Vascularity of the Fasciocutaneous Flap; Further Delineation of Anatomy: Blood Supply to the Skin

 

 

X. Wang*

J.L. Xia*

D.M. Wang*

Wyatt G. Payne, MD^†

Martin C. Robson, MD^†

 

*Plastic Surgery Research Center and Department of Anatomy

The Third Clinical Medical College

Beijing Medical University

Beijing, China

 

^†The Institute for Tissue Regeneration, Repair, and Rehabilitation

Department of Veterans Affairs Medical Center

Bay Pines, Florida

and

The Department of Surgery

University of South Florida

Tampa, Florida

 

 

ABSTRACT

Introduction:            The fasciocutaneous flap has been intensively studied, including such aspects as the diameter of the vasculature, the source artery for each flap, and development of classification schemes. Reasons for flap skin and subcutaneous tissue necrosis remain elusive. The purpose of this study was to analyze the fasciocutaneous arterial circulation of the lower extremities to further delineate the vascular anatomy of the skin and fascia of the leg.

Materials and Methods: The study was carried out in 19 fresh cadavers (38 legs), which were injected with various media for radiography, histologic studies, and electron microscopic examination. The largest diameter perforator vessels were dissected in continuity with the fascial vascular network, the subcutaneous network, and the dermal/epidermal network.

Results: Multiple levels of anastomosing small vessels including U-shaped willowlike capillaries form multiple vascular intersections, located in the skin. Diminished vascularity is noted in the subcutaneous fat.

Conclusion: Ischemia and necrosis of the subcutaneous fat and skin of failing fasciocutaneous flaps of the lower extremity are, in part, due to disruption of anastomosing “choke” vessels of the terminal branches in the dermal and subcutaneous layers of the skin.

 

INTRODUCTION

In 1981, Ponten described a way to raise a skin flap based on the vascular plexus of the underlying fascia. He confirmed its reliability in a series of 23 patients, with 17 complete successes, 3 partial losses, and 3 total losses.¹ These flaps were all proximally based local flaps that included skin, subcutaneous fat, and fascia. More than 50% of the flaps were longer than 15 cm with an average length to width ratio of 2.5:1 and did not require a delay procedure for elevation. The discovery that undelayed fasciocutaneous flaps could be used with confidence to cover defects has proven to be invaluable not only in reducing the cost and time of treatment but also in giving the surgeon an effective new technique. Although Ponten is credited with the description of the fasciocutaneous flaps, the anatomical basis for the flaps’ success was subsequently delineated by Haertsch² and later by Barclay et al.³

            In 1984, Tolhurst et al not only confirmed the usefulness of the fasciocutaneous flap in the lower extremity but also expanded the concept to encompass reconstruction of the entire body, particularly the trunk and axilla.^4,5 More recently, Fix and Vasconez described the vascular supply of the fasciocutaneous flaps and the principles of flap transfer in the lower extremity.⁶

            Inquiry into the blood supply of the fascia has shown that the fasciocutaneous system consists of perforating vessels that arise from regional arteries and pass between muscle bellies along the fibrous septa. These vessels then spread out above and below the plane of the fascia to form plexi, which in turn distribute perforating branches to the skin. Schafer helped to delineate the structure of the fascia’s major vascular network, showing that the fasciocutaneous system is not homogenous but rather varies from region to region and also within a specific anatomic site.⁷

            In 1984, Cormack and Lamberty proposed five categories of fasciocutaneous flaps according to their vascular patterns.⁸ They found a marked directionality to the fascial plexus longitudinal to the main vascular system and the existence of a large major plexus on the superficial surface of the fascia. They also noted that although the preferred direction of vessels in the leg is lengthwise, the vascular network is so rich that the fasciocutaneous flaps could be safely oriented obliquely.

            Despite these observations and discoveries, the following questions have been raised:

•           What is the anatomical relationship of fascia to subcutaneous tissue to skin?

•           What is the cause of tissue necrosis in failing/failed flaps?

