Analysis of Vector Alignment with the Zitelli Bilobed Flap :A Comparsion Of Flap Dynamics in Human Cadavers
Richard A. Zoumalan, Caryl Hazan, Vicki Levine, Anil R. Shah*
* Corresponding Author
Department of Otolaryngology-Head and Neck Surgery
Division of Facial Plastic and Reconstructive Surgery
New York University School of Medicine
7 West 51st Street, New York, NY 10019
Phone: 212.644.7400 Fax: 212.644.0742
In a Zitelli bilobed flap, determine whether differences of angles between the alar rim and the long axis of the secondary defect affects alar displacement in a fresh cadaver model.
In fresh cadaver heads, identical unilateral 1 cm circular defects were created at the superior alar margin. Three different laterally based bilobed flap templates for reconstruction were utilized. One template, used on three cadavers, had an angle of 60 degrees between the alar rim and the long axis of the secondary defect. Another template, used on three cadavers, had an angle of 90 degrees. The last template had an angle of 135 degrees and was used on three cadavers. Photographs were taken before the repair and after with the camera and cadaver heads in the same spatial relationship to each other.
In the three cadavers which had repair using an angle of 60 degrees, all cadavers experienced alar retraction, with an average displacement of 1.3 mm. This was not a statistically significant change (P=0.07). In the defects which underwent repair using an angle of 90 degrees, there was no significant alar displacement (P=0.72). In the two three defects which underwent repair using an angle of 135 degrees, both ala underwent depression by 1.0 mm. When comparing the differences achieved between the different angles, there was a significant difference in measured distortion between the cadavers that had 90 degree and 60 degree vector placement (P=0.02). There were no measureable changes to the contralateral maximal nostril distance.
Vector alignment can have an impact on nostril displacement. In bilobed flaps, the axis of the secondary defect may play an important role. This study suggests that secondary defects aligned perpendicular to the nostril have the least amount of alar distortion.
First described by Esser in 1918, the bilobed flap is a transposition flap used to reconstruct defects of the lower third of the nose.1 It is a random-pattern single-stage flap which lacks a large caliber vessel at its base. A bilobed flap uses two adjacent lobes/flaps that are rotated around a pivot point. The primary lobe, usually the same size as the defect, is used to restore the defect. The secondary lobe is used to repair the donor site of the primary lobe. The donor site of the secondary lobe is closed primarily.2
The bilobed flap is the reconstruction of choice for most small to medium-sized defects of the lower third of the nose, especially the lateral tip, supratip, or ala near the tip. In this area, it is more versatile than any other flap. Because it takes skin from adjacent areas, it provides excellent color match and is relatively free from distortion. Contour deformities are rare.3
The bilobed flab recruits lax tissue to allow for closure with less tension. This lax tissue comes from the loose skin of the upper dorsum and nasal sidewall.2 However, the potential for tension-related complications exists. A major disadvantage of the bilobed flap is the potential for alar retraction. This complication rate has been reported to be around 5%.4
To ensure a safe blood supply, the width of the second flap should approach the width of the first. While Esser described the second flap as having the same size as the first, this is not necessary. The first flap is usually larger than the second.1 Under-sizing the primary or secondary lobe will result in increased tension which leads to alar distortion. Cho and Kim attributed this to excessive tension on closure of the primary lobe and distal defect due to a tethering at the base of the pedicle. By increasing the length of the primary flap by 10% compared to the standard design, Cho and Kim demonstrated in fresh cadaveric specimen that a significantly decreased amount of distortion can be attained.5 Zitelli responded to this study with a recommendation that a longer flap is only necessary when there is skin that is too tight for rotation of the flaps and closure of the secondary flap donor site. This type of situation exists at the immobile skin of the inner canthus, where there is little loose skin.6Over-sizing of the flaps may lead to trapdoor deformity and uneven contours. In cases of thick skin, the primary lobe should be the same size as the defect due to limited ability to stretch the primary lobe.
