The Chimeric Propeller Flap

Abstract

A chimeric flap consists of multiple discrete tissues or flaps connected only by a common source vessel. Each component must have an independent source of circulation. Rotation of any included part only about its specific vascular supply, such as done with a propeller flap, would be possible. These characteristics, whereby the chimeric flap concept and propeller flap concept are combined, would result in a chimeric propeller flap . Such a choice will enhance overall flap insetting capabilities and versatility, while often limiting the reconstructive need to but a single donor site!

A chimeric flap is a subtype of compound flaps, where the latter's subdivisions differ in their source of vascularization to multiple tissue components and/or consist of multiple flaps or polyflaps that are found in some arrangement or combination. ^{1 2 3 4} Specifically, a chimeric flap consists of “multiple flap territories, each with an independent vascular supply, and independent of any physical interconnection, except where linked by a common source vessel.” ⁴ A propeller flap has a nourishing pedicle or hub to its component tissues, which otherwise is disconnected from all surrounding attachments as an “island,” and then reaches the given recipient site by a rotation and not advancement about that hub. ^{5 6} A chimeric propeller flap can thereby be defined as a combination of multiple flap components, each independent of any physical interconnection except where linked for the most part to a common source vessel, and where each component can be independently rotated like a propeller about its separate vascular supply to reach the desired recipient site. Unlike a “true” chimeric flap, the nomenclature can be tweaked a little in that the vascular hub of the rotated flap usually will not have been completely freed back to the common source vessel; so, there will still be some additional minor interconnections with the other flaps in the combination.

Methodology

Usually, a chimeric propeller flap will initially most simply be a composite flap consisting of at least two potential discrete flap components. A good example would be a musculocutaneous flap. This is a composite form of compound flap consisting of a muscle and overlying skin, subcutaneous tissues, and deep fascia, where all receive their nutritional circulation from the same solitary source vessel. ⁴ Yet with the advent of the perforator flap concept, those tissues overlying the muscle could be considered to be a fasciocutaneous flap supplied by musculocutaneous perforators. ⁷ Spinelli et al first showed clinically that the so-called fasciocutaneous component of a latissimus dorsi (LD) musculocutaneous free flap could be partially separated reliably from the muscle if some musculocutaneous perforators are preserved for its vascularization, and then turned over to allow extension of that flap for greater reach. ⁸ Cavadas and Teran-Saavedra in their “razor flap” went a step further and totally separated the skin paddle from the LD muscle, except for an identified musculocutaneous perforator that served as a hub to allow a 180-degree rotation of that cutaneous tissue about that perforator for even greater freedom of insetting ( Fig. 1 ). ⁹ This “combined latissimus dorsi–thoracodorsal artery perforator (TAP) free flap” consisted of two flaps connected only by their branches from the thoracodorsal vessels, about which each could be independently rotated if desired, thus perhaps the first example of a chimeric propeller flap. ⁹ Kuroki et al have further confirmed the advantages of this LD-TAP flap version. ¹⁰ Innocenti et al provided a different example using a medial gastrocnemius musculocutaneous local flap, for joint coverage by the muscle, and the skin paddle elevated as a medial sural artery perforator flap that then would be rotated like a propeller flap to facilitate knee closure. ¹¹ This truly was a chimeric flap as stated in the title of the latter's article, ¹¹ but more importantly a chimeric propeller flap!

Fig. 1.

( A ) Lateral exposure of total knee prosthesis with vertical skin deficit; ( B ) latissimus dorsi (LD) musculocutaneous flap still pedicled in donor site. The Y-branched musculocutaneous perforator to the skin paddle, noted on microgrid, will be dissected to just below the muscle surface. The innate axis of the skin component is parallel to the lateral LD border; ( C ) LD–thoracodorsal artery perforator (TAP) free flap. The TAP flap has been freed from the LD muscle, and then rotated on the perforator ( p ) like a propeller flap (arrows) for 90 degrees in a direction clockwise to the thoracodorsal source vessel axis, ( D ) the LD muscle was inset over the knee prosthesis, and brought underneath the subcutaneous layer to the popliteal vessels as the recipient site at the medial knee, with the rotated TAP flap used to close the vertical knee skin incision.