The purpose of this study was to further delineate the vascular anatomy of

fasciocutaneous flaps in the lower extremities with respect to the skin and subcutaneous tissue, to theorize the causes of vascular insufficiency, and to postulate reasons for necrosis of the subcutaneous fat and skin in flaps based on our anatomical observations.

 

MATERIALS AND METHODS

Both legs from nineteen fresh cadavers were studied (38 specimens total). In all cadavers, the femoral artery was cannulated and infused prior to the dissection of the vascular network.

 

Anatomic Dissections

Four of the cadaveric legs were injected with acronitrile butadiene styrene for gross observation of vessels 50 microns and greater. Incisions were made directly to the subfascial plane, and the fasciocutaneous vessels were meticulously dissected, taking care to document shape, position, and dimensions of the vascular network within the fascia, fat, and subdermal layers. All data were photographically documented.

           

Histologic and Radiologic Study

Six legs were injected with Chinese ink for horizontal and sagittal plane histologic sectioning for light microscopic evaluation. Twenty-six legs were injected with red lead powder liquid (red lead powder = terpentine oil) for radiologic study. The remaining two legs were injected with methyl acrylic resin for electromicroscopic evaluation.

 

RESULTS

The sagittal and horizontal radiographs and vascular casts of the fasciocutaneous layer (Figures 1 and 2) show that the musculocutaneous vessels branch out in a three-dimensional structure from the fascia to supply the overlying skin with a mean vessel diameter of 264.3 microns + 18.2 microns (Table 1). They can then be seen anastomosing with each other, with their main anastomosis (first grade anastomosis of the perforators) lying deep to the dermis (Figure 1). These commonly comprise the densest vascular plexus of the fasciocutaneous flap.

            The series of tangential radiographs of the facial layer deep (Figure 3), progressing to the subcutaneous layers located more superficially (Figures 4 and 5), demonstrates that each vascular network is separated by a space, with the subfascial perforators linking the separate networks within the fat layer to form an integrated fasciocutaneous vascular network. These separated segments demonstrate that the main arterial network of the fasciocutaneous flap is a three-dimensional structure that allows for the distribution of blood supply between the fascia and skin.

            The anastomosing branches that link the adjacent perforators in the fasciocutaneous flap are located mainly within the subdermal layer (Figure 1), with a mean vessel diameter of 129.8 microns + 11.7 microns. Due to the existence of these branches, the vascular network of the flap is preserved during elevation of the flap.

            The superficial vascular network is mainly derived from the first grade anastomosed branches, which are lying in the deep dermal layer. They give off various willow-shaped descending branches that provide blood supply to the middle and upper third of the fat layer and anastomose with each other to form a U-shaped arcade (Figure 1). This network is partially derived from the main trunk of the perforators. The short descending branches that supply the upper two thirds of the fat layer give off branches that distribute around the individual fat globules (Figures 6 and 7). These vessels average 22.19 microns + 2.75 microns.

            The dermal vascular network is also derived from the first grade anastomosed branches of perforators (Figure 1). This rich network of vessels runs along the dermal level with fairly uniform continuity and vessels of a mean diameter of 11.34 microns + 0.46 microns.

 

DISCUSSION

The fasciocutaneous system consists of perforators that pass along the fascial septa between adjacent muscle bellies and then fan out at the level of the fascia to form a plexus from which branches are given off to supply the overlying subcutaneous tissues and dermis.⁸ The presence of a fascial plexus explains why a fasciocutaneous flap of the lower extremity can be raised with greater safety, reliability, and a much greater length to width ratio than an equivalent random cutaneous flap.

