The aim of this study was to evaluate the capacity of the DH Pressure Relief Shoe™ to offload high pressure areas under the neuropathic foot in diabetes. The DH Pressure-relief Shoe™ was selected for investigation in this study as it is currently being marketed and used for offloading plantar foot ulceration in diabetes. To the authors’ knowledge, there has been no independent research that has previously investigated the capacity of the DH Pressure Relief Shoe™ to reduce pressure. In contrast, the DH Pressure Walker™, Royce Medical (now the Active Offloading Walker™, Ossur, CA) a related product in a below-knee walker style, has been investigated previously
[18, 19]. The DH Pressure Relief Shoe™ is a less bulky version of the DH Pressure Walker™. It is also light, easy to fit and use, and is cost effective at around AUS $100 per unit. Of particular interest is the insole design in the DH Pressure Relief Shoe™, which allows for customisation of offloading by the selective removal of the hexagonal-shaped plugs over high pressure sites. The DH Pressure Relief Shoe™ is designed as a removable intervention and while in some clinical circumstances this might be preferable, research has shown non-removable offloading to be associated with superior healing rates
In this study the DH Pressure Relief Shoe™ was shown to reduce mean peak plantar pressure by 117.7 kPa when compared to standard shoes and 160.5 kPa when compared to canvas shoes. This equates to a 43% and 50% reduction respectively, which is comparable in magnitude to studies using specific types of padding and insoles
[21, 22]. While there is no established pressure cut-off point or threshold above which ulceration will occur, a relationship has been shown to exist whereby the greater the pressure the higher the ulcer risk
. With this in mind, we believe that this amount of pressure reduction is clinically important. We powered our study to detect a 100 kPa reduction (or difference between shoes) and the amount of reduction offered by the DH Pressure Relief Shoe™ was well above this. Therefore, the removable plug design insole that is integral to the DH Pressure Relief Shoe™ shows promise for offloading focal plantar pressure. Accordingly, this device may be useful for the treatment of neuropathic ulcers, in the event that these results carry over into trials that use healing as a primary outcome.
It is important to note that the investigators in this project had some concerns about the fixation of the DH shoe in its current form and the stability of some participants while walking. In two cases the ankle straps did not sit flat, which may potentially cause rubbing and irritation to the skin. In another case the medial heel counter was pushed down substantially during gait due to the high degree of rigid foot deformity, rendering the shoe too unstable to be worn during extended periods of walking. Suitability of this device as an offloading modality for some participants was questioned, particularly when dealing with a sub-population known to be at risk of falls. In addition, the aesthetics of the device may be a limitation to its acceptance by some patients. Therefore, the DH Pressure Relief Shoe™ may be a useful alternative to current off-loading modalities but further clinical trials are warranted to determine its safety in everyday activities and relative contraindications.
Several possible explanations exist as to why peak pressures were substantially reduced by the DH Pressure Relief Shoe™. Due to the relatively thick and cushioning make-up of the DH Pressure Relief Shoe™ insoles, it is likely that the plantar surface of the foot sinks into the materials to redistribute force. This, in combination with the removal of the plugs over pressure sites, may explain the levels of offloading recorded. We also found a statistically significant difference in whole foot contact area where the DH Pressure Relief Shoe™ had a 9% greater contact area than the canvas shoe. However, this result did not extend to differences in contact area between the DH Pressure Relief Shoe™ and standard shoe.
Interestingly, peak pressure values in the patients’ own shoes (i.e. the standard shoe condition) did not differ statistically from the canvas control shoe. This finding is consistent with the 2007 evidence-based guidelines of the International Working Group on the Diabetic Foot, which recommend that standard or therapeutic footwear alone should not be used for offloading during ulcer treatment as better modalities are available
. It should be noted, however, that the participant’s own shoes were included only to allow comparison of plantar pressures experienced in routinely worn footwear with the DH Shoe. It was not the intention of this study to evaluate footwear as an alternative offloading device.
Our findings should be interpreted in light of the study limitations. Firstly, we measured peak pressure, not healing, as a primary outcome measure and results cannot be directly extrapolated. Pertinent issues that effect healing, such as compliance, functional effectiveness of the device and health-related quality of life, would not be borne out by this study design. Secondly, the study was not designed as a randomised controlled trial, it was an initial exploration of the effects of the DH Pressure Relief Shoe™ on plantar pressure. A larger, high-quality randomised trial with a comparison group is now needed to evaluate the effectiveness of the DH Pressure Relief Shoe™ on ulcer healing. Finally, despite the pedar® system being valid and reliable, it only measures forces acting vertical to the pedar® insole and it is likely that the forces that shoes exert against the plantar surface of the foot are more complex in nature. As the pressure-mapping insoles had to contour the inside of each shoe condition tested, rather than lie flat, they only record resultant force
[23, 24]. As such, the shear component of such forces are not recorded and some inherent measurement errors are likely to occur