9Foot Pressure Abnormalities in the Diabetic Foot

Thomas E. Lyons, DPM, Barry I. Rosenblum, DPM,and Aristidis Veves, MD, DSc

INTRODUCTION

For more than 50 years, foot pressure measurements have been used to evaluatemany medical conditions. Early techniques to assess plantar foot pressure were simple,innovative methods that provided investigators with semiquantitative data. The intro-duction of the optical pedobarograph significantly improved the accuracy of foot pres-sure measurements. Furthermore, computer technologies have allowed accurate andreproducible measurements that can be used not only for research purposes, but also fortreating patients with diabetes mellitus.

Foot pressure measurements and plantar ulceration have been extensively researchedin the insensate foot (1–19). In western societies, the principal cause of the insensatefoot is diabetes mellitus; in other regions of the world, leprosy remains an importantcontributing factor (19). In fact, the study of patients with Hansen’s disease has allowedan understanding of the pathophysiology of the insensate foot and its principles of treat-ment (19). Moreover, the foot pressure measