Off-loading the diabetic foot for ulcer prevention and healing

Transcription

1 Off-loading the diabetic foot for ulcer prevention and healing Peter R. Cavanagh, PhD, DSc, a and Sicco A. Bus, PhD, b Seattle, Wash; and Amsterdam, The Netherlands Background: Retrospective and prospective studies have shown that elevated plantar pressure is a causative factor in the development of many plantar ulcers in diabetic patients and that ulceration is often a precursor of lower extremity amputation. In this article, we review the evidence that relieving areas of elevated plantar pressure (off-loading) can prevent and heal plantar ulceration. Results: There is no consensus in the literature concerning the role of off-loading through footwear in primary or secondary prevention of ulcers. This is likely due to the wide diversity of intervention and control conditions tested, the lack of information about off-loading efficacy of the footwear used, and the absence of a target pressure threshold for off-loading. Uncomplicated plantar ulcers should heal in 6 to 8 weeks with adequate off-loading. The total contact cast and other nonremovable devices are most effective because they eliminate the problem of nonadherence to recommendations for using a removable device. Conventional or standard therapeutic footwear is not effective in ulcer healing. Recent United States and European surveys show a large discrepancy between guidelines and clinical practice in off-loading diabetic foot ulcers. Many clinics continue to use methods that are known to be ineffective or have not been proven effective, while ignoring methods that have been demonstrated to be efficacious. Conclusions: A number of strategies are proposed to address this situation, notably the adoption and implementation of recently established international guidelines, which are evidence-based and specific, by professional societies in the United States and Europe. Such an approach would change the often poor current expectations for healing diabetic plantar ulcers. (J Vasc Surg 2010;52:37S-43S.) WHAT IS OFF-LOADING AND HOW CAN IT BE MEASURED? In the sensate foot, for example in a patient with rheumatoid arthritis, relieving the local pressure (off-loading) at painful regions of the foot is both driven and evaluated by the patient s perceived pain. 1 However, up to about 50% of people with diabetes mellitus (depending on ethnicity 2 ) will eventually have loss of sensation in the feet secondary to peripheral neuropathy that is sufficient to allow them to injure the soft tissues of the plantar surface, a condition that has been termed loss of protective sensation. 3 These areas need to be off-loaded, but because the patient has inadequate sensation, his or her feedback is not useful in judging whether or not pressure relief has been obtained. 4 From the Department of Orthopaedics and Sports Medicine, University of Washington, Seattle; a and the Department of Rehabilitation, Academic Medical Center, Amsterdam. b Competition of interest: Peter R. Cavanagh holds equity in DIApedia LLC. He is an inventor on U.S. patents 6,610,897, 6,720,470, and 7,206,718, which elucidate a load-relieving dressing and a method of insole manufacture for off-loading. He has received honoraria from Merck, Eli Lilly, and ConvaTec and is the recipient of grants from the National Institutes of Health and NASA. This article is being co-published in the Journal of Vascular Surgery and the Journal of the American Podiatric Medical Association. Correspondence: Peter R. Cavanagh, PhD, DSc, Department of Orthopaedics and Sports Medicine, University of Washington, Seattle, WA ( cavanagh@uw.edu). The editors and reviewers of this article have no relevant financial relationships to disclose per the JVS policy that requires reviewers to decline review of any manuscript for which they may have a competition of interest /$36.00 Copyright 2010 by the Society for Vascular Surgery and the American Podiatric Medical Association. doi: /j.jvs The design of footwear and in-shoe devices to off-load at-risk areas of the diabetic foot has traditionally been considered to be an art rather than a science. This is despite the fact that a report of one of the first studies to actually measure the pressure relief from therapeutic footwear was published almost 50 years ago. 5 Pressure measurement inside footwear is now more widespread, although because of economic and reimbursement issues, it is more common in a research setting than in clinical practice. An example of what the technique can demonstrate is shown in Fig 1. The substantial difference in off-loading, which can be seen between the two footwear conditions, is apparent, but the practitioner would not be able to determine this difference without the benefit of the measuring device. This is one of the reasons why off-loading the diabetic foot is so difficult and prone to failure. WHY IS OFF-LOADING NEEDED? Retrospective and prospective studies have shown that elevated plantar pressure is a cause of the development of plantar ulcers in diabetic patients 6-8 and that ulceration is often a precursor of lower extremity amputation. 9 Many structural abnormalities in the foot have been associated with increased levels of plantar pressure. 10 In a person with diabetes, claw-toe deformity and Charcot neuroarthropathy are among the most important abnormalities that may cause significant disruption to the architecture of the foot 11,12 and elevated local foot pressures. 13,14 The combination of foot deformity, loss of protective sensation, and inadequate off-loading leads to tissue damage and ulceration. Once an ulcer has formed, studies described below indicate that unless the ulcerated area is off-loaded, healing may be chronically delayed, even in an adequately perfused 37S

