Shear stress and diabetic foot ulcers

NewsBot · May 9, 2006

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Effect of peak pressure and pressure gradient on subsurface shear stresses in the neuropathic foot.
J Biomech. 2006 May 3;

The pressure distribution on the plantar surface of the foot may provide insights into the stresses within the subsurface tissues of patients with diabetes mellitus and peripheral neuropathy (PN) who are at risk for skin breakdown. The purposes of this study were to (1) estimate the stress distribution in the subsurface soft tissue from a measured surface pressure distribution and determine any differences between values in the forefoot and rearfoot, and (2) determine the relationship between maximum shear stress (MSS) (magnitude and depth) and characteristics of the pressure distribution. The measured in-shoe pressure distributions during walking characterized by the peak plantar pressure and maximum pressure gradient on the plantar surface of the feet for 20 subjects with diabetes, PN and history of a mid foot or forefoot plantar ulcer were analyzed. The effects of peak pressure and maximum pressure gradient at the peak pressure location on the stress components in the subsurface soft tissue were studied using a potential function method to estimate the subsurface tissue stress. The calculated MSSs are larger in magnitude and located closer to the surface in the forefoot, where most skin breakdown occurs, compared to the rearfoot. In addition, the MSS (magnitude and depth) is highly correlated with the pressure gradient (r=-0.77 & 0.61) and the peak pressure (r=-0.61 & 0.91). The peak pressure and the maximum pressure gradient obtained from the surface pressure distribution appear to be important variables to identify where MSSs are located in the subsurface tissues on the plantar foot that may lead to skin break down.
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Admin2 · May 9, 2006

Related thread:
Plantar padding and shear effects

NewsBot · Apr 25, 2007

Plantar shear stress distributions: Comparing actual and predicted frictional forces at the foot-ground interface.
Yavuz M, Botek G, Davis BL.
J Biomech. 2007 Apr 19; [Epub ahead of print]

Plantar shear stresses are believed to play a major role in diabetic ulceration. Due to the lack of commercial devices that can measure plantar shear distribution, a number of mathematical models have been developed to predict plantar frictional forces. This study assessed the accuracy of these models using a custom-built platform capable of measuring plantar stresses simultaneously. A total of 48 (38 healthy and 10 diabetic) human subjects (75+/-20kg, 41+/-20 years, 32 males, 16 females) were recruited in the study. Plantar force data were collected for 2s at 50Hz. Two models (M1 and M2) reported in the literature by different groups were used to predict local shear stresses. Root mean squared errors (RMSE) were calculated to compare model data with the actual data, focusing on three parameters: location, magnitude and timing of peak shear components. RMSE values of estimated peak AP and ML shear locations were 3.1 and 2.2cm for M1 and 3.1 and 2.1cm for M2, respectively. Magnitude RMS error values for M1 were found to be 86.6kPa in AP shear and 38.5kPa in ML shear, whereas these values were determined to be 97.8 and 63.5kPa, respectively by M2. Time to peak shear RMSE values averaged 17.2% in terms of the gait duration. In conclusion, distribution of plantar shear should be measured rather than predicted, particularly if one is interested in the magnitudes of shear components
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NewsBot · Dec 7, 2007

Temporal characteristics of plantar shear distribution: Relevance to diabetic patients.
Yavuz M, Tajaddini A, Botek G, Davis BL.
J Biomech. 2007 Nov 28 [Epub ahead of print]

