Chapter Design principles and the keystone technique Logic will get you from A to B, imagination will get you everywhere Albert Einstein (1879–1955) INTRODUCTION The keystone island flap is an easy reconstructive tool to master As a single flap, it offers the greatest versatility of any locoregional flap design It has a simple design that can be applied as a direct extension of elliptical defects, and its diameter can be increased readily to improve the chances of perforator/vessel incorporation when the local neurovascular anatomy is uncertain Unlike various random pattern flaps that rely on ratios of length to breadth of dermal attachment with significant variation for different body regions, the keystone perforator island flap can be used in any region where perforator or neurovascular support exists Having examined the vascular basis of these flaps in Chapter 2, the purpose of this chapter is to look at the design of a standard keystone island flap and demonstrate some of the variations that can be undertaken in specific circumstances to optimise its functional and aesthetic results Numerous variations in design are possible, including skin island shape, basis of vascular support, and presence or absence of incorporated named nerves The islanded nature of the flap permits various flap manipulations to facilitate closure, such as advancement, rotation, folding and flap-on-flap techniques with inset of these islanded flaps, producing even physiological tension for good wound healing The eventual scars are difficult to see due to the combination of non-parallel straight lines and parallel arcs of different lengths, with good aesthetics as a result PLANNING A KEYSTONE ISLAND FLAP The keystone design The classic design of all keystone flaps bears a resemblance to the keystone of archways (see Fig 1.4) This consists of a trapezoid bent into the shape of an arc, with the longest side on the convex surface of the arc Variations in the angles and relative lengths of each of the sides of the keystone can be used but, most commonly, the shape consists of a short arc formed by the margin of the defect (with or without lateral extensions to form an ellipse), followed by incisions formed at right angles to the tangent of the ends of this short arc (Fig 3.1) These incisions are made the same or a greater length than the transverse width of the defect A long, curving arc-shaped incision then joins the tips of these two incisions, staying parallel to the short arc to complete the keystone shape (Behan 2003) With certain characteristics of a bipedicled flap, the keystone flap is actually two V–Y flaps side by side but at an angle to each other so that their advancements are directed towards the centre of the defect (Fig 3.2) In a conventional bipedicled flap design, the secondary defect is usually larger than the primary defect and may require skin grafting By converting this bipedicled flap into an island with V–Y advancement at each end, the longitudinal tension in the flap is released, thus maximising elasticity in the transverse direction and aiding defect and donor site closure V–Y closure at the periphery narrows the whole defect complex so that the flap does not have to move as far transversely Similarly, the secondary defect on the opposite side of the flap is reduced by this manoeuvre (see Fig 2.11) (Behan 2003) Placement, size and orientation of keystone island flaps Beyond the basic flap geometry, there are further considerations when planning keystone flaps so as to facilitate replacement of like tissues with like, ease wound and donor site closure, and incorporate appropriate neurovascular support While many flap types necessitate the use of preoperative imaging (e.g computed tomographic or magnetic resonance angiography, Doppler ultrasonography), this has not been our practice for the vast majority of defects 28 Downloaded for Anonymous User (n/a) at Epworth HealthCare from ClinicalKey.com.au by Elsevier on May 11, 2017 For personal use only No other uses without permission Copyright ©2017 Elsevier Inc All rights reserved Chapter Design principles and the keystone technique FIGURE 3.1 General shape of a keystone island flap (a) An elliptical defect (b) Fundamental design of the keystone island flap (Reproduced with permission from Behan 2003, Fig 3.) D a ([FLVLRQDO ZLGWK 5DWLR )ODS ZLGWK ,VODQG IODS E b D a 7KHVHUHSUHVHQWWKHVFLVVRUWHFKQLTXH XVHGIRUWKHEOXQWGLVVHFWLRQ Advancement and closure of V–Y flaps into an island FIGURE 3.2 (a) Blunt dissection mobilisation around the limits of the flap (b) Vertical mattress sutures (numbered 1–3) bring the flap into alignment, creating lines of tension Closure of the double V–Y apposition points at the limits of the flap creates a relative redundancy in the central portion of the flap The redundant shaded areas (numbered and 5) are excised The wound closure is completed with the hemming suture (Reproduced with permission from Behan 2003, Fig 4.) because of the reliability of perforator supply where a minimum of a 1:1 ratio of defect width to flap width is maintained (Behan 2003) One simple method to assist flap placement is to design the flaps so that their longitudinal axis runs in the lines of the dermatomes A pinch test is then used to assess whether sufficient tissue elasticity and laxity are present to permit elevation and closure (elasticity is better than laxity) The keystone island flaps are commonly raised parallel to the long axis of dermatomes similar to the elongation of tissue during intrauterine development, often within a single dermatome and placed over muscle bellies wherever possible to improve perforator incorporation and flap movement during closure Where the underlying neurovascular anatomy is uncertain, this approach increases the chance that the flaps will run parallel to longitudinal neurovascular structures, which can then be incorporated into the flap as their lateral mobility facilitates ready advancement of the flap into the defect (Behan 1992, 2003) While flap planning should be included as part of the planning for the excision of lesions so that the orientation of the excision occurs in an axis that permits easy flap formation and advancement, the robust nature of the vascular supply to these flaps and 9±< 9±< 9±