Flap classification and design

本章介绍了书中皮瓣的分类，主要采用的按照转移方式进行分类。并介绍了修复不同部位的缺损时，作者偏好使用的皮瓣类型。

Terminology

• the primary defect & the secondary defect
• the primary movement & the secondary movement
• wound closure tension & skin extensibility & RSTLs & LME & mechanic creep & biologic creep
• aesthetic regions & aesthetic units & aesthetic borders
  • The face can be divided into specific areas or aesthetic regions, which are covered by skin that has common characteristics. These skin characteristics include thickness, quantity of subcutaneous fat, degree of adherence to underlying fascia, color, texture, and hair growth. The principal aesthetic regions of the face are forehead, eyelids, cheeks, nose, lips, mentum and auricles
  • the aesthetic borders are identified by facial landmarks including eyebrows, melolabials creases, mental crease, philtral crests, vermilion borders, and anterior hairline.
    • The concept of facial aesthetic regions, and the borders that separate them, is important in designing local flaps for facial reconstruction. The preferred flap for reconstruction is frequently one that can be designed within the same aesthetic region as that containing the primary defect. Scars are best camouflaged by placing incisions along aesthetic borders. When a defect involves two or more aesthetic regions, it is usually best to compartmentalize the repair. Individual skin flaps are designed to construct the separate components of the defect that are located within separate aesthetic regions. This may ensure likeness of skin quality but, more important, places scars in the aesthetic borders. It is often a benefit to enlarge the primary defect by extending the defect to an aesthetic border or even to enlarge the defect to occupy an entire aesthetic unit. Repair of the defect with a local flap will then position a border of the flap in an aesthetic border for improved scar camouflage.
      

Local flap classification

• classified by location, local flap, regional flap and distant flap.
  • a regional flap is one in which tissue is harvested from a site not located on the face, scalp, or neck. However, the pedicle is sufficiently long to enable the flap to reach the primary defect.
• by blood supply, random flap and axial flap
• by method of transfer
  

Pivot flaps

• moving about a pivotal point at the base of the pedicle.
• Except for island flaps skeletonized to the level of their nutrient vessels, the greater the pivot, the shorter is the effective length of the flap.
• There is a positive correlation between the degree of pivoting and the size of the standing cutaneous deformity (dog ear).

Rotation flaps

• are pivotal flaps with a curvilinear configuration.
• designed immediately adjacent to the defect.
• are best used to close triangular defects.
• minimal mechanical benefit at the defect site in extending the arc of rotation flaps beyond 90° from the axis of the primary defect.
• A back cut at the base
• the unequal length of the flap’s border compared with the length of the primary and secondary defect.
  • Burow triganle
  • change the movement of the flap from one that is purely pivotal to one that is both pivotal and advancement (wound is repaired by principle of halving sutures). As a general rule, in designing rotation flaps on the face, the length of the incision should be four times the width of the defect (to streche the flap).
• The flap has only two sides; thus it lends itself to placement of one side in a border between aesthetic regions of the face.
• The flap is broad based.

Transposition flaps

• have a linear configuration.
• the base of the flap is contiguous with the defect with one border of the flap being also a border of the defec or borders being removed from the defect.
• the ability to construct a flap some distance from the defect with its axis independent from the linear axis of the defect is one of the greatest advantages of transposition flap.
  • rhombic flap
    • The greatest wound closure tension with a rhombus flap is at the donor site and has been calculated to be 20° from the short diagonal line across the base of the flap.
    • Wide undermining of the surrounding tissue has minimal effect on the wound closure tension. Thus, in designing the flap, skin mobility and extensibility are important.
    • approximately half of the entire length of the scar that results from use of the flap is not parallel or does not lie within RSTLs. The resulting scar from the use of a rhombus flap tends to blend better with adjacent skin in the cheek where RSTLs are less important, the skin is thinner, and the creases are not as prominent as in the forhead.
  • biloble flap
    • double transposition flap that shares a single base.
    • frequently been used to reconstruct nasal defect and cheek defects.
    • In the classic design of the bilobe flap, the axes of the first and second lobes as well as the defect were all separated by an angle of 90°.
    • The major disadvantage of the bilobe flap is that the majority of the incision necessary to create the two lobes of the flap produces scars that do not parallel RSTLs.However, the configuration of the lobes may often be designed to have an angular shape that may conform to RSTLs better than curvilinear designs.

Interpolated flap

• has a linear configuration
• differs from transposition flaps in that its base is not contiguous with the defect
• the pedicle must cross over (two surgical stages) or under (one stage) intervening tissue
• If the pedicle passes over intervening tissue, the pedicle must subsequently be divided in a second surgical procedure 3 weeks later
• paramedian forehead flap used for nasal reconstruction & the melolabial interpolated flap transferred from the cheek

Island flap

• may be designed with any configuration
• no cutaneous attachments between the skin of the flap and the adjacent skin of the donor site
• The pedicle of the flap consists only of subcutaneous tissue or an individual artery and vein unencumbered by surrounding tissue
• may be transferred to a defect by pivoting or by stretching (advancement)

Advancement flaps

• have a linear configuration
• one standing cutaneous deformities on either side.

