Key Insights On Split-Thickness Skin Grafts
The goal of soft tissue coverage is to restore form and function. However, due to the anatomic complexity of the foot and ankle, soft tissue coverage in this area often falls short of Sir Harold Gillies’ adage to “… replace like with like.”1,2 Ideally, soft tissue coverage of the foot and ankle would involve primary repair free of tension and utilize neighboring sensate native tissue that is capable of withstanding the forces sustained during gait.1-3 Soft tissue wound coverage employs various forms of conservative and surgical techniques aimed at creating rapid, durable and functional closure using the simplest and least invasive techniques.4-9 Delayed primary closure, skin grafting, local, pedicle or free tissue transfer are some of the surgical tools that one may employ in his or her armamentarium.8,9 Whether it is the result of a severe infection or aggressive surgical debridement, extensive soft tissue loss should not be a major concern as properly performed skin grafting, local flaps, muscle flaps and distant pedicle flaps represent viable and cost-effective means of providing early and durable soft tissue coverage of diabetic foot and ankle wounds. How To Ensure Adequate Preparation Of The Recipient Site In order to achieve successful outcomes with skin grafting procedures, one must properly prepare the recipient site to accept soft tissue coverage. First and foremost, clinicians must ensure that the patient’s medical comorbidities have been fully addressed prior to attempting soft tissue wound coverage.10-12 Infected diabetic ulcers with osteomyelitis can be a major source of disability and morbidity. When it comes to severe diabetic foot infections, one should consider aggressive surgical debridement, vascular reconstruction when indicated, antibiotic therapy, adjunctive local wound care and appropriate offloading. Paramount to the successful treatment of diabetic foot infections is a well educated and compliant patient. In this regard, it is important to view the patient as a complete individual and not simply a wound. Clinicians should emphasize proper and ongoing patient and family education.13-15 Regarding debridement, one must completely remove all necrotic and infected soft tissue and/or bone from the wound initially, converting the defect to a surgically clean acute wound.11,16-23 Clinicians should obtain intraoperative cultures of the deepest exposed soft tissues and/or bone in order to facilitate more reliable identification of the causative microorganisms. Researchers have shown that using a power irrigation system or “high-pressure pulsatile lavage” is more effective than using a handheld bulb-syringe lavage during surgery.24,25 However, surgeons should employ caution with these devices since several studies have demonstrated increased edema within the already traumatized soft tissues, seeding of bacteria deeper within the wound interstices, and extensive aerosolization throughout the operating room.19-21,25-27 In this regard, some authors have found it helpful to place the lower extremity inside of an X-ray cassette cover or “extra” Mayo-stand cover during irrigation in order to avoid inadvertently spraying operating room personnel and to limit aerosolizing the irrigation fluid.27 When vascular status is intact, one should consider primary wound closure for the surgically clean wounds based upon the aforementioned principles for wound closure. In regard to those wounds that are deemed contaminated but clean or are too large for primary closure, surgeons should pack these open initially and close by secondary intention or delayed primary closure. One may use negative pressure wound therapy (NPWT) to optimize the wound bed, allowing for more timely and less invasive wound closure techniques.13,15 An Overview Of Skin Grafting Procedures Skin grafting is the workhorse of wound closure due to the fact that it is simple to perform, reliable, minimally invasive and cost-effective. One may repeat this procedure as necessary in order to facilitate full soft tissue wound coverage. When it comes to skin grafts, surgeons should consider their application to clean surgical wounds free from any necrotic or infected tissue. The skin grafts will fail if the recipient site is draining, actively bleeding or grossly infected. In the diabetic foot, one should use skin grafts in non-weightbearing areas and for coverage of donor sites of locally based flaps. Surgeons may harvest these grafts as either split-thickness skin grafts (STSGs), full-thickness skin grafts (FTSGs) or pinch grafts (PGs).28-30 Split-thickness skin grafts consist of the epidermis and a portion of the dermis.28,29 Depending on the needs of the patient, one may harvest thin grafts (i.e., 0.005 to 0.012 inches), medium grafts (i.e., 0.012 to 0.018 inches) or thick grafts (i.e., 0.018 to 0.030 inches). These thicknesses vary only in the amount of dermis that one includes.28,29 While STSGs are most commonly harvested from the lateral thigh, medial non-weightbearing arch of the foot, posterior-medial calf or posterior-lateral calf of either lower extremity, we prefer to harvest them from the ipsilateral extremity since it is already exposed and sterile. The donor sites heal easily and are harvested under local anesthesia with epinephrine. Full-thickness skin grafts consist of the entire thickness of the epidermis and dermis.28,29 They are most commonly harvested from redundant soft tissue folds about the lateral hindfoot and from the dorsal intermetatarsal spaces where one is afforded direct, tension-free closure.31,32 However, the close proximity to the cutaneous nerves is of concern so one should take great care to identify, protect and retract these structures during harvest.31-33 Other sites include the flexor surfaces of joints and the inguinal creases. Pinch grafts consist of irregular segments of the epidermis and dermis harvested as a small cone of tissue.34 Although pinch grafts are rarely used, surgeons most commonly harvested these grafts from the medial arch or lateral hindfoot regions of the foot.31,35,36 However, one may obtain these grafts from just about any location along the entire lower leg. Harvesting The STSG: What You Should Know When harvesting the STSG from the foot, one would use a regional field infiltrative