The individual characteristics of each nose plays an important role in the potential of alar distortion. The strength of cartilage and thickness of skin are the two important aspects of the alar architecture that have potential sequal. Lower lateral cartilages with more thickness, and thus less compliance, are less likely to be distorted by soft tissue tension vectors. Given its ability to stretch, thin skin will be more compliant with tension forces than thick skin. Ideal patients have thin and mobile skin. Sebaceous skin has less mobility for transfer and an increased risk of complications such as necrosis, trapdoor deformity, and depressed scars. Because of limitations of the lax donor skin or the upper nose, the flap should not be used for areas larger than 1.5 cm.2
The bilobed flap has a high flexibility of flap design variation and tissue movement. Esser stated that the angle of tissue transfer had to be 90 degrees.1 However, subsequent authors have found that the angle can be decreased significantly to suit the situation.7 The chosen angle has effects on tension vectors. The direction of vector alignment plays a central role in alar retraction.
The secondary lobe may play a larger role in alar displacement than previously thought.8 Closure of the secondary donor site involves tension. The vector of this tension can vary depending on the angle between the axis of the secondary lobe and long axis of the ala. Different variations of the angle exist, with most falling between 60 degrees and 135 degrees. If the sum of forces has a vector component that is perpendicular to the long axis of the ala, this will act to either retract the ala cephalically or displace it caudally. On the contrary, if the sum of vector forces is parallel to the long axis of the ala, the tension should have no effect on alar position in a rostral/caudal direction. No previous study has evaluated vector alignment’s effect on nostril appearance. The objective of this study is to determine whether differences in this vector alignment affects the degree of alar distortion.
MATERIALS AND METHODS
Eight fresh cadaver heads were obtained. Using a 1 cm circular template, standardized 1 cm circular defects were created in the same location in each cadaver head. The full thickness skin defect was placed with its center at the superior alar margin.(See Figure 1). Each cadaver’s nose was limited to one defect.
Three different templates for reconstruction were utilized. Three defects (on three separate cadavers) were repaired with a template which had an angle of 60 degrees between the long axis of the secondary lobe defect and the long axis of the ala. Figure 1 demonstrates the repair outline from this template. Three defects (on three separate cadavers) were repaired with an angle of 90 degrees between the long axis of the secondary lobe defect and the long axis of the ala. On two separate cadavers, two defects repaired with an angle of 135 degrees between the long axis of the secondary lobe defect and the long axis of the ala. All defects were repaired by the same surgeon (CH) using similar technique and similar amount of undermining.
Using a camera held in a fixed position, standardized profile photographs were taken using a digital camera with 100-mm Ultrasonic lens (Canon model EOS D30 camera; Canon, USA, Inc, Lake Success, NY). Photographs were taken before and after repair with the camera and cadaver heads in the same spatial relationship to each other. Pre-repair and post-repair photographs were also taken from the contralateral profile position.
Alar retraction was calculated using Adobe Photoshop CS (Santa Clara, CA). Alar retraction was defined by drawing a line from the anterior aspect of the nostril to the posterior aspect. A point of maximal retraction was calculated. Figure 2 is an example of how the measurement was performed on a cadaver before repair. Figure 3 demonstrates the measurement after repair. The 1 cm defect was used as a fixed measurable distance to calibrate the measured point of maximal retraction and give a distance in actual millimetres. This also increased accuracy of standardization of distance/position between pre-repair and post-repair photographs.
See Table 1. In the three cadavers which had repair using an angle of 60 degrees, all cadavers experienced alar retraction, with an average displacement of 1.3 mm. This was not a statistically significant change (P=0.07).
In the defects which underwent repair using an angle of 90 degrees, two of three cadaver ala had measured retraction. The other cadaver experienced a depression of the ala. The average direction of distortion was in cephalad, by 0.1 mm. However, this did not demonstrate statistically significant retraction of the position of the ala (P=0.72).
