Cath Lab Digest

Offloading plays a key role in the management of diabetic foot ulcerations. With this in mind, these authors review the literature and discuss a variety of modalities ranging from non-weightbearing options and therapeutic half-shoes to removable cast walkers and total contact casts.

   The combination of sensory neuropathy and high plantar pressures is the main factor responsible for plantar foot ulcer development in patients with diabetes mellitus.^1,2 Neuropathic foot ulcers affect up to 15 percent of patients with diabetes and neuropathic foot ulcers are the primary factor leading to lower extremity amputations.³ Among the diabetic population, amputation is associated with re-amputation, contralateral limb amputation, placement in an extended care facility, a decrease in the quality of life and death.^4-8

   Diabetic foot ulcers occur due to a combination of isolated pressure and repetitive stress. Researchers have shown that two key forces act on the foot. Vertical mechanical forces act perpendicular to the skin surface and shear forces act parallel to the skin surface.⁹ These forces act in tandem in the pathogenesis of diabetic foot wounds.

   Several studies have shown that vertical and shear forces are highest at the edge, not the center, of pressure application and that this is the area of maximum soft tissue damage. This tissue damage, resulting from both vertical stress and shear forces, is described as the “edge effect.”^10,11

   Various researchers have described increased plantar foot pressures in patients with diabetic neuropathy and have shown they are related to the development of plantar foot ulcers.^12-15 A recent multicenter prospective clinical trail showed that high peak plantar pressures > 6 kg/cm2 have high specificity in identifying patients at risk of developing plantar foot ulcers.¹⁶ Researchers have reported multiple factors that lead to high plantar pressures. These factors include obesity, sensory impairment, foot deformities, limited joint mobility, callus formation and reduced plantar soft tissue thickness.^9,17-22

   In addition to peak plantar pressure, researchers have shown the forefoot to rearfoot peak plantar pressure ratio (F/R ratio) to be a predictor of foot ulceration. A F/R ratio >2 is reportedly as specific as a peak pressure >6 kg/cm2 in identifying patients who will develop foot ulceration.¹² Motor impairment, functional shortening of the Achilles tendon (by way of advanced glycosylation of soft tissues) and possible rupture of the plantar fascia all have the potential to produce equinus deformity and subsequently increase the pressure under the forefoot area.^23-26 Additionally, limited dorsiflexion of the ankle results in earlier heel rise in the gait cycle and subsequent earlier and extended loading of the forefoot.

   Healing ulcerations requires adequate blood supply, control of infection, appropriate wound care, debridement and offloading. One can best achieve offloading by spreading force over a wide area of contact, thus decreasing pressure.

   In addition to decreasing plantar pressures, ensuring patient adherence is another key component of offloading devices. There are numerous modalities clinicians can choose from when it comes to offloading diabetic foot ulcers. The ideal device reduces plantar pressures, both vertical and shear, while ensuring patient adherence. With this in mind, let us take a closer look at several of the currently available offloading modalities.