2 38S Cavanagh and Bus JOURNAL OF VASCULAR SURGERY September Supplement 2010 Fig 1. A, Peak plantar pressure distribution shown for the right foot during barefoot walking. The highest pressure experienced by each area of the foot through the support phase is shown on the diagram. The pressure distribution inside the shoe of the same patient is shown while (B) a flat cushioning insole and (C) a custom-made insole are being used. The red and purple colors represent the areas with the highest measured pressure. Note the superior off-loading of high-pressure regions identified during barefoot walking (C) in the custom insole compared with (B) the insole. limb. After an ulcer is healed, the risk of recurrence is high 40% in a median 4 months in one recent study 15 showing the need for continuous off-loading in these patients. In this article, we will demonstrate that effective offloading of diabetic feet is important for ulcer healing and the prevention of ulcer recurrence. There is not yet sufficient evidence to support primary prevention of ulcers by off-loading, although clinical opinion strongly favors such an approach. Many new potential solutions for healing diabetic foot ulcers such as topically applied growth factors, bioengineered skin, and stem cells have been proposed. What all solutions have in common is that they require a mechanical environment that will not destroy the healing construct. This must be achieved by some device that will effectively remove mechanical stress from the wound and its immediate environment. The effectiveness of off-loading must be judged both by the relief of stress and by the patient s adherence to the treatment. THE EVIDENCE BASE: WHAT WORKS AND WHAT DOES NOT WORK? Pressure off-loading. Total contact casts (TCCs) and removable walkers have been shown to be extremely effective in off-loading the diabetic foot, with reported peak pressure reduction in the forefoot up to 87% compared with a control condition (Fig 2) This effect may be achieved, among other mechanisms, by limiting ankle motion and redistributing load to the device itself. 20 For these reasons, devices that only extend to the ankle, such as cast shoes and forefoot off-loading shoes, may be less effective in off-loading the foot than devices that extend above the ankle, as do TCCs and walkers. Reported off-loading values for such devices range from 44% to 64% compared with control. 18,19,21,22 Various therapeutic footwear designs can effectively off-load at-risk foot regions. Among these designs, rocker-bottom outsoles, custom-made insoles, and some shoe inserts (eg, metatarsal pads and medial arch supports) may reduce forefoot peak pressure between 16% and 52% compared with control. 18,23-28 The design and placement of such devices is critical, however, and difficult to establish without pressure. The surgical approaches of Achilles tendon lengthening and liquid silicon injections under the metatarsal heads may only temporarily reduce pressure underneath the forefoot. 29,30 Callus removal can reduce pressures by as much as 30%, although the durability of such relief is unknown. 31,32 Different interventions exhibit a great variation in off-loading capacity (Fig 2), and this likely influences their efficacy in preventing or healing foot ulcers in diabetic patients. Ulcer healing. The largest evidence base on off-loading available is for the treatment of primarily uncomplicated neuropathic plantar foot ulcers (Fig 3). A number of different metrics are used in wound healing studies to characterize progress toward healing. These include percentage of wound closure in a given time and time to complete healing. It is generally assumed that time to complete healing is the most important consideration in clinical practice because this affects treatment costs and, presumably, lowers the risk for infection. Several randomized controlled trials (RCTs) have shown that the TCC is more effective than removable devices, both in healing proportions and time to healing One recent RCT showed similar healing rates between the TCC and an ankle-high removable walker. 37 A meta-analysis of 11 studies using the TCC 33,34,38-46 showed that 92% of the 277 treated ulcers healed in a mean

3 JOURNAL OF VASCULAR SURGERY Volume 52, Number 12S Cavanagh and Bus 39S Fig 2. The off-loading capacity of different modalities used for the prevention and treatment of diabetic plantar foot ulcers is expressed as percentage of peak pressure reduction at the first metatarsal head region compared with a control condition. The lighter bars show the range in measured peak pressure reduction over different studies. Fig 3. Histogram showing the proportion of healed ulcers expressed as a percentage (black bars) and time to healing expressed as a number of days (dark gray bars) for different off-loading modalities used to treat noncomplicated neuropathic plantar foot ulcers in diabetic patients. The light gray bars show the range found in different studies. The number of studies on which the bars showing percentage healing are based is also indicated. duration of 42 days (range, days; Ulbrecht JS, private communication). These ulcers had existed for an average of 282 days before treatment was initiated. Adverse effects with TCCs may occur, however, including reduced activity level, difficulty with sleeping or driving a car, and iatrogenic ulcers due to poor casting. Alternatively, below the knee removable walkers that have been made nonremovable may be as effective as TCCs and more effective than standard removable walkers in healing plantar foot ulcers Ulcer healing using removable devices is complicated by patients not adhering to recommendations for using