Diabetic foot ulcers are known to have a biomechanical etiology. Among the mechanical factors that cause foot lesions, shear stresses have been either neglected or underestimated. The purpose of this study was to determine various plantar pressure and shear variables in the diabetic and control groups and compare them. Fifteen diabetic patients with neuropathy and 20 non-diabetic subjects without foot symptoms were recruited. Subjects walked on a custom-built platform capable of measuring local normal and tangential forces simultaneously. Pressure-time integral quantities were increased by 54% (p=0.013) in the diabetic group. Peak AP and resultant shear magnitudes were found to be about 32% larger (p<0.05), even though diabetic subjects walked at a slower velocity. Lower AP and ML stress range (peak-to-peak) values were observed in the control subjects (p<0.05). Shear-time integral values were increased in the diabetic group by 61% and 132% for AP and resultant shear cases, respectively (p<0.05). Plantar shear is known to be a factor in callus formation and has previously been associated with higher ulcer incidence. During gait, shear stresses are induced with twice the frequency of pressure characteristically. Therefore, plantar shear should be investigated further from a broader perspective including the temporal specifications and fatigue failure characteristics of the affected plantar tissue.
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NewsBot · Dec 7, 2007

Pressure gradient and subsurface shear stress on the neuropathic forefoot
Donovan J. Lottab, Dequan Zoub, Michael J. Muellerab
Clinical Biomechanics

Background
Stresses within the neuropathic foot’s tissues can be estimated by pressure distributions and may provide information regarding the potential for skin breakdown. The purposes of this study were to: (1) determine the magnitude of peak plantar pressure, pressure time integral, peak pressure gradient, and peak maximum shear stress; and (2) determine the association of these variables with one another.

Methods
Forefoot peak plantar pressure, pressure time integral, peak pressure gradient, peak maximal shear stress, and depth of peak maximal shear stress were calculated for 16 controls, 16 people with diabetic neuropathy, and 22 people with diabetic neuropathy and a history of ulceration from pressure assessments.

Findings
Peak plantar pressure, pressure gradient, and maximal shear stress were greater in subjects with a history of ulceration relative to control subjects (P<0.03), pressure gradient was greater in subjects with diabetic neuropathy and a history of ulceration compared to subjects with diabetic neuropathy and no history of ulceration (P<0.02), and depth of maximal shear stress was less in both groups of subjects with diabetic neuropathy compared to controls (P<0.03). Strong relationships existed between the variables.

Interpretation
Although these variables are associated with one another, peak pressure gradient and peak maximal shear stress provide information concerning plantar pressure distribution and the potentially injurious internal stresses within the foot’s soft tissues. Peak pressure gradient and peak maximal shear stress may perhaps be more discriminating than peak plantar pressure alone in distinguishing between groups of individuals who are at risk for developing a foot ulcer.
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John Spina · Dec 20, 2007

Shear lesions are underdiagnosed by many in the podiatric community.I was at the recent wound care seminar at Columbia University and the speakers stressed repeatedly:DEBRIDE al callus.I agree with this and find that without debridement,you are lessening your chances of a good outcome.

NewsBot · Oct 20, 2012

Shear-Reducing Insoles to Prevent Foot Ulceration in High-Risk Diabetic Patients.
Lavery LA, Lafontaine J, Higgins KR, Lanctot DR, Constantinides G.
Adv Skin Wound Care. 2012 Nov;25(11):519-524.

OBJECTIVE:: The objective of this study was to evaluate the effectiveness of a shear-reducing insole compared with a standard insole design to prevent foot ulceration in high-risk patients with diabetes.

RESEARCH DESIGN AND METHODS:: A total of 299 patients with diabetic neuropathy and loss of protective sensation, foot deformity, or history of foot ulceration were randomized into a standard therapy group (n = 150) or a shear-reducing insole group (n = 149). Patients were evaluated for 18 months. Standard therapy group consisted of therapeutic footwear, diabetic foot education, and regular foot evaluation by a podiatrist. The shear-reducing insole group included a novel insole designed to reduce both pressure and shear on the sole of the foot. Insoles were replaced every 4 months in both groups. The primary clinical outcome was foot ulceration. The authors used Cox proportional hazards regression to evaluate time to ulceration.

RESULTS:: There were 2 significant factors from the Cox regression model: insole treatment and history of a foot complication. The standard therapy group was about 3.5 times more likely to develop an ulcer compared with shear-reducing insole group (hazard ratio, 3.47; 95% confidence interval, 0.96-12.67).

