Plantar pressures are higher in cases with diabetic foot ulcers compared to controls despite a longer stance phase duration

Background

Current international guidelines advocate achieving at least a 30 % reduction in maximum plantar pressure to reduce the risk of foot ulcers in people with diabetes. However, whether plantar pressures differ in cases with foot ulcers to controls without ulcers is not clear. The aim of this study was to assess if plantar pressures were higher in patients with active plantar diabetic foot ulcers (cases) compared to patients with diabetes without a foot ulcer history (diabetes controls) and people without diabetes or a foot ulcer history (healthy controls).

Methods

Twenty-one cases with diabetic foot ulcers, 69 diabetes controls and 56 healthy controls were recruited for this case-control study. Plantar pressures at ten sites on both feet and stance phase duration were measured using a pre-established protocol. Primary outcomes were mean peak plantar pressure, pressure-time integral and stance phase duration. Non-parametric analyses were used with Holm’s correction to correct for multiple testing. Binary logistic regression models were used to adjust outcomes for age, sex and body mass index. Median differences with 95 % confidence intervals and Cohen’s d values (standardised mean difference) were reported for all significant outcomes.

Results

The majority of ulcers were located on the plantar surface of the hallux and toes. When adjusted for age, sex and body mass index, the mean peak plantar pressure and pressure-time integral of toes and the mid-foot were significantly higher in cases compared to diabetes and healthy controls (p?<?0.05). The stance phase duration was also significantly higher in cases compared to both control groups (p?<?0.05). The main limitations of the study were the small number of cases studied and the inability to adjust analyses for multiple factors.

Conclusions

This study shows that plantar pressures are higher in cases with active diabetic foot ulcers despite having a longer stance phase duration which would be expected to lower plantar pressure. Whether plantar pressure changes can predict ulcer healing should be the focus of future research. These results highlight the importance of offloading feet during active ulceration in addition to before ulceration.

     

Method for in-shoe shear stress measurement

A methodology is described for use of a shear transducer, based on a magneto-resistive principle, to measure stresses under the plantar surface of the foot in-shoe during walking. Particular attention is paid to a projected application for study of diabetic plantar ulceration and its management by footwear. The transducer has a disc construction, approximately 4 mm thick by 16 mm diameter, and measures two orthogonal axes of shear simultaneously; this disc is mounted into an inlay that can be inserted into any stock orthopaedic shoe of the type commonly prescribed for diabetic foot problems. The transducer is located in the metatarsal head region of the inlay; exact placement of the transducer is determined by reference to the direct pressure distribution, the common method of palpation shown to be imprecise. Pilot trials on normal subjects are presented to evaluate the method.     

Simultaneous shear and pressure sensor array for assessing pressure and shear at foot/ground interface

Foot ulceration is a diabetic complication estimated to result in over $1 billion worth of medical expenses per year in the United States alone. This multifaceted problem involves the response of plantar soft tissue to both external forces applied to the epidermis and internal changes such as vascular supply and neuropathy. Increasing evidence indicates that a combination of elevated external forces (pressure and shear) and altered tissue properties is key to the etiology of foot ulcers. The overall goal of this research is to develop a platform-type hardware system that will allow a clinician to measure three-dimensional stress tensors (i.e. pressure and shear patterns) on the plantar surface and identify areas of concern. Experimental results have demonstrated that an optical approach can provide clear indication of both shear and pressure from 50 to 400 kPa with a frequency response of 100 Hz, a stress measurement accuracy of 100 Pa and a spatial resolution of 8.0mm. Initial evaluation of the system shows strong correlation between (i) applied shear and normal stress loads and (ii) the optical phase retardance computed for each stress axis of the polymer-based stress-sensing elements. These special sensing elements are designed to minimize the need for repeated calibration procedures-an issue that has plagued other attempts to develop multisensor shear and pressure systems.     

