Current Concepts With Bioengineered Alternative Tissues
Living and non-living skin equivalents can be valuable adjunctive treatments for chronic lower extremity wounds. Accordingly, these authors review the current literature, discuss the role of advanced therapies in facilitating wound closure and provide pertinent case studies.
The management of chronic non-healing ulcerations continues to be a challenge for healthcare practitioners today. Not only can ulcers eventually lead to serious complications such as infection and amputation, they also affect the quality of life and bring about a significant economic burden.
Foot ulcers develop in approximately 15 percent of patients with diabetes with an incidence of nearly 2 percent per year.1-3 Ultimately, 14 to 20 percent of patients with a diabetic foot ulcer will require an amputation of the affected limb with nearly 85 percent of lower limb amputations preceded by a foot ulcer.1,2,4,5
Lower extremity ulcers can be caused by ischemia, neuropathy, pressure and venous hypertension. Regardless of the etiology, recalcitrant ulcers cause significant morbidity and mortality.6 The increased rate of mortality in diabetic patients with a foot ulcer has been well documented.
A prospective, population-based study followed 155 diabetic patients with a history of a foot ulcer, 1,339 diabetic patients without a history of a foot ulcer and 63,632 non-diabetic patients for 10 years in Norway.6 Researchers found that 49 percent of diabetic patients with a history of a foot ulcer died within that 10-year follow-up period. Only 35.2 percent of diabetic patients without a history of a foot ulcer and 10.5 percent of non-diabetics died. The study demonstrated that having diabetes and a history of a foot ulcer was associated with more than a twofold risk of mortality in comparison to that of non-diabetic patients.
Another prospective, population-based cohort study included adults with type 1 and type 2 diabetes mellitus presenting with their first foot ulcer.7 Researchers found a threefold increased risk of mortality in diabetic patients with moderate ischemia or peripheral arterial disease (PAD), and a threefold increased risk of recurrent ulceration in those study patients with one or more microvascular complications.
Similarly, venous leg ulcers affect up to 2.5 million patients per year with a prevalence rate ranging from 0.06 to 2 percent.8,9 Eighty percent of leg ulcers result from venous disease, which is more common with increasing age.9 Arterial disease accounts for 10 to 25 percent of venous leg ulcers, possibly coexisting with venous disease.9
In addition to the high incidence of venous ulcers, there is an increased recurrence rate with venous ulcers. The recurrence rate is reportedly as high as 72 percent in treated patients.9,10 Venous leg ulcers cause significant morbidity, impaired mobility and social isolation with substantial costs to all healthcare systems.11
A Closer Look At The Wound Healing Society Guidelines
In 2006, the Wound Healing Society selected a panel of advisers to develop guidelines for the treatment of lower extremity diabetic ulcers based on the evidence.12 The panel formulated guidelines in eight categories and also listed the strength of evidence supporting each guideline as Level I, Level II or Level III.
Level I is evidence based on meta-analysis of multiple randomized controlled trials or at least two randomized controlled clinical trials that support the intervention of the guideline.12 Level II is evidence based on at least one randomized controlled trial and at least two significant clinical series. Level III is evidence based on suggestive data of proof of principle but lacking any Level I or Level II evidence.
Ideal wound management should include proper diagnosis, verification of blood supply, debridement, infection control and offloading.12 The ultimate goal in the treatment of wounds is complete closure although increasing the rate of healing is equally as important. Expeditious wound closure not only improves the quality of life and decreases costs, but also helps to lessen the chances of complications such as infections and amputations.
When Should You Consider Using Advanced Therapies?
Sheehan and colleagues conducted a large, prospective, multicenter trial involving patients with diabetic foot ulcers.4 The study noted a percent change in wound area in four weeks was a strong predictor of complete healing over a 12-week period. These authors suggested that four weeks should be a critical clinical decision point at which time one should reassess the wound for progress and reduction in size. If the ulcer size has not reduced by half over the first four weeks of treatment, it is unlikely to achieve wound healing over a reasonable period. Accordingly, this would require more aggressive or advanced therapies. This is Level I evidence.
Boulton and co-workers also suggested that one should consider “adjuvant therapy” if a reduction in ulcer size over a four-week period has not occurred despite standard of care treatments such as debridement and offloading.2
Numerous wound care products and advanced treatment approaches such as living and non-living skin equivalents are on the market today. It may seem overwhelming to some and the choice of product is subjective based on the information received. For this reason, we will present a brief description along with case studies in order to elucidate some of the advanced therapies available today.
