Continuing Education Course #157: October 2007
I am pleased to introduce the latest article, “A Guide To Current Concepts In Skin Grafting,” in our CE series. This series, brought to you by the North American Center for Continuing Medical Education (NACCME), consists of complimentary CE activities that qualify for one continuing education contact hour (.1 CEU). Readers will not be required to pay a processing fee for this course. Podiatrists commonly use skin grafts to help close difficult wounds in the lower extremity. Accordingly, Tod Storm, DPM, offers key insights on full-thickness and split-thickness skin grafts. He also offers a closer look at wound bed preparation, graft harvesting, graft placement, and provides pearls on postoperative care. At the end of this article, you’ll find a 10-question exam. Please mark your responses on the enclosed postcard and return it to NACCME. This course will be posted on Podiatry Today’s Web site (www.podiatrytoday.com) roughly one month after the publication date. I hope this CE series contributes to your clinical skills. Sincerely, Jeff A. Hall Executive Editor Podiatry Today INSTRUCTIONS: Physicians may receive one continuing education contact hour (.1 CEU) by reading the article on pg. 77 and successfully answering the questions on pg. 82. Use the enclosed card provided to submit your answers or log on to www.podiatrytoday.com and respond via fax to (610) 560-0502. ACCREDITATION: NACCME is approved by the Council on Podiatric Medical Education as a sponsor of continuing education in podiatric medicine. DESIGNATION: This activity is approved for 1 continuing education contact hour or .1 CEU. DISCLOSURE POLICY: All faculty participating in Continuing Education programs sponsored by NACCME are expected to disclose to the audience any real or apparent conflicts of interest related to the content of their presentation. DISCLOSURE STATEMENTS: Dr. Storm has disclosed that he has no significant financial relationship with any organization that could be perceived as a real or apparent conflict of interest in the context of the subject of his presentation. GRADING: Answers to the CE exam will be graded by NACCME. Within 60 days, you will be advised that you have passed or failed the exam. A score of 70 percent or above will comprise a passing grade. A certificate will be awarded to participants who successfully complete the exam. TARGET AUDIENCE: Podiatrists RELEASE DATE: October 2007 EXPIRATION DATE: October 31, 2008 LEARNING OBJECTIVES: At the conclusion of this activity, participants should be able to: • review the characteristics of full-thickness skin grafts (FTSGs) and split-thickness skin grafts (STSGs); • compare the potential benefits and drawbacks of FTSGs and STSGs; • list possible donor sites for FTSGs; • discuss keys to preparing the wound bed to receive the skin graft; and • discuss postoperative considerations, including proper dressing usage. Sponsored by the North American Center for Continuing Medical Education. Podiatric surgeons commonly use skin grafting for the closure of cutaneous wounds secondary to trauma, post-amputation wounds and chronic ulcerations. Accordingly, this author details the pros and cons of various types of skin grafts, including full-thickness and split-thickness skin grafts, and offers step-by-step insights on graft application. The skin is the body’s first defense in preventing the invasion of pathological organisms. When a disruption of this envelope occurs, the surgeon’s primary goal is closing the wound as quickly as possible with the least amount of risk to the patient. The methods of wound closure available to a surgeon include primary closure, skin grafting and soft tissue flaps. Skin grafting involves transferring a portion of the skin, devoid of its blood supply, from one area to another. In some situations, skin grafting can have some advantages over other methods. Grafts are relatively simple to perform, reliable and can cover large areas. The popularity of skin grafting has certainly stood the test of time. In India, the Hindus used skin grafting 2,000 to 3,000 years ago to repair damage that was done to the noses of criminals as a form of punishment.1 In 1869, Reverdin performed an “epidermal pinch graft.” He also observed that thinner grafts had a better success rate than thicker grafts.2 Ollier’s work with split-thickness grafts in 1875 is also historically notable.3 Today, dermatologists and plastic surgeons commonly use skin grafts following the removal of skin lesions to replace lost skin in burn victims, and, in more recent years, for hair restoration. Podiatric surgeons commonly use skin grafting to help close cutaneous wounds secondary to trauma, following amputations and for chronic ulcerations. Surgeons also use skin grafts to cover the donor site following certain types of soft tissue flaps. Skin grafts provide rapid closure to full thickness wounds that might otherwise take a prolonged period of time to heal. The longer it takes a wound to close, the greater the cost and risk to the patient. In patients with diabetes, the risk of resistant strains of bacteria developing in chronic wounds is always a concern to the podiatric physician. An Overview Of The Types Of Skin Grafts Skin grafts can be classified as autografts (from the same individual), allografts (from the same species) or xenografts (from different species). Surgeons have used cadaver skin when they needed to cover large areas, such as the case with burn victims, and this may initially show some degree of incorporation or “take.” However, the host will eventually reject the graft, limiting its use to a temporary biological dressing. Xenografts never take and surgeons only use them as biological dressings.4 These types of grafts are rarely necessary in foot wounds due to the relatively small areas that one needs to cover. The most common types of grafts used in foot wounds are autogenous skin grafts and are divided into two general types: full-thickness skin grafts (FTSGs) or split-thickness skin grafts (STSGs). Both types of grafts use the entire epidermis but vary as to the amount of