Single-stage surgical treatment of noninfected diabetic foot ulcers

A retrospective study was undertaken to evaluate a single-stage approach in the treatment of noninfected, chronic, well-perfused diabetic foot wounds. This single-stage approach consisted of total excision of the ulcer with broad exposure, correction of the underlying osseous deformity, and immediate primary closure using a local random flap. Four hundred cases of pedal ulcers were analyzed by chart review. Of those, 67 cases underwent a single-stage surgical treatment and were analyzed for length of hospital stay, postoperative complications, time to heal, recurrence of the ulcer, and postprocedure ambulatory status. The age of the ulcers before surgery was 12 +/- 12 months (mean +/- SD), with a range of 1 to 60. The median perioperative hospital stay was 5 +/- 7.6 days. All patients were followed until the wounds were healed or to amputation. The median total time to heal was 30.8 +/- 40 days. Ninety-seven percent of the wounds healed. The recurrence rate of ulceration was 10.4 percent (seven of 67), over a time span of up to 6 years. All but one patient returned to previous levels of ambulation, and many patients had improved levels of ambulation. The single-stage approach eliminated the need for additional surgical procedures, with their associated costs and risks. In addition, healing times were significantly reduced, resulting in decreased hospital stays and subsequent costs and providing the patient with an expedient return to footwear so that bipedal function could be restored. Most importantly, by addressing the underlying bony pathologic findings, the recurrence rates were also drastically reduced.     

The compressive mechanical properties of diabetic and non-diabetic plantar soft tissue

Diabetic subjects are at an increased risk of developing plantar ulcers. Knowledge of the physiologic compressive properties of the plantar soft tissue is critical to understanding the possible mechanisms of ulcer formation and improving treatment options. The purpose of this study was to determine the compressive mechanical properties of the plantar soft tissue in both diabetic and non-diabetic specimens from six relevant locations beneath the foot, namely the hallux (big toe), first, third, and fifth metatarsal heads, lateral midfoot, and calcaneus (heel). Cylindrical specimens (1.905 cm diameter) from these locations were excised and separated from the skin and bone from 4 diabetic and 4 non-diabetic age-matched, elderly, fresh-frozen cadaveric feet. Specimens were then subjected to biomechanically realistic strains of ～50% in compression using triangle wave tests conducted at five frequencies ranging from 1 to 10 Hz to determine tissue modulus, energy loss, and strain rate dependence. Diabetic vs. non-diabetic results across all specimens, locations, and testing frequencies demonstrated altered mechanical properties with significantly increased modulus (1146.7 vs. 593.0 kPa) but no change in energy loss (68.5 vs. 67.9%). All tissue demonstrated strain rate dependence and tissue beneath the calcaneus was found to have decreased modulus and energy loss compared to other areas. The results of this study could be used to generate material properties for all areas of the plantar soft tissue in diabetic or non-diabetic feet, with implications for foot computational modeling efforts and potentially for pressure alleviating footwear that could reduce plantar ulcer incidence.     

Real-time subject-specific monitoring of internal deformations and stresses in the soft tissues of the foot: a new approach in gait analysis

No technology is presently available to provide real-time information on internal deformations and stresses in plantar soft tissues of individuals during evaluation of the gait pattern. Because internal deformations and stresses in the plantar pad are critical factors in foot injuries such as diabetic foot ulceration, this severely limits evaluation of patients. To allow such real-time subject-specific analysis, we developed a hierarchal modeling system which integrates a two-dimensional gross structural model of the foot (high-order model) with local finite element (FE) models of the plantar tissue padding the calcaneus and medial metatarsal heads (low-order models). The high-order whole-foot model provides real-time analytical evaluations of the time-dependent plantar fascia tensile forces during the stance phase. These force evaluations are transferred, together with foot-shoe local reaction forces, also measured in real time (under the calcaneus, medial metatarsals and hallux), to the low-order FE models of the plantar pad, where they serve as boundary conditions for analyses of local deformations and stresses in the plantar pad. After careful verification of our custom-made FE solver and of our foot model system with respect to previous literature and against experimental results from a synthetic foot phantom, we conducted human studies in which plantar tissue loading was evaluated in real time during treadmill gait in healthy individuals (N = 4). We concluded that internal deformations and stresses in the plantar pad during gait cannot be predicted from merely measuring the foot-shoe force reactions. Internal loading of the plantar pad is constituted by a complex interaction between the anatomical structure and mechanical behavior of the foot skeleton and soft tissues, the body characteristics, the gait pattern and footwear. Real-time FE monitoring of internal deformations and stresses in the plantar pad is therefore required to identify elevated deformation/stress exposures toward utilizing it in gait laboratories to protect feet that are susceptible to injury.     

The microvascular pathophysiology of chronic venous insufficiency.