The advanced living cell therapies can be divided into topical agents and devices aimed at accelerating wound healing.12 Platelet derived growth factor (PDGF), a topical agent that stimulates angiogenesis and granulation tissue formation, is FDA approved and is included under the guidelines of the Wound Healing Society. This is Level I evidence. Platelet derived growth factor promotes recruitment and mitogenesis of chemotactic cells and synthesis of protein and extracellular matrix components.13,14
What You Should Know About Living Skin Equivalents
To date, Dermagraft® (Advanced Biohealing) and Apligraf® (Organogenesis) are the two living dermal skin equivalents aimed at accelerating wound healing that are available and FDA approved for use in lower extremity ulcerations. These products demonstrated efficacy and safety in well controlled clinical trials, meeting or exceeding FDA requirements for pre-market analysis.5 Living cells provide growth factors, cytokines and extracellular matrix to the wound, stimulating more rapid healing. This is Level I evidence.
Dermagraft is a single layer, cryopreserved, human fibroblast derived dermal substitute. It is indicated for full thickness diabetic ulcers of more than six weeks’ duration that extend through the dermis but without tendon, bone or muscle exposure. Dermagraft is composed of fibroblasts, extracellular matrix and a bioabsorbable matrix that produces multiple growth factors, cytokines and matrix proteins similar to human dermis.
When one implants Dermagraft into an adequately prepared diabetic foot ulcer, it assists in the restoration of the dermal bed. Dermagraft allows the patient’s wound to achieve re-epithelialization, accelerates healing and minimizes the detrimental effects of chronic ulcerations.5,15-17
Apligraf is a living bilayered skin substitute with the dermal layer composed of human fibroblasts cultured in bovine type I collagen and the epidermal layer composed of human keratinocytes. Apligraf is indicated for venous stasis ulcers of at least one month’s duration. It is also indicated for full thickness neuropathic ulcers of greater than three weeks’ duration that extend through the dermis but without tendon, muscle, capsule or bone exposure.18 Like its counterpart, Apligraf produces all cytokines and growth factors that normal skin regularly produces.8,18-21 It also effectively and safely increases the incidence of complete wound closure and decreases healing time.8,18-21
Living skin equivalents increase the rate of healing, decreasing severe complications such as infection, amputation and hospital admission. Living skin equivalents, however, do come with a high price tag. Nevertheless, despite their high initial costs, they are cost-effective over time because the initial expense is offset by more rapid wound closure, higher healing rates, fewer complications and fewer inpatient episodes.5 For this reason, one should take the total cost of care into account in deciding when to use these living skin equivalents.
Case Study: When There Is Osteomyelitis In The Fourth And Fifth Metatarsals And Cuboid
A 62-year-old female with diabetes and renal insufficiency presented with osteomyelitis of the fourth and fifth metatarsals and cuboid due to a non-healing ulceration caused by her neuropathy and Charcot foot deformity. The patient subsequently underwent fourth and fifth ray resections, a cuboidectomy and a peroneal tendon transfer.
After six weeks of aggressive outpatient wound care that included debridements and offloading with a total contact cast, the ulceration progressed to a healthy wound bed in preparation for Dermagraft. After just three weekly applications of Dermagraft, rapid wound closure occurred with complete epithelialization in four weeks.
Key Insights On Non-Living Skin Equivalents
Non-living skin substitutes provide biologic coverage for at risk tissue and bone. Allografts and xenografts have been commonly used as temporary dressings prior to an autograft or the use of a living skin equivalent. Likewise, there are multiple products available on the market today. They have their advantages in terms of providing proteins and extracellular matrix as well as a biologically compatible wound cover. Most are composed of collagen in combination with other components.
Examples of non-living skin equivalents are PriMatrix® (TEI Biosciences), Matrix HD® (RTI Biologics), AlloDerm® (LifeCell) and Integra® (Integra Life Sciences).
Other grafts such as GammaGraft® (Promethean Life Sciences) originate from cadaveric sources. GammaGraft is a gamma-irradiated, human skin allograft consisting of epidermis and dermis. This biologic graft comes from cadaveric sources that are irradiated and serves as both a preservative and a sterilizing adjuvant.22 Upon application, GammaGraft can promote granulation tissue and provide a moist wound environment while advancing chronic wounds toward healing with coverage of vital structures.23 GammaGraft is also readily available and storable at room temperature.
