Use of Random Subdermal Flaps to Repair Extensive Skin Defects

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Dena L. Lodato, DVM, and Jennifer L. Wardlaw, DVM, MS, Diplomate ACVS

In veterinary medicine, many surgical problems, including tumor resection and trauma, can result in skin defects that can be extensive and require additional repair techniques beyond undermining (separating the skin from the underlying tissue) and simple suture closure.

When wide surgical margins are created in an effort to achieve clean surgical margins after tumor resection, skin defects often cannot be closed due to excessive tension. Several different techniques have been described to address these types of extensive wounds, such as:^1-12

• Vascularized Flaps: Local or subdermal, axial pattern, myocutaneous, and distant flaps
• Free Grafts.

Since a skin flap has a tethered vascular attachment, this limits transfer of donor skin to a local adjacent skin defect unlike grafts, which do not contain a vascular supply.^1,2,5-7 Distant flaps and free grafts can be transferred to remote areas, such as those on the lower limbs.^1,2,5,7,12

Due to the extensive nature of this topic, this article will provide an overview of the use of random subdermal flaps (local flaps). For skin defects that require axial pattern flaps, myocutaneous flaps, or skin grafts, we recommend referral to a surgical specialty clinic or more advanced training.

RANDOM SUBDERMAL FLAPS

Random subdermal flaps do not contain a direct cutaneous artery and vein and are reliant on the subdermal plexus located at their base.^1,2,5-7,9,12 This plexus is maintained by small subdermal branches from nearby direct cutaneous arteries, and care must be exercised to ensure that this plexus is maintained during flap elevation since flap survival is dependent on its intact circulation.^1,2,9,12 Because of this circulation, random subdermal flaps can be used for immediate coverage of exposed musculature, tendons, vessels, and nerves.¹

FLAP CREATION

Donor Sites

Skin tension lines and pliability are important when considering a donor site to ensure that the donor site is amenable to primary closure.^1,2,5 Ideally, a donor bed should have adequate skin available to close the recipient bed without creating a significant defect at the donor site that cannot be closed.^1,5-7 Common areas with ample redundant skin for donation include the neck, axilla, and flank fold.

Local flaps created in distal limb areas are not recommended because there is little donor skin to use without causing difficulty closing the donor defect. Additionally, donor sites susceptible to excessive motion and stress can result in dehiscence after closure.^1,2,5-7 In essence, donor sites allow closure of one defect but create another skin defect, which is less than ideal; in some instances, further reconstructive techniques or second intention healing is required.^1,5

Flap Template

A template created with cloth, surgical glove wrapper, or foam rubber is beneficial for planning flap dimensions.^1,5

1. The template can be held over the defect; then the proposed flap base is held stationary as the template is rotated to the donor site.^1,5
2. After the flap dimensions have been established, a felt-tip pen can be used to outline the flap boundaries, providing a guide for skin incision.^1,5
3. Plan on creating flaps at least 20% larger than the defect to avoid excess tension on the repair edges.

Flap Formation

When creating flaps, it is imperative that:

1. The base be slightly wider than the body of the flap to avoid narrowing the pedicle and damaging the cutaneous vessels.^1,2,5-7
2. The flap length be as long as, or preferably longer, than the defect to prevent production of excessive tension during closure.^1,2,5-7
3. When undermining underneath the panniculus muscle layer, such as the cutaneous trunci, the plexus, along with any branches from nearby direct cutaneous vessels, must be maintained.¹
   • Flaps created from sites lacking subdermal muscle, such as the extremities, are undermined just superficial to the muscle fascia.¹
   • In areas where skin is intimately associated with underlying muscle fascia, a portion of this fascia may need to be included in elevation of the flap, such as with the skin overlying the superficial pectoral muscle.¹
4. When skin edges are manipulated, instruments (skin hooks or DeBakey thumb forceps) only should be used if absolutely necessary to avoid compromising circulation.⁵ In addition, avoid use of electrosurgical instruments to cut flap margins or coagulate bleeding vessels along the flap edge.
5. Local skin perfusion should be allowed to return by, ideally, waiting several days or more after the initial injury before considering flap closure. Immediate creation of flaps in the local area of trauma could devitalize more skin if an effort is made to quickly close the defect.