Severe chronic venous insufficiency (CVI) demonstrates as chronic, hard-to-heal wounds of the lower extremity. The wound is the result of poor skin perfusion due to a complex series of pathologic events, often initiated by a deep vein thrombosis (DVT). As years pass, the DVT causes venous valvular damage and incompetence. The calf muscle pump fails to augment venous return, and venous blood pressure is chronically elevated upon standing. Mechanisms that normally prevent the transmission of venous hypertension back upstream to the dermal microcirculation are lost. Early dermal microvascular responses include increased fluid filtration and edema. An inflammatory response induces white cell activation and adhesion. It is thought that activated white cells are trapped in dermal capillaries and increase microvascular permeability. Plasma proteins leak into the tissue space, increasing the edema. Ischemic damage to the epidermis leads to epithelial cell necrosis and ulceration. The ulcer is often slow to heal, due to inadequate perfusion and delivery of substrates required for proper wound healing. Current treatments aim to improve calf pump function, reduce edema, improve perfusion, and enhance wound healing.     

What Has Finite Element Analysis Taught Us about Diabetic Foot Disease and Its Management? A Systematic Review

Background

Over the past two decades finite element (FE) analysis has become a popular tool for researchers seeking to simulate the biomechanics of the healthy and diabetic foot. The primary aims of these simulations have been to improve our understanding of the foot’s complicated mechanical loading in health and disease and to inform interventions designed to prevent plantar ulceration, a major complication of diabetes. This article provides a systematic review and summary of the findings from FE analysis-based computational simulations of the diabetic foot.

Methods

A systematic literature search was carried out and 31 relevant articles were identified covering three primary themes: methodological aspects relevant to modelling the diabetic foot; investigations of the pathomechanics of the diabetic foot; and simulation-based design of interventions to reduce ulceration risk.

Results

Methodological studies illustrated appropriate use of FE analysis for simulation of foot mechanics, incorporating nonlinear tissue mechanics, contact and rigid body movements. FE studies of pathomechanics have provided estimates of internal soft tissue stresses, and suggest that such stresses may often be considerably larger than those measured at the plantar surface and are proportionally greater in the diabetic foot compared to controls. FE analysis allowed evaluation of insole performance and development of new insole designs, footwear and corrective surgery to effectively provide intervention strategies. The technique also presents the opportunity to simulate the effect of changes associated with the diabetic foot on non-mechanical factors such as blood supply to local tissues.

Discussion

While significant advancement in diabetic foot research has been made possible by the use of FE analysis, translational utility of this powerful tool for routine clinical care at the patient level requires adoption of cost-effective (both in terms of labour and computation) and reliable approaches with clear clinical validity for decision making.     

Elevated plantar pressures in neuropathic diabetic patients with claw/hammer toe deformity

Elevated plantar foot pressures during gait in diabetic patients with neuropathy have been suggested to result, among other factors, from the distal displacement of sub-metatarsal head (MTH) fat-pad cushions caused by to claw/hammer toe deformity. The purpose of this study was to quantitatively assess these associations. Thirteen neuropathic diabetic subjects with claw/hammer toe deformity, and 13 age- and gender-matched neuropathic diabetic controls without deformity, were examined. Dynamic barefoot plantar pressures were measured with an EMED pressure platform. Peak pressure and force-time integral for each of 11 foot regions were calculated. Degree of toe deformity and the ratio of sub-MTH to sub-phalangeal fat-pad thickness (indicating fat-pad displacement) were measured from sagittal plane magnetic resonance images of the foot. Peak pressures at the MTHs were significantly higher in the patients with toe deformity (mean 626 (SD 260)kPa) when compared with controls (mean 363 (SD 115) kPa, P<0.005). MTH peak pressure was significantly correlated with degree of toe deformity (r=-0.74) and with fat-pad displacement (r=-0.71) (P<0.001). The ratio of force-time integral in the toes and the MTHs (toe-loading index) was significantly lower in the group with deformity. These results show that claw/hammer toe deformity is associated with a distal-to-proximal transfer of load in the forefoot and elevated plantar pressures at the MTHs in neuropathic diabetic patients. Distal displacement of the plantar fat pad is suggested to be the underlying mechanism in this association. These conditions increase the risk for plantar ulceration in these patients.     

Prediction of peak pressure from clinical and radiological measurements in patients with diabetes

Background

Various structural and functional factors of foot function have been associated with high local plantar pressures. The therapist focuses on these features which are thought to be responsible for plantar ulceration in patients with diabetes. Risk assessment of the diabetic foot would be made easier if locally elevated plantar pressure could be indicated with a minimum set of clinical measures.