            The suprafascial vascular plexus is an intricate network that is constructed of U-shaped arcades, which are mainly derived from the willow-shaped descending branches derived from the first-grade anastomoses of muscle perforators. The capillaries around the fat lobules are terminal branches with very few anastomoses (Figures 6 and 7) and relatively small vessels (Table 1). Any decreased blood flow resulting from flap elevation, perforator interruption, or direct trauma will lead to ischemia with subsequent necrosis of fat lobules. The small size of dermal/epidermal vessels also lead to susceptibility of vascular insult. The increased number of anastomosing capillaries lends some protection that is not seen within the fat layer. An element of random vascular supply can become important in the fasciocutaneous flap. U-shaped arcades that supply the upper two thirds of the fat layer appear to form chokelike anastomoses and may contribute significantly to increasing the width and length of fasciocutaneous flaps, making possible the survival of flaps exceeding the usual random pattern alone.

 

CONCLUSION

This study and vascular evaluation of the fasciocutaneous region of the lower extremity has allowed a further look at the blood supply of the fasciocutaneous flap. It answers questions regarding how the subcutaneous fat is supplied by fascial and cutaneous vessels and may explain why fat necrosis and skin loss may occur in some fasciocutaneous flaps. Careful dissection of the lower extremity fasciocutaneous flap in the subfascial plane should allow preservation of the delicate vasculature that supplies the essential subcutaneous tissue and dermis/epidermis needed for wound coverage in the lower extremity.

 

REFERENCES

1.         Ponten B: The fasciocutaneous flap: Its use in soft tissue defects of the lower leg.

        Br J Plast Surg 34:215, 1981.

2.         Haertsh PA: The surgical plane in the leg. Br J Plast Surg 34:464, 1981.

3.         Barclay TL, Cardoso E, Sharpe DT, et al: Repair of lower leg injuries with

        fasciocutaneous flaps. Br J Plast Surg 35:127, 1982.

4.         Tolhurst DE, Haeseker B: Fasciocutaneous flaps in the axillary region. Br J Plast

        Surg 35:430, 1982.

5.         Tolhurst DE, Haeseker B, Zeeman RJ: The development of the fasciocutaneous

        flap and its clinical applications. Plast Reconstr Surg 71:597, 1983.

6.         Fix RJ, Vasconez LO: Fasciocutaneous flaps in reconstruction of the lower

        extremity. Clin Plast Surg 18(3):571, 1991.

7.         Schafer K: Das subcutane gefabetasystem (untere extremitant): Mikropaparatorische

        untersuchungen. Gegenbaurs Morphol Jahrb (Leipzig) 121:492, 1975.

8.         Cormack GC, Lamberty BGH: The Arterial Anatomy of Skin Flaps, ed 2.

        London, Churchill Livingstone, 1994.

9.         Nakajima H, Fujimoto T: Island fasciocutaneous flaps of dorsal trunk and their

        application to myocutaneous flaps. Kieo J Med 33:59, 1984.

10.   Lang J: Uber die textur und die vascularisation der fascien. Acta Anat 48:61, 1962.

 

Table 1. Mean Calibers of Vessels

Musculocutaneous Vessel        264.3 microns + 18.2 microns

Anastomosing Branches        129.8 microns + 11.7 microns

Superficial Fascia            22.19 microns + 2.75 microns

Deep Fascia                             18.78 microns + 2.74 microns

Cutis                                        11.34 microns + 0.41 microns

 

Figure 1. Radiograph of sagittal section of fasciocutaneous layer.

Figure 2. Tangential vascular cast of the fasciocutaneous network following acronitrile butadiene styrene injection of the fascial layer demonstrating the main perforating system with sparse communicating anastomoses.

Figure 3. Tangential radiograph of the fascial layer. The perforators (P) are distributed segmentally in the deep fascia and show few anastomosing vessels.

Figure 4. Tangential radiograph superficial to the fascial layer. Fascia has been removed. The arrows show the densest areas of anastomsis.

Figure 5. Tangential radiograph (more superficial) of the dermal/cutaneous layer demonstrating the rich vascular network of the anastomosing vessels.

Figure 6. Terminal vessels and capillaries within the fat layer (f).

Figure 7. Vascular cast showing anastomosis between fat globules. The branches of the fat globules (1) terminate in the fat globule capillaries (f; magnification x 100).