October 2013

Location, location: High pressures don’t predict all ulcers

In the moment: Diabetes

10ITM-diabetes-iStock24843By Emily Delzell

Practitioners often deem all areas of elevated peak plantar pressure in patients with diabetes at some risk for ulceration. A study published in September, how­ever, suggests this risk varies with the specific location of pressure, and investigators say findings highlight the importance of monitoring plantar pressure as part of preventive care. 

Researchers from the US Department of Veterans Affairs (VA) and the University of Washington in Seattle analyzed baseline in-shoe plantar pressure measurements from 591 patients with diabetes seen at a VA clinic between 1996 and 2002.

Patients wore their usual footwear to walk at a self-selected pace as investigators measured peak plantar pressure (PPP) in eight areas: the heel, lateral midfoot, medial midfoot, first metatarsal, second through fourth metatarsals, fifth metatarsal, hallux, and other toes.

During follow-up (average, 2.4 years) 47 patients for whom researchers had complete data developed diabetic foot ulcers (DFU), including 19 at the hallux, 12 at the combined metatarsals, and 10 at the heel. Patients who developed ulcers had a significantly longer duration of diabetes (19 vs 15 years) and higher baseline rates of diabetic neuropathy (81% vs 48%) than those in the nonulcer group.

Overall, areas where ulcers developed had higher PPP than ulcer-free locations (219 kPa vs 194 kPa). However, while meta­tarsal ulcers developed in areas of elevated peak pressure compared to nonulcer sites, ulcers at the heel or hallux had lower peak pressures than regions that did not develop ulcers (241 kPa for heel ulcers vs 266 kPa for nonulcer sites, 172 kPa for hallux ulcers vs 200 kPa for nonulcer sites).

The study’s lead author,  William Le­doux, PhD, an affiliate associate professor in the departments of mechanical engineering and orthopaedics & sports medicine at University of Washington, said the results surprised him and his colleagues, as they expected to see all ulcers associated with high baseline pressure.

“This is one more piece of data in a very complex, multifactorial problem,” Ledoux told LER. “The unique contribution of this work was to look at pressure at a location with subsequent ulcer development at that same location. The lack of a relationship at some locations begs the question, ‘What is causing the ulcers at these locations?’”

Ledoux said ulcers at the heel and the hallux may have been caused by a mechanism not measured in this study, which he noted included a relatively small number of ulcers.

“Despite its mixed findings, I think this study indicates the importance of monitoring plantar pressure,” he said. “But it also suggests that something else is at work, perhaps shear stress, [and answering this question] hopefully will be an active area of research in the future.”

The findings were e-published in September by the Journal of Diabetes and Its Complications.

Bijan Najafi, PhD, associate professor of surgery and director of the interdisciplinary Consortium on Advanced Motion Performance (iCAMP) at the University of Arizona in Tucson, re- viewed the paper for LER and said other factors, including gait speed and variability, might have influenced the findings.

He noted plantar pressure is highly dependent on gait velocity, which the Seattle researchers didn’t control for.

“Although this study tested plantar pressure during habitual gait velocity, it doesn’t guarantee that subjects are walking at their normal speed,” he said.

Najafi also noted that high intersubject gait speed variability may influence how plantar loading affects risk of DFUs, and that peak pressure is highly dependent on footwear type, a broad category among people with diabetes.

“Irrespective of these limitations, peak pressure is not a reliable measure of plantar pressure and does not indicate the dynamics of plantar loading,” he said “Measuring plantar pressure may not be enough to predict a prospective foot ulcer. Plantar pressure should be assessed in the context of patients’ daily activities. If somebody doesn’t walk often, having a high peak pressure may not be so important.”

Source:

Ledoux WR, Shofer JB, Cowley MS, et al. Diabetic foot ulcer incidence in relation to plantar pressure magnitude and measurement location. J Diabetes Complications 2013 Sep 5. [Epub ahead of print]

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