Methods

Ninety three patients were evaluated through vascular, orthopaedic, neurological and radiological assessment. A pressure platform was used to quantify the barefoot peak pressure for six forefoot regions: big toe (BT) and metatarsals one (MT-1) to five (MT-5). Stepwise regression modelling was performed to determine which set of the clinical and radiological measures explained most variability in local barefoot plantar peak pressure in each of the six forefoot regions. Comprehensive models were computed with independent variables from the clinical and radiological measurements. The difference between the actual plantar pressure and the predicted value was examined through Bland-Altman analysis.

Results

Forefoot pressures were significant higher in patients with neuropathy, compared to patients without neuropathy for the whole forefoot, the MT-1 region and the MT-5 region (respectively 138 kPa, 173 kPa and 88 kPa higher: mean difference). The clinical models explained up to 39 percent of the variance in local peak pressures. Callus formation and toe deformity were identified as relevant clinical predictors for all forefoot regions. Regression models with radiological variables explained about 26 percent of the variance in local peak pressures. For most regions the combination of clinical and radiological variables resulted in a higher explained variance. The Bland and Altman analysis showed a major discrepancy between the predicted and the actual peak pressure values.

Conclusion

At best, clinical and radiological measurements could only explain about 34 percent of the variance in local barefoot peak pressure in this population of diabetic patients. The prediction models constructed with linear regression are not useful in clinical practice because of considerable underestimation of high plantar pressure values. Identification of elevated plantar pressure without equipment for quantification of plantar pressure is inadequate. The use of quantitative plantar pressure measurement for diabetic foot screening is therefore advocated.     

Method of healing diabetic forefoot ulcers.

Six diabetic patients with neuropathic ulceration of the sole of the foot (seven feet, eight ulcers) were treated by the application of a below knee walking plaster with a rubber rocker. All the ulcers healed with this treatment, greatly reducing the usual period of hospital inpatient stay. After healing, study of the forces acting on the sole of the foot showed that these ulcers occur at the site of maximal horizontal shear force and confirmed that they occur at the site of maximal vertical force. This treatment is highly effective for neuropathic ulcers of the sole not affecting bone or complicated by deep sepsis. There may be a high rate of recurrence, however, reflecting inadequacy of methods of protecting damaged neuropathic feet.     

Pinch skin grafting or porcine dermis in venous ulcers: a randomised clinical trial.

Chronic venous ulcers are common, and even with effective compression or elevation large ulcers may take months to heal. Pinch skin grafting may allow healing from epithelial islands throughout the surface area of the ulcer, and a prospective randomised trial was therefore conducted comparing this treatment with porcine dermis dressings. Most patients were treated as outpatients, 25 ulcers being randomised to treatment with pinch skin grafts and 28 to treatment with porcine dermis. Though the groups were well matched, the mean healing rate in the first week was 15 cm2 for pinch skin grafts compared with 3.5 cm2 with porcine dermis (p less than 0.02). By life table analysis 64% of ulcers treated by pinch grafts were healed at six weeks and 74% by 12 weeks compared with 29% and 46% of ulcers, respectively, treated with porcine dermis dressings (chi2 = 4.1; p less than 0.05). All ulcers that failed to heal within 12 weeks included an area posterior to the medial malleolus, where local compression may have been inadequate. Pinch skin grafting improves the rate of healing in large venous ulcers and is a simple technique that may be performed as an outpatient procedure under local anaesthesia.     

Temperature as a predictive tool for plantar triaxial loading

Diabetic foot ulcers are caused by moderate repetitive plantar stresses in the presence of peripheral neuropathy. In severe cases, the development of these foot ulcers can lead to lower extremity amputations. Plantar pressure measurements have been considered a capable predictor of ulceration sites in the past, but some investigations have pointed out inconsistencies when solely relying on this method. The other component of ground reaction forces/stresses, shear, has been understudied due to a lack of adequate equipment. Recent articles reported the potential clinical significance of shear in diabetic ulcer etiology. With the lack of adequate tools, plantar temperature has been used as an alternative method for determining plantar triaxial loading and/or shear. However, this method has not been previously validated. The purpose of this study was to analyze the potential association between exercise-induced plantar temperature increase and plantar stresses. Thirteen healthy individuals walked on a treadmill for 10 minutes at 3.2 km/h. Pre and post-exercise temperature profiles were obtained with a thermal camera. Plantar triaxial stresses were quantified with a custom-built stress plate. A statistically significant correlation was observed between peak shear stress (PSS) and temperature increase (r=0.78), but not between peak resultant stress (PRS) and temperature increase (r=0.46). Plantar temperature increase could predict the location of PSS and PRS in 23% and 39% of the subjects, respectively. Only a moderate linear relationship was established between triaxial plantar stresses and walking-induced temperature increase. Future research will investigate the value of nonlinear models in predicting plantar loading through foot temperature.     

