Effect of foot sole hardness, thickness and footwear on foot pressure distribution parameters in diabetic neuropathy

This paper presents details of the study undertaken to find the effects of foot sole hardness, thickness and footwear on walking-foot pressure distribution parameters (power ratio (PR)) in diabetic neuropathy. The foot sole hardness is characterized by Shore level. PR represents the ratio of high-frequency power to the total power in the power spectrum of the walking-foot pressure image distribution obtained from the optical pedobarograph. Spatial frequency distributions in the walking-foot pressure images were analysed to calculate the PR in each of the foot sole areas at different levels of foot sole sensation loss and mechanical and geometrical properties. The results show that the increase in PR in the upper foot sole Shore ranges (30-40) is 1.2-2.5 times the corresponding increase in lower Shore ranges (20-30) for some foot sole areas, implying a higher possibility of development of plantar ulcers when combined with deterioration of foot sole sensation. Plantar ulcers are found in feet with foot sole Shore values of 30, a sensation level of 45 mN and PR of 35; for Shore values of 40, sensation levels of 100 mN, with PR 52; and for Shore values above 40, sensation level > 100 mN with PR 58. Providing microcellular rubber insole footwear based on optimum hardness and thickness was found to be helpful in healing plantar ulcers in three to four weeks. Wearing preventive footwear for six months reduced hardness of the foot sole and PR values to near-normal values.

Texture analysis of foot sole soft tissue images in diabetic neuropathy using wavelet transform

The paper presents a new method of characterisation of texture changes in foot sole soft tissue ultrasound (US) images, as observed to occur in diabetic subjects, using wavelet transforms. US images of the soft tissue subcutaneous layer were taken with a 7.5 MHz linear transducer probe placed parallel to the skin surface. The foot sole hardness was characterised by Shore level. A 2D discrete wavelet transform was performed on the US images to extract features that encode the internal state of the foot sole soft tissue. The global energy feature computed at the output of each wavelet channel was found to achieve excellent delineation between the normal and the diabetic groups. An important finding was a strong correlation, in the order of 0.84 and above, between the feature values that reflect changes in the internal arrangement of the tissue, and the externally measurable hardening of the skin, characterised by the Shore levels, with the latter known to be high for diabetics. A comparison drawn between diabetic ulcer and non-ulcer groups established a change in the order of 122-311% in the textural parameter, as influenced by a corresponding 66.7-200% change in the respective Shore values. Thus US examination of foot sole soft tissue and its texture analysis may serve as sources of valuable information regarding the internal changes taking place with progressive hardening of the soft tissue and thereby help the clinician in taking appropriate preventive measures.

Simultaneous determination of lamotrigine, phenobarbitone, carbamazepine and phenytoin in human serum by high-performance liquid chromatography

A simple reversed-phase high-performance liquid chromatography (HPLC) method was developed for the simultaneous estimation of the antiepileptic drugs (AEDs) lamotrigine (LTG), phenobarbitone (PB), carbamazepine (CBZ) and phenytoin (PHT) in human serum. The procedure involves extraction of the AEDs by mixing 200 microl of serum with 200mul of acetonitrile containing 10 microg/ml of pentobarbitone as internal standard (IS). After centrifugation, 10 microl of the supernatant was injected onto a NOVA PAK C-18 column (250 mm x 4.6mm, 5 microm Hypersil ODS) and eluted with a mobile phase consisting of phosphate buffer (10 mM)-methanol-acetonitrile-acetone in the ratio of 55:22:12:11 (v/v) adjusted to pH 7.0. A UV detector set at 210 nm was employed for detection. The AEDs were well resolved from the human serum constituents and the internal standard. The method can quantify LTG, PB, CBZ, and PHT at concentrations as low as 0.2 microg/ml. The method was quantitatively evaluated in terms of linearity, accuracy, precision, recovery, selectivity, sensitivity, and specificity. The method is simple, convenient, and suitable for the analysis of AEDs from human serum.

Three-dimensional stress analysis for the mechanics of plantar ulcers in diabetic neuropathy

In diabetic neuropathic subjects, the hardness of foot sole soft tissue increases, and its thickness reduces, in different foot sole areas. Finite element analysis (FEA) of a three-dimensional two-arch model of the foot was performed to evaluate the effect of foot sole stresses on plantar ulcer development. Three sets of foot sole soft-tissue properties, i.e. isotropic (with control hardness value), diabetic isotropic (with higher hardness value) and anisotropic diabetic conditions, were simulated in the push-off phase, with decreasing foot sole soft-tissue thicknesses in the forefoot region, and the corresponding stresses were calculated. The results of the stress analyses for diabetic subject (anisotropic) foot models showed that, with non-uniformly increased hardness and decreased foot sole soft-tissue thickness, the normal and shear stresses at the foot sole increased (compared with control values) by 52.6% and 53.4%, respectively. Stress analyses also showed high ratios of gradients of normal and shear stresses of the order of 6.6 and 3.3 times the control values on the surface of the foot sole, and high relative values of stress gradients for normal and shear stresses of 6.25 and 4.35 times control values, respectively, between the foot sole surface and the adjacent inner layer of the foot sole, around a particular region of the foot sole with anisotropic properties. These ratios of high gradients and relative gradients of stresses due to changes in soft-tissue properties may be responsible for the development of plantar ulcers in diabetic neuropathic feet.

