by the lateral cutaneous nerve of calf or the sural communicating nerve. We found that the medial cutaneous nerve of calf was superficial and large in57cases, and that accounted only for16.7% of all142cases. The types of vascular networks on the deep fascia could roughly be decided in102cases, which included63(62.8%) of medial type,17(16.7%) of internal type and22(21.6%) of lateral type. All flaps survived without necrosis and no vascular problem occurred. The Follow-up in all patients for2to27months revealed that the texture, appearance and color of the flaps were all satisfactory. In those who were followed up for more than one year and the flaps were innervated, static two point discrimination was6～12mm. Moreover, we didn’t find obvious difference in the results of inervation between our new reversed method and the traditional way. Using the techniques of propeller flap and cutaneoadipofascial flap, most of the donor sits could be closed, and in those for repairing defects of the ankle and foot, the shape of recipient sites were nearly normal. The defects over dorsal hand and foot could be covered without bulking by using super-thin technique. All of the complicated defects were efficiently and freely reconstructed with other advanced techniques of the flap, such as composite-tissue and double-leaf flap, and the results were satisfactory.The flap has been clinically used in our center since October,2005. Because it’s so versatile and efficient, after2010,85.3%of all kinds of defects (except small ones of the finger) were repaired with this flap, which even accounted for98%of free flaps used. We retrospected597similar cases treated in our center from2000to2005, and found that17kinds of surgical flaps were used; the most frequently applied free flaps were thoraco-umbilical and anterolateral thigh flaps. In many ways such as donor sacrifice, operation indications, repairing effects, and operating time, the new flap was much better than traditional ones.Conclusions1. This flap is a special perforator one supplied through neurocutaneous vascular axis:①blood supply is safe and sufficient.DPPA, the relatively large perforator is able to perfuse enough blood into the flap, and the individual axis for flap planning based on the type of the vascular chains of the deep fascia ensures the flap’s integrate and reasonable circulation network. The significantly increased PSFV of the perforator on which the flap is based further enhances blood supply, and there is no problem of reverse-flowing by the small saphenous vein.②Tt is a perforator flap.The pedicle can be rotated freely without bulking and if designed as a propeller flap the cosmetic results are satisfactory both at donor and recipient sites.③With a relatively large diameter, the DPPA can be anastomosed easily, and the flap transplanted freely to repair any defects without limits of location.2.The morphologic research and anatomic classification of DPPA benefits individual and accurate flap planning, such as choosing an optimal perforator as the blood supply pedicle for a specific flap, and the tactics for efficiently designing and harvesting the composite-tissue flap, the multi-leaf flap, and even the assembled flap or the chimeric flap. The distribution characteristics of DPPA provide the anatomical bases for the design of the three elementary types of the flap.3. The form and distribution of the flap’s vascular networks in different layers of tissue provides anatomic basis for designing and harvesting the super-thin and cutaneoadipofascial flap. There is no bulking in recipient sites using the super-thin flap, and most of the donor sits can be closed directly with the techniques of cutaneoadipofascial flap.4. The phenomenon of crossing angiosomes of the flap’s blood supply through neurocutaneous vascular axis can be explained from a hemodynamic view by the significantly increasing of PSFV at the perforator on which the flap based, and which obeys the rules of non-Newtonian fluid indicating that the blood supply pedicle should be dissected thoroughly and all irrelevant branches arising from it cut and ligated.5.CDFI is one of the most important methods for locating DPPAs preoperatively.3-D images of CTA can provides direct and vivid images of anatomic structures for the surgeon to learn the locations and types of DPPAs before operation and even planning and harvesting the flap in virtual environments, but the peripheral branches of DPPA, and most of the DPPAs located in the distal third of the leg can not be shown. CTA and CDFI have their own advantages and disadvantages and are complementary for flap planning preoperatively. The techniques of computer-assisted 3D image processing is useful and with brilliant prospects in anatomic research, locating and morphological assessment of perforators, and surgical training, but can not take the place of traditional ways at the present time.6.This kind of flap combines the advantages of the nerocutaneous flap, the perforator flap and the free flap, and with the techniques of the super-thin, cutaneoadipofascial, composite-tissue, assembled and multi-leaf flap, as well as our new reversed method of innervation, it can be used to repair any defects anywhere freely, accurately and efficiently.7.There are benefits from early repairing of defects, such as reduced risk of infection, easier flap designing and transplanting, shortened in-hospital time, bone healing and better functional rehabilitation of limbs, but the principles of damage control should be obeyed. Vascular monitoring of the flap, especially those by objective methods, such as laser Doppler flowmetry is important to ensure the survival of the flap.