Bilobe flaps

Biomechanics

• 双叶皮瓣实质上一个Modified double Z-plasty；
• 可以利用远离缺损部位的皮肤，同时由于第二个lobe的存在，使得缝合张力明显减小；
• 双叶皮瓣总的旋转角度在90°上下，相较于一般旋转皮瓣45°到60°左右的旋转角度，也有助于减小缝合张力，避免周围组织牵拉移位。

Flap design

第一叶与缺损间以及两叶之间的夹角有最初的90°改成45°的设计，有利于消除猫耳朵及避免发生明显的trap-door deformity。这一点在鼻部缺损修复中很重要。而在颊部缺损的修复中，可以根据缺损的位置、可获取的皮肤的位置以及瘢痕隐蔽的需求，而需要将双叶皮瓣放置在最合适的位置，必要时可以使得第二叶和缺损去长轴成180°夹角。

The bilobe flap is a preferred flap for reconstruction of the nose in the area of the tip and caudal dorsum.

缺点：

• 皮瓣切口不能和RSTL平行；
• 曲线状的切口容易发生trap-door deformity（尤其在on the nose in patients with thick skin or with sebaceous gland hyperplasia）。避免/减轻的方法一是避免曲线状的切口设计，比如改为四边形，以及广泛的潜行分离（extensive peripheral undermining of the nasal skin as far laterally as the cheek.），另外削薄第一叶皮瓣的厚度也有助于减轻畸形的发生。

Clinical application

Cheek

Not all the incisions required to create the flap lie parallel to the natural lines of the face, and the aesthetic result could be disappointing.

The flap is best used to repair large to moderate-sized defects of the central cheek. In such cases, the remaining lateral preauricular skin is used to construct the first lobe, and the posterior auricular orsuperior cervical skin is the source of the second lobe.

Ear

Free grafts, helical rim advancement flaps, or pedicle flaps are often more useful for reconstruction than the bilobe flap.

Nose

尽管蒂在内的双叶皮瓣are hardy，但是大部分情况下仍尽量设计使用蒂在外的设计。

双叶皮瓣在鼻部非常适用于1.5cm以下的位于鼻尖症状或侧面不波及鼻翼的缺损（Ideally, the defect should be at least 0.5 cm above the margin of the nostril）。Defects of the cephalic half of the nose are not well suited for reconstruction with a bilobe flap unless they are 0.5 cm or less in size。

设计方法：

The radius of the defect is measured. For laterally based flaps, a point lateral to the border of the defect is marked in the alar groove that is the distance of the length of the radius. This point is used to design both lobes of the flap. Two arcs are drawn with their centers at the marked point. The first arc makes a tangent with the border of the defect most distal to the point, and the second arc passes through the center of the defect. Calipers and rulers are not used to draw the arcs because these devices measure straight-line distances. In contrast, the topography of the nose is convex in the area of the tip and dorsum. Therefore, a flexible measuring device is used. A needle with an attached suture is passed full thickness through the nose at the point marked in the alar groove. A knot is tied in the suture inside the nasal vestibule. The suture is draped from the point across the defect, and a clamp is applied to the suture at the periphery of the defect. The clamp with attached suture is then rotated about its pivotal point to indicate the first arc, which is marked with a pen. The clamp is advanced along the suture to the center point of the defect, and a second arc is drawn through the center of the defect and parallel to the first arc (Fig. 10-5B). The bases of the two lobes are designed to rest on the lesser arc. The height of the first lobe extends to the greater arc, so its height is equal to the distance between the two arcs. The width of the first lobe is equal to the width of the defect. The width of the second lobe is the same as or slightly less than that of the first lobe. The height of the second lobe is approximately 1.5 to 2.0 times greater than the height of the first lobe. The first lobe has the configuration of the defect, and the second lobe is triangular. The linear axes passing through the center of each lobe are positioned at approximately 45° from each other, with the axis of the first lobe positioned 45° from the central axis of the defect. This orientation of the lobes inevitably positions the axis of the second lobe along the center of the nasal sidewall or diagonally at the junction of the sidewall with the dorsum. The design also creates a triangular peninsula of skin between each lobe with a 45° angle. A triangle representing the eventual standing cutaneous deformity resulting from the pivot of the first lobe is marked with its apex pointing laterally and one side parallel to or in the alar groove. The base of the triangle is the lateral border of the defect, and the height of the triangle is equal to the radius of the defect. The flap is elevated after local anesthetic is injected. Like other nasal cutaneous flaps, it is dissected in the tissue plane between the nasal muscles and underlying perichondrium and periosteum. The flap and the remaining skin of the entire nose are completely undermined, sometimes extending the dissection into the cheek a short distance. Wide peripheral undermining of all the nasal skin is essential to reduce wound closure tension, to facilitate flap transfer, and to minimize trap-door deformity (Fig. 10-6). The donor site for the second lobe is closed first by primary approximation of the muscle layer. The first lobe is then transposed to the nasal defect and secured with a few deep dermal sutures. Next, the standing cutaneous deformity is removed in or cephalad and parallel to the alar groove. The second lobe is transposed, trimmed of its excess height so that it fits snugly without redundancy in the donor defect of the first lobe. If the thickness of the first lobe is greater than the depth of the defect, the undersurface of the lobe may be trimmed even to the level of the subdermis if necessary to match the skin thickness of the recipient site. Typically, the second lobe is thinner than the depth of the donor site for the first lobe because it is derived from the thinner skin of the cephalic nasal sidewall. This may create a mismatch in thickness that may cause a depressed contour over the nasal bridge. To prevent this, muscle and subcutaneous tissue commonly trimmed from the undersurface of the first lobe are used as free grafts. The grafts are sutured to the deep surface of the second lobe. When tissue is not removed from the first lobe, additional soft tissue augmentation of the second lobe may be accomplished with free grafts of muscle and fat harvested from the subcutaneous tissue at the junction between the nasal sidewall and the cheek. Skin incisions are approximated with 5-0 fast gut vertical mattress and simple sutures. A compression dressing is applied overnight. Dermabrasion 6 weeks after flap transfer is recommended for the majority of patients. This is accomplished in the office with local anesthesia. The entire flap and adjacent nasal skin are abraded.

Case report

Case 4

Trap-door deformity refinement:
Resection of depressed scar –> wide underminning and multiple small Z-plasties (Each triangular flap of the Z-plasty measured approximately 5 mm in length and had a 30° to 40° angle. The flaps were transposed and secured at each apex with a single 6-0 polypropylene suture placed through the tip of the flap.) –> Dermabrasion of the scar and adjacent nasal skin (8 weeks after scar revision).