Recipient Bed

It is very important that the recipient bed be healthy and not contain debris, necrotic tissue, or active infection.^1,2 If a chronic granulation bed, indicated by excessive granulation tissue overlying the wound, is present, it should be excised or freshened before flap transfer to allow a healthy granulation bed to form.^1,2 In addition, inverted epithelialized borders of the skin defect should be excised to create a fresh perpendicular sharp edge.¹

TYPES OF SUBDERMAL PLEXUS GRAFTS

Rotation Flaps

When a triangular skin defect is present, a rotation flap can be used effectively.^1,5 This rotating flap is created when a semicircle is fashioned adjacent to the border of the defect (Figure 1).^1,2,5-7

The creation of the semicircle incision occurs in a stepwise fashion:^1,2,5-7

1. The curved incision begins next to the shortest side of a triangular wound.
2. The incision is then progressively lengthened until the flap is long enough to cover the defect.
3. The general guideline when creating this flap is to make the arc 4× the length required to rotate the flap sufficiently to close the defect.¹

Wider or rectangular defects can be repaired by using paired rotation flaps; however, this type of flap is not commonly used.^1,2,5,7 Any dog ears (slight elevations of the skin at either end of the suture line) created are left intact because they typically resolve within several weeks without intervention.¹

Transposition Flaps

A transposition flap is a “tongue-shaped” rectangular pedicle graft that is adjacent to and created 45° to 90° in relation to the long axis of the defect (Figure 2).^1,2,5,7 The width of the flap is normally equivalent to the recipient bed width, while the length is determined by measuring the distance from the pivot point to the farthest point of the defect.^1,2,5-7

When using this flap, it is important to be aware that the length of the flap will decrease as the arc of the rotation increases; however, increasing the angle the flap is rotated results in less tension on the repaired defect.^1,2,6 As mentioned earlier, as the flap is rotated, there is a tendency for a dog ear to develop, but this will regress with time.^1,2,6 This type of flap allows loose skin from a region not adjacent to the defect to be transferred to the defect, allowing closure.

Interpolation Flaps

The difference between a transposition flap and an interpolation flap is that the latter does not share a common border with the defect (Figure 3).^1,2,5,6

• These flaps are created by rotating a rectangular flap across intact skin to cover a defect.
• The width of the flap is equal to that of the defect.⁵
• Length is calculated by measuring from the pivot point to the most distant aspect of the wound, including the length of the intact skin the flap must bridge.^5,6

The excessive skin covering the intact skin can be excised 14 to 21 days post surgery and the remaining edges sutured.^5,6 Alternatively, a “bridge incision” between the donor site and recipient bed can be performed to allow the incision edges to be sutured to the flap.^1,2,5,6

Advancement Flaps

This type of flap moves skin parallel to the lines of least tension in order to cover the defect.^1,2,5-7

• A single pedicle advancement flap is created when 2 skin incisions equal to the width of the defect are created with the distant edge of the flap bordering the defect (Figure 4).^1,2,5

• An H-plasty, or two single pedicle advancement flaps, can be used to close larger square or rectangular defects (Figure 5).^1,2,5,7
  • H-plasties have a wider base:length ratio, improving blood supply when compared to a single pedicle advancement flap.²
  • The length of the flap is determined by the length necessary to close the defect without tension.¹

• A bipedicle advancement flap is created by making an incision parallel to the long axis of the defect.^1,2,5 This flap can be used to close adjacent defects; however, the main drawback is the elastic retraction and tension that is transferred to the suture line.^2,5,6

• The width of the flap is equal to the width of the defect and length is equal to the length of the defect (Figure 6).^1,2,5
• The total length should not exceed twice the width of the flap base.²
• Tension can be relieved by making the incision curved with the concave side facing the defect border.^1,5
• Two pedicles allow for longer flaps, but necrosis can occur at the interface between the pedicles if vascularity is compromised.¹

FLAP VIABILITY

During the healing process, flaps are nourished from the pedicle vascular supply. Flap viability can be assessed by:¹

• Color
• Warmth
• Pain sensation
• Bleeding.

However, using pain sensation as a guideline for viability may not be accurate because some flaps are denervated during elevation. In addition, bleeding along the flap edges does not provide any information on venous return and vasospasm may result in a transient decline in circulation.¹

Flaps that suffer from arterial or venous obstruction change color from red (due to inflammation) to lavender to dark purple to black over 1 to 6 days, ultimately leading to necrosis.^1,2,6,7 When necrotic skin is observed, evidenced by either the presence of a demarcation line between viable and nonviable skin, liquefactive necrosis, or eschar, the necrotic skin should be debrided as soon as possible to encourage wound healing.² It is also important to recognize that regional plexus variations affect flap survival.¹

COMPLICATIONS

Complications associated with these procedures include:^2,7

• Infection
• Seromas
• Dehiscence
• Necrosis.