Just as the pedicle to a propeller flap does not have to be a perforator, a subcutaneous pedicle could be used to allow rotation perhaps of the skin of a fasciocutaneous flap about the underlying subcutaneous tissues as suggested by Aoki et al's flap-in-flap idea, ¹² with numerous potential possibilities to form chimeric propeller flaps. However, most would agree that retention of just a capillary perforator instead would be a more reliable option. ¹³ An even better option that commonly connects chimeric flaps is to capture a septocutaneous perforator. For example, a fibular osteoseptocutaneous flap could provide vascularized bone with a cutaneous component that can be rotated like a propeller about it for independent three-dimensional insetting ( Fig. 2 ).

Fig. 2.

( A ) Left nasomaxillary defect after tumor excision; ( B ) chimeric fibula and peroneal artery perforator (PNAP) free flap, with long peroneal vascular pedicle to allow reach to the superficial temporal vessels. The septocutaneous perforator to the PNAP component, as seen on microgrid, was dissected only to the lateral border of the fibula; ( C ) CT scan shows healed fibula (arrow) inset along floor of maxilla; ( D ) white-appearing PNAP flap was rotated to replace the missing palatal and oral mucosa, proving an advantage in simplification of the three-dimensional insetting capabilities of a chimeric propeller flap.

Discussion

Usually, a chimeric propeller flap will have only one component rotate while the other remains static, which could be documented simply in the record by the degrees of such rotation in a clockwise or counterclockwise direction. However, if all or multiple parts are rotated about their independent vascular pedicle, the “Clock Flap” concept of Antonini et al ¹⁴ with some modifications may be a reasonable way to denote how each has been ultimately inset relative to the other, but for details a review of that article is left to the discretion of the reader.

As with all propeller flaps, chimeric propeller flaps also have to observe the same restrictions that could cause vascular insufficiency. If perforator based, as determined by Wong et al, the angle of twist should be no more than 180 degrees, selected perforator approximately 1 mm in diameter, and length of dissection of that perforator at least 3 mm, if possible. ¹⁵ Thus, in a musculocutaneous composite flap altered to become a chimeric propeller flap as seen in Cavadas and Teran-Saavedra's “razor flap,” ⁹ the dissection of the chosen musculocutaneous perforator that will serve as the rotation hub for the fasciocutaneous flap need not be excessive, thereby preserving some connections with the other components of the combination ( Fig. 1 ). As always, be wary of venous congestion, as the vein will be more prone to occlusion. If these parameters are obeyed, reduced rotational angles below 180 degrees as Brunetti et al have shown, should result in virtually no flap compromise. ¹⁶ Whether a clockwise or counterclockwise twist would be preferential for overall vascular sufficiency often is determined by clinical observations alone. ¹⁷ However, Song et al have used color duplex ultrasound flow dynamics to show that the choice with higher perforator flow volume and flow velocity will have fewer untoward events. ¹⁸ Another option available is to use smartphone thermal imaging after any component flap rotation to assess surface temperature, which is directly correlated to flap perfusion as demonstrated in another overview in this issue. ¹⁹

Conclusion

A chimeric propeller flap essentially is a chimeric flap where one or more of its component flap tissues are rotated like a propeller flap about its specific vascular source. Only this nomenclature is new, as the concept itself has previously been shown to better extend the reach of flaps, optimize their configuration, and facilitate three-dimensional insetting. ¹⁰ However, capturing all these attributes can now more efficiently be limited to a single donor site, which is a sine qua non of chimeric flaps. This blend of the propeller flap concept and that of the chimeric flap has now extended the versatility of both.