CONCLUSIONS:: These results suggest that a shear-reducing insole is more effective than traditional insoles to prevent foot ulcers in high-risk persons with diabetes.
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NewsBot · Aug 12, 2014

A Novel Shear Reduction Insole Effect on the Thermal Response to Walking Stress, Balance, and Gait
James S. Wrobel et al
J Diabetes Sci Technol August 7, 2014

Shear stresses have been implicated in the formation of diabetes-related foot ulcers. The aim of this study was to evaluate the effect of a novel shear-reducing insole on the thermal response to walking, balance, and gait. Twenty-seven diabetes peripheral neuropathy patients were enrolled and asked to take 200 steps in both intervention and standard insoles. Thermal foot images of the feet were taken at baseline (1) following a 5-minute temperature acclimatization and (2) after walking. Testing order was randomized, and a 5-minute washout period was used between testing each insole condition. Sudomotor function was also assessed. Gait and balance were measured under single and dual task conditions using a validated body worn sensor system. The mean age was 65.1 years, height was 67.3 inches, weight was 218 pounds, and body mass index was 33.9, 48% were female, and 82% had type 2 diabetes. After walking in both insole conditions, foot temperatures increased significantly in standard insoles. The intervention insole significantly reduced forefoot and midfoot temperature increases (64.1%, P = .008; 48%, P = .046) compared to standard insoles. There were significant negative correlations with sudomotor function and baseline temperatures (r = .53-.57). The intervention demonstrated 10.4% less gait initiation double support time compared to standard insoles (P = .05). There were no differences in static balance measures. We found significantly lower forefoot and midfoot temperature increases following walking with shear-reducing insoles compared to standard insoles. We also found improvements in gait. These findings merit future study for the prevention of foot ulcer.
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NewsBot · Feb 24, 2017

Establishment of a measurement method for in-shoe pressure and shear stress in specific regions for diabetic ulcer prevention.
Amemiya A, Noguchi H, Oe M, Sanada H, Mori T, Amemiya A, Noguchi H, Oe M, Sanada H, Mori T, Oe M, Amemiya A, Sanada H, Noguchi H, Mori T.
Conf Proc IEEE Eng Med Biol Soc. 2016 Aug;2016:2291-2294. doi: 10.1109/EMBC.2016.7591187.

Pressure and shear stress are the factors of diabetic foot ulcers and callus formation. However, in-shoe shear stress of callus measurement could not have been measured because of technical difficulties. The purpose of this study is to verify reliability and validity of the established measurement system for in-shoe pressure and shear stress. For reliability, coefficients of variation (CV) and intraclass correlation coefficients (ICC) were confirmed. For known-groups validity, callus and non-callus feet were compared. Mean CV was 9.7%. Mean ICC was 0.943. For validity test, mean peak pressure and shear stress of the six callus feet was significantly higher than that of the eighteen non-callus feet. The pressure and shear stress that causes callus and diabetic foot ulcer will be identified in diabetic neuropathy patients.
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NewsBot · Jan 1, 2019

Biomechanical Efficacy of Shear-Reducing Diabetic Insoles
Elaborations on Future Design Criteria
Yavuz, Metin, DEng; Ersen, Ali, PhD; Richardson, Mike, PT, DPT; Adams, Linda S., BSME; Holmes, Clayton F., PT, EdD, MS, ATC; Wijesundara, Muthu B.J., PhD; Wukich, Dane K., MD; La Fontaine, Javier, DPM, MS
JPO: Journal of Prosthetics and Orthotics: December 28, 2018 - Volume Publish Ahead of Print - Issue - p

Introduction Increasing evidence suggests that plantar shear forces and related stresses play a major role in diabetic foot ulcerations. Several orthotic devices are commercially available to reduce plantar shear forces within the shoe. The biomechanical efficacy of these devices was not tested in vivo. To measure spatiotemporal characteristics of gait to assess the efficacy of such shear-reducing insoles (SRIs), control insoles were also tested for comparison purposes.