All non-living skin equivalents to date have been approved for use through the 510K process. The 510K process requires no statistical data to show improvement over control or standard care. The 510K process merely demonstrates the product’s safety and that it is comparable to other like products already on the market. With this process, products do not have to demonstrate any increased healing rates or improvement in wound healing.
Case Study: When A Patient Presents With Cellulitis, A Chronic Ulcer And Ischemic Changes In The Fifth Toe
A 60-year-old female presented with a right lower extremity cellulitis. She had an extensive medical history, which included non-insulin dependent diabetes mellitus, hypertension, congestive heart failure, cerebrovascular events and a right lower extremity deep venous thrombosis.
Upon the physical examination, the patient presented with a non-healing ulceration on her right fourth web space with ischemic changes to her right fifth toe. Once the physician noted moderate arterial insufficiency to the right lower extremity, she underwent a vascular consultation.
The patient had no improvements with IV antibiotics and also had gangrenous changes and purulent drainage from the right fifth toe. Surgical intervention to eliminate infection included a right fifth partial ray resection. The surgeon left the site open and initiated VAC therapy (KCI). Vascular intervention resulted in some improvements in blood flow.
In spite of continual wound care for two weeks and hyperbaric oxygen therapy, degenerative changes occurred to the right lateral plantar aspect of the foot with necrosis and non-viable tissue. Further surgical interventions included debridement of non-viable tissue and bone, followed by a proximal transmetatarsal amputation, which ultimately resulted in some areas of dehiscence.
Despite six weeks of aggressive wound care performed on an outpatient basis, a non-healing ulceration on the distal lateral aspect of the flap remained with areas of exposed tendon and bone. The patient returned to the operating room and underwent excisional debridement with application of GammaGraft to preserve vital structures and stimulate granulation tissue.
The patient underwent close follow-up on an outpatient basis. After three weeks, sloughing and incorporation of GammaGraft into the wound base occurred, resulting in healthy granulation tissue in preparation for a living skin equivalent. Full closure occurred after four applications of Dermagraft.
Recommending Key Algorithms For Making Treatment Decisions
There are two useful algorithms that can assist in the decision making process. The first algorithm illustrates a treatment plan for the management of a non-limb threatening plantar ulcer in a patient with diabetes and neuropathy (see “Managing A Non-Limb-Threatening Plantar Ulcer In A Patient With Diabetic Neuropathy” at right).2 If no healing has occurred at four weeks after appropriate evaluation, diagnosis and standard of care treatment such as debridement, offloading and infection control, then one should consider adjuvant therapy.
Physicians can implement the second algorithm following wound debridement when bone or vital structures are exposed in a chronic wound (see “When There Is Exposure To Bone Or Vital Structures In A Chronic Wound” at left).24 One can use this algorithm with all non-living bioengineered tissue to preserve not only vital structures but also provide a matrix for granulation and form a barrier against microbial infection.
Stagnant ulcerations have proven to cause significant morbidity and mortality, creating high healthcare costs and affecting a person’s quality of life and life expectancy. Preventing complications and healing these ulcerations more rapidly should be the ultimate goal of every healthcare practitioner who treats patients with wounds.
Evidence-based medicine has resulted in guidelines to help clinicians reach this goal and new bioengineered technologies have provided more treatment choices. Living skin equivalents have Level I evidence to support their efficacy, especially when the ulcer is not progressing after four weeks. Their use can help decrease healthcare costs with decreases in the amount of wound care necessary, hospitalizations, infections and amputations.
Although non-living skin equivalents are not part of the Wound Healing Society guidelines for the treatment of diabetic ulcers, they also play a vital role in the treatment of recalcitrant ulcers. They assist in the coverage of vital structures while delivering a matrix and preparing the wound bed for either living skin equivalents or autografts.
In combination with other evidence-based protocols on the proper treatment of wounds, the algorithms in this article can help in the decision making process of when to use which type of skin equivalent. Facilitating the rapid closure of wounds with an evidence-based treatment strategy should be a priority for every patient. Physicians who pursue this goal will help decrease the morbidity and mortality associated with chronic ulcers, improve quality of life and help decrease costs.
Dr. Hanft is the Director of Podiatric Medical Education at Baptist Health in South Florida. He is a Fellow of the American College of Foot and Ankle Surgeons.
Dr. Henao is a second-year resident at South Miami Hospital in South Miami.
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