Introduction

Dr. Felix Behan first introduced the keystone flap in the literature in 2003 as a new method for closing skin defects following skin cancer resection.¹ The flap was described as a curvilinear-shaped trapezoidal design flap forming essentially two V–Y advancement flaps in an end to side arrangement. Since this first description, several other publications have demonstrated the reliability of this reconstructive method for several areas of the body.^2,3

Although the use of the keystone flap has yet to gain widespread popularity, it is still a very useful option for both small and large defects in the head and neck region.

The keystone was described in the initial manuscript as having several variances.

• The Type I flap is a standard flap design where the curvilinear flap is transferred to the defect and the donor site is closed primarily. This can be done in defects up to 2 cm in width.
• The Type IIA flap is a modification where the reconstruction is over a muscular compartment and the deep fascia on the outer compartment is divided in order to facilitate mobility.
• The Type IIB is when the flap is transferred and the donor site is repaired with a split thickness skin graft.
• The Type III is the use of a double Keystone flap to repair larger defects.
• The Type IV incorporates the use of a rotation component in the flap. In order to perform this maneuver, a maximum of 50% of the flap is elevated and then rotated to close the defect.

Surgeons from the Sydney Melanoma Unit described a modification of the keystone flap.⁴ The modification enables preservation of the central portion of the outer skin bridge along the outer arc. This modification increases the vascularity of the flap.

The main advantage of the flap is that it transfers adjacent tissues to repair the defect therefore taking the advantage of tissue color, pliability, and texture. The final esthetic result obtained using this flap is very pleasing. This advantage puts this flap in the same category as the V–Y advancement flap as well as other flaps already described in this book.

The final result of the reconstruction when using a keystone flap is one that shows a reconstructed defect with a flap, yet the donor site remains an enigma to all except the surgeon who performed the reconstruction.

The disadvantage of the keystone flap is that the main attraction of the flap, i.e. the ability to repair a defect without evidence of donor site harvest, is restricted to smaller defects. In cases where large defects need to be repaired, the use of the standard Type I keystone becomes more limited and the alternative Type III or IV can be contemplated. For larger defects, other flap options may often be considered.

Anatomy

The vascular anatomy of the keystone flap varies with its location. The flap is based as a random flap, which receives its blood supply from perforating vessels emerging from the fascia to profuse to the dermal and subdermal layers via small capillaries. The venous drainage of the flap is based on a similar system with larger deep veins draining the flap.

Flap harvest

• Once the resection is completed, the shape of the defect should resemble that of an ellipse or a shape similar to it.
• The width of the excision is measured then transferred to the adjacent tissue to be moved to the defect.
• A curvilinear mark is made parallel to the shape of the ellipse while maintaining the same width.
• At each end of the ellipse, the connecting point between the edge of the ellipse and the marked line should form a 90 degree angle.
• The ratio between the defect and the width of the flap should be one to one.
• An incision is made circumferentially around the marked flap and carried down deep to the dermis and to the subcutaneous fat.
• The fascia along the outer aspect of the flap may be incised to gain mobility if needed.
• Minimal undermining is done just along the edge of the flap but preferably no undermining should be attempted underneath the flap as the perfusion to the flap is gained from the perforating vessels penetrating the fascia and p/>
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