September 2012

Rethinking device design to improve compliance

Reducing the shaft height of a removable cast walker, which results in a lighter device and may also help improve postural stability, can help improve compliance in patients at risk for diabetic foot ulcers without compromising the device’s offloading capability.

By Sai Vikas Yalla, PhD, and Ryan T. Crews, MS, CCRP

Offloading is a technique used to reduce plantar pressure. It is a key component of treatment for diabetic foot ulceration.1-3 Conservative care for diabetic ulceration generally starts with external offloading designed to either prohibit loading of the foot or shift plantar pressure during gait from the wound area to an unaffected area.4 Offloading techniques are based on the ambulation needs of patients with diabetic ulcers and range from bed rest, wheelchairs, total contact casts, removable cast walkers, crutches, canes, in-shoe and ankle foot orthoses, and therapeutic shoes.2,5 The higher the reductions in plantar pressure at the site of ulceration, the greater the chances for successful healing.5-7

Patient ambulation

According to the US Census Bureau’s population projections for 1995 to 2025, an estimated 10,000 people reach age 65 each day.8 Researchers have observed that ambulation in older adults ranges from 2000 to 9000 steps per day9 and that older diabetic patients who are at risk of developing ulceration from diabetic peripheral neuropathy happen to be on the higher end of ambulation, about 9000 steps per day.9 Hence, neuropathic patients who tend to walk more than their similarly aged peers also end up needing to offload their feet. Bed rest and wheelchairs can provide total offloading, but are too restrictive for independent ambulatory patients. In-shoe orthoses, ankle foot orthoses, and therapeutic shoes allow greater ambulation with minimal restriction, but have relatively low (16%-52%) offloading capacity compared with a control condition (canvas shoes with flat rubber insoles)7 and are more suitable for ulcer prevention than treatment7,10,11 (Figure 1).

Figure 1. Various offloading techniques and their impact on ambulation.

The best balance between patient ambulation and offloading is generally considered either removable cast walkers (RCWs) or total contact casts (TCCs). These devices allow ambulation while providing offloading between 64% to 92% compared with canvas rubber insole shoes.7,12 Armstrong et al13 compared TCCs to RCWs and half shoes and found significant wound healing in a shorter time when patients wore TCCs compared with RCWs and half shoes. The study also found a reduction in patient activity for TCCs compared with RCWs and half shoes. The main difference between TCCs and RCWs is a patient’s ability to remove the RCW at their own discretion. Unfortunately, the peripheral neuropathy that contributes to formation of diabetic foot ulcers also negates what would typically be a large incentive for patients to consistently wear their RCWs. The peripheral neuropathy results in a loss of protective sensation to the foot (or the “gift” of pain, in the words of physician and author Paul Brand, MD) so that patients do not feel any discomfort when walking directly on their wounds. RCWs are removable and provide convenience, allowing patients to take them off for sleeping or dressing changes, but, not surprisingly, compliance is more difficult to enforce; in contrast, TCCs prohibit patient removal and force continual compliance.

Comfort and compliance

Despite findings that the best ulcer healing outcomes are accomplished with TCCs,5 they are not commonly used by practitioners.16 The comfort and ease of application associated with RCWs, both for the patient and the practitioner, make RCWs the more commonly prescribed offloading footwear in ulcer treatment and might also make them more acceptable for current and future diabetic populations. Studies have shown that RCWs provide levels of plantar pressure reduction that are similar to those of TCCs,17,18 though an increase in wound healing times has also been observed.13 The key contributor to the increased times needed for healing was compliance issues with RCWs among ambulatory patients.

Assessing compliance in patients is generally done through questionnaires and interviews. In-person interviews and survey analysis of 52 subjects wearing prescribed footwear revealed that only 22% of all patients reported wearing their prescribed footwear all day.6 The major concerns of patients that resulted low compliance were appearance, comfort, cost, and ignorance of the benefits.6 A similar study19 of 161 patients found that only 28% wore their prescribed diabetic footwear more than 80% of the day. Appearance, comfort, and ignorance of benefits were the main factors for low compliance in that study. Reported compliance levels are low, but the real figures may be even worse. Accuracy of self-reported compliance data is highly questionable, as highlighted by Knowles et al,6 who reported that one patient provided survey responses indicating that they wore their prescribed footwear all the time, yet the same patient was not wearing the prescribed footwear while answering the questionnaire.

