It is well known and documented that foot ulceration is perhaps the most common and serious long-term complication of diabetes. Within the UK, patients with diabetes should be seen on an annual basis for a diabetes review. As part of this process, feet ought to be screened and stratified for ulceration risk using well-determined risk factors. Prevention is paramount given that published data suggest that up to 25–90% of lower-extremity diabetes-related amputations are preceded by foot ulcers (Pecoraro et al, 1990; Global Lower Extremity Amputation Study Group, 2000). Determining ulcer risk is clearly important, however, the implementation of individualised prevention strategies is pivotal, if success is to be achieved. The focus of this article, is to discuss the role of offloading in preventing the first ulcer and/or relapse.
As the published evidence for offloading and ulcer prevention is meagre, a review of such would not be very helpful. Therefore, this article will provide a practical and clinical view of the way in which offloading can be beneficial in ulcer prevention. The overriding caveat is that prevention is only successful when it is implemented and regularly reviewed by both practitioners and patients alike.
As stated above, the first steps in ulceration prevention are identifying those who are at risk and then stratifying ulcer risk for each patient. The next stage is facilitating access to differing levels of diabetic foot-care commensurate with an individuals’ risk. For those at medium to high risk, the keys to success in preventing a foot ulcer is two-fold. Firstly, clinicians should equip patients and/or their carers with repeated, clear, simple, targeted and tangible education. Secondly, the patient should be offered an adequate, specialised, well-organised and easy accessible service with a dedicated diabetic foot care team. Staff within these should be enabled to recognise the very early subtle signs of tissue damage, identify their causes and implement directed interventions. Obviously, tissue damage can occur at any time during activity periods or, in the case of pressure sores, during protracted rest. Thus, educating patients to recognise and respond to ulceration danger signs and symptoms together with how/when to access services is vital if prevention is to be achieved.
Before exploring the different preventative offloading modalities and their implementation, it is wise to firstly consider two fundamental topics:
- The mechanism of ulceration
- What do we mean by “offloading”?
It is important that clinicians take a step back and consider what processes are involved in developing a diabetic foot ulcer. Unless these processes are clearly understood from a clinical perspective, ulcer prevention will most likely only be achieved by chance. It is essential to translate classroom-taught theory into clinical practice. Additionally, to understand or conceptualise the interactions and reactions of normal/altered physiology and pathomechanics. To illustrate this thought process, consider one aspect of what happens to soft tissues under the third metatarsal head in a normal foot during walking. The tissues in this area should be considered as they are about to be fully loaded.
In Figure 1, some of the forces that are applied to the metatarsal head during gait are displayed. The reader should consider and try to visualise the magnitude, duration, velocity and direction of these, as they will change throughout this localised loading cycle. Figure 2 shows a very simplified view of some of the soft tissue reaction to full loading. As the foot moves forward, the footwear and ground moves back. With this in mind, picture rotational shear and compressive forces applied to the tissues, not just directly under, but also surrounding the metatarsal head. Now add in the frictional force applied over these stretched, twisted and squashed tissues. Lastly, consider the components of time, velocity, magnitude of internal/external loading and changing direction of these forces.
Normal healthy soft tissues are able to withstand this assault predominately due to their visco-elastic nature. The blood vessels are also able to accommodate these effects without rupturing. Of course, if the nature or magnitude of these become too much, neural responses are evoked, i.e. pain and soreness leading to alterations in gait, whereby offloading and, thus, protection of the tissue prevents tissue damage.
Apply the above to a person with diabetes, then add peripheral neuropathy and impaired blood flow. Below are some points for consideration regarding the effects upon soft tissue mechanics. These are very important, with some more subtle than others, but resultant tissue failure is often manifested and observed in the skin. The authors believe that addressing these effectively is integral in preventing the progression of pre-ulcers to ulceration:
- Glycation of soft tissues — stiffer with loss of visco-elasticity
- Altered rheology (blood flow dynamics)
- Stiffer, less elastic or more fragile blood vessel walls
- Loss of protective sensation and or proprioception
- Altered muscular/articular mechanics
- Diminished/absent skin hydration
- Reduced or increased inflammatory responses.
The above list details the components in the pathway to tissue damage and potential ulceration. Understanding each component and their influence upon each other and their relation to tissue damage is essential to help drive successful preventative interventions. Thus, simply arranging regular follow-up visits with a podiatrist to reduce plantar callus formation in a patient with peripheral neuropathy should be considered suboptimal ulcer prevention.
Ulcer relapse considerations
Definition: ulcer relapse is a second or subsequent ulcer occurring at a previous ulcer site.