In the two three defects which underwent repair using an angle of 135 degrees, both ala underwent depression by 1.0 mm.
When comparing the differences achieved between the different angles, there was a significant difference in measured distortion between the cadavers that had 90 degree and 60 degree vector placement (P=0.02). There were no measureable changes to the contralateral maximal nostril distance.
For the repair of a nasal defect, no standard approach exists. Each defect is unique and must be assessed based on its location, size, skin type, and support. The bilobed flap has been a workhorse for small to medium size defects less than 1.5 cm. Many techniques have been developed to decrease the probability of alar distortion.
This study demonstrates that the angle between the alar rim and long axis of the secondary defect can affect alar distortion. The least amount of alar retraction is achieved with an angle of 90 degrees between the long axis of the alar rim and the long axis of the secondary defect. When analyzing the tension vectors produced by closing the secondary defect, the axis of tension vector is parallel to the alar rim. Therefore, one would expect that this tension would not cause the ala to be pulled cephalically. Figure 4 demonstrates a design in which the angle between the alar rim and axis of the secondary defect is close to 90 degrees. Figure 5 demonstrates the direction of pull when the secondary defect is closed. The direction of pull of the arrows is parallel to the alar rim. Thus, no retraction takes place due to the tension at the site of the secondary defect.
On the other hand, a more acute angle is more likely to result in alar retraction. When a more acute angle is used, a tension vector angle is produced which lies in a direction that can potentially pull the alar rim in a cephalad direction. Figure 6 demonstrates a design in which the angle between the alar rim and axis of the secondary defect is close to 60 degrees. Figure 7 demonstrates the direction of pull when the secondary defect is closed. The arrows along the side of the secondary defect demonstrates the direction of pull from the closure of the secondary defect. The arrow near the nostril shows the vector component perpendicular to the alar rim which may cause alar retraction. Using an angle larger than 90 degrees between alar rim and axis of the secondary defect demonstrated alar depression in both cadavers. When the angle becomes more obtuse, there is potential for vectors of the secondary defect to affect the position of the ala.
Individual differences between each cadaver head may have led to different amounts of retraction or depression. Although all defects and repairs had the same dimensions, the cadaver noses were different sizes. There were also noticeable differences in skin thickness and cartilage within the ala. In spite of this, the technique was not altered.
This study does not account for long term wound healing dynamics. Scar contracture may lead to delayed alar retraction. Scar and flap contracture is an expected process in the healing of any flap. Minimizing risk of delayed alar contraction due to scar and flap contraction must be prioritized. The vector analysis conducted in this study supports that larger bilobed flaps with more acute angles have more alar retraction. Less initial retraction due to less tension in the cephalad direction may lead to less ultimate alar retraction.
It is important to note that there were no measureable changes to the contralateral side in any of the patients. We did not use the contralateral side as a control due to the potential of “interference” from secondary lobe tension factors.
Vector alignment can have an impact on nostril displacement. In bilobed flaps, the axis of the secondary defect may play an important role. This study suggests that secondary defects aligned perpendicular to the nostril have the least amount of movement on the cadaver model.
All authors had full access to all of the data in the study and take responsibility for the integrity of the data and the accuracy of the data analysis. There was no financial or material support for the study.
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2. Zitelli JA: The bilobed flap for nasal reconstruction. Arch Dermatol 1989 Jul; 125(7): 957-9
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6. Zitelli, JA. Comments on a Modified Bilobed Flap Arch Facial Plast Surg. 2006 Nov-Dec;8(6): discussion 410.
7. Crowley RT, Nickel WO. Definitive treatment of decubitus ulcers in paraplegic patients by coverage with transposition bilobed flap grafts. Surg Gynecol Obstet. 1955 Apr;100(4):468-72.
8. Cook J, Zitelli JA. Primary closure for midline defects of the nose: a simple approach for reconstruction. J Am Acad Dermatol. 2000 Sep;43(3):508-10.