Compliance monitoring

The lack of pain associated with diabetic foot ulcers can build a mental confidence that one’s ulcerated feet are safe from injury, especially when patients are at home. This false sense of safety in household settings results in reduced compliance that is independent of the reduced compliance associated with the appearance and comfort of offloading devices.

Researchers have developed ways to objectively monitor  compliance with offloading in the natural environment through the use of accelerometer-based activity monitors20 as well as with in-shoe thermal sensors.21 These methods have been shown to reliably and objectively track patient compliance during activity, thereby eliminating patient recall and bias errors that may occur if compliance monitoring is dependent upon patient self reports.

Armstrong et al, for example, used the accelerometer-based activity monitor technique to assess compliance among patients with neuropathic diabetic ulcers who wore RCWs.22 They found patients wore their RCWs for only about 28% of their total daily activities. Even the subpopulation of patients who recorded a majority of daily activity with their RCWs on wore them for only 60% of their total activity. Among patients with diabetes, comfort, lack of know­ledge, and appearance seem to play a significant role in level of compliance with offloading footwear.6,19,23

Design modifications

The primary focus of designers is producing devices that maximize offloading, and consequently limited attention has been given to design features that may make devices more tolerable to patients. If compliance is to be increased, however, RCW design needs to take into account not only the offloading of a wound, but also how these devices affect patients’ general physical functioning.

RCWs, like TCCs, are traditionally cumbersome to walk in. Diminished plantar sensation, ulceration, and medications can all negatively affect postural stability during gait in diabetic patients with peripheral neuropathy.24 Adding footwear that is difficult to walk in might further decrease postural stability, affecting a patient’s willingness to comply, yet postural stability is often overlooked when making design modifications.

Van Deursen25 found that offloading devices negatively affect static and dynamic balance. Compared with TCCs, RCWs were found to have slightly better postural stability.26 Considering that peripheral neuropathy puts individuals at risk of falls27 and that individuals with diabetic foot ulcers have been shown to have an even poorer balance than individuals with diabetic neuropathy alone,28 it should come as no surprise that diabetic ulcer patients are reluctant to wear RCWs that will further compromise their balance.

Figure 2. The knee-high, ankle-high, and shoe-high RCWs and a standard athletic shoe and the resultant walking peak plantar pressures on the right foot of the same patient in 3D graphs (the heel is presented at the top of the 3D graphs and the toes at the bottom).

Researchers have observed that the gait initiation phase that constitutes the first few steps to reach the habitual speed of walking is risky for patients with poor postural stability.29 Given that the majority of steps for patients at high risk of diabetic foot ulcers are taken at home,30 there must be many cycles of short walking periods and hence many gait initiations for this population. This further highlights the need to minimize the compromising of balance by offloading devices.

Offloading devices also commonly create limb length discrep­ancies that, in addition to reducing postural stability, might also result in a higher risk of ulceration on the shorter leg.31 Care providers should consider means of mitigating this length discrepancy. Lastly, the weight of the offloading footwear might also influence postural stability, and attempts should be made to minimize the weight of future RCW designs.

Strut height

RCWs are typically bulky, heavy devices that patients generally find uncomfortable.  Traditionally, RCWs have been constructed with struts or casings that extend up to the knee similar to a TCC. A 2012 study by Crews et al sought to determine whether shorter, lighter offloading devices could be utilized without compromising offloading functionality.32 Ankle-high RCWs (walkers that extend only a little above the malleoli), are utilized for a variety of conditions such as injured or weak ankles but rarely for offloading diabetic foot ulcers. This study compared a standard RCW that extended up to the knee to an ankle-high RCW and a shoe-high RCW (Figure 2) in 11 patients with type 1 or 2 diabetes mellitus at moderate to high risk for foot ulceration.

While different offloading modalities were compared in an earlier study,12 this was the first study to compare variation of strut heights. The shoe-high RCW provided no struts extending up the ankle, therefore the foot was allowed to plantar flex and dorsiflex while in the device. All three of the RCWs featured the same rocker bottom outer sole and offloading insole. The only difference between them was the extent to which they extended up the leg. Subjects were given one to two minutes to become accustomed to each RCW and plantar pressure data were collected during a 20-m walking trial.