It is well documented that the highest risk factor for ulceration is a previous ulcer. The literature cited ulcer recurrence/relapse as high as 30–40% within 12 months (Pound et al, 2013; Bus et al, 2013), as opposed to an annual incidence of 7.5% for first ulcers in patients with neuropathy (Abbott et al, 2002). There are reasons why ulcer relapse rates are higher than for new ulcers and identifying these is paramount if prevention is to be achieved. Several causes for ulcer relapse that have been suggested, including inadequately addressed existing first ulcer aetiologies, e.g. neuropathy, deformity, high plantar pressures, etc. or, delays in providing prescribed footwear (Bus and van Netten, 2016). Additionally, the failure of healthcare professionals to provide recommended treatment, including foot care, therapeutic footwear, and patient education (Lavery et al, 2010), patients not following foot care advice or wearing prescribed shoes (Waaijman et al, 2013).
However, while these causes are credible, it is the authors view that perhaps the most important reason for ulcer relapse is being overlooked. As stated above, non-ulcerated foot soft tissues are visco-elastic and have very specifically biomechanical properties designed to accommodate walking and standing. However, scar tissue at a healed ulcer site is fairly rigid with dramatically altered soft tissue mechanics in this and surrounding tissues. In short, the repaired tissue is even less able to withstand the forces that caused the original ulcer. Moreover, each subsequent time an ulcer relapses and repairs, it becomes less and less able to withstand them, thus leading to high ulcer relapse rates.
It is even more important to appreciate the forces applied to the foot when considering offloading strategies to prevent ulcer relapse. Focusing resources upon these may prove successful, however, little data are available to substantiate this approach.
“Offloading”: what do we mean?
The term “offloading” is principally one that is associated with foot ulcer management or pressure sore treatment/prevention. The main method in ulcer management is to immobilise the foot and ankle by use of either casts or removable walker boots. However, this is not practical in ulcer prevention strategies as this approach dramatically curtails everyday activities including employment. Thus, offloading in the prevention of first ulcers or their relapse would be better described as “lesion preventative force management”. The principal is similar in one broad respect, i.e. to relieve tissue damaging forces applied to the foot whereby preventing tissue damage.
Offloading interventions and practices are used worldwide in many different settings. Some have been studied, including foot screening, treatment of pre-signs of foot ulceration, footwear advice, and foot-care education, these are reported in the the International Working Group on the Diabetic Foot (IWGDF) Guidance on Prevention (Bus et al, 2016). However, the use of these interventions is based on low quality of evidence or expert opinion rather than good quality research evidence.
There have been several prospective studies that have shown that therapeutic footwear compared with standard footwear can help prevent ulcer relapse (Uccioli et al, 1995; Litzelman et al, 1997; Dargis et al, 1999; Viswanathan et al, 2004).
The rationale for providing a protective environment for feet in order to prevent new ulcer occurrence makes perfect sense, but the body of evidence to support this is currently poor. It is confounded by the fact that most studies combine new and recurrent ulcers in their study populations. One study provided intensive footwear therapy versus standard care with footcare advice, but no prescribed shoes. This showed an incidence of foot ulceration of 11.5%, 17.6% and 23.5% at 1,3 and 5 years respectively in the intensive footwear therapy group, compared with 38.6%, 61% and 72% for 1, 3 and 5 years in the group that was not prescribed shoes. One fifth of the cohort had a history of ulceration (Rizzo et al, 2012). A small cohort study found no difference in ulcer occurrence between those wearing prescribed shoes versus those who wore their own (Reike et al, 1997). However, another study comparing prescribed shoes group versus a normal shoe group showed an ulcer recurrence rates of 15% versus 62% respectively over 2 years (Busch and Chantelau, 2003).
Thus, from a few selected studies it is clear to see the discrepancies, which are probably due to study bias and poor study design. Equally, it is difficult to identify from the literature what the most effective features of a shoe and/or foot orthosis design are. Some features including rocker-bottom soles, custom-made insoles and some shoe inserts (e.g. metatarsal pads and medial arch supports) may reduce forefoot peak pressure between 16% and 52% compared with controls (Schaff and Cavanagh, 1990; Lord and Hosein, 1994; van Schie et al, 2000; Praet and Louwerens, 2003; Bus et al, 2004; Beuker et al, 2005; Guldemond et al, 2007). The design of foot orthoses, including the choice and combination of materials, requires considerable thought. In addition, regarding therapeutic shoes, determining the placement, size and angle of rocker sole is critical. When reflective consideration is given to these factors together, ulcer prevention is achievable. However these decisions in reality are more guided by clinical experience of preference than available robust research evidence. Incorrectly designed footwear can increase ulcer risk rather than reduce it.