Predictors of Barefoot Plantar Pressure during Walking in Patients with Diabetes,Peripheral Neuropathy and a History of Ulceration

ObjectiveElevated dynamic plantar foot pressures significantly increase the risk of foot ulceration in diabetes mellitus. The aim was to determine which factors predict plantar pressures in a population of diabetic patients who are at high-risk of foot ulceration.MethodsPatients with diabetes, peripheral neuropathy and a history of ulceration were eligible for inclusion in this cross sectional study. Demographic data, foot structure and function, and disease-related factors were recorded and used as potential predictor variables in the analyses. Barefoot peak pressures during walking were calculated for the heel, midfoot, forefoot, lesser toes, and hallux regions. Potential predictors were investigated using multivariate linear regression analyses. 167 participants with mean age of 63 years contributed 329 feet to the analyses.ResultsThe regression models were able to predict between 6% (heel) and 41% (midfoot) of the variation in peak plantar pressures. The largest contributing factor in the heel model was glycosylated haemoglobin concentration, in the midfoot Charcot deformity, in the forefoot prominent metatarsal heads, in the lesser toes hammer toe deformity and in the hallux previous ulceration. Variables with local effects (e.g. foot deformity) were stronger predictors of plantar pressure than global features (e.g. body mass, age, gender, or diabetes duration).ConclusionThe presence of local deformity was the largest contributing factor to barefoot dynamic plantar pressure in high-risk diabetic patients and should therefore be adequately managed to reduce plantar pressure and ulcer risk. However, a significant amount of variance is unexplained by the models, which advocates the quantitative measurement of plantar pressures in the clinical risk assessment of the patient.     

The safety and efficacy of mesenchymal stem cell therapy in diabetic lower extremity vascular disease: a meta-analysis and systematic review

Background aimsSeveral studies have shown the efficacy of mesenchymal stem cell (MSC) therapy for lower extremity vascular disease (LEVD) in diabetic patients, but the results are not consistent. Therefore, the authors conducted a meta-analysis of randomized controlled trials (RCTs) to examine the safety and efficacy of MSC therapy in diabetic patients with LEVD.MethodsEight available databases were searched in both English and Chinese to identify RCTs comparing MSC therapy-based conventional treatment with conventional treatment alone in diabetic patients with LEVD. Three investigators independently screened the literature, extracted the data and assessed the risk bias. Meta-analysis was performed using RevMan 5.4.1 and Stata 14.0.ResultsA total of 10 studies involving 453 patients were included. Compared with conventional treatment only, patients receiving MSC therapy-based conventional treatment had a higher ulcer healing rate, greater number of reduced ulcers and shorter complete healing time. MSC therapy also increased ankle–brachial index and transcutaneous oxygen pressure. In addition, four of the included studies showed that MSC therapy significantly improved the number of new collateral vessels. Moreover, no more adverse events were recorded in the MSC group.ConclusionsThis meta-analysis suggests that MSC therapy promotes ulcer healing in diabetic LEVD patients with ulcers, improves blood supply and has a favorable safety profile. More large and well-designed RCTs with long-term follow-up are still needed to explore the safety and efficacy of MSC therapy in diabetic patients with LEVD.     

Community clinics for leg ulcers and impact on healing.