Diabetic feet at risk: a new method of analysis of walking foot pressure images at different levels of neuropathy for early detection of plantar ulcers

Studies were performed on a large number of diabetic patients with three levels of plantar sensation loss by analysing walking foot pressure images in the frequency domain. The feet of diabetic subjects were scanned over ten specified areas using Semmes-Weinstein's nylon monofilaments to determine quantitatively the three levels of neuropathy. A new parameter, the power ratio (PR, ratio of high frequency power to the total power in an image) was used to distinguish discretely between normal and diabetic feet in three levels of sensation loss. Analysis of results showed that the differences in PR values for diabetic feet (in all three levels of sensation loss) compared to normal feet were found to be highly significant (p<0.0005) in the areas of the foot where there was a high incidence of plantar ulcer formation, even at the early stage of neuropathy characterised by a sensation level of 45mN. This result could help in the early detection of plantar ulcer formation in the initial stage of sensation loss and may be utilised by orthopaedic surgeons to consider early corrective methods to protect these feet from further damage due to neuropathic ulcer formation.

Mechanics of tarsal disintegration and plantar ulcers in leprosy by stress analysis in three dimensional foot models

This paper describes three dimensional two arch models of feet of a normal subject and two leprosy subjects, one in the early stage and the other in the advanced stage of tarsal disintegration, used for analysis of skeletal and plantar soft tissue stresses by finite element technique using NISA software package. The model considered the foot geometry (obtained from X-rays), foot bone, cartilages, ligaments, important muscle forces and sole soft tissue. The stress analysis is carried out for the foot models simulating quasi-static walking phases of heel-strike, mid-stance and push-off. The analysis of the normal foot model shows that highest stresses occur at push-off over the dorsal central part of lateral and medial metatarsals and dorsal junction of calcaneus and cuboid and neck of talus. The skeletal stresses, in early state leprosy with muscle paralysis and in the advanced stage of tarsal distintegration (TD), are higher than those for the normal foot model, by 24% to 65% and 30% to 400%, respectively. The vertical stresses in the soft tissue at the foot-ground interface match well with experimentally measured foot pressures and for the normal and leprosy subjects they are the highest in the push-off phase. In the leprosy subject with advanced TD, the highest soft tissue stresses and shear stresses (about three times the normal value) occur in push-off phase in the scar tissue region. The difference in shear stresses between the sole and the adjacent soft tissue layer in the scar tissue for the same subject is about three times the normal value. It is concluded that the high bone stresses in leprosy may be responsible for tarsal distintegration when the bone mechanical strength decreases due to osteoporosis and the combined effect of high value of footsole vertical stresses, shear stresses and the relative shear stresses between two adjacent soft tissue layers may be responsible for plantar ulcers in the neuropathic leprosy feet.

New on-line parameters for analysis of dynamic foot pressures in neuropathic feet of Hansen's disease subjects

Pressures on the foot during walking are affected by the weight of the person and the walking velocity. It is also found that both the magnitude and duration of the dynamic foot pressures are important in ulcer formation in the neuropathic feet of persons with Hansen's disease (HD). Therefore, new parameters, Normalized Peak Pressure (NPP) and Pressure Contact Ratio (PCR), are calculated from dynamic foot pressure data in 10 defined areas of the feet of 52 nonimpaired controls and 108 persons with HD with different pathologies, using a long barograph that could accommodate at least two foot prints in one walking cycle. Statistical study of these new parameters, for various classes of HD subjects, shows significantly different mean values in the foot areas and hence could aid the clinician in better diagnosis and therapy planning. The second part of the article deals with on-line calculations and gray scale display of these parameter transforms for all the points on the plantar surfaces of both feet in a way that could help the clinician in quick analysis and better management and care of neuropathic feet.

New on-line methods for analysis of walking foot pressures in diabetic neuropathy

In this paper, studies are performed on a large number of diabetic patients belonging to different classes, using new on-line foot pressure parameters, i.e. normalized peak pressure (NPP) and pressure contact ratio (PCR), which include effects of the weight of the subject, velocity of walking and duration of high pressures in any region of the foot. A statistical study of the mean maximum value of these parameters in different plantar areas of the feet, for different classes of diabetic subjects, indicates distinguishing trends and hence could aid the clinician in better diagnosis and therapy planning. The NPP and PCR transforms calculated on-line (using specially developed software) help the clinician to quickly determine the heavily loaded foot areas that are potential sites of ulceration in insensitive feet and take the necessary action to prevent further damage to the foot sole.