Material and Methods Eighteen healthy volunteers walked along a 30.5-m line while wearing three types of insoles in randomized order. Spatiotemporal parameters of gait were quantified. Statistical comparisons between the control and SRIs were conducted using repeated measures analysis of variance. Intraclass correlation coefficients (ICCs) were also calculated to reveal the repeatability of the trials. Step length, gait speed, and cadence of the subjects remained similar regardless of the insole type.

Results No significant difference was observed in any variable. The ICC values revealed excellent repeatability.

Conclusions The lack of changes in gait parameters in these results suggest that shear-reducing diabetic inserts did not decrease plantar shear forces as intended. This might be caused by unrealistic in vitro testing conditions during the prototype development. Future designs should also consider friction at the lateral walls of the inserts, an increase in step repetition that accompanies a decrease in gait speed and/or step length, and a possible temperature increase within the shoe. We conclude that the future SRIs need to be redesigned based on comprehensive biomechanical guidelines.
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NewsBot · Nov 8, 2019

The Effect of Shear Force on Skin Viability in Patients with Type 2 Diabetes
Luuk A. de Wert et al
Journal of Diabetes Research; Volume 2019

Background. Shear is a major risk factor in the development of diabetic foot ulcers, but its effect on the skin of patients with type 2 diabetes mellitus (DM) remains to be elucidated. The aim was to determine skin responses to shear in DM patients with and without diabetic polyneuropathy (DNP). Methods. The forearm skin was loaded with 14.5 N shear (+2.4 kPa pressure) and with 3.5 kPa pressure for 30 minutes in 10 type 2 DM patients without DNP, 10 type 2 DM patients with DNP, and 10 healthy participants. A Sebutape collected IL-1α (measure of tissue damage). A laser Doppler flowmeter measured cutaneous blood cell flux (CBF) as a measure of the reactive hyperaemic skin response. Findings. Reactive hyperaemia and IL-1α release was significantly increased after shear loading in all three groups and was higher compared to the responses to pressure loading. The reactive hyperaemic response after shear loading was impaired in patients with type 2 DM compared to healthy participants but did not differ between patients with and without DNP. The reactive hyperaemic response was negatively correlated with the blood glucose level but did not correlate with the DNP severity score. Interpretation. Shear is important in the development of tissue damage, but the reparative responses to shear are impaired in patients with type 2 DM. DNP was not associated with altered skin responses, suggesting that the loss of protective sensation to sense shear to skin remains a key factor in the development of diabetic foot ulcers in patients with DNP.
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NewsBot · Dec 1, 2019

The Effect of Shear Force on Skin Viability in Patients with Type 2 Diabetes.
de Wert LA et al
J Diabetes Res. 2019 Nov 4

BACKGROUND:
Shear is a major risk factor in the development of diabetic foot ulcers, but its effect on the skin of patients with type 2 diabetes mellitus (DM) remains to be elucidated. The aim was to determine skin responses to shear in DM patients with and without diabetic polyneuropathy (DNP).

METHODS:
The forearm skin was loaded with 14.5 N shear (+2.4 kPa pressure) and with 3.5 kPa pressure for 30 minutes in 10 type 2 DM patients without DNP, 10 type 2 DM patients with DNP, and 10 healthy participants. A Sebutape collected IL-1α (measure of tissue damage). A laser Doppler flowmeter measured cutaneous blood cell flux (CBF) as a measure of the reactive hyperaemic skin response.

FINDINGS:
Reactive hyperaemia and IL-1α release was significantly increased after shear loading in all three groups and was higher compared to the responses to pressure loading. The reactive hyperaemic response after shear loading was impaired in patients with type 2 DM compared to healthy participants but did not differ between patients with and without DNP. The reactive hyperaemic response was negatively correlated with the blood glucose level but did not correlate with the DNP severity score.

