Everything You Wanted to Know About SplitThickness Skin Grafts But Were Afraid to Ask

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Could split thickness skin grafts (STSGs) be beneficial in improving wound healing in patients with diabetes? These authors explore the viability of STSGs in this population and offer a step-by-step guide for using this modality. They also discuss the emergence of indocyanine green angiography to help enhance grafting results.

In 2011, there were an estimated 366 million people worldwide diagnosed with diabetes, a number that is expected to increase with time.¹ The Centers for Disease Control and Prevention (CDC) projected that as many as 552 million individuals could be living with diabetes by 2030.¹

   Approximately 26 million Americans have been diagnosed with diabetes mellitus.¹ The most severe and common complications of diabetes are foot ulcerations, half of which develop a serious infection.^2,3 Through an evidence-based prevention program, patient education, foot ulcer treatment by a multidisciplinary team, assessment of the structural and vascular abnormalities in the patient and routine surveillance, the rate of ulceration and subsequent amputation can decrease by 49 to 85 percent.⁴

   Numerous factors contribute to delayed lower extremity wound healing. These factors include inadequate vascular supply, lack of proper offloading, poor glycemic control and inadequate wound care. One should treat these wounds aggressively to help facilitate timely healing and prevent the numerous complications associated with chronic wounds.

   Wound care clinics have adopted many modalities to assist in wound closure. These modalities include negative pressure wound therapy (NPWT), bioengineered tissue, aggressive offloading and split thickness skin grafting (STSG). Often, these modalities get credit for achieving the best results. The goal of treatment is to reduce the size and complexity of the foot ulcer, and prevent infection and amputation.

   At the Southern Arizona Limb Salvage Alliance, we prefer what we call a “horizontal and vertical approach” to ulcer healing. Generally, we reduce wound depth and exposed structures via NPWT, which encourages margins to adhere. We reduce wound surface area through either secondary intention and biologics or skin grafting.⁵ For split thickness skin grafts, we offer a 10-step path to success.

Emphasizing The Benefits Of Thorough Debridement And NPWT To Facilitate Granulation Tissue

Step 1. The patient goes to the operating room for aggressive surgical debridement. The patient also undergoes an appropriate revascularization procedure, if necessary, as deemed by the vascular surgical team. Surgeons excise all nonviable soft tissue and bone, and assess the vascular status to the extremity before proceeding with NPWT.

   Step 2. Following the debridement of all nonviable tissue, the patient begins treatment with a NPWT device. Negative pressure wound therapy has gained momentum over the past 20 years as a safe, effective modality for treatment of diabetic foot ulcerations.⁶ For NPWT, we use reticulated, open cell foam covered by a semi-permeable adhesive drape. This connects to a negative pressure therapy unit with evacuation tubing.⁶ Patients utilize the device until virtually all bone, tendon and deep tissue are covered with granulation tissue. This process typically takes four weeks.

How To Harvest And Prepare The Graft

Step 3. When the patient achieves appropriate soft tissue coverage, the team schedules the patient for harvesting and application of the split thickness skin graft. Excision and evacuation of nonviable tissue, bacteria and contaminants from wounds, burns and soft tissue injuries prepare the wound site for STSG application. Removal of any dysvascular or necrotic tissue will return the wound to an active metabolic state.⁷

   The Southern Arizona Limb Salvage Alliance uses multiple debridement methods such as surgical debridement, chemical debridement or even medical maggot therapy. Currently, we use the hydroscalpel (Versajet, Smith and Nephew), which provides accurate debridement of the wound to a predictable level in the operating room just prior to application of the graft. We like to bevel the edges of the skin until punctate bleeding occurs, giving a healthy wound margin that facilitates anchoring of the STSG to the wound bed.

   Step 4. Appropriate preparation and measurement of the wound margins and harvest site must occur prior to harvesting. In addition, one should utilize a local anesthetic. We prefer the injection of 1% lidocaine with epinephrine via a 23 gauge spinal needle to minimize injections at the site. Epinephrine allows for better hemostasis at the surgical site post-grafting and improves postoperative pain management. Lubrication with an abundance of mineral oil is also helpful as it facilitates smooth movement of the dermatome over the donor site.

   Step 5. Harvesting from the donor site occurs using either an electronic or nitrous oxide powered dermatome, commonly from the thigh. While we prefer a slightly thicker graft for the foot (~0.018 inch thickness), many prefer much thinner grafts. Our rationale for the use of a thicker graft lies in the balance of skin take versus viscoelastic strength.

   A quick and easy way to verify that the dermatome has been accurately assembled and is ready to use is to place a blade between the dermatome blade and the dermatome. If the blade is able to fit in this space, the dermatome is properly calibrated.

   When harvesting with a dermatome or even a manual Humby knife (if an electric dermatome is not available), hold the device at a 45 degree angle to the donor site. While the dermatome is active, hold it tightly against the harvest site until you obtain an appropriate amount of graft. Do not turn the dermatome off when it reaches the end of the graft. Simply pull up and away. The motion should appear much like an airplane landing and subsequently departing. If there is any adherent skin after this motion, one can free the skin with a blade or scissors.