4 40S Cavanagh and Bus JOURNAL OF VASCULAR SURGERY September Supplement 2010 their prescription device. One study found that patients used their prescribed removable device for an average of only 29% of their total daily number of steps. 50 This may explain the lower effectiveness of removable devices and points to the importance of continued pressure relief to promote healing. Half-shoes, forefoot off-loading shoes, and cast shoes may be effective in healing neuropathic forefoot ulcers (healing proportions, 58%-91%), although their efficacy requires confirmation in prospective trials. 34,51-54 Conventional or standard therapeutic footwear is not effective in ulcer healing, and the role of custom footwear in this context is not yet clear. 55 Several prospective controlled studies have shown that surgical interventions such as Achilles tendon lengthening, metatarsal-phalangeal joint arthroplasty, and metatarsal head resection may have only limited additional value in ulcer healing compared with conservative treatment Neuroischemic or infected wounds can also be treated with off-loading, although success rates are much lower than for purely neuropathic wounds. 61 In summary, the data on ulcer healing support the use of nonremovable off-loading modalities, whereas the role of certain removable devices and surgical procedures requires further definition in prospective controlled studies. Ulcer prevention. Several prospective studies have shown a beneficial effect of the use of therapeutic footwear compared with standard footwear in preventing ulcer recurrence However, one RCT showed no effect. 66 These contrasting results are likely due to the wide diversity of intervention and control conditions tested and the lack of information about off-loading efficacy of the footwear used. This lack of standardization complicates the comparison of studies and limits the definition of the role of special footwear in ulcer prevention. In this context, a recent prospective 5-year analysis on the use of a previously defined footwear prescription algorithm 67 showed much lower primary and secondary ulceration rates (21%) compared with the rates in the preceding 5 years in the same study center (70%). This demonstrates the usefulness of such a structured approach for ulcer prevention. 68 Surgical interventions may reduce ulcer recurrence rates in selected patients compared with conservative treatment However, complications with these procedures may occur, such as transfer ulcers and impaired balance during walking. 69,70 Overall, the evidence base to support the safe use of therapeutic footwear and surgical procedures for ulcer prevention is still weak, 71,72 although some recent studies show promising results in this regard. We do not yet know the exact pressure threshold that will prevent plantar tissue damage from occurring. Our group recently examined patients who had remained healed after plantar ulceration and found a mean pressure of approximately 200 kpa at the prior ulcer site. 73 It may be that such a threshold is unique to each individual, but the 200 kpa value can serve as a goal for plantar off-loading until better evidence is available. Clinical recommendations. Efforts have recently been made by the International Working Group on the Diabetic Foot to develop specific evidence-based guidelines on the use of footwear and off-loading for ulcer prevention and healing in the diabetic foot. 72,74 Recommendations for the use of off-loading in treating noncomplicated neuropathic plantar foot ulcers are: Relieving pressure on ulcers should always be a part of the treatment plan. TCCs and nonremovable walkers are the preferred interventions; however, the clinician should be aware of possible adverse effects of these devices. Forefoot off-loading shoes or cast shoes may be used when above the ankle devices are contraindicated or not tolerated by the patient. Conventional or standard therapeutic footwear should not be used since many other devices are more effective. Recommendations for the use of off-loading in ulcer prevention in patients with an at-risk foot at-risk are: Regular callus removal should be provided by a skilled health care professional. Patients should be urged to not walk barefoot at any time. Therapeutic footwear, including a custom-molded insole in a shoe with adequate depth, is the preferred intervention. Although surgical procedures may be effective for ulcer healing or secondary prevention in selected patients, more studies are needed to better define the role of surgery compared with conservative treatment before it can be recommended for widespread use. DISCUSSION We have presented strong evidence that uncomplicated plantar ulcers can be healed in approximately 6 to 8 weeks. This time frame is in sharp contrast to reported clinical experience in the standard-of-care arms of U.S. clinical trials in which only 24% and 31% of uncomplicated ulcers were healed after 12 and 20 weeks, respectively. 75 We believe that inadequate use of off-loading explains this difference. The guidelines discussed above are clear: nonremovable off-loading is the gold standard. But Wu et al 76 found that 41% of 895 U.S. clinics responding to a survey attempted to off-load patients with shoes, whereas 2% used TCCs. Similarly, Fife et al 77 reported only 6% of ulcer patients received a TCC. However, among those patients who received it, the average cost of treatment was half as much as the cost incurred by patients who did not. In Europe, the situation is not markedly different. Prompers et al 78 found that an average of only 35% (range 0%-68%) of plantar foot ulcers were treated with casting in 14 specialized centers across the continent. A large discrepancy exists between guidelines and clinical practice in off-loading diabetic foot ulcers. How can this gap between recommendations and practice be bridged? One solution would be for professional societies to help change the expectations among their

