Polar coordinate view of the wide, intermediate, and acute flaps. r indicates the distance equal to 1 radius of the defect.
Diagram depicting the average extent of undermining (shaded area).
Reading tension of closure from the tensiometer.
A defect with a 90° arc of available tissue on either side is often well suited to an O-to-Z closure.
A, Scalp defect. B, O-to-Z flap drawn. C, Flap developed and initial transfer. D, After flap closure; note minimal distortion of hairline.
The flap is sometimes rounded at point A. Occasionally, excision of a small amount of tissue at point B also assists in a smooth closure.
Buckingham ED, Quinn FB, Calhoun KH. Optimal Design of O-to-Z Flaps for Closure of Facial Skin Defects. Arch Facial Plast Surg. 2003;5(1):92-95. doi:
From the Department of Otolaryngology, Division of Facial Plastic and Reconstructive Surgery, The University of Texas Medical Branch at Galveston.
Objective To determine the optimal design of an O-to-Z flap for closure of facial skin defects.
Methods Prospective cadaver study. Multiple 2-cm-diameter circular skin defects were created in fresh cadavers. Three types of O-to-Z flaps were designed, varying the angle of a curved line about concentric radii of the defect: acute, intermediate, or wide angle flap. The tension of closure of each was measured and compared at different lengths of incision and extents of undermining.
Results The acute angle flap had a significantly lower closing tension at all lengths of incision and extents of undermining than the intermediate and wide angle flaps. Increasing the amount of undermining alone without incising the flap did not significantly decrease the closing tension. Incising the acute angle flap to 4 radii created a nearly tension-free closure.
Conclusions The optimal design for reducing tension of the O-to Z flap is an acute angle flap. The optimal length of incision and undermining necessary to minimize closing tension is discussed.
THE O-TO-Z flap is a double advancement flap useful for closure of skin defects where tissue is available on opposing sides of the defect. It is created with 2 curvilinear incisions on opposite sides of a roughly circular defect. Each flap is advanced, rotated, and fixed 90° from its incision point. The 2 flaps can be of equal or unequal length depending on the available surrounding tissue. The final closure forms a curving zigzag scar, resembling a "Z."
Although the general concept of this flap is well documented,1-3 there is little published information on flap design specifics such as the optimal angle of incision, length of the opposed flaps, or undermining necessary to produce the lowest tension closure. This cadaver study was undertaken to investigate these variables to determine an ideal O-to-Z flap design.
Fresh cadaver (N = 3) torsos, buttocks, and thighs were used for all experiments. A circular defect 2 cm in diameter (radius = 1 cm) was drawn and excised in a subcutaneous plane. Four more concentric circles were drawn, each successively 1 radius larger than the defect. Three different O-to-Z flaps were designed: acute, intermediate, and wide, by creating 4 unique points for each flap using a polar coordinate system; each flap originated from a common coordinate at the defect edge (1r [radius of defect], 0°) (Table 1 and Figure 1). The second side of the flap was created with its origin at 1r, 180° as an inverted mirror image of the first side. Ten flaps of each design were created and tested. The 3 different flaps (acute, intermediate, and wide) were placed adjacent to each other on similar regions of the cadaver (torso, buttock, thigh) in sequential order to optimize tissue similarity between flap designs.
Using separate defects for each of the flap types, the first side was incised to 3 radii and undermined in a subcutaneous plane from the origin, to the 3-radii circle, to the point on the defect 180° opposite the origin point (Figure 2). A silk suture was secured to the flap tip and to the tip of a calibrated tensiometer (Haag-Streit, Berne, Switzerland; distributed by Geneva Gage Inc, Albany, Ore). The defect edge 90° from the flap origin was secured with an 18-gauge needle; without suturing the sides of the flap, the flap tip was advanced to this point, and the tension read in centi-Newtons (Figure 3). This was repeated 3 times, allowing the flap to relax back to its initial position each time, and the average recorded. Without incising the flap edge, undermining was carried out to the 4-radii circle and the tension measurements repeated. Tension measurements were repeated with the flap incised to this point. The procedure was repeated again with the flap undermined, then incised to the 5-radii circle.
Once the entire first side had been incised, this flap was sutured to the defect at the point of the previous tension measurements. The second side flap was then created and measurements repeated as for side one. When measured tension was less than 10 cN (the lower limit of our tensiometer's range) there was clinically almost no tension on the suture. The flaps were noted either to pull slightly away from the defect edge or to lay without tension adjacent to the defect edge. Tension for the slightly pulled-away flap was recorded as 10 cN, and for "no-tension" flap, as 0. Following incising both flaps to 5 radii and suturing both tips to their respective predetermined points of advancement, lateral tension measurements were recorded from the 2-radii point on the flap to the adjacent point of the flap incision.