Sequence data analysis reveals a relationship between LSR2, the recombinant fusion protein mimicing M. Leprae and VIF of bovine immunodeficiency virus (BIV)

In the course of computer simulation study looking for active sites for the interaction between MHC II and T7--a 12 residue long peptide of LSR2--a recombinant fusion protein mimicing the native bacillus M.Leprae--an interesting relationship between the antigenicity of LSR2 and VIF of BIF has come to light. Computer analysis study has revealed this stretch of residue from 36 to 48 of LSR2 is highly antigenic. The experimental observation seems to confirm the role of this 12 residue peptide in antibody response. In an effort to determine whether a significant sequence level relationship exists between this and any other known protein, the sequence homology of both protein and nucleic acid was studied. It is found that this 12 residue long peptide (T7) of LSR2 is homologous with Viral Infectivity Factor (VIF) of the Bovine Immunodeficiency Virus (BIV). Homology with translated nucleic acid sequence also indicate the same fact. The VIF gene which codes for this protein is known to be essential for ability of cell-free virus preparation to infect cells. These results lead to the question--whether this 12 residue long peptide which is common to both proteins play a role in their infectivity. Whether mutations in the peptide or elimination of this peptide from the protein and studying the effect of this on the diseases themselves may help in controlling them is another important question relevant to medical researchers.

A new DSP-based multichannel EMG acquisition and analysis system

This paper describes the design of a digital signal processor based system for a personal computer for EMG data acquisition to monitor muscle activity during gait and to estimate the power spectrum of the acquired data under normal and pathological conditions. It also gives the hardware details of the velocity meter which is used to monitor the muscle activity with speed of walking. Software has been developed for system initialization, data acquisition, processing of acquired data, and data display for five channels. The developed equipment will be useful to clinicians for enhancing the understanding of a patient's dynamic performance.

Analysis of stresses in two-dimensional models of normal and neuropathic feet

A two-dimensional model of the normal foot skeleton, which includes cartilages and ligaments, is used in this analysis of stresses during three quasi-static walking phases: heel-strike, mid-stance and push-off. It is found that in all the walking phases the maximum values of principal stresses occur in the dorsal anterior region of the talus, whereas the highest stress occurs in the push-off phase. The model is used for the simulation of muscle paralysis and its effect on the distribution of principal stresses. Subsequently, the model is used to analyse stresses in the deformed feet of three leprosy patients with complete paralysis of certain muscles. The results demonstrate that both the shape of the foot and the type of muscle paralysis contribute to the development of high stresses in different regions of the foot. These high stresses in regions with reduced mechanical strength could be one of the important factors in the process of tarsal disintegration in leprosy.

A new modular six-bar linkage trans-femoral prosthesis for walking and squatting

Four-bar linkage mechanisms produced by many designers of knee joints for trans-femoral prostheses can provide knee rotation to permit walking only. In Afro-Asian countries people are accustomed to a squatting posture in their daily activities. A six-bar linkage knee-ankle mechanism trans-femoral prosthesis is described which was developed and fitted to an amputee. The motion patterns of the ankle, knee and thigh during walking and squatting (obtained using a flickering light emitting diode system) for the above prosthesis is compared with motion patterns obtained for normal subjects. The closeness between both the patterns establishes the suitability of the new modular trans-femoral prosthesis for producing near normal patterns of motion during walking and squatting. The additional facility of cross-legged sitting provided in the prosthesis makes it functionally suitable for Afro-Asian amputees.

Analysis of a new polycentric above-knee prosthesis with a pneumatic swing phase control

The four-bar linkage mechanism used by many designers for the knee joint of an above-knee prosthesis can provide knee rotation suitable for walking only. In Afro-Asian countries people are habituated to the squatting posture in their daily activities. A six-bar linkage knee-ankle mechanism above-knee prosthesis with a pneumatic swing phase control is developed and its analysis shows its suitability for producing a motion closely resembling that of a normal subject during walking and squatting.

New image-processing system for analysis, display and measurement of static and dynamic foot pressures

A new image-processing system, using a video digitiser with an IBM-compatible PC/AT, is developed for acquisition and processing of low-contrast, low-intensity barographic images of both feet for assessment of pressure distribution during standing and walking. Data displays, in the form of centres of pressures, isopressures contours, perspective views of pressures, grey scale image and walking pressure patterns, combined image of walking pressures, paths of centres of pressures and pressure variations with time, are developed. These have provided very useful and early information regarding the internal structural changes in the bones of the foot and sites at risk of ulcer development in leprosy subjects and enable suitable corrective orthopaedic procedures to be adopted.

Foot pressure measurement in leprosy and footwear design

Leprosy patients deprived of sensory feedback allow excessive pressures to be applied to feet, thereby cause foot ulcers. Quantitative knowledge of the pressure distribution under leprotic feet is helpful to prevent further damage to foot by designing suitable footwear. This paper describes barographic technique for measurement of pressures under the leprotic feet and the design of special footwear for prevention of foot ulcers.