Inside Insights On STSG Application

Step 6. Then mesh the graft in a 1:1.5 ratio and place the graft on the wound. We mesh the graft with the deep side (or dermis) facing up. This allows adequate control of the borders of the graft, which can curl upward on longer grafts. We minimize the curling of the borders by lubricating the graft with normal saline prior to meshing. Overall, appropriate orientation and lubrication simplifies the STSG transfer from the donor site to the wound. Use caution to ensure that the ridged portion of the carrier is touching the graft during the meshing process or the graft will turn into thin strips resembling spaghetti rather than a meshed graft.

   Step 7. Transfer the meshed graft and apply it to the wound. At this point, the clinician has a great deal of flexibility in which to manipulate the STSG over the wound bed. Slightly moistened fingers or forceps are useful to gently coax the graft across the bed. Staples or sutures can anchor the graft. We prefer to anchor one or two sides of the wound to afford a pivot point (or points) from which we can then manipulate the rest of the graft once in a generally acceptable position.

   Step 8. Apply a non-adherent NPWT dressing to bolster the graft. Keep the dressing in place at 75 mmHg continuous pressure for three days to one week. Use white polyvinyl alcohol foam if using VAC therapy (KCI) or a non-adherent dressing followed by standard foam if using other NPWT devices. Negative pressure improves the adherence of a STSG. The bolstering action of low pressure NPWT prevents fluid accumulation beneath the skin graft site while increasing contact of the graft with the wound bed.

What You Should Know About Post-Op Care

Step 9. One should dress the donor site with a petroleum-based dressing. At our facility, we have also noticed some decreased pain during the postoperative period with the placement of platelet rich plasma at the donor site in the operating room. The dressing should remain intact for 72 hours for optimal results. Regardless of what one uses on the donor site, comfort is of primary importance as impaired donor healing is far less likely than graft failure.

   Step 10. Appropriate protection (offloading) of the surgical area is paramount for a successful outcome during the postoperative period. Many of the offloading devices available can mitigate pressure on the skin graft, whether you have the patient in an immediate postoperative prosthesis after a TMA or a non-weightbearing off-the-shelf splint. Identifying your patients’ needs is of utmost importance as adherence is critical during this crucial period.

How Indocyanine Green Angiography Can Bolster Grafting Success

In addition to our step-by-step application of STSG and the horizontal and vertical wound healing approach used by the Southern Arizona Limb Salvage Alliance, we have begun using indocyanine green angiography prior to application of our grafts.

   As an adjunct to hemodynamic testing, indocyanine green angiography can provide intuitive and immediate perfusion information when the tissue surrounding the wound bed may have been compromised. Although it is not a predictor of wound outcome, the potential of indocyanine green angiography lies in its utility as an indicator of regional tissue necrosis. For wounds with macerated borders, tissue regions of clinical ambiguity or skin with a mild violaceous hue, one may include indocyanine green angiography in step 1 of the STSG process prior to debridement.

   Clinicians have used indocyanine green angiography for over a decade to determine perfusion deficits in internal and external tissue.⁸ Only recently has the modality been introduced to wound care specialists, primarily as a method of identifying flap necrosis.⁹

  Indocyanine green angiography requires intravenous injection of indocyanine green, a tricarbocyanine dye that fluoresces at 800 nm. The device we use (Spy-Elite, LifeCell) supports a low power laser (40 mW/cm²) and a charge-coupled device camera on an articulating head that is positioned perpendicular to the wound site prior to the perfusion study.¹⁰

   Once one administers this, indocyanine green rapidly binds to the plasma proteins of the blood and, to a lesser extent, the albumin, preventing significant diffusion into the surrounding tissue.⁹Thus, when excited, indocyanine green fluoresces and the entirety of light in the infrared emitted by the dye corresponds to delivery of blood and dye by the capillaries. If a section of tissue exhibits diminished photon emission because perfusion or global flow is compromised, the region will appear on the monitor with reduced pixel values in comparison to the maximum pixel value of tissue in that region.¹¹ In our experience, less than 15 percent of the maximum pixel absolute value has consistently indicated compromise. In practice, one should outline any tissue that fluoresces poorly with a surgical pen and then debride appropriately.

In Conclusion

People with diabetes have at least a 25 percent lifetime risk of developing a foot ulcer.² Ulceration is the most common single precursor to amputation and researchers have identified ulceration as a component in 85 percent of lower extremity amputations.¹² Many of these ulcers lead to infection and progress to major amputation. Patients with major lower extremity amputations have a 50 percent mortality rate in the five years following the initial amputation.² By applying a “horizontal and vertical approach” to treating diabetic foot ulcers, one can preserve life and limb with the rapid closure of chronic wounds.

   Although the use of STSG in the diabetic population remains somewhat controversial, skin graft application has been successful for many of our patients. By using a routine approach to a multifaceted surgical process, we have maximized healing after split thickness skin grafting, furthering our limb salvage goals.

   Dr. Pappalardo is a Clinical Instructor and Fellow in Diabetic Limb Salvage in the Department of Surgery at the University of Arizona in Tucson, Ariz.

   Ms. Perry is a research assistant at the Southern Arizona Limb Salvage Alliance in Tucson, Ariz.

   Dr. Armstrong is a Professor of Surgery and the Director of the Southern Arizona Limb Salvage Alliance at the University of Arizona College of Medicine in Tucson, Ariz.