The mean tension measurements for the 30 flaps with first and second sides incised from 3 radii to 5 radii with varying degrees of undermining is given in Table 2. The 3 different flap designs were statistically analyzed using Kruskal-Wallis rank order analysis of variance, followed by group comparison of each flap design at increasing lengths of incision and degrees of undermining using the Mann-Whitney U test. The results of this analysis comparing the 3 designs are presented in Table 3 (shaded areas, P≤.05). For both sides of the flap, at all incision lengths and degrees of undermining, the acute angle flap design had significantly less closing tension than either the intermediate or wide angle flap design. There was no significant difference in tension at any point between the intermediate and the wide angle flap design. In addition, lateral tension measurements recorded at the 2-radii point were not significantly different between any of the flaps.
Tension measurements for the acute angle design were reexamined comparing tension with and without undermining as well as advancing incision lengths. These results are presented in Table 4. No significant tension decrease was obtained by undermining alone (P>.05, Mann-Whitney U test). The only significant decrease in tension was achieved when the flap was incised from 3 to 4 radii after undermining. Further undermining or lengthening of the incision beyond 4 radii did not significantly decrease the tension.
The O-to-Z flap design is useful for closing facial or other cutaneous defects on the body following the excision of cutaneous malignancy or following trauma with soft tissue loss. The flap may be performed anywhere that tissue is available on opposing sides surrounding an approximately circular defect (Figure 4). The most common use for the design in the head and neck has been described in the scalp region; however, other locations such as the forehead and temple also lend themselves to this type of reconstruction, if tissue is available without distorting surrounding structures and incisions approximate relaxed skin tension lines.
Our study addresses flap design for minimizing closing tension and flap size. The optimal angle of flap incision is described by the 4 polar coordinates—2r,45°; 3r,90°; 4r,112.5°; 5r,135°—with the opposing flap created 180° from the first with the same curve. Described another way, the flap is designed by selecting an origin on the defect and creating a curve-linear flap with points 45° from each other at 2, 3, and 5 radii. In our study, use of these coordinates for the flap design with incision and undermining of one flap side to 4 radii resulted in mean closing tensions less than 10 cN (Table 2). Flap lengthening or increased undermining beyond 4 radii did not confer any advantage.
When an O-to-Z flap is used clinically for closure of a facial skin defect (Figure 5), modifications for accommodation of anatomic subunits and facial landmarks may be necessary. The 2 opposite flaps, theoretically the same size and shape, can tolerate some dissimilarity in angle or length, if necessary. We begin defect closure by drawing the concentric circles, cross lines, and acute flap design out to 4 to 5 radii. We then incise each side to about 3 radii and undermine. If the defect location and intrinsic tissue properties cause this closure to be under more than optimal tension, the skin incision and undermining are extended in 1-radius increments until satisfactory. For an anterior scalp defect, for example, it is often necessary to extend the scalp flap incision farther than the forehead/temple flap to achieve equivalent mobility of the inelastic scalp tissue. It is sometimes helpful to round the points of the flaps (Figure 6, point A), or excise a small amount of tissue to straighten the small point between the defect and proximal flap (Figure 6, point B). This versatile flap is most useful for roughly circular defects with moveable tissue available on opposite sides of the flap. We use it primarily for skin defects of the scalp, forehead, and temple.
The optimal design of the O-to-Z flap to minimize tension for closure of skin defects is an acute angle flap and its inverse mirror image with points of the curve drawn at successive 45° angles at 2, 3, and 5 radii from the defect center. Closing tension less than 10 cN for a single flap side can usually be obtained by incising and undermining the flap to a distance of 4 radii from the center point of the defect. Undermining alone confers no advantage to decrease closing tension without accompanying flap incision, and incising the flap farther than 4 radii did significantly reduce the closing tension in this study.
Corresponding author: Karen H. Calhoun, MD, Department of Otolaryngology, University of Texas Medical Branch, 301 University Blvd, Galveston, TX 77555-0521 (e-mail: email@example.com).
Accepted for publication December 4, 2001.
We thank Shawn Newlands, MD, PhD, for assistance with statistical analysis and the UTMB Willed Body Program, and individual donors for the material used in data acquisition.