As shown in Figure  2, the 2012 study showed the loading stress was significantly reduced at the forefoot while walking in the knee-high and ankle-high RCWs compared with a standard athletic shoe. While the area colored in black represents a low pressure of 15 kPa, dark blue, light blue, green, yellow, red, and pink represent increasing levels of pressure up to 150 kPa. Overall, the study results showed the ankle-high RCW and the knee-high RCW provided similar offloading. The shoe RCW, however, could not achieve the same levels of offloading. Mean peak pressure reduced 61% under the hallux in patients wearing a knee-high RCW compared with the athletic shoe. On the other hand, a similarly high 54% reduction of mean peak pressure under the hallux was observed while patients wore an ankle-high RCW.

The study results show that inclusion of a strut did play a role in effective offloading. This was most likely attributable to the associated locking of the ankle joint, which prohibited normal heel-to-toe progression during gait. Practitioners should consider recom­mending an ankle-high RCW, which has a similar offloading capacity but a smaller size and weight than the knee high RCW, as it may improve compliance without compromising offloading performance. Although only a nonsignificant trend was observed in this initial study, the results also suggested the ankle-high RCW may provide less of a compromise to postural stability than the knee-high RCW.

Postural stability

Another aspect affecting compliance that is mostly overlooked is the postural stability of the patients while wearing prescribed footwear. Van Deursen25 found that offloading devices negatively affect static and dynamic balance. Compared with TCCs, RCWs were found to confer slightly better postural stability.26 Considering that peripheral neuropathy puts individuals at risk of falls27 and that patients with diabetic foot ulcers have been shown to have even poorer balance than individuals with diabetic neuropathy alone,28 it is not surprising that patients with these wounds are reluctant to wear RCWs that will further compromise their balance.

Utilizing technology

If patients could feel more comfortable and stable while wearing offloading footwear, it seems likely that compliance would increase. New devices are routinely developed in the hopes of better offloading of diabetic foot ulcers, but patient compliance with these devices is rarely measured. Utilizing the latest techniques in monitoring adherence, the impact of modified RCW designs on compliance should be measureable. Monitoring patient compliance also helps generate new techniques for reminding the patient to wear the prescribed footwear. Manufacturers should focus on creating RCWs that look like normal footwear and could use technologies such as wireless transmission and radio frequency identification31 to monitor and alert the patient through cell phones or watches that the technology has not detected patient use of prescribed footwear.

Simply reminding patients to wear their prescribed footwear is not enough—clinicians also need to educate them about the importance of offloading. Using the latest medium of communication, the Center for Lower Extremity Ambulatory Research in North Chicago, IL, has recently published a YouTube video titled “A patient’s guide to understanding offloading treatment for diabetic foot ulcers” (www.youtube.com/watch?v=XRolebcoL2g), which explains the science behind offloading and why continual compliance is necessary. Educating the patient might not only improve wound healing, but it may also aid in preventing ulcer recurrence. Thus, combining modified device designs with education might be the key to improving compliance.

Summary

There is a steady increase in the population of ambulatory diabetic patients with neuropathy,34,35 which in turn increases the risk of ulceration. This creates a growing need for offloading footwear, not only to heal ulcerations, but also to avoid ulcer recurrence. Of the offloading techniques utilized to heal diabetic foot ulcers RCWs seem to strike the best balance between ambulation and comfort. However, poor compliance with RCW wear has been observed. Research suggests that better appearance, reduced weight, and limiting the impact on balance might be the design modifications needed for improved patient compliance with RCWs.

Educating the patient regarding the science behind offloading and the negative effects of poor compliance might also help improve adherence with prescribed footwear. Using the latest technologies to create a foolproof compliance monitoring system that reminds individuals to wear their offloading footwear could help further improve compliance.

Sai Vikas Yalla, PhD, is a lecturer and research fellow and Ryan T. Crews, MS, CCRP, is a clinical research scientist and operations manager at the Center for Lower Extremity Ambulatory Research (CLEAR), Dr. William M. Scholl College of Podiatric Medicine, Rosalind Franklin University of Medicine and Science, in North Chicago, IL.

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