Critical analysis of the Limberg flap

Analysis of the shape of the defect

A wound/defect of various shapes can be closed primarily or with a flap. The common patterns of excision are ellipse, circle, rhomboid, mosque, etc.^3,4 The skin wastage is minimal for a rhomboid defect.⁴ Less normal skin needs to be excised along the long axis. It also results in defects with straight lines, which are far simpler than similar defects with round margins to manage.³

The flap is the result of the extension of Limberg’s classical studies on transposed triangular flaps. These are equilateral triangles. The defect is composed of two equilateral triangles sharing a common base. The resultant shape of the defect is a rhombus.³ The transposed flap, too, is an equilateral triangle. As a result, the angles of the defect and of the flap are 60 and 120° and all the limbs are of equal length [Figure 3].³

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Figure 3: Components of Limberg flap. (a) Rhomboid shaped defect ABCD, all sides equal (b) Rhomboid ABCD = ∆ABC + ∆BCD where ∆ABC = ∆BCD = Equilateral triangles; (c) ∆ABC to be covered by movement of ∆CEF having equal dimensions (green triangles are for identification of traingle ABC and triangle CEF).

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Analysis of the angles of the defect

It is a well-known fact that for primary tension-free closure, the defect should have an angle at its apices be 30° and length: width ratio 3–4:1.^5-8 This holds true for a rhombus defect but not an “elliptical” defect.⁴ As the angle increases, there is stress on the skin during suturing with an increased tendency for unfavorable conical deformation.² Bray in 1983 mentioned that defects with an angle of 60° or less can be primarily closed linearly.⁹ It follows then that above 30° and up to 60° elliptical/rhomboid defects can still be closed directly in a linear fashion, but the tension along the suture line increases. Above 60°, it becomes increasingly difficult to close the defect primarily. Therefore, when tension-free primary closure cannot be accomplished, local transposition or rotation flaps should be used.⁹

Primary closure of the rhomboid defect with 60 and 120° angles along the short diagonal would result in closure of the acute angle and opening of the obtuse angle. This would produce “dog ear” (or “standing cone deformity” at the closing angle.^1,2 At the opening angle, this results in a depressed area and tightness. In Limberg’s flap, therefore, a transposition flap is done. It has been concluded by Topp et al. that the likelihood of standing cone deformity is least for 60/120° rhombhoid defect.¹⁰ It minimizes dog ear deformity along the suture line and thus the need for a subsequent longer scar line. According to Topp et al., there is no utility in elongating the defect height beyond 60°.¹⁰ In Limberg’s design the primary defect is closed by movement of the Limberg flap. The secondary defect resulting due to movement of the Limberg flap closes by movement of the sides of the secondary defect itself [Figure 4].

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Figure 4: Movements in Limberg flap (a) Defect aka primary defect (red strips), flap aka primary flap (green strips) (b) Primary defect closure by movement of the primary flap into it (light black arrow). Secondary defect (solid black triangle) created due to movement of the primary flap closure by movements of the sides of the secondary defect (solid black arrow).

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Analysis of the orientation of the defect

The rhomboid defect created for the target lesion should not be oriented in any random direction. The defect should be oriented to take advantage of the laxity of the surrounding skin while designing the flap. The defect is usually placed between the lines of maximal extensibility (LMEs) such that two sides of the rhombus are along the lines of maximal extension. It results in the placement of the base of the triangular flap along the LME.¹¹ The flap then has maximum mobility and least strain.

Analysis of the angles of the flap

Replacement of like with like is one of the basic principles of plastic surgery. With this in mind, it is desirable to replace the defect with healthy tissue of the same dimensions and native tissue characteristics. This translates into the requirement of a rhomboid flap of the same size, preferably volume, and same angles as the defect, i.e., the sides of the flap and the sides of the defect are of equal length and the angles of the flap are 60 and 120°. Kos added that any angle other than 60° will theoretically result in either compression or stretching of the flap itself.¹²

Bray, on the other hand, stated that the angles of the rhomboid defect need not always be 60/120° for achieving closure due to wide undermining and distensibility of the involved skin.⁹ Fee and Gunter¹³ established that the acute angle in the rhomboid defect can vary from 60 to 90°. In practice, however, the angle of 60–75° is the best. Flap with an angle less than 60° too is also viable. In fact, it has been shown experimentally by Topp et al.¹⁰ that a decrease in the acute angle of the flap while still along the short diagonal of the defect results in distributed closure force and thus decreased vascular compromise of the flap. It requires recruitment from opposing wound edges. For this, Topp et al.¹⁰ concluded that for 60/120° rhomboid defect, the best closure would be with a flap along the short diagonal and having an acute angle of 30°. The reason for this finding is the recruitment of tissue from the defect margins by undermining and stretching to close a larger defect with a smaller flap for closure. This is in contrast to the observation by Bray⁹ that the relative tension distribution is not changed by wide undermining of the defect margins. Furthermore, according to Bray, the size of the flap decreases by 40% for a 90°/square defect.⁹

Analysis of the orientation of the flap

The Limberg flap is drawn along the short diagonal. In other words, the angle between the short diagonal of the defect and the flap (θ in [Figure 5]) is 0°. As this angle θ is increased, the force of closure along the defect side increases. This results in increased tension along the closure line ABD, which is undesirable for a large defect and for thicker skin. To mitigate this, a wide undermining of the defect margin is needed.¹⁰ In other words, for closure without undermining of the defect margins, for large defects, and for thicker skin, the flap should be designed along the short diagonal of the defect.

