Neuropathic diabetic patients do not have reduced variability of plantar loading during gait.

The objective of this study was to measure the variability of plantar loading during gait and explore the differences between neuropathic and non-neuropathic patients. At least 50 cycles of in-shoe plantar pressure data were recorded as 39 patients (13 non-diabetic, 13 diabetic non-neuropathic, 13 diabetic neuropathic) walked overground in two different types of footwear. As measured by both log mean squared error and coefficient of variation, the results showed that variability was not significantly influenced by the diagnostic group for any shoe condition or for any region of the foot. These findings suggest that reduced variability in plantar loading is not a factor in the development of plantar lesions in neuropathic patients. Copyright 1998 Elsevier Science B.V. All rights reserved

In-shoe force measurements from locomotion in simulated zero gravity during parabolic flight.

INTRODUCTION:: No effective countermeasure for space-induced bone loss has yet been identified. It has been hypothesized that an effective exercise regimen would elicit loads on the lower extremity which resemble those encountered on Earth. Although a treadmill has been used on shuttle flights, the loads to which the lower extremity was exposed have not yet been quantified. It is believed that these loads are much less than the loads experienced in 1G. The purpose of this study was to determine the magnitude of lower extremity loading during tethered treadmill exercise in a 0G environment. METHODS:: Data were collected on five subjects (avg. ht. 177.3+/-10.1 cm, avg. mass 78.3+/-18.0 kg) onboard the KC-135, a NASA airplane used to simulate periods of zero gravity through parabolic flight. Subjects ambulated at 4 speeds: a walk (1.56m/sec), fast walk (2.0m/sec) slow jog (2.75m/sec), and jog (3.35m/sec) on the NASA treadmill operated in either a passive or motorized mode. Each subject wore a harness connected to the Subject Load Device (SLD) to tether them to the treadmill. The tension in the SLD was subjectively adjusted for comfort by each subject. Force data were collected at 60 Hz using Pedar insoles. The number of parabolas per subject was variable due to motion sickness and hardware problems. RESULTS:: Analysis of the insole data showed that the average SLD load was only 35.2% BW, although the values ranged from 20.1% to 56.6%. Maximum ground reaction force values increased with increasing speed and were not affected by treadmill mode. The impulse was higher during walking with the treadmill in the passive mode than in the active mode, but this difference diminished with increasing speed. Subjects tended to run on their forefeet, as shown from the extremely small heel impulse values. At higher speeds, heel contact was absent, while forefoot impulse became more pronounced. DISCUSSION:: All force values were lower than those reported from 1G studies, where typical peak ground reaction forces are 1.2xBW and 2.5xBW for walking and running, respectively. At every speed, the ratio of the rearfoot to forefoot impulse was much lower than reported from 1G studies, and this ratio decreased with increasing speed. CONCLUSIONS:: If the exposure to forces similar to those in 1G is a requirement for countermeasures against space-induced osteoporosis, the loads in the SLD must be greatly increased and should be directly measured before exercise.

Structural and functional aspects of the diabetic foot.

INTRODUCTION:: It has been well documented that, on average, patients with diabetes mellitus (DM) have higher plantar pressures than persons without DM, and there are several hypotheses why this may be -- many focused on the role of peripheral neuropathy. The purposes of this study were: (A) To identify and quantify structural differences between age-matched diabetic and non diabetic subjects, and (B) to develop predictive equations for peak pressure in these same patients. METHODS:: Standardized lateral and dorsi-plantar weight bearing plain radiographs of the right foot and ankle of 50 symptom free (NDM), 32 diabetic with no signs of neuropathy (NNP), and 73 diabetic neuropathic (NP) subjects were taken by a single radiographer. Twenty six angular and linear measurements were then made from the films. Plantar pressure distribution from three first step walking trials were collected and peak pressures at 10 discrete sites were determined for each step, and averaged. A one-way ANOVA with Tukey post hoc tests was conducted to test for differences between the means of each of the 26 radiographic measurements at the 0.01 significant level. Regression analysis was also used to predict the ln(pressure) under the heel, midfoot, mth1, mth2, and mth5 regions from the radiographic measurements, range of motion at the talocrural and first metatarsophalangeal joints and weight, for each of the 3 groups independently. RESULTS:: Significant differences were found among the three groups in 5 of the 26 radiographic measurements (Table 1). These included the thickness of the first, second and third metatarsals from the AP view (MT1, MT2 and MT3 -- generally > in NP), and the sesamoid height (NP > others) and fifth metatarsal head height (NDM < others). In addition, non significant trends were found in 4 other radiographic measurements. Regression analysis identified groups of up to five[Table: see text] predictors which accounted for between 27% and 62% of the variance in peak plantar pressure in different subject groups and foot regions. DISCUSSION AND CONCLUSIONS:: We conclude that objective differences in foot structure are present in diabetic neuropathic subjects, and that DM per se is apparently not a factor in these differences. We also concluded that static foot structure accounts for anywhere between approximately 30% to 60% of the variance in regional peak pressure, depending on the region investigated. In most cases predictions were higher in the midfoot and forefoot.

Ground reaction force and plantar pressure reduction in an incremental weight bearing system.