dermis each uses. Distinct differences exist between these grafts. Accordingly, selecting one graft over the other is dependent on each specific case. Split-thickness skin grafts include the epidermis and a portion of the dermis. They are generally divided into thin (0.008 to 0.012 inch) grafts, intermediate (0.013 to 0.016 inch) grafts and thick (0.017 to 0.02) grafts, depending on the amount of dermis taken. The thinner the graft, the more likely a graft is to take. The higher initial success rate is the main advantage to using a thin graft over thicker grafts. The main disadvantage to using thin grafts is they are much less durable. One must consider this fact when using grafts in foot surgery. In addition, thin grafts contract much more than thicker grafts and are less cosmetically appealing. Full-thickness skin grafts include the epidermis and all of the dermis, which includes most of the dermal appendages. The retention of these dermal appendages and the greater amount of dermis make these grafts more durable. The FTSG also contracts much less than a STSG. Full-thickness skin grafts are not normally meshed and are therefore usually more cosmetically appealing. In regard to the donor site for FTSG, one would use primary closure. This helps eliminate the prolonged healing one might see with STSG donor sites. The major disadvantage to a FSTG is a significantly higher failure rate than a STSG. It is also more difficult to reestablish blood flow with FTSGs and they have more tissue to be supported during this phase of healing. Skin grafting in the foot provides some unique challenges due to the stresses applied to the grafts by weightbearing forces and contact with shoe gear. As a general rule, one should avoid applying grafts to areas, such as underneath the metatarsal heads, that directly bear weight. Grafts in these areas tend to break down over time and a soft tissue flap may be more appropriate. What You Should Know About Preparing The Recipient Wound Bed Preparation of the recipient bed is the most critical component of skin grafting. It begins with the removal of all necrotic, fibrotic or avascular tissue. Do not use skin grafts to cover structures, such as tendon, cartilage and bone, that are relatively avascular.5 Tendon covered by paratenon or bone covered by periosteum may support a graft. One may use grafts to cover small avascular regions by a process known as bridging.6 In these cases, the graft is supplied by the wound’s periphery. If possible, practitioners should debride wounds and then allow them to granulate for several days prior to applying the graft. One should remove most of the granulation tissue since it has a tendency to harbor bacteria. A wound that is infected or contaminated will invariably cause the graft to fail. A quantitative bacterial culture of less than 1 x 106 is preferred prior to grafting.7 Researchers have shown that applying silver sulfadiazine to the wound for 10 days prior to grafting reduces the bacterial count greatly.8 Hemostasis of the recipient bed is critical. Excessive bleeding may result in a hematoma, which separates the graft from the bed and prevents it from taking. One may achieve hemostasis by using direct pressure, electrocautery, topical thrombin or epinephrine soaked gauze. Carefully assess patients on anticoagulation therapy or those with coagulopathies preoperatively since uncontrolled bleeding would be a contraindication to skin grafting. A Closer Look At Harvesting Skin Grafts After preparing the wound or recipient bed, one would begin harvesting the graft. Obtaining a STSG is easier with the use of an electric, gas or battery powered dermatome. In regard to the graft thickness and width, the surgeon can predetermine this by adjusting the dermatome that he or she uses. The surgeon may also harvest grafts by using non-powered, handheld instruments such as a Wecht or Humby knife. The Wecht knife is useful for obtaining small grafts while one can use the Humby knife to harvest larger grafts. In regard to harvesting grafts with power dermatomes, these grafts tend to be much more uniform in width and thickness in comparison with grafts harvested with handheld instruments. Using handheld instrumentation can be difficult and usually requires significant experience to obtain a consistent, uniform graft. The most common donor harvest site for the podiatric surgeon is the calf. The donor site will remain obvious even after it has completely healed. The calf is a convenient donor site for foot surgeries but one should warn the patient of the cosmetic appearance since this area is often visible when one wears shorts or dresses. This is especially the case for dark skinned individuals. One should also inform patients that the donor site for a STSG tends to be the area that is most painful after surgery. Using a semi-permeable membrane can alleviate much of this discomfort. However, fluids tend to build up under this type of dressing and the patient may need to drain the fluids periodically. When harvesting a STSG, the surgeon should prepare the donor site with saline or mineral oil. This allows the instrument to slide smoothly across the skin surface. Binding or bunching up of the skin will lead to uneven graft thickness and serrated edges. When using a dermatome, an assistant can use a tongue blade to flatten and tighten the skin in front of the advancing dermatome. This aids in getting an even, uniform graft. The surgeon holds the dermatome at approximately 45 degrees to the skin, and applies firm and constant pressure while advancing the dermatome. An assistant can help guide the graft as it presents itself in the dermatome. After obtaining enough graft, the surgeon should lift the dermatome from the surface in a scooping type action. Surgeons should keep the dermatome running until it leaves the skin surface. This allows clean separation of the graft. Surgeons should take adequate graft to cover the wound and keep in mind that meshing a graft will increase the area it can cover. If extra graft is leftover, one can place it back on the donor site and it will aid in the reepithelialization of