anesthesia block and intravenous sedation. When the STSG is harvested from the calf or thigh region, the surgeon would perform the procedure with the patient under spinal or general anesthesia.33,37,38 Surgeons commonly use a power air-driven dermatome (Zimmer), which is set between 0.0016 and 0.018 inches. The surgical assistant applies a tongue depressor or moistened gauze sponge both behind and in front of the power dermatome as it is advancing since they function more efficiently on a flat surface under tension.32,33 One would then proceed to fenestrate the harvested graft manually with repeated passes of a surgical scalpel (i.e., “pie crusting”) or mesh it at a ratio of 1:1.5 or greater using a commercially available mesher.33,39 (Surgeons can save any unused skin in a saline-soaked gauze sponge and refrigerate it for up to 21 days. If any graft failure occurs, one can reapply this unused skin for the patient as long as one has properly addressed the reason for failure.33,40) One should add a non-adherent or occlusive dressing to the harvest site and proceed to apply an absorptive gauze pad, and either a compression wrap or foam-type tape. How To Apply The STSG To The Recipient Wound Site Once the skin graft is harvested, the surgeon should apply it to the recipient site as expeditiously as possible. The recipient site should be free of any active bleeding in order to avoid hematoma or seroma formation between the skin graft and underlying recipient bed, which would prohibit fibrin anchorage and subsequent vascular in-growth.28,29,41-43 The surgeon would proceed to apply a bolster dressing in order to firmly secure the STSG in place. A number of elaborate bolster dressings have been described in the literature.28,29,44-46 However, if the wound recipient site does not possess variable depth and irregularity, the authors prefer to use either a simple surgical glove or a non-adherent dressing cover, which one can staple around the perimeter of the wound and the wound itself over saline-soaked cotton balls or gauze sponges. This provides an inexpensive, simple and effective bolster dressing alternative.47,48 If the wound is not of uniform depth or is highly irregular, researchers have shown that using topical negative pressure wound therapy (VAC therapy, KCI) can serve as an effective bolster. Using VAC therapy also provides the added benefits of improved exudate removal, promotion of vascular ingrowth and prevention of shearing forces about the graft application site.49,50 Inosculation of skin grafts by vascular buds usually begins by the fifth postoperative day. It is important to avoid changing the dressings the first postoperative week as the graft’s viability is maintained by a diffusion process called plasmatic inhibition.15,33 A First-Line Option For Soft Tissue Wound Coverage? Once one has ensured proper preparation of the host and recipient wound sites, skin grafting represents a simple, cost-efficient technique that is powerful in providing rapid and stable soft tissue wound coverage. One recent study involved plastic surgeons as part of the multidisciplinary team for treating patients with diabetic foot wounds. In the study of 38 patients with diabetic foot wounds that required soft tissue coverage, more than 50 percent of the patients underwent skin grafting as the primary procedure for wound coverage.51 This data rightly positions skin grafting techniques as a first-line soft tissue wound coverage option in treating diabetic foot and ankle wounds when flap coverage is either unnecessary or inappropriate, and the use of topical wound care agents and living skin equivalents is considered too expensive and would prolong full wound coverage. Final Notes Soft tissue coverage of diabetic foot and ankle wounds is an evolving process that involves an elaborate series of potential conservative and surgical techniques. Unfortunately, few existing studies critically analyze long-term, follow-up reulceration rates when it comes to soft tissue coverage techniques of the plantar aspect of the foot.1,52-55 Most propose that no one form of soft tissue coverage is entirely satisfactory, and that patient education and proper shoe gear modifications are more important than the type of soft tissue wound coverage utilized.1,52-55 Gidumal, et. al., believed that the soft tissue coverage choices one utilizes should be governed by the surgeon’s discretion and donor site considerations alone.54 Levin and Serafin believe the choice of soft tissue wound coverage depends on the needs of the patient, the location of the lesion on the foot and the need for eliminating contour defects.2 Regardless of the technique one employs, it is essential to ensure that the host is medically prepared in order to maximize wound healing. The use of skin grafts and various flaps involving the foot and lower leg as donor sites represent advanced concepts based on sound, time-honored principles. When one ensures proper patient selection and technique, these procedures represent a simple, reproducible, minimally invasive and cost-effective means for surgical management of diabetic foot and ankle wounds in patients with well controlled medical comorbidities.56-58 Dr. Zgonis is an Assistant Professor within the Department of Orthopaedics/Podiatry Division at the University of Texas Health Science Center in San Antonio. He is also the Director of Fellowship Training Programs at the aforementioned institution. Dr. Zgonis is a Fellow of the American College of Foot and Ankle Surgeons, and is a Diplomate of the American Board of Podiatric Surgery. He can be reached via e-mail at: firstname.lastname@example.org Dr. Roukis is a Fellow of the American College of Foot and Ankle Surgeons, and is a Diplomate of the American Board of Podiatric Surgery. Dr. Cromack is an Assistant Professor within the Department of Orthopaedics/Hand and Plastic Surgery Division at the University of Texas Health Science Center in San Antonio. He is a Diplomate of the American Board of Plastic Surgery. For related articles, see “A Guide To Closure Techniques For Open Wounds” in the July 2003 issue of Podiatry Today or “Conquering Plastic Surgery Complications In Wound Care” in the July 2005 issue. Also visit the archives at www.podiatrytoday.com.
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