OBJECTIVE--To evaluate the effectiveness of community clinics for leg ulcers. DESIGN--All patients with leg ulceration were invited to community clinics that offered treatment developed in a hospital research clinic. Patients without serious arterial disease (Doppler ankle/brachial index > 0.8) were treated with a high compression bandage of four layers. SETTING--Six community clinics held in health centres in Riverside District Health Authority supported by the Charing Cross vascular surgical service. PATIENTS--All patients referred to the community services with leg ulceration, irrespective of cause and duration of ulceration. MAIN OUTCOME MEASURES--Time to complete healing by the life table method. RESULTS--550 ulcerated legs were seen in 475 patients of mean (SD) age 73.8 (11.9) years. There were 477 venous ulcers of median size 4.2 cm2 (range 0.1-117 cm2), 128 being larger than 10 cm2. These ulcers had been present for a median of three months (range one week to 63 years) with 150 present for over one year. Four layer bandaging in the community clinics achieved complete healing in 318 (69%) venous ulcers by 12 weeks and 375 (83%) by 24 weeks. There were 56 patients with an ankle/brachial arterial pressure index < 0.8, indicating arterial disease. The 50 patients with pressure index < 0.8 > 0.5 were treated with reduced compression, and 24 (56%) healed by 12 weeks and 31 (75%) by 24 weeks. The figures for overall healing for all leg ulcers were 351/550 (67%) at 12 weeks and 417/550 (81%) at 24 weeks, compared with only 11/51 (22%) at 12 weeks before the community clinics were set up. CONCLUSIONS--Community clinics for venous ulcers offer an effective means of achieving healing in most patients with leg ulcers.     

Simple finite element models for use in the design of therapeutic footwear

Therapeutic footwear is frequently prescribed in cases of rheumatoid arthritis and diabetes to relieve or redistribute high plantar pressures in the region of the metatarsal heads. Few guidelines exist as to how these interventions should be designed and what effect such interventions actually have on the plantar pressure distribution. Finite element analysis has the potential to assist in the design process by refining a given intervention or identifying an optimal intervention without having to actually build and test each condition. However, complete and detailed foot models based on medical image segmentation have proven time consuming to build and computationally expensive to solve, hindering their utility in practice. Therefore, the goal of the current work was to determine if a simplified patient-specific model could be used to assist in the design of foot orthoses to reduce the plantar pressure in the metatarsal head region. The approach is illustrated by a case study of a diabetic patient experiencing high pressures and pain over the fifth metatarsal head. The simple foot model was initially calibrated by adjusting the individual loads on the metatarsals to approximate measured peak plantar pressure distributions in the barefoot condition to within 3%. This loading was used in various shod conditions to identify an effective orthosis. Model results for metatarsal pads were considerably higher than measured values but predictions for uniform surfaces were generally within 16% of measured values. The approach enabled virtual prototyping of the orthoses, identifying the most favorable approach to redistribute the patient’s plantar pressures.     

Temporal characteristics of plantar shear distribution: relevance to diabetic patients

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.     

Becaplermin gel (PDGF-BB) as topical wound therapy. Plastic Surgery Educational Foundation DATA Committee

Becaplermin gel is the first topical growth factor to demonstrate therapeutic efficacy in the healing of diabetic wounds. For diabetic patients who have poorly healing ulcers despite good perfusion and a reasonable trial of wound care, this product may be of considerable benefit. It should be tried for a 2-week time period and the results objectively assessed before continuation of therapy.     

Local plantar pressure relief in therapeutic footwear: design guidelines from finite element models

A major goal of therapeutic footwear in patients with pain or those at risk for skin injury is to relieve focal loading under prominent metatarsal heads. One frequent approach is to place plugs of compliant material into the midsole of the shoe. This study investigated 36 plug designs, a combination of three materials, six geometries, and two placements using a two-dimensional (2D) finite element model. Realistic loading conditions were obtained from plantar pressures (PP) recorded during walking in five subjects who wore control midsoles manufactured using Microcell Puff. Measured peak pressures underneath the second metatarsal head were similar to the results of the control model. PP obtained from simulations with the plugs built into a firm midsole were compared to the simulation results of the control midsole. Large plugs (e.g. 40 mm width), made out of Microcell Puff Lite or Plastazote Medium, placed at peak pressure sites, resulted in highest reductions in peak pressures (18-28%). Smaller plugs benefited from tapering when placed at high pressure areas. Case studies were completed on a healthy male subject and a diabetic female patient to address the efficacy of a plug design favored by our simulations (pressure based placement, 40 x 20 mm, Plastazote Medium). Successful reductions of second metatarsal head pressures were observed with a mediolateral load redistribution that was not represented by our model. 2D computer simulations allowed systematic investigation of plug properties without the need for high volume experimentation on human subjects and established basic guidelines for plug selection. In particular, plugs that are placed based on plantar pressure measurements were proven to be more effective when compared to those positioned according to the projection of the bony landmark on the foot-shoe plantar contact area.