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Logo for the Journal of Rehab R&D
Vol. 36 No. 3,
July 1999


New On-line Parameters for Analysis of Dynamic Foot Pressures in Neuropathic Feet of Hansen's Disease Subjects

Mahesh M. Bhatia, MS and K.M. Patil, DSc

Biomedical Engineering Division, Department of Applied Mechanics, Indian Institute of Technology, Madras-600036, India

Abstract--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.

Key words: dynamic foot pressures, Hansen's disease, neuropathy, on-line pressure parameters, optical pedobarograph.


Address all correspondence and requests for reprints to: Prof. K. M. Patil, Biomedical Engineering Division, Department of Applied Mechanics, Indian Institute of Technology, Madras-600036, India; email: patilkm@hotmail.com.
 

INTRODUCTION

  Hansen's disease (HD), if left untreated, causes nerve damage that can result in loss of muscle control and crippling of hands and feet. The pathologies (loss of sole sensation, intrinsic muscle paralysis, foot drop, early bone changes, and complete tarsal disintegration in the advanced stage) can be expected to be reflected in the walking foot pressure patterns of persons with this disease (1).

  Dynamic foot pressure measurements reported in the literature (2-7), except those reported recently (8,9), present variations of foot pressures only on one foot at a time. In the neuropathic feet of persons with HD as well as those with diabetes, it is necessary to have foot pressure measurements made on both the feet simultaneously, for at least two steps, such that it could help in proper interpretation of foot pressure data and in detecting changes in both the foot pressures, since both feet could be affected. It is found that foot pressures are affected by the weight of the person (10) and walking velocity (2). It is also reported (11) that the high magnitude of pressure and the duration of its action is also important for the formation of plantar ulcers as well as bone deformities. In an earlier publication (9), one of the authors made an attempt to make on-line pressure measurements on a few controls and typical HD subjects using an optical pedobarograph that could record at least two foot prints at one measurement. The above work only considered the effect of weight on the walking foot pressure and made no attempt to perform the parameter calculation on-line. Therefore, in the present work, two new foot pressure parameters are defined that take into consideration the effect of the weight of the person and walking velocity on foot pressures. The magnitude of peak pressure as well as its duration are calculated for 10 areas of the feet of 52 controls and of 108 persons with HD. Subsequently, these parameters are used to quantify the effects of different pathological disorders on the foot pressure patterns seen in HD. Statistical analysis of these parameters is done to distinguish pathologies that could help the clinician in better diagnosis. Since the calculations of these parameters take considerable time for each patient, it is made on-line to help the clinician in quick analysis and better management and care of neuropathic feet.

 

METHODS

Classification of Subjects
  The pathologies found in HD are mainly divided into the following categories: insensitive foot and claw toes, foot drop, and early and advanced bone changes.

  Insensitive Foot and Claw Toes: partial or complete loss of sensation of the plantar surface and paralysis of intrinsic muscles that causes clawing of toes.

  Foot Drop: paralysis of the peroneal nerve causes paralysis of the dorsiflexors and evertors of the foot. The plantar flexors and invertors remain unaffected. As a result, the affected person cannot have a proper heel strike and tends to walk on the lateral border of the foot.

  Early Bone Changes: these involve decalcification or osteoporosis in the bones, fuzziness in the joints, decrease of joint space, and disappearance of trabeculae.

  Advanced Bone Changes: these involve destruction of the foot bones, namely, navicular, cuneiform, metatarsals, calcaneus, or talus, which may be followed by a complete collapse of the foot arch. Damage in this stage is irreversible.

  A particular foot may have one or more of these pathologies. Accordingly, based on the clinical and radiological data provided by the doctors from the Central Leprosy Teaching and Research Institute (CLTRI), Chengalpattu, India, and the Central Jalma Institute of Leprosy (CJIL), Agra, India, the feet of HD subjects are classified in seven categories with nonimpaired feet used for comparison purposes. They are:

  1. Normal feet that show no external (clinical or radiological) manifestations of the disease.
  2. Insensitive and claw toes.
  3. Insensitive, claw toes, and foot drop.
  4. Early bone changes.
  5. Insensitive, claw toes, and early bone changes.
  6. Insensitive, claw toes, foot drop, and early bone changes.
  7. Insensitive, claw toes, foot drop, and advanced bone changes.

