Introduction

Offloading devices are commonly used to facilitate wound healing in the diabetic foot. These devices work on the principle of reducing pressure loading at the active wound site, thereby allowing the wound to heal without the constant pressure applied to the wound. Several offloading devices have been developed over the years that include commercial off-the-shelf and custom-made devices. Offloading devices are often bulky and heavy in order to allow offloading, which may potentially lead to asymmetrical gait or problems with maintaining balance during walking.

A history of foot ulceration is one of the strongest risk factors for future foot ulceration. Consequently, closely monitoring the contralateral foot when providing an offloading device to a patient is important. Although several authors have shown that offloading devices are effective in wound healing and reducing the pressure at the ulcerated foot,[1–8] few have shown the effects offloading devices may have on the contralateral foot. Lavery and colleagues reported on pressures measured in the contralateral foot in patients wearing total contact casts for offloading their foot ulcers.[9] The authors reported that reducing the peak pressure with a total contact cast on the ulcer site did not increase pressures on the contralateral foot.

The purpose of this study was to examine the effect of two different offloading devices on foot pressures on the contralateral foot. The two devices tested were the Scotchcast boot (SCB), which is a custom-made up-to-ankle-level device, and an Aircast device (AIR) (Aircast Inc., Lincolnshire, United Kingdom), an off-the-shelf, below-knee device. The authors hypothesized that there may be a different effect on the contralateral foot between an ankle- and a knee-level offloading device caused by differences in limitation of movement at the ankle joint.

The results presented in this paper are part of a larger study looking at the efficiency of the two offloading devices.

Methods

Twenty-two consecutive diabetic patients with active or recently healed plantar ulcers were recruited from the Manchester Diabetes Centre. All patients were using the SCB as part of their foot ulcer treatment.

The study was approved by the local ethics committee; all patients received full information about the study and gave informed consent before any testing was carried out.

Foot pressures were measured in three different footwear conditions, as follows: the post-op sandal (SAN) (Benefoot UK Ltd, Prestwich, United Kingdom)was used as a control condition and the SCB and the AIR were used as the two offloading devices. The offloading devices were worn on the affected feet only. In each footwear condition, a SAN was worn on the unaffected foot. No stockings were worn during testing on either foot in order to standardize the pressure measurements. Dressings were worn at the ulcer site throughout the experiment as necessary.

The SAN was used as the control condition. It features a dual density 3/16-inch insole, a flared outsole with a rocker bottom, a reinforced heel counter, a padded collar and top-line, and an upper shoe made from mesh nylon.

The SCB is custom made for each patient and has been used for more than 15 years at the Manchester Foot Hospital and Manchester Diabetes Centre.[10,11] It is made by first applying ribbed stockinette from beyond the toes to above the ankle. Nine-millimeter–thick orthopedic felt (at half thickness) is then wrapped around the ankle, crossing over the top of the foot and securing it with tape. Felt is placed under the sole of and around the foot. Orthopedic wool is applied over the felt, and over this layer, a layer of foam roll is applied. Fiberglass tape is finally applied, making the boot solid and durable. The boot is reinforced under the sole with a sheet of fiberglass. A windowed area is cut to relieve pressure from the ulcer site.