High plantar pressures in people with diabetic foot ulcers stay high over time

A new Australian study from one of DFA’s favourite sons Dr Mal Fernando has completed his PhD that investigated the gait and plantar pressures of people with diabetic foot ulcers. We have showcased some of Mal’s previous studies on gait characteristics and plantar pressures right here.

Unlike his previous baseline studies, in this study Mal assessed patients with plantar diabetic foot ulcers over 6 months to see if their gait and plantar pressures changed. Surprisingly, such a study had never previously been performed. His new paper – published in the journal PLoS ONE – followed the same 21 patients with diabetic foot ulcers and 69 control diabetes patients with no ulcer history at 3-months and 6-months using the same barefoot plantar pressure protocols as his baseline paper.

In the baseline paper he found that the two main measures of plantar pressures (mean peak plantar pressure and pressure-time integral) were significantly higher in patients with diabetic foot ulcers compared to controls in the toes and midfoot. This was the case even after he controlled for age, sex, BMI and walking speed. However, one of the main limitations of his baseline paper was that it didn’t control for foot deformity and peripheral neuropathy. So what did Mal find over time?

This time he found that after adjusting for age, sex, BMI, foot deformity, peripheral neuropathy and time that patients with foot ulcers still had higher mean peak plantar pressures under the toes and midfoot, and higher pressure-time integral under the hallux and 1st metatarsal area compared with controls. This seems to confirm what we had always thought, that patients with diabetic foot ulcers have higher plantar pressures when they develop their ulcer and they stay that way over time.

A further interesting finding though, was that plantar pressures did decrease slightly at the second (3-months) and third (6-months) measures in both foot ulcers patients and control diabetes patients. This seems to suggest that perhaps patients get familiar with plantar pressure measures over time and adopt a more relaxed natural gait on later measures. This finding should be taken into account in future and especially so when we consider we are looking for a >30% reduction in plantar pressures using footwear modifications in patients with a history of diabetic foot ulcers.

Although this study had more strengths than Mal’s last study – had very few drop outs, followed patients over time, used a protocol demonstrated to be reliable, and controlled for multiple confounding factors such as peripheral neuropathy in complex statistical models – it wasn’t without limitations. These limitations included: a relatively small sample of ulcer patients, used barefoot pressures rather than in-shoe pressures (however, this is also a strength as they are the more ‘natural’ pressures of patients as they aren’t influenced by shoes), ulcer patients had to have had the ulcer for >3months to be included (more long-term chronic ulcers), only a small proportion healed, and therefore there was not analysis of the impact of plantar pressure on ulcer site or healing.

Regardless, this Australian study is the first ever study to investigate the plantar pressures of patients with diabetic foot ulcers over time. They concluded, “plantar pressures assessed during gait are higher in diabetes patients with chronic foot ulcers than controls at several plantar sites throughout prolonged follow-up. Long term offloading is needed in diabetes patients with diabetes-related foot ulcers to facilitate ulcer healing.”

This last sentence is arguably the most important point of the study. These findings confirm that it is vital to continually reduce these consistently high plantar pressures in patients with plantar diabetic foot ulcers using offloading devices as recommended in international guidelines. Yet, the next step for researchers is to find an optimal level of plantar pressure reduction and the most appropriate offloading devices to achieve those reductions. Whilst it has been demonstrated that reducing >30% plantar pressures with footwear modifications in patients with a foot ulcer history reduces ulcer recurrence; such a threshold has not been identified for patients with active foot ulcers.

As Mal nicely highlights in his thesis for James Cook University, the next steps in this vital research area of diabetic foot ulcer healing is how to best: i) optimize the offloading approach; ii) obtain good offloading adherence; and iii) monitor the appropriateness of offloading over time. With Mal now applying his findings to clinical practice and more research at the Queensland University of Technology plantar pressure-guided offloading clinic we may not be too far away from a threshold and these objectives … watch this space.