Optical Pedobarograph
  Foot pressure patterns during walking are obtained by using a 1.8 m long optical pedobarograph mounted on load cells; for foot image formation, a video camera for image capturing, an Image-640 video digitizer card (Matrox Electronic Systems Ltd., Dorval, Quebec, Canada), and specially developed image processing software (9) on the IBM PC-AT converted image information into foot pressures (as shown in Figure 1). A module in the program calculates the load acting on the barograph at the instant of image grabbing. The raw load and image data are converted to give the pressures acting on the foot at various stages of the walking cycle.

schematic of the foot image and load data acquisition
and processing system
Figure 1.
Block schematic of the foot image and load data acquisition and processing system.

  The subjects are asked to walk at self-selected speeds. A velocity meter, consisting of two infrared transmitters and receivers placed a fixed distance apart, calculates their speed by dividing this fixed distance by the time interval between the cutting of the two beams. The subjects are given some trial walks to adapt to the experimental environment and to practice walking as normally and consistently as possible. Regarding the starting and stopping characteristics of walking, it has been reported that two steps from starting and three steps from stopping should be excluded from the data due to acceleration and deceleration during those steps (12). Accordingly, we have provided 1.8 m platforms before and after the barograph, so that the subjects walked on the instrument at their average velocities.

Foot Pressure Parameters
Normalized Peak Pressure
  A single frame does not generally contain enough of the footprint to enable visualization of all areas of interest, so a 'combined' display is produced by selecting the maximum pressure from all frames for each element of the display (13). The combined pressure image has been a conventional tool in dynamic foot pressure studies. Foot pressures (P) have been shown to be affected by the body weight (W) and walking velocity (v) of the subject (2,10); hence, the pressures have been normalized with reference to the W and v of the subject to obtain the Normalized Peak Pressure (NPP). The foot is divided into 10 anatomically significant areas as shown in Figure 2, and each area in the foot is scanned for pressure variation with time.

Division of the sole into ten areas
Figure 2.
Division of the sole into ten areas.

The NPP value is calculated at the site of peak pressure in each of the 10 areas by using Equation 1.

  where P=peak pressure in the specified foot area (kPa), W=weight of the subject (N), v=walking velocity of the subject (ms-1). Multiplication by 100 is done to convert the fractions into whole numbers. The unit of NPP is kPaN-1(ms-1)-1.

Pressure Contact Ratio
  In HD with sensory paralysis, it is found (11) that the foot subjected to moderate pressures over a long time is more prone to ulcers than the one subjected to high pressures for a short time. Therefore, a new parameter known as Pressure Contact Ratio (PCR) takes into account both the pressure and the time over which it acts. PCR is defined as shown in Equation 2 for 10 areas of the foot. Foot pressures have been shown to be affected by the W and v of the subjects (2,10); hence, PCR has been normalized with respect to these variables. The foot is divided into the 10 areas shown in Figure 2, and PCR value is calculated for each using Equation 2.

  where t=time (s) during which greater than or equal to50 percent of peak pressure acts on the specified foot area, T=total contact time of the same foot (s), P=peak pressure in the specified foot area (kPa), W=weight of the subject (N), v=walking velocity of the subject (ms-1). Multiplication by 100 is done to convert the fractions into a whole number. The unit of PCR is kPaN-1(ms-1)-1.

On-line Calculation of Parameters
  Since it takes considerable time to calculate NPP and PCR by scanning each of the 10 areas of the foot, an on-line method of calculation of both parameters is devised for quick assessment of foot under the high and long-term loading that leads to ulcers on the sole.

NPP Transform
  The on-line NPP transform is computed (using Equation 1) by finding the maximum pressure at each point on the feet during the walking cycle and then plotting all the maximum pressure points (normalized with reference to W and v) as a gray-scale image (see Figure 3). Thus, it represents in one image the history of maximum pressures occurring during the entire walking cycle.

Start
down arrow
Capture Background image
down arrow
Start grabbing foreground image
when load 10% dead load
down arrow
Acquire foreground images for 48
frames or until the subject leaves the barograph
down arrow
Subtract background image from
foreground image
down arrow
Apply thresholding function to
resultant image
down arrow
Select the region of interest by
interactive windowing
down arrow
Read the stored significant pixel value,
load cell factor, and pixel area
down arrow
Convert image intensity to pressure,
using calibration curve shapes and
corner points
down arrow
Walking velocity Right arrow Normalize and display 7-level pseudo
color NPP and PCR transforms
Body
Left arrow Weight
down arrow
End 

Figure 3. Flowchart for the on-line acquisition, processing and analysis of the image and load data.