Seromas

Seroma formation is more likely to occur if there is loose skin or dead space present, particularly in high-motion areas, such as the flank or axilla.² The use of closed suction drains, bandages, and exercise restriction for 2 to 3 weeks post surgery decreases the risk of seroma formation.^2,7

Dehiscence

Some causes of dehiscence include excessive tension on the flap edges (due to inappropriate planning), infection, surgical trauma, or inadequate blood supply which causes necrosis.^2,5,7

The risk of complications can be decreased by using good surgical technique and planning appropriately before performing surgery.⁷

CONCLUSION

Skin defects can be difficult to correct without the aid of ancillary techniques, such as skin flaps. Local subdermal flaps can be performed in general practice if extreme care is used during the performance of the procedure and appropriate aftercare is instituted.

More extensive wounds may benefit from advanced flaps, such as distant, axial pattern, and myocutaneous flaps, or free skin grafts; for these procedures, referral to a specialist is recommended. These types of wounds include those:

• Located over bone, tendons/ligaments, or large arteries and veins
• Involved with body cavities
• Covering more than 30% of the body surface
• Located circumferentially around extremities.

Another indication for referral is if the patient requires 24-hour care either due to its health status or a tendency to interfere with the bandage protecting the flap.

Figure Credit
Figures 1 through 6 adapted from Pavletic MM. Atlas of Small Animal Reconstructive Surgery. Philadelphia: WB Saunders, 1999.

References

1. Pavletic MM. Pedicle grafts. In Slatter D (ed): Textbook of Small Animal Surgery, 3rd ed. Philadelphia: WB Saunders, 2003, pp 292-321.
2. Hunt GB. Local or subdermal plexus flaps. In Tobias KM, Johnston SA (eds): Veterinary Surgery: Small Animal. St. Louis: Elsevier, 2012, pp 1243-1255.
3. Wardlaw JL, Lanz OI. Axial pattern and myocutaneous flaps. In Tobias KM, Johnston SA (eds): Veterinary Surgery: Small Animal. St. Louis: Elsevier, 2012, pp 1256-1270.
4. Bohling MW, Swaim SF. Skin grafts. In Tobias KM, Johnston SA (eds): Veterinary Surgery: Small Animal. St. Louis: Elsevier, 2012, pp 1271-1290.
5. Pavletic MM. Atlas of Small Animal Reconstructive Surgery. Philadelphia: WB Saunders, 1999.
6. Hedlund CS. Surgery of the integumentary system. In Fossum TW (ed): Small Animal Surgery, 2nd ed. St Louis: Mosby, 2002, pp 134-228.
7. Hedlund CS. Large trunk wounds. Vet Clin Small Anim 2006; 36:847-872.
8. Hunt GB, Tisdall PLC, Liptak JM, et al. Skin-fold advancement flaps for closing large proximal limb and trunk defects in dogs and cats. Vet Surg 2001; 30:440-448.
9. Hunt GB. Skin fold advancement flaps for closing large sternal and inguinal wounds in cats and dogs. Vet Surg 1995; 24:172-175.
10. Allen SW, Miller MA, Haas KM. Repair of a facial defect with an interpolation skin flap in a cat. JAVMA 1997; 210(9):1319-1321.
11. Schmidt K, Bertani C, Martano M, et al. Reconstruction of the lower eyelid by third eyelid lateral advancement and local transposition cutaneous flap after “en bloc” resection of squamous cell carcinoma in 5 cats. Vet Surg 2005; 34:78-82.
12. Szentimrey D. Principles of reconstructive surgery for the tumor patient. Clin Tech Small Anim 1998; 13(1):70-76.

Dena L. Lodato, DVM, is a second-year small animal surgical resident at Mississippi State University College of Veterinary Medicine. Her clinical interests include reconstructive surgery, wound care, fracture repair, and physical therapy. Dr. Lodato received her DVM from Mississippi State University. After graduation, she completed a rotating internship at Louisiana State University School of Veterinary Medicine followed by a surgical internship at Louisiana Veterinary Referral Center in Mandeville, Louisiana.

Jennifer L. Wardlaw, DVM, MS, Diplomate ACVS, is an assistant professor of small animal surgery in the Department of Clinical Sciences at Mississippi State University College of Veterinary Medicine. Her interests include arthritis, reconstructive surgery, wounds, nutraceuticals, and developmental orthopedic diseases. Dr. Wardlaw has spoken at numerous national meetings as well as published various research articles and book chapters. She received her DVM from University of Missouri and completed her internship, residency, and MS at Mississippi State University.