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Adherence to prescribed footwear is essential to prevent diabetes-related foot ulcers. The aim was to compare different measures of adherence and wearing time of prescribed footwear with a reference adherence measure, among people with diabetes at high risk of foot ulceration. We followed 53 participants for 7 consecutive days. A temperature sensor measured wearing time of prescribed footwear and a triaxial accelerometer assessed weight-bearing activities. Subjective wearing time was self-reported. Reference adherence measure was proportion of weight-bearing time prescribed footwear was worn. We calculated Spearman’s correlation coefficients, kappa coefficients, and areas under the curve (AUC) for the association between the reference measure and other measures of adherence and wearing time. Proportion of daily steps with prescribed footwear worn had a very strong association (r = 0.96, Κ = 0.93; AUC: 0.96–1.00), objective wearing time had a strong association (r = 0.91, Κ = 0.85, AUC: 0.89–0.99), and subjective wearing time had a weak association (r = 0.42, Κ = 0.38, AUC: 0.67–0.81) with the reference measure. Objectively measured proportion of daily steps with prescribed footwear is a valid measure of footwear adherence. Objective wearing time is reasonably valid, and may be used in clinical practice and for long-term measurements. Subjective wearing time is not recommended to be used.

Movement of skin markers with respect to their underlying bone (i.e. soft tissue artifacts (STAs)) might corrupt the accuracy of marker-based movement analyses. This study aims to quantify STAs in 3D for foot markers and their effect on multi-segment foot kinematics as calculated by the Oxford and Rizzoli Foot Models (OFM, RFM). Fifteen subjects with asymptomatic feet were seated on a custom-made loading device on a computed tomography (CT) table, with a combined OFM and RFM marker set on their right foot. One unloaded reference CT-scan with neutral foot position was performed, followed by 9 loaded CT-scans at different foot positions. The 3D-displacement (i.e. STA) of each marker in the underlying bone coordinate system between the reference scan and other scans was calculated. Subsequently, segment orientations and joint angles were calculated from the marker positions according to OFM and RFM definitions with and without STAs. The differences in degrees were defined as the errors caused by the marker displacements. Markers on the lateral malleolus and proximally on the posterior aspect of the calcaneus showed the largest STAs. The hindfoot-shank joint angle was most affected by STAs in the most extreme foot position (40° plantar flexion) in the sagittal plane for RFM (mean: 6.7°, max: 11.8°) and the transverse plane for OFM (mean: 3.9°, max: 6.8°). This study showed that STAs introduce clinically relevant errors in multi-segment foot kinematics. Moreover, it identified marker locations that are most affected by STAs, suggesting that their use within multi-segment foot models should be reconsidered.

Reducing high mechanical stress is imperative to heal diabetes-related foot ulcers. We explored the association of cumulative plantar tissue stress (CPTS) and plantar foot ulcer healing, and the feasibility of measuring CPTS, in two prospective cohort studies (Australia (AU) and The Netherlands (NL)). Both studies used multiple sensors to measure factors to determine CPTS: plantar pressures, weight-bearing activities, and adherence to offloading treatments, with thermal stress response also measured to estimate shear stress in the AU-study. The primary outcome was ulcer healing at 12 weeks. Twenty-five participants were recruited: 13 in the AU-study and 12 in the NL-study. CPTS data were complete for five participants (38%) at baseline and one (8%) during follow-up in the AU-study, and one (8%) at baseline and zero (0%) during follow-up in the NL-study. Reasons for low completion at baseline were technical issues (AU-study: 31%, NL-study: 50%), non-adherent participants (15% and 8%) or combinations (15% and 33%); and at follow-up refusal of participants (62% and 25%). These underpowered findings showed that CPTS was non-significantly lower in people who healed compared with non-healed people (457 [117; 727], 679 [312; 1327] MPa·s/day). Current feasibility of CPTS seems low, given technical challenges and non-adherence, which may reflect the burden of treating diabetes-related foot ulcers.

To better understand stress-related foot ulceration in diabetes, the cumulative plantar tissue stress (CPTS) should be quantified accurately, but also feasibly for clinical use. We developed multiple CPTS models with varying complexity and investigated their agreement with the most comprehensive reference model available. We assessed 52 participants with diabetes and high foot ulcer risk for barefoot and in-shoe plantar pressures during overground walking at different speeds, standing, sit-to-stand transitions, and stair walking. Level of these weight-bearing activities along with footwear adherence were objectively measured over seven days. The reference CPTS-model included the pressure–time integrals of each walking stride (barefoot and shod), specified for speed; standing period (barefoot and shod); transition and stair walking stride. We compared four CPTS-models with increasing number of input parameters (models 1–4) with the reference model, using repeated measures ANOVA, Pearson’s correlation and Bland-Altman plots. For the clinically-relevant metatarsal 1 region, calculated CPTS was lower for the four CPTS-models compared to reference (Δ770, Δ466, Δ24 and Δ12 MPa.s/day, respectively). CPTS associated moderately with the reference model for model 1 (r = 0.551) and very strongly for models 2–4 (r ≥ 0.937). Limits of agreement were large for models 1 and 2 (−728;2269 and −302;1233 MPa.s/day), and small for models 3 and 4 (−43;92 and −54;78 MPa.s/day). CPTS in models 3 and 4 best agreed with the reference model, where model 3 required fewer parameters, i.e., pressure–time integrals of each walking stride and standing period while barefoot and shod. These parameters need to be included for accurate and feasible CPTS assessment.