PCR Transform
  The on-line PCR transform is computed (using Equation 2) by finding the PCR values at each point on the foot during the walking cycle and then plotting these as a gray-scale image (the process is similar to the one shown in Figure 3).

 

RESULTS

Comparison of NPP Values between Controls and Persons with Hansen's Disease
  Table 1 presents variations of mean NPP values in the 10 areas of the foot for controls and HD subjects with different pathologies. Statistical study is done to compare the variations of NPP values. The mean NPP values for normal feet of HD subjects are found to be significantly greater in lateral heel, indicated by area 2 (p<0.0125), lateral mid-foot (area 4, p<0.05), second metatarsals (area 6, p<0.025), third to fifth metatarsals (area 7, p < 0.01) and first toe (area 8, p<0.0005). The mean NPP values of HD subjects with early bone changes differ significantly only in areas 1 and 3 (p<0.05). The mean values for insensitive feet with claw toes are significently higher in areas 1 (p<0.05), 5 (p<0.01), 6 (p<0.005) and 7 (p<0.0025). No differences in mean NPP values are found between controls and the feet with insensitivity, claw toes, and foot drop. The mean NPP values for the feet with insensitivity, claw toes, and early bone changes, are significantly higher only in metatarsal regions: areas 5 (p<0.01), 6 (p<0.05), and 7 (p<0.01). Feet with insensitivity, claw toes, foot drop, and early bone changes show significantly higher values only in areas 6 and 7 (p<0.05). The most significant differences are observed in feet with insensitivity, claw toes, foot drop and advanced bone changes; their values are much higher in the mid-foot (areas 3 and 4 (p<0.0005)) and lower in first and second toes (areas 8 (p<0.0005) and 9 (p<0.0025)) and in the lateral metatarsals (area 7 (p<0.05)).


Table 1.
Comparative NPP values [kPaN-1(ms-1)-1] in ten areas of the foot for controls and subjects with Hansen's disease (HD) with different pathologies.
 
Areas of the Foot 1 2 3 4 5 6 7 8 9 10

Controls
(n=52)
36.0
(14.3)
36.1
(14.7)
1.1
(5.0)
21.7
(13.3)
38.8
(14.8)
41.4
(13.7)
41.9
(14.2)
40.8
(17.2)
32.5
(14.0)
30.6
(16.0)
HD Patients
Normal
foot
(n=19)
43.3
(27.9)
47.8**
(26.9)
0.9
(3.8)
35.4++
(31.1)
44.6
(32.4)
60.7+
(58.1)
70.3*
(43.6)
63.2x
(37.5)
31.1
(24.4)
30.5
(28.3)
Early bone changes (n=15) 28.8++
(14.0)
30.0
(16.4)
4.2++
(6.4)
25.7
(10.1)
33.6
(17.9)
38.2
(17.0)
49.2
(28.9)
41.5
(35.9)
28.7
(28.5)
25.0
(20.1)
Insensitive foot, claw toes (n=19) 44.4++
(21.0)
42.8
(19.7)
2.1
(9.3)
24.4
(16.9)
50.0*
(21.7)
58.0xx
(36.7)
67.1@
(55.7)
54.1
(51.0)
31.8
(17.2)
28.3
(18.0)
Insensitive foot, claw toes, foot drop (n=9) 43.3
(10.5)
41.1
(11.2)
0.0
(0.0)
25.3
(16.4)
46.5
(18.6)
44.6
(11.5)
45.7
(11.1)
43.8
(17.9)
36.9
(20.8)
36.0
(17.9)
Insensitive foot, claw toes, early bone changes (n=18) 40.0
(15.9)
41.2
(14.8)
2.9
(9.3)
25.0
(14.1)
52.1*
(26.4)
50.1++
(22.4)
59.5*
(41.9)
32.5
(31.5)
25.9
(17.1)
25.7
(14.3)
Insensitive foot, claw toes, foot drop, early bone changes (n=5) 38.1
(25.8)
38.2
(24.1)
0.0
(0.0)
23.0
(7.1)
47.1
(22.8)
56.1++
(33.7)
55.5++
(28.0)
35.8
(38.0)
41.3
(35.0)
39.7
(34.6)
Insensitive foot, claw toes, foot drop, ad-
vanced bone changes
(n=9)
37.7
(15.8)
42.5
(19.5)
25.6x
(23.8)
48.0x
(21.4)
39.3
(20.2)
40.0
(19.9)
31.2++
(19.0)
11.1x
(22.1)
14.2@
(30.7)
27.0
(33.1)

Values in the table indicate the mean and those in parentheses the standard deviation; the number of samples in a class is denoted by n, and all calculations are done at 95% confidence level. The student t test p values are indicated as xp<0.0005; xxp<0.005; @p<0.0025; *p<0.01; **p<0.0125; +p<0.025; ++p<0.05.
 

