Effect of different casting design characteristics on offloading the diabetic foot

Highlights

• The TCC gives superior offloading for plantar diabetic foot ulcers.

• This offloading results from its optimal shaft effect.

• A removable TCC is inferior compared to a non-removable TCC.

• The superior offloading effect of the TCC comes at some walking comfort expense.

• The TCC is the first treatment option for neuropathic plantar diabetic foot ulcers.

Abstract

Background

Non-removable knee-high devices, such as a total contact cast (TCC), are recommended for offloading diabetic plantar forefoot ulcers. However, it is insufficiently known how each of the different design characteristics of these devices contribute to offloading the diabetic foot.

Research question

What is the offloading effect of the different design characteristics that make up a non-removable knee-high cast for people with diabetes and active or previous plantar forefoot ulcers?

Methods

Sixteen persons with diabetes, peripheral neuropathy and a healed or active plantar forefoot ulcer had their plantar pressures measured during walking in a non-removable knee-high device (TCC), in that device made removable (BTCC), in that device made below-ankle (cast shoe), in that cast shoe worn with a different walking sole and in a newly made cast shoe without a custom-moulded foot-device interface. Peak pressures, force-time integral, and perceived walking comfort were assessed.

Results

Compared with the BTCC, peak pressures in the TCC were 47% (P = 0.028), 26% (P = 0.003) and 15% (P = 0.050) lower at the hallux, midfoot and (previous) ulcer location, respectively. Compared to the cast shoe, peak pressures in the BTCC were 39–43% and 47% (both P < 0.001) lower in the forefoot regions and (previous) ulcer location, respectively. The total force-time integral was 21% and 11% (P < 0.007) lower in the TCC and BTCC compared to the cast shoe. Perceived walking comfort was 5.6 in the TCC and 6.5 in the BTCC (P = 0.037). Effects of the other design characteristics (i.e. walking sole and plantar moulding) were non-significant.

Significance

The TCC gives superior offloading, mostly because of being a knee-high and non-removable device, providing an optimal ‘shaft effect’. The TCC does, however, negatively affect walking comfort. These results aid decision-making in offloading diabetic plantar forefoot ulcers.

Introduction

Among people with diabetes mellitus and peripheral neuropathy, foot ulcers are a serious and debilitating long term complication that significantly increases the risk of infection, hospitalization and lower limb amputation [1]. Yearly incidence of developing a foot ulcer in diabetic patients is 2–4%, and lifelong incidence 19–34% [2]. Most ulcers occur on the plantar side of the foot, in the forefoot and toe regions [3]. In the presence of neuropathy, elevated plantar pressure is one of the most important risk factors for foot ulcer formation and maintenance [4,5].

Offloading areas of high plantar pressure is a cornerstone of treating plantar diabetic foot ulcers, and is achieved by redistributing plantar pressure to other areas [4,[6], [7], [8], [9]]. Different devices are available for ulcer offloading, such as a total contact cast (TCC), a knee-high walker or specially designed shoes [10]. International guidelines recommend the use of non-removable knee-high devices as first option of treatment [1,10], as meta-analyses and health technology assessment shows that these devices have higher healing rates than other devices [4,6,8,9]. Removable devices and special shoes are only recommended when non-removable knee-high devices are contraindicated or not tolerated by the patient [10]. However, these latter do represent ‘standard of care’ in offloading plantar foot ulcers, as non-removable devices are underused in clinical practice [3,[11], [12], [13], [14], [15]].

The design characteristics differ between these devices: e.g. knee-high vs. ankle-high, non-removable vs. removable, and custom-made vs. prefabricated. Furthermore, the plantar foot-device interface can be individualized, and different walking soles can be attached to the device. While healing outcomes of these devices have been widely studied [4,6,8,9], these different design characteristics all contribute to the offloading effect of such a device. However, the (relative) contribution of these design characteristics on offloading itself is insufficiently studied. Knee-high devices are more effective in reducing plantar pressure than below-the-ankle devices, mostly because the shaft of a knee-high device can pick up a significant portion of the load on the lower-extremity [[16], [17], [18]]. The knee-high devices in these studies were either removable or non-removable [[16], [17], [18]], and it can be questioned whether the removability influences the offloading capacity. Furthermore, other design characteristics mentioned have not been investigated in a controlled study setting. Such an investigation is needed, to better understand the design characteristics, to drive the development of standardized casting protocols, and to improve clinical decision-making in the offloading treatment of diabetic plantar forefoot ulcers.

The aim of this study was to investigate the offloading effect of the different design characteristics that make up a non-removable knee-high cast for people with diabetes and active or previous plantar forefoot ulcers. We hypothesized that the total contact shaft portion of the knee-high cast, its non-removability, the custom-moulding of the foot-device interface, and the type of walking sole attached, all significantly contribute to the offloading effect.