the donor site. Frequently, a STSG will be meshed and this allows the graft to expand and cover more surface area. In foot surgery, since the surface areas are usually relatively small, meshing at a ratio greater than 1.5 to 1 is rarely necessary. In addition to graft expansion, meshing allows for drainage of fluid from beneath the graft. This prevents seroma or hematoma formation. However, bear in mind that meshed grafts provide a poor cosmetic appearance since the gaps produced remain apparent indefinitely. The surgeon may also mesh grafts by hand. This technique is known as pie crusting. One would make many small slits in the harvested graft with a scalpel. Pie crusting serves the same general purpose as meshing. However, the amount of expansion and drainage one obtains is significantly less. The most commonly used donor sites for FTSGs include the flexor creases. The sinus tarsi is a convenient area to obtain grafts of adequate size for many foot wounds. Harvest the graft in a 3:1 length to width ratio that is parallel to the relaxed skin tension lines. This will allow for primary closure of the donor site with minimal tension. With this technique, only a linear scar would remain. A paper template can be useful to ensure that one harvests an adequate graft. With the outline of the graft drawn on the skin, use a #15 blade to cut down through the dermis, taking as little adipose tissue as possible. Using a curved Kay scissor with the graft stretched over your finger, remove all remaining fat on the dermal side of the graft. Pertinent Insights On Graft Placement With the recipient bed and the graft prepared, the next step is placing the graft. This is usually the easiest part of the procedure. Apply the graft to the wound and ensure the entire graft is in contact with the wound. If the recipient bed is not flat, take care to ensure that the graft falls into all low areas and is not allowed to “tent” across them. Lightly flushing the graft with saline can help draw the graft down into the low areas. It is also very important to make sure the dermal side of the graft is down. In patients with light complexions, the dermal and epidermal sides may not always be apparent. One may allow a small portion of the graft to overlap the wound bed as the surgeon can trim back the portion of the graft at a later date. Suture the periphery of the graft with 5-0 monofilament nylon. It is not necessary to get overly aggressive with the number of sutures since sutures alone will not adequately stabilize a graft if it is subjected to shearing forces. Excessive sutures may also increase the risk of ischemia at the wound margins. What You Should Know About Post-Op Considerations The dressing is a very important postoperative component for ensuring graft take. The dressing can stabilize the graft against shear forces, provide a moist, sterile environment, and can prevent the accumulation of fluids under the graft. Researchers have often cited the formation of a seroma or hematoma as the most common cause of postoperative graft failure.9 There are various dressing techniques. A stent or tie-over type dressing is especially useful in foot surgery since flat surfaces are a rarity and it can be difficult to keep a dressing in place once the patient goes home. This type of dressing consists of a fine-meshed non-adherent gauze (i.e. xeroform) that one would place over the graft. Then one would subsequently apply glycerin or saline soaked fluffs, and a gauze wrap on top. Then space long sutures evenly around the periphery and tie them over the top of the dressing, securing it in place. It is very important the graft stays moist during the first few days postoperatively. Perform the first dressing change between one and seven days post-op. I prefer to change the dressing on the third day. At this time, if the graft has been disrupted or if a hematoma has formed, one could reapply the graft and still expect it to survive.10 Graft healing begins with the formation of a fibrin layer between the wound and the graft. This layer helps stabilize the graft and allows passive movement of fluid and nutrients from the bed to the graft.5 This phase of graft healing is called the plasmatic imbibition phase and occurs during the first 24 to 48 hours. During the end of this phase, capillary budding from the recipient bed begins but the graft remains ischemic and is white and dusky in appearance. At approximately 48 hours, the capillaries make contact with the graft and the phase of inosculation begins. Blood flow is usually reestablished by day four through a combination of new vessel growth and reanastomosis of existing vessels. The graft will appear mottled at first and will then become erythematous. One should not confuse this vascular “blush” with infection. Strict elevation of the foot is still important at this point since the lymphatics do not start to function until about one week post-op. The final phase of healing is reinnervation and reorganization. This phase can continue for one to two years.11 In Conclusion Rarely are medical procedures around for as long as skin grafting has been and remain relatively unchanged. It is conceivable, however, that in the not too distant future, donor sites may become obsolete. Significant advances are being made with bioengineered products and cultured epithelium. Currently, these products have limitations and the expense can be prohibitive. However, these problems may be overcome in the future. Until that day, skin grafting in its current state will continue to be a valuable tool for podiatric surgeons. Dr. Storm is a Fellow of the American College of Foot and Ankle Surgeons and is board-certified by the American Board of Podiatric Surgery. He has a private practice in Bozeman, Mt.
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For related articles see “Key Insights On Split-Thickness Skin Grafts” in the March 2006 issue of Podiatry Today, “Conquering Plastic Surgery Complications In Wound Care” in the July 2005 issue and “A Closer Look At Plastic Surgery Techniques” in March 2003 issue.
Also check out the archives at www.podiatrytoday.com.