  In Figure 4, Plot a shows that the NPP values of HD subjects with normal feet are greater than those of controls, especially in the heel, metatarsal head regions, and big toe. This may be an indicator of some changes that have yet to manifest themselves in clinical and radiological tests. Plot b illustrates that the values for controls and HD with early bone changes are almost similar in all the areas; thus, these values do not distinguish well between these two classes. Plot c shows that the NPP values of feet with advanced bone changes (such as tarsal disintegration) are much higher in the mid-foot region than those of controls, because of the complete collapse of the arch in these feet. Further, in most of the subjects belonging to this class, the forefoot is partially or totally absorbed, and toes are severely clawed and lifted off the ground, thus showing lower NPP values in those areas. It is clear from Plot d that HD with insensitive feet and claw toes show higher NPP values in the metatarsal head regions than controls. This high loading, coupled with loss of sensation on the plantar surface, may explain the high incidence of ulcers in the metatarsal head regions of HD subjects (11).

Comparison of mean NPP values
Figure 4.
Comparison of mean NPP values (with 95 percent confidence level) of controls with those of HD subjects with various pathologies (I=insensitive foot, C=claw toes, A=advanced bone changes (tarsal disintegration), F=foot drop).

Comparison of PCR Values between Controls and Hansen's Disease Subjects
  Table 2 presents variations of mean PCR values in different areas of the foot for controls and for the different pathologies connected with HD. Significantly higher mean PCR values are shown by the normal feet of HD subjects in the lateral mid-foot (area 4 (p<0.025)), and lateral metatarsals (3rd, 4th, and 5th combined) indicated by area 7 (p<0.0005). Differences in mean values are observed in more areas of the feet of HD subjects with early bone changes: they are significantly lower in the heel (areas 1 and 2 (p<0.05)), and higher in the mid-foot (area 3 (p<0.0025) and area 4 (p<0.0125)). The values of those with insensitive foot and claw toes are significantly higher in the heel (areas 1 and 2 (p<0.05)), the forefoot (areas 5 and 6 (p<0.0005), area 7 (p< 0.0025)), and in the first toe (area 8 (p<0.05)). In the pathology of insensitive foot, claw toe, and foot drop, significantly higher mean values are observed in a part of the forefoot (areas 5 (p<0.025) and 7 (p<0.05)); while in insensitive foot, claw toes, and early bone changes, the mean values are significantly higher in the heel (area 1 (p<0.0025), area 2 (p<0.01)), and forefoot (areas 5 (p<0.005), 6, and 7 (p<0.0025)). The insensitive feet with claw toes, foot drop, and early bone changes show significantly higher mean values in areas 6 (p<0.05), 7 (p<0.005), 9, and 10 (p<0.05). The most significant differences in mean PCR values are observed in the HD subjects with insensitive feet, claw toes, foot drop, and advanced bone changes: these are much higher in the mid-foot (areas 3 and 4 (p<0.0005)) and lower in the forefoot (areas 5 (p<0.05), 6 (p<0.01)), and toes (areas 8, 9 (p<0.0005), and 10 (p<0.0125)).


Table 2.
Comparative PCR values [kPaN-1(ms-1)-1] in ten areas of the foot for controls and subjects with Hansen's disease (HD) with different pathologies.
 