INTRODUCTION:: With increasing frequency, harness-supported treadmill ambulation has been advocated in patient use in order to provide reduction in weight-bearing to healing tissues and as a method which reduces the energy cost of treadmill ambulation. The purpose of this study was to analyse the ability of one of these devices (Zuni Exercise System) to support a percentage of a subject's body weight during walking and running and to explore the relationship of unloading to pressure reduction in selected plantar surface regions of the foot. METHODS:: Ten healthy male volunteers with no known foot pathology participated in this study. In-shoe plantar pressure (PEDAR) and vertical ground reaction force (GRF) were measured during walking and running at full body weight and at a 20% body[Figure: see text][Figure: see text] weight supported setting. Statistical evaluation used a one way ANOVA and a post-hoc paired t-test with significance set at p < 0.05. RESULTS:: Walking with a setting of 20% body weight supported was achieved with a reduction of the first and second vertical force peaks of 23.8+/-7.3% and 27.2+/-4.1% respectively, somewhat greater than the selected setting (Figure 1). The total force time integral during walking unloaded was 22.8+/-3.3%, which was only slightly greater than the selected 20% reduction. During running the active vertical force peak and total force time integral were reduced by 19.9+/-6.0% and 20.0+/-3.3% respectively during the unloaded condition (Figure 2). Plantar pressures were reduced from 6.8 - 27.8% during body weight supported conditions. The reduction in plantar pressure was variable across different regions of the foot with the toes in walking and the medial forefoot region in running being the least unloaded. DISCUSSION AND CONCLUSIONS:: The Zuni Exercise System appears to be a valid device to predictably reduce the vertical component of the GRF during walking and running with 20% body weight supported. Plantar pressures were reduced during body weight supported conditions but the reduction varied at different regions of the foot. However, the variability of the reduction across subjects was substantial, implying that a given regional pressure may not be as predictably reduced during a body weight supported condition. This highlights the difficulty a practitioner has in the ability to confidently reduce pressure by a set amount in a selected foot region by using assistive devices without direct in-shoe measurements.

Finite element modelling of plantar pressure beneath the second ray with flexor muscle loading.

INTRODUCTION:: Little is understood about the effects of flexor loading on plantar pressure distribution. The goal of the current work is to model flexor muscle loading applied to the distal phalanges in order to study the effect of these loads on plantar normal stress (pressure) beneath the metatarsal head. METHODS:: The finite element model is a two-dimensional, plane strain sagittal section incorporating the second metatarsal, proximal phalanx, and plantar and dorsal soft tissue (Figure 1). The metatarsophalangeal joint is simulated by a nodal hinge that transfers loads and produces reasonable kinematic motion between the articular surfaces of the proximal[Figure: see text] phalanx and metatarsal head. Soft tissues are simulated by a uniform continuum. A single flexor tendon passes over the condyle of the metatarsal heads with sliding contact against intervening soft tissue, and is attached to the distal end of the proximal phalanx. A rigid element at the proximal end is fixed by boundary conditions to simulate reactions at the distal cuneiform joint. Material properties of bone are from published values, one tenth the stiffness of bone is used for the flexor tendon, and the soft tissue continuum is hyperelastic using coefficients obtained from compression of the heel plantar fat pad. A 188 N vertical ground reaction force and a flexor tendon load at a 10 degree angle from the X (horizontal) axis are applied to the model. RESULTS:: Figure 2 shows Y direction normal stress distribution along the plantar surface for two load cases: no load and a 250 N load to the flexor tendon. DISCUSSION:: Bending moments at the proximal metatarsal correspond to values obtained by Sharkey et al. Tension in the flexor tendon served to counter the moment in the metatarsal created by the vertical load, and at the same time, to apply an additional axial load. Under flexor loading, focal plantar pressure shifts toward the proximal phalanx and yields a 60% reduction in peak pressure, indicative of the load sharing between the sub-metatarsal head and subphalangeal regions. [Figure: see text] CONCLUSIONS:: The model yields verifiable and reasonable reactions and a significant relationship between flexor muscle loading and peak plantar pressure. Refinement of the model, such as adding the middle and distal phalanges, should reveal further insight into the mechanics of plantar loading.

Analytical approaches to the determination of pressure distribution under a plantar prominence.

INTRODUCTION:: The purpose of the current research was to develop an analytical model for the interface between the metatarsal head, surrounding soft tissue, and the shoe. Results of 'peak plantar pressures' computed from this model were compared to previous results obtained from clinical data and from a finite element (FE) model. METHODS:: An analytical model for determining the pressure distribution at the interface between the foot and shoe insole was developed based on the solution[Figure: see text] for a rigid cylinder and a single elastic layer mounted on a rigid half-space originally developed by Meijers (see Figure 1). The rigid cylinder was used to represent the metatarsal head region (including bone and soft tissue). Material properties and loading conditions were chosen to reflect those used by Lemmon et al. for 'Normal' and 'Reduced' soft tissue thickness cases. RESULTS:: Peak pressures computed from the analytical model are plotted against insole thickness in Figure 1, alongside experimental and FE model data from Lemmon et al. Correlations between analytical, FE, and experimental results for both the Normal and Reduced soft tissue cases were all highly significant (r(2) = 0.86, p < 0.01). DISCUSSION:: The analytical model produced unrealistically high peak pressures compared to the FE and experimental results, with differences of approximately one order of magnitude. This was not surprising, given that the entire metatarsal head region (soft tissue included) was modelled as a rigid cylinder. The soft tissue on the bottom of the foot, and the much greater surface area over which the loads are carried in the real case, contribute greatly to reducing these peak pressure values. However, the downward trend in peak pressure with increased insole thickness was retained. CONCLUSION:: It is anticipated that the use of more accurate and detailed models will greatly improve the initial results.