The evidence base for footwear in the prevention of new and relapse ulcers is very useful even if the quality of this research is poor (Bus et al, 2008). Arguably, however, even if the current research quality was good, it is only partly useful. Patients are mainly older and weight-bearing activity occurs mainly indoors. Several articles also point to this; existing activity data of ulcer patients show they are less active than non-ulcer patients (Armstrong et al, 2001; Maluf and Mueller, 2003) and spend more time indoors (Armstrong et al, 2001). Regarding prescribed footwear, the authors’ experience has been that many patients will not wear their prescribed shoes or special insoles while indoors, preferring to wear slippers or nothing instead. This is another reason why ulcer relapse rates may be so high.
Callus formation is the skins protective response to abnormal and potentially harmful applied force. Excessive callus formation in patients with sensory loss has been shown to be an ulcer risk factor and its reduction can cut plantar pressures by up to 30%, although the durability of such relief is unknown (Young et al, 1992; Pitei et al, 1999). Providing silicone digital orthoses, soft insoles, debridement and extra depth footwear demonstrated a reduction in ulcer rates, but also callus growth compared with control groups (standard care comrpised of debridement, extra depth shoes and a flat cushioning insole) of 1.1% and 15.4% for ulcers and 51% versus 84% callus suggesting intervention benefit (Scire et al, 2009). It cannot be overemphasised that regular reduction of plantar callus is essential, however, understanding and addressing its causes needs equal attention.
One recent study showed that adding semi-compressed felt to footwear to offload high-risk sites on the foot reduced peak pressure by 50% immediately and after one week there was still a 33% reduction (Raspovic et al, 2016). This technique, which has been used in podiatry for many years, is perhaps useful as a quick temporary method of offloading. Its effect is shown in Figures 3,4 and 5.
The use of infrared thermometers to measure skin temperatures on a daily basis to identify hot spots followed by periods of rest has been studied. This has been shown to be of benefit in helping to prevent foot ulceration (Armstrong et al, 2007; Lavery et al, 2004; 2007). This patient-mediated reactive offloading may be very useful as part of an ulcer relapse prevention programme it can be implemented and sustained by patients.
Soft tissue augmentation
As already stated, once an ulcer has healed, the resultant scar tissue is functionally unable to deal with the damaging forces that caused the initial ulcer. Thus, any modality that can restore, mimic or, better still, enhance the original soft tissue function would be perhaps the most effective way of preventing ulcer relapse. The use of injected liquid silicone has been used to achieve this with some success, but more investigations are required in this field (van Schie et al, 2002).
The authors of a recent Cochrane review stated that it appears there is little evidence available to support the effectiveness of patient education for ulcer and amputation prevention (Dorresteijn et al, 2010). While this is disappointing, it is not surprising, especially in light of a recent study by Natovich (2016) that showed cognitive impairment in those with neuropathic foot ulcers suggesting an inability to learn or apply health education as it is currently delivered. Empowering patients with not only understanding, but also necessary skills to identify and react to tissue damage, is fundamental if prevention strategies are to be successful.
Another approach for offloading is to remove or alter any bony prominences over ulceration sites or reduce soft tissue restrictions in selected patients. Achilles tendon lengthening, single or pan-metatarsal head resection and metatarsophalangeal joint arthroplasty in patients with previously recalcitrant ulcers seem to reduce ulcer relapse compared with non-surgical treatment (Piaggesi et al, 1998; van Schie et al, 2002; Armstrong et al, 2003; 2005; 2012; Mueller et al, 2003; Dorresteijn et al, 2010; Natovich et al, 2016;). Additionally, osteotomies may also reduce ulcer relapse (Downs and Jacobs, 1982; Lin et al, 2000). However, consideration must be given to surgically induced altered foot mechanics. If force is removed or reduced from one area it must be relocated elsewhere.
In conclusion, offloading or force management used for the prevention of first and relapse ulcers makes perfect sense, however it is difficult to draw any clear directions from the research evidence base. This is in part due to a lack of well-designed prevention studies solely dedicated about this topic. Despite this “offloading” is an important facet of care in preventing diabetic foot ulcers. It is only really effective when underlying aetiological pathways of tissue failure are understood as this can be used in formulating offloading strategies and modalities. In this area, as well as in all diabetic foot management integrated team work is essential to achieve successful outcomes.