Segment coordinate systems (CSs) of marker-based multi-segment foot models are used to measure foot kinematics, however their relationship to the underlying bony anatomy is barely studied. The aim of this study was to compare marker-based CSs (MCSs) with bone morphology-based CSs (BCSs) for the hindfoot and forefoot. Markers were placed on the right foot of fifteen healthy adults according to the Oxford, Rizzoli and Amsterdam Foot Model (OFM, RFM and AFM, respectively). A CT scan was made while the foot was loaded in a simulated weight-bearing device. BCSs were based on axes of inertia. The orientation difference between BCSs and MCSs was quantified in helical and 3D Euler angles. To determine whether the marker models were able to capture inter-subject variability in bone poses, linear regressions were performed. Compared to the hindfoot BCS, all MCSs were more toward plantar flexion and internal rotation, and RFM was also oriented toward more inversion. Compared to the forefoot BCS, OFM and RFM were oriented more toward dorsal and plantar flexion, respectively, and internal rotation, while AFM was not statistically different in the sagittal and transverse plane. In the frontal plane, OFM was more toward eversion and RFM and AFM more toward inversion compared to BCS. Inter-subject bone pose variability was captured with RFM and AFM in most planes of the hindfoot and forefoot, while this variability was not captured by OFM. When interpreting multi-segment foot model data it is important to realize that MCSs and BCSs do not always align.

We aimed to comprehensively and systematically review studies associating key foot-loading factors (i.e., plantar pressure, weight-bearing activity, adherence or a combination thereof) with ulcer development and ulcer healing in people with diabetes. A systematic literature search was performed in PubMed and EMBASE. We included studies if barefoot or in-shoe plantar pressure, weight-bearing activity or footwear or device adherence was measured and associated with either ulcer development or ulcer healing in people with diabetes. Out of 1954 records, 36 studies were included and qualitatively analyzed. We found low to moderate quality evidence that lower barefoot plantar pressure and higher footwear and device adherence associate with lower risk of ulcer development and shorter healing times. For the other foot-loading factors, we found low quality evidence with limited or contradictory results. For combined measures of foot-loading factors, we found low quality evidence suggesting that lower cumulative plantar tissue stress is associated with lower risk of ulcer development and higher ulcer healing incidence. We conclude that evidence for barefoot plantar pressure and adherence in association with ulcer outcome is present, but is limited for the other foot-loading factors. More comprehensive investigation in particularly the combination of foot-loading factors may improve the evidence and targeting preventative treatment.

Background: In evaluating the biomechanical properties of therapeutic footwear, most often in-shoe plantar pressure is obtained during mid-gait steps at self-selected speed in a laboratory setting. However, this may not represent plantar pressures or indicate the cumulative stress experienced in daily life, where people adopt different walking speeds and weight-bearing activities. Research question: In people with diabetes at high risk of ulceration, 1) what is the effect of walking speed on plantar pressure measures, and 2) what is the difference in plantar pressure measures between walking at self-selected speed and other weight-bearing activities. Methods: In a cross-sectional study, we included 59 feet of 30 participants (5 females, mean age: 63.8 (SD 9.2) years). We assessed in-shoe plantar pressure with the Pedar-X system during three standardized walking speeds (0.8, 0.6 and 0.4 m/s) and eight types of activities versus walking at self-selected speed (3 components of the Timed Up and Go test (TUG), standing, accelerating, decelerating, stair ascending and descending and standing). Peak plantar pressure (PPP) and pressure-time integral (PTI) were determined for the hallux, metatarsal 1, metatarsal 2-3 and metatarsal 4-5. For statistical comparisons we used linear mixed models (α<0.05) with Holm-Bonferroni correction. Results: With increasing walking speed, PPP increased and PTI decreased for all regions (p≤0.001). Standing, decelerating, stair ascending and TUG showed lower PPP than walking at self-selected speed for most regions (p≤0.004), whereas accelerating and stair descending showed similar PPP. Stair ascending and descending showed higher PTI than walking at self-selected speed (p≤0.002), standing showed lower PTI (p≤0.001), while the other activities showed similar PTI for most regions. Significance: To best evaluate the biomechanical properties of therapeutic footwear, and to assess cumulative plantar tissue stress of people with diabetes at high risk of ulceration, plantar pressures during different walking speeds and activities of daily living should be considered. Keywords: Peak pressure, pressure-time integral, diabetic foot, footwear, ambulatory monitoring, cumulative plantar tissue stress Competing Interest Statement The authors have declared no competing interest.