(Bilateral) Unipedicled advancement flap

• The two standing cutaneous deformities forming at the base of advancement flaps may require excision or may be eliminated by a halving suture technique.
• Unlike with the pivotal flap, in which the standing cutaneous deformity must be dealt with at the base of the flap, the deformities that develop from advancement can be excised anywhere along the length of the flap and not necessarily juxtaposed to the base.
• Unipedicle advancement flaps and rotation flaps have one characteristic that is inherent only in these two flap designs. Owing to their specific design and use, when either type of flap is transferred to its respective recipient site, it results in a situation in which there are unequal lengths to the borders of the wound.
  • Burow triangle
  • inverted Burow triangle excision

V-Y or Y-V advancement flaps

Bipedicle advancement flaps

Hinge flap

Preferred flap

• Location and size of the facial defect are the two most important factors governing the selection of a specific local flap.

Scalp

• Large (6 cm or greater) partial-thickness scalp defects are best repaired with a full-thickness skin graft.
• The galea aponeurosis severely limits tissue movement, causing flap repair of even small defects to be difficult. The preferred method of reconstruction of th majority of small to intermediate-sized defects(defined as those that can be repaired with the remaining scalp tissue) is by use of two or more rotation flaps.
• Because of the inelasticity of scalp tissue, advancement flaps are poorly suited for scalp reconstruction.
• When a single rotation flap is used, the parameter of the arc of the flap should be at least four times the diameter of the scalp defect.
• Standing cutaneous deformities at the base of scalp flaps are not resected at the time of flap transfer because resection has the effect of reducing the width of the base of the flap and may impair vascularity. In addition, deformities tend to flatten during a 4- to 6-week interval. Usually after 6 weeks, any remaining deformity may be removed safely.

Forehead

• The most effective technique for reconstruction of the forehead usually involves one or more advancement flaps.
• Defects of the cental third of the forehead may be repaired with a vertical orientatioin with a predictably good aesthetic result. This is probably due to the natural dehiscence or attenuation of the frontalis muscle in this portion of the forehead. In contrast, defects located solely within the paramedian and lateral zones of the forehead are best repaired with wound closure oriented in a horizontal axis when possible
• Except in the midline of the forehead, advancement flaps should be elevated in the subcutaneous plane to preserve the supraorbital and supratrochlear nerves. Defects in the midline are best closed without making horizontal incisions. Rather, they are treated like a primary wound closure, using advancement by dissecting in the subgaleal plane, because all sensory nerves are superficial to this plane of dissection.

Medial cheek

• surgeon has a number of options. The preferred method of flap repair is usually by a transposition or advancement flap.
• Transposition flaps used for repair of medial cheek defects are best designed so that the donor site is in the vicinity of the jowl
• The V-Y subcutaneous tissue pedicle island advancement flap is an option for repair of medial cheek skin defects at or below the level of the nasal alae.
• Cutaneous pedicled advancement flaps are less useful compared with island advancement flaps and transposition flaps in repair of medial cheek defects.

Lateral cheek

• Lateral cheek skin has less subcutaneous fat and is more adherent to the underlying fascia than is medial cheek skin.
• The preferred flap for smaller defects of the lateral cheek is the transposition flap. Larger defects are best repaired with rotation advancement flaps designed to recruit upper cervical skin into the flap. Transposition flaps are usually superiorly based, and the skin immediately above the angle of the mandible serves as the donor tissue for the flap.
• rotation advencement flaps: From the lateral inferior border of the defect, a curvilinear incision extends downward and posteriorly below the earlobe and then backward to the posterior hairline. From there, the incision extends inferiorly along the posterior border of the sternocleidomastoid muscle.

Central lip

• cutaneous defects approaching half the width of the lip may be converted to full-thickness excisions of the lip followed by primary wound closure.

Lateral lip

• Cutaneous defects of the lateral aspect of the upper and lower lips that cannot be repaired primarily are best repaired with rotation flaps or subcutaneous tissue pedicle island advancement flaps.
• Rotation flaps should be designed so that the incision for the flap lies in or parallel.
• Subcutaneous tissue pedicle island advancement flaps are ideally suited for repair of lateral skin defects of the upper lip. They do not work as well for defects of the lower lip.to the melolabial crease.

Nose

• The two most commonly used local flaps for repair of cutaneous defects of the nose and in which the donor site of the flaps is confined to the nose are the subcutaneous tissue pedicle island advancement flap and the bilobe flap.
  • subcutaneous tissue pedicle island advancement flap
    • Small defects (1.5 cm or less in size) in the region of the anterior alar groove between the ala and tip.
  • Bilobe nasal flaps
    • are the preferred flap to repair 1- to 1.5-cm cutaneous defects of the central tip or caudal dorsum.

Eyelid