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Figure 5: Orientation of Limberg flap. (a) General rhombhoid flap (∠BAC = ∠CEF = θ, ∠CEP = θ, All sides are equal); (b) Standard Limberg flap (∠BAC= ∠CEF= θ= 60°, ∠CEP=θ=0°).

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It is important here to bring forth the observation of Topp et al.¹⁰ that in cases with asymmetric undermining or with directional distensibility and laxity, the flap can be oriented in a direction different from that aligned to the short diagonal of the defect.

A similar flap along the long diagonal will be incongruent with respect to the dimensions, area, and angle of the defect. Applying the concepts of Scott for designing transposition flaps, if it is designed along the long diagonal of the defect, there is an increase in primary flap movement and an increase in pivotal restraint.¹⁴ This leads to a loss of height of the leading edge of the flap as it moves into the defect. At the same time, the acute angle of the flap decreases, resulting in the flap being smaller than the defect by 30%. In addition, orienting the flap along the long diagonal will result in the base of the transposition flap being almost perpendicular or at wide angulation to the (lines of maximum extensibility) LME, which will increase the tension and decrease the ease of defect closure significantly. This is directly against the intention of Limberg’s flap, where the base of the flap should be along the (LME) to take advantage of skin extensibility.^13,15,16

The flap drawn along the long diagonal is shorter than the defect. There is a loss of height as it is moved into the defect. The flap is unable to cover the defect completely. The donor site for the flap can be closed primarily as the flap moves into the defect. The defect can only be closed partially with the flap. Thus, suturing cannot be done for all margins of the flap and the defect. Additionally, there is a lot of strain at its base as it is moved into the defect. These are shown in [Figure 6].

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Figure 6: Limberg flap drawn along long diagonal (lint model). (a) Marking for Limberg flap for lesion ABCF along long diagonal. (b-d) The flap is unable to close the defect completely.

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Biomechanics of limberg flap

It follows that four Limberg flaps are possible along each short diagonal of the rhomboid defect. Their base is along the maximum skin extensibility, leading to easier recruitment of the available lax surrounding skin for closure of the defect. The flaps are such that the upper triangle is closed by transposition, and the lower triangle is closed by opposition of adjacent sides of the defect and the flap. The primary movement of the flap is by 60° to close the upper triangular defect by transposition. Interestingly, the movement of the lower triangular defect margins is again by 60° for primary closure of the lower triangular defect. The secondary flap movement is also by 60° for primary closure of the at the flap donor site with no secondary defect. The base of the triangular flap to be transposed should be along the LME. This is possible in two out of four flaps along each short diagonal for the rhomboid defect.^3,15,16 LME is perpendicular to the relaxed skin tension lines (RSTL). This placement of the flap design allows transposition of the flap with the greatest ease and least tension, according to Borges [Figure 7].¹¹

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Figure 7: Final suture lines in various possible Limberg’s flap in relation to relaxed skin tension lines. (a) Rhomboid shaped defect with various possible flaps i.e.1,2,3,4. (b-e) Sutureline of various flaps. LME: Lines of maximum extensibility, RSTL: Relaxed skin tension line.

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Esthetics of the limberg flap

For the best esthetic result, suture lines should be oriented along the RSTL. It is important to note that in the final suture line of the Limberg flap, the orientation of two of its limbs is perpendicular to the RSTL. The other two limbs, including one along the short diagonal is at 30° to the RSTL. The resulting scar is not esthetically oriented. In fact, two limbs of the final scar are positioned along the worst orientation for esthetic result.¹⁷ It is important in youthful-toned skin and not such a concern in old age skin, which is a lot lax with multiple gyri and sulci for the scar to hide. There appears to be a compromise between the laxity of the available skin and the esthetic orientation of the flap. Therefore, esthetically speaking, the Limberg flap results in a suboptimal scar.

For demonstration of the basics and nuances of the Limberg flap, a figure [Figure 8] and video description of designing the Limberg flap are attached [Video 1].

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Figure 8: Limberg flap planning and execution for greater trochanter pressure ulcer. (a) Pressure ulcer at right greater trochanter, (b) Rhombus shaped defect marking around the ulcer lesion showing placement of the rhomboid defect between LMEs, (c) Marking of limberg flap, (d): Suture line after closure of the rhomboid defect with Limberg flap, (e) Follow up at one year.

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Modifications in design of limberg flap

Modifications according to the defect location and properties of the surrounding skin should be incorporated while designing the flap. Many variations in the design of Limberg’s flap have been tried and used. The most popular variations are (a) Dufourmental flap and (b) Webster flap. Both have been devised for variations in the rhomboid defect and their various locations. It may not always be possible to design a defect of 60/120° combination due to various lesions such as dimensions and location of the lesion, properties, and availability of the surrounding skin. Dufourmental flap has been used for rhomboid defect of any angle combination. The flap transposition angle is less than that for the Limberg flap.

The flap can have a base as short as half of the short diagonal of the defect (i.e., base of the defect). Sides of the flap can be as short as three-quarters of the sides of the defect.^3,10,13,14 In the Webster modification, the defect’s shape has been changed from the classical rhombus defect of Limberg’s flap. One of the acute angles has been divided into three angles of 30° each by incorporating a W-shaped modification, while the other acute angle is still 60°. This results in easier closure of this angle without undue tension or dog-earing. The flap’s acute angle, too, has been decreased to 30°. It has been oriented away from the short diagonal.^10,13,14 The base of the flap lies along the extension of the side limb of the defect.