5 JOURNAL OF VASCULAR SURGERY Volume 52, Number 12S Cavanagh and Bus 41S members regarding the time that diabetic foot ulcers take to heal. Societies such as the American Podiatric Medical Association and the Society for Vascular Surgery could also formally adopt the international guidelines, 74 which are presently not well known in the United States. Such lack of guidelines leads to heterogeneity of treatment that does not benefit the patient. Many providers resist guidelines because, as they correctly point out, every patient is unique and many additional intrinsic and extrinsic factors such as technical difficulty, time of application, cost-effectiveness, and reimbursement issues affect the choice of treatment. We believe that poor off-loading is poor treatment, regardless of the constellation of other factors that must be considered. Previous recommendations may have been too general, but recent evidence-based guidelines are specific and support implementation. In addition, in the same way that decubitus ulcers, hip fractures, and six other reasonably preventable conditions that occur after admission to the hospital are not reimbursed in the United States by Medicare, the future may bring a similar change in the burden of financial responsibility for what have traditionally been called nonhealing neuropathic ulcers. Many ulcers are indeed complicated by such factors as infection and vascular disease, 79,80 and the same expectations for time to heal cannot be applied to infected neuroischemic wounds. But off-loading is still important in such complex wounds perhaps even more important because of the enhanced risk of limb loss in these patients. An additional barrier to appropriate prescription may be that some practitioners are not trained to specify appropriate footwear interventions and may resist referring patients to qualified specialists. Establishing a good relationship with qualified providers of therapeutic footwear and orthotic interventions is an important component of comprehensive care for the diabetic foot. If a provider does not have such expertise in-house, then locating a qualified individual, perhaps with the help of specialized societies (such as the Pedorthic Footwear Association in the United States, should be considered. Another major advance for off-loading the diabetic foot for ulcer prevention and healing would be a requirement that measurable and effective pressure reduction should result from all prescribed interventions and that preferably such pressure reduction be optimal (see Fig 1). Requirements for demonstrated efficacy have recently been introduced in Germany. This will not be possible at every treatment location because of cost, but specialized centers should consider adding the capability for pressure measurement to their prescription approach. Current clinical practice includes several modalities for healing diabetic foot ulcers that may be effective, although no evidence base for their use now exists. We strongly urge clinicians and researchers to prove the effectiveness of these devices to support their use in clinical practice. Documented pressure reduction is, of course, necessary but not sufficient for healing or preventing foot ulcers. Approaches that force adherence to off-loading in ulcer treatment by the application of some nonremovable device must be given consideration in all cases where there is no contraindication. Considerations for preventing ulcer recurrence are somewhat different, although no less important. Ulcer-free survival is poor, 15 and a major challenge that needs to be faced is a reduction of the number of ulcer recurrences. Nonremovable devices cannot be used, and a behavioral intervention combined with footwear that effectively off-loads previously injured regions is required. Unfortunately, effective strategies to increase adherence have not yet been well established. The provider can increase the chance that the interventions will be used by providing attractive footwear and by accepting the fact that outdoor therapeutic shoes (the typical prescription) are unlikely to be worn at home. The provision of off-loading sandals or slippers may reduce barefoot walking at home, but currently it is likely the patient will have to bear the cost of the additional footwear. If future studies can show a reduction in reulceration when multiple types of footwear are dispensed, this would be a powerful rationale to petition for change in reimbursement policies. Currently, Medicare allows only one pair of shoes and three pairs of insoles per calendar year, and insurance companies in Europe generally do not reimburse multiple types of footwear in the same calendar year. CONCLUSION We have presented the evidence for the role of offloading in the prevention and treatment of plantar ulcers in the diabetic foot. We point out that there is a gap between evidence-based guidelines and current practice, particularly regarding the use of nonremovable off-loading devices to heal uncomplicated neuropathic ulcers. A number of strategies are proposed to address this gap, notably the adoption and implementation of recently established evidence-based and specific international guidelines by professional societies in the United States and Europe. Such an approach would change the current poor expectations for healing of diabetic plantar ulcers. REFERENCES 1. van der Leeden M, Steultjens MP, Terwee CB, Rosenbaum D, Turner D, Woodburn J, et al. A systematic review of instruments measuring foot function, foot pain, and foot-related disability in patients with rheumatoid arthritis. Arthritis Rheum 2008;59: Sosenko JM. 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