Areas of the Foot 1 2 3 4 5 6 7 8 9 10

Controls
(n=52)
19.3
(9.9)
19.1
(10.3)
0.1
(0.9)
10.0
(6.8)
21.8
(10.2)
25.1
(9.6)
24.6
(9.4)
21.1
(13.8)
12.8
(8.5)
12.3
(9.3)
HD Patients
Normal
foot
(n=18)
24.0
(14.2)
22.4
(12.8)
0.2
(0.8)
15.0+
(12.2)
20.9
(13.9)
28.6
(12.5)
35.9x
(16.4)
26.9
(21.4)
10.9
(7.0)
11.4
(9.2)
Early bone changes (n=15) 14.0++
(7.6)
13.7++
(6.5)
1.6@
(3.0)
14.8**
(7.7)
20.5
(8.1)
24.4
(10.4)
23.3
(11.1)
21.6
(18.2)
12.9
(12.2)
15.3
(15.1)
Insensitive foot, claw toes (n=19) 24.7++
(11.2)
24.1++
(12.3)
0.8
(3.5)
10.5
(7.6)
33.3x
(12.5)
36.5x
(16.6)
35.5@
(18.2)
29.2++
(23.8)
13.8
(8.8)
13.4
(10.1)
Insensitive foot, claw toes, foot drop (n=8) 23.1
(7.3)
20.5
(8.0)
0.0
(0.0)
14.2
(14.0)
30.7+
(16.8)
30.2
(8.1)
30.8++
(6.0)
19.1
(11.2)
13.7
(10.9)
20.4+
(12.0)
Insensitive foot, claw toes, early bone changes (n=25) 27.4@
(14.3)
25.7*
(12.4)
0.6
(2.9)
11.6
(9.7)
34.3xx
(29.1)
33.4@
(13.4)
38.9@
(29.0)
23.0
(21.1)
9.9
(7.4)
12.2
(10.4)
Insensitive foot, claw toes, foot drop, early bone changes (n=5) 23.2
(18.3)
21.4
(14.7)
0.0
(0.0)
10.2
(5.9)
27.7
(16.9)
37.6++
(26.1)
38.6xx
(23.6)
16.4
(22.0)
21.4++
(23.8)
21.3++
(25.9)
Insensitive foot, claw toes, foot drop, ad-
vanced bone changes
(n=9)
18.7
(10.2)
20.5
(14.8)
13.0x
(11.0)
31.8x
(16.5)
15.3++
(6.8)
16.3*
(10.4)
19.7
(12.3)
2.2x
(4.5)
0.6x
(1.2)
4.7**
(6.2)

Values in the table indicate the mean and those in parentheses the standard deviation; the number of samples in a class is denoted by n, and all calculations are done at 95% confidence level. The student t test p values are indicated as xp<0.0005; xxp<0.005; @p<0.0025; *p<0.01; **p<0.0125; +p<0.025; ++p<0.05.
 

  In Figure 5, Plot a shows that the PCR values of HD subjects with normal feet are higher than those of the controls, especially in the heel, metatarsal head regions, and big toe. This may be an indicator of some changes that have yet to manifest themselves in clinical and radiological tests. Plot b illustrates that the values for controls and feet with early bone changes are almost similar in all areas, and thus not useful for clearly distinguishing between the two classes. Plot c shows that the PCR values of feet with advanced bone changes are much higher in the mid-foot region, because of the complete collapse of the arch in these feet. Further, in most of the subjects in this class, the forefoot is partially or totally absorbed, and toes are severely clawed and lifted off the ground, thus showing lower PCR values in the forefoot and toes. It is clear from Plot d that HD subjects with insensitive feet and claw toes have higher PCR values in the metatarsal head regions than controls. This high loading, coupled with a loss of sensation on the plantar surface, may explain the high incidence of ulcers in the metatarsal head regions in these persons (11).

Comparison of mean PCR values
Figure 5.
Comparison of mean PCR values (with 95 percent confidence level) of controls with those of HD subjects with various pathologies (I=insensitive foot, C=claw toes, A=advanced bone changes (tarsal disintegration), F=foot drop).

NPP Transforms
  Figure 6 shows the gray-scale NPP transform of the dynamic image of a control subject. The maximum NPP value is 86.62 kPaN-1(ms-1)-1.

Gray-scale NPP transform
Figure 6.
Gray-scale NPP transform of the dynamic image of a control (NPP scale in kPaN-1(ms-1)-1).

There is no localization of pressures, and they are well distributed on the entire plantar surface. Figure 7 illustrates the gray-scale NPP transform of the dynamic image of a HD subject with completely insensitive feet and complete tarsal disintegration of the right foot.

HD subject with complete tarsal disintegration
Figure 7.
Gray-scale NPP transform of the dynamic image of a HD subject with a complete tarsal disintegration of the right foot (NPP scale in kPaN-1(ms-1)-1).

Compared to the value of NPP in the medial mid-foot region for controls (mean value 1.1 kPaN-1(ms-1)-1, obtained from Table 1), this subject shows very high values of NPP in the mid-foot region of the right foot (89.59 kPaN-1(ms-1)-1), clearly indicating the collapsed arch of his right foot.