INTERPRETATION:
Shear is important in the development of tissue damage, but the reparative responses to shear are impaired in patients with type 2 DM. DNP was not associated with altered skin responses, suggesting that the loss of protective sensation to sense shear to skin remains a key factor in the development of diabetic foot ulcers in patients with DNP.
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NewsBot · Apr 4, 2023

A Wearable Insole System to Measure Plantar Pressure and Shear for People with Diabetes
Jinghua Tang et al
Sensors (Basel). 2023 Mar 15;23(6):3126

Pressure coupled with shear stresses are the critical external factors for diabetic foot ulceration assessment and prevention. To date, a wearable system capable of measuring in-shoe multi-directional stresses for out-of-lab analysis has been elusive. The lack of an insole system capable of measuring plantar pressure and shear hinders the development of an effective foot ulcer prevention solution that could be potentially used in a daily living environment. This study reports the development of a first-of-its-kind sensorised insole system and its evaluation in laboratory settings and on human participants, indicating its potential as a wearable technology to be used in real-world applications. Laboratory evaluation revealed that the linearity error and accuracy error of the sensorised insole system were up to 3% and 5%, respectively. When evaluated on a healthy participant, change in footwear resulted in approximately 20%, 75% and 82% change in pressure, medial-lateral and anterior-posterior shear stress, respectively. When evaluated on diabetic participants, no notable difference in peak plantar pressure, as a result of wearing the sensorised insole, was measured. The preliminary results showed that the performance of the sensorised insole system is comparable to previously reported research devices. The system has adequate sensitivity to assist footwear assessment relevant to foot ulcer prevention and is safe to use for people with diabetes. The reported insole system presents the potential to help assess diabetic foot ulceration risk in a daily living environment underpinned by wearable pressure and shear sensing technologies.
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NewsBot · Sep 14, 2023

Evaluation of in-shoe plantar pressure and shear during walking for diabetic foot ulcer prevention
Jinghua Tang et al
J Wound Care. 2023 Sep 2;32(9):587-596. doi: 10.12968/jowc.2023.32.9.587.

Objective: To investigate reliability and changes of in-shoe plantar pressure and shear during walking at three cadences with two insole designs. This was a precursor to the investigation of plantar loading in people with diabetes for potential foot ulcer prevention.

Method: A sensorised insole system, capable of measuring plantar pressure and shear at the heel, fifth metatarsal head (5MH), first metatarsal head (1MH) and hallux, was tested with ten healthy participants during level walking. Reliability was evaluated, using intra-class correlation coefficient (ICC), while varying the cadences and insole types. Percentage changes in pressure and shear relative to values obtained at self-selected cadence with a flat insole design were investigated.

Results: Mean±standard deviation of maximum pressure, medial-lateral and anterior-posterior shear of up to 380±24kPa, 46±2kPa and -71±4kPa, respectively, were measured. The ICC in ranges of 0.762-0.973, 0.758-0.987 and 0.800-0.980 were obtained for pressure, anterior-posterior and medial-lateral shear, respectively. Opposite anterior-posterior shear directions between 5MH and 1MH (stretching), and between 1MH and hallux (pinching) were observed for some participants. Increasing cadence increased pressure and anterior-posterior shear (by up to +77%) but reduced medial-lateral shear at the heel and hallux (by up to -34%). Slower cadence increased anterior-posterior shear (+114%) but decreased medial-lateral shear (-46%) at the hallux. The use of a flexible contoured insole resulted in pressure reduction at the heel and 5MH but an increase in anterior-posterior shear at the heel (+69%) and hallux (+75%).

Conclusion: The insole system demonstrated good reliability and is comparable to reported pressure-only systems. Pressure measurements were sensitive to changes in cadence and insole designs in ways that were consistent with the literature. However, our plantar shear showed localised shear changes with cadences and insoles for the first time, as well as stretching and pinching effects on plantar tissue. This opens new possibilities to investigate plantar tissue viability, loading characteristics and orthotic designs aimed towards foot ulcer prevention.
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