Elsevier

Clinical Biomechanics

Volume 53, March 2018, Pages 86-92
Clinical Biomechanics

An exploratory study on differences in cumulative plantar tissue stress between healing and non-healing plantar neuropathic diabetic foot ulcers

https://doi.org/10.1016/j.clinbiomech.2018.02.012Get rights and content

Highlights

  • Cumulative tissue stress was 25% lower in healed plantar diabetic foot ulcers.

  • This effect was 49% in adherent patients.

  • Plantar pressure or ambulatory activity alone resulted in smaller differences.

  • Measuring cumulative tissue stress may provide insight beyond pressure or activity.

Abstract

Background

Mechanical stress is important in causing and healing plantar diabetic foot ulcers, but almost always studied as peak pressure only. Measuring cumulative plantar tissue stress combines plantar pressure and ambulatory activity, and better defines the load on ulcers. Our aim was to explore differences in cumulative plantar tissue stress between people with healing and non-healing plantar diabetic foot ulcers.

Methods

We analyzed a subgroup of 31 patients from a randomized clinical trial, treated with a removable offloading device for their plantar diabetic forefoot ulcer. We measured in-device dynamic plantar pressure and daily stride count to calculate cumulative plantar tissue stress at the ulcer location and associated this with ulcer healing and ulcer surface area reduction at four weeks (Student's t and chi-square test for significance, Cohen's d for effect size).

Findings

In 12 weeks, 68% (n = 21) of the ulcers healed and 32% (n = 10) did not. No statistically significant differences were found for cumulative plantar tissue stress, plantar pressure or ambulatory activity between people with healed and not-healed ulcers. Cumulative plantar tissue stress was 25% lower for people with healed ulcers (155 vs. 207 MPa·s/day; P = 0.71; Effect size: d = 0.29). Post-hoc analyses in the 27 patients who self-reported to be adherent to wearing the device showed that cumulative plantar tissue stress was 49% lower for those who reached ≥75% ulcer surface area reduction at four weeks (140 vs. 275 MPa·s/day; P = 0.09; d = 0.76); smaller differences and effect sizes were found for peak pressure (24%), peak pressure-time integral (30%) and ambulatory activity (26%); (P-value range: 0.14–0.97; Cohen's d range: 0.14–0.70).

Interpretation

Measuring cumulative plantar tissue stress may provide insight beyond that obtained from plantar pressure or ambulatory activity alone, with regard to diabetic foot ulcer healing using removable offloading devices. These explorative findings provide baseline data for further studies on this relevant topic.

Introduction

Foot ulcers are a frequent complication of diabetes mellitus, with a lifetime incidence between 19 and 34% and a 40% recurrence rate in the first year once an ulcer is in remission (Armstrong et al., 2017). It is a costly complication, in morbidity, mortality, and healthcare expenditure, and in reducing a patient's quality of life (Armstrong et al., 2017; Kerr et al., 2014; Nabuurs-Franssen et al., 2005; Skrepnek et al., 2015). Almost 50% of these ulcers are located at the plantar surface of the foot (Prompers et al., 2007). Changes in foot biomechanics lead to increased mechanical stress on the plantar surface of the foot, and are a strong contributor to these ulcers (Monteiro-Soares et al., 2012; Schaper et al., 2016). A vital aspect of treatment to heal these ulcers is offloading treatment that aims to relieve mechanical stress on the ulcer (Bus et al., 2016a; Schaper et al., 2016). Results from various reviews indicate that, on average, shorter healing times can be found when patients are treated with devices providing a higher degree of plantar pressure offloading (Bus, 2016; Bus et al., 2016b; Lewis and Lipp, 2013). However, the degree of plantar pressure offloading can be different across patients wearing the same device, dependent on the characteristics of the (custom) device and the individual characteristics of the patient's foot regarding deformity present, tissue properties, and ulcer location. These variations in offloading may relate to the differences in healing rates found between patients using similar devices, but studies on offloading comparing similar devices are limited (Bus, 2016).

With peak plantar pressure often the only biomechanical characteristic considered in healing (Bus et al., 2016b), a missing link in our understanding of plantar foot ulcer healing is the role of the ambulatory activity level of the patient. The stress that occurs at an ulcer location does not only depend on the plantar pressure, but also on how frequent this pressure is applied (by the number of steps the patient takes each day). The total load is a combination of these two, expressed as the cumulative plantar tissue stress (Maluf and Mueller, 2003). If plantar pressure is low in a highly active patient, cumulative stress may be similar compared to a patient with higher plantar pressure who takes only a limited number of steps each day. The only study that measured ambulatory activity level in the context of foot ulcer healing found that patients who were less active had shorter healing times (Armstrong et al., 2001). The lack of plantar pressure data in this study prevented the opportunity to investigate the association between cumulative plantar tissue stress and ulcer healing.

Despite our current understanding of plantar pressure offloading and the biomechanical and clinical efficacy of various offloading modalities, the association between cumulative plantar tissue stress and ulcer healing has never been investigated. We hypothesize that the total load on the ulcer, as expressed by the cumulative plantar tissue stress, is lower in people with ulcers that heal compared to people with ulcers that do not heal. The aim of this explorative study is therefore to examine differences in cumulative plantar tissue stress between healing and non-healing plantar neuropathic foot ulcers in people with diabetes.

Section snippets

Methods

This exploratory study was performed on a subset of patients that participated in an investigator-initiated parallel-group single-blinded multicenter randomized controlled trial (RCT; registration number: ISRCTN89989776) on the efficacy of removable offloading devices in the healing of plantar neuropathic diabetic foot ulcers (Bus et al., 2017). Because of equipment and personnel restrictions, not all patients in the RCT could be included for objective assessment of their biomechanical load; a

Clinical outcomes

In 12 weeks, 68% (n = 21) of the ulcers healed and 32% (n = 10) did not heal. With the numbers available, no significant difference could be detected for patient characteristics, type of offloading device used, or ulcer characteristics between those patients who healed and those who did not (Table 1). Mean percentage change in ulcer surface area at four weeks was a 76% reduction (Standard Deviation (SD): 30), with a significantly greater reduction in ulcer surface area in those patients who

Discussion

This is the first study to explore the differences in cumulative plantar tissue stress (a combination of plantar pressure and ambulatory activity) in people with healing and with non-healing plantar neuropathic diabetic foot ulcers. We did not demonstrate a statistically significant difference for cumulative plantar tissue stress, nor for plantar pressure or ambulatory activity separately, between patients whose ulcer healed or showed a good healing tendency and patients with an ulcer that did

Conflicts of interests

None.

Author contributions

Author contributions: J.v.N. contributed to data acquisition, researched data, performed the data analysis, and wrote the manuscript. J.v.B. contributed to the study design, data acquisition and discussion, researched data, and reviewed/edited the manuscript. A.B. contributed to data acquisition, researched data and reviewed/edited the manuscript. M.H. contributed to data acquisition, researched data and reviewed/edited the manuscript. S.B. designed the study, contributed to data acquisition,

Funding source

This work was supported by funding from the European Union INTERREG IIIA program (project ID: 2-EUR-II-2=60). The sponsor had no involvement in the study.

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