PCR Transforms
  Figure 8 shows the gray scale PCR transform of the dynamic image of a control. The maximum value of PCR is 53.2 kPaN-1(ms-1)-1. The values are uniformly and symmetrically distributed over both the feet and there is no localized concentration of values of PCR in small areas. Figure 9 illustrates the gray scale PCR transform of the dynamic image of a HD subject with completely insensitive feet and complete tarsal disintegration of the right foot.

dynamic image of a control
Figure 8.
Gray-scale PCR transform of the dynamic image of a control (PCR scale in kPaN-1(ms-1)-1).
HD subject with a complete tarsal disintegration
Figure 9.
Gray-scale PCR transform of the dynamic image of a HD subject with a complete tarsal disintegration of the right foot (PCR scale in kPaN-1(ms-1)-1).

Compared to the value of PCR in the medial mid-foot region for controls (mean value 0.1 kPaN-1(ms-1)-1, obtained from Table 2), this subject shows very high values of PCR in the mid-foot region of the right foot (41.7 kPaN-1(ms-1)-1), clearly indicating the collapsed arch of his right foot. Thus this subject shows high values of both NPP and PCR in the mid-foot region of the right foot. Figure 10 shows the gray scale PCR transform of the dynamic image of a HD subject with a complete loss of sensation on the soles of both feet and also scars on the fifth metatarsal head of the right foot and first metatarsal head of the left foot. The site of scars can be easily detected on the image in a form of localized concentration of PCR values (49.9 kPaN-1(ms-1)-1) at their place of occurrence. Since the feet have no sensation, the sites of scars are at risk of reulceration, if proper care is not taken.

HD subject with completely insensitive feet
Figure 10.
Gray-scale PCR transform of the dynamic image of a HD subject with completely insensitive feet and scar on the first metatarsal head (left foot) and fifth metatarsal head (right foot) (PCR scale in kPaN-1(ms-1)-1).

 

DISCUSSION

  Values of both the foot pressure parameters (mean NPP and PCR) of the clinically and radiologically normal feet of HD subjects are significantly higher than those of the controls. This could possibly indicate some early changes that have yet to manifest themselves externally. Significantly lower values of both the mean NPP and PCR in areas 1 and 3 are observed for HD subjects with early bone changes, and those having insensitive feet and claw toes show significantly higher mean NPP and PCR values in the heel (area 1) and metatarsal head regions (areas 5, 6, and 7). HD subjects with insensitive feet, claw toes, early bone changes and foot drop show significantly higher values of both the NPP and PCR in the forefoot (areas 6 and 7). This high loading, coupled with a loss of sensation on the plantar surface, may explain the high incidence of ulcers in the metatarsal head regions of such persons (11). For those with insensitive feet, claw toes, foot drop and advanced bone changes, both NPP and PCR are significantly higher (p<0.0005) in the mid-foot (areas 3 and 4) and toes (areas 8 and 9). Thus, the high loading with loss of plantar sensation and tarsal bone disintegration could be responsible for incidence of ulcers in the mid-foot and toe regions (14).
 

CONCLUSIONS

  A statistical study of the new foot pressure parameters, NPP and PCR, for various classes of HD subjects indicates significantly different mean values of these new parameters, compared to those of controls, in the foot areas, and hence may aid the clinician in better diagnosis and therapy planning. On-line calculation and gray scale display of NPP and PCR transforms for plantar surfaces of both feet help the clinician to quickly assess the areas of the feet subjected to high and long duration loading. These areas, with both parameters being high, are at a great risk of ulceration if there is no plantar sensation in these areas. The above-mentioned gray-scale plots can aid the clinician to prescribe suitable footwear to redistribute the localized high pressures, so that the foot can be saved from further degenerative changes such as recurrent ulceration and amputation.

  The foot pressure parameters proposed in this article need not be confined to the study of the neuropathic feet of HD subjects alone, but can also be used in the study of diabetic feet, as both have neuropathy as a common pathological condition. Use of these parameters can be made even in diseases such as rheumatoid arthritis and other foot anomalies that alter gait and affect foot pressure patterns.


ACKNOWLEDGMENTS

  The authors are grateful to Dr. P. K. Oommen, Joint Director, Central Leprosy Teaching and Research Institute, Chengalpattu and Dr. G. N. Malaviya, Deputy Director, Central Jalma Institute of Leprosy, Agra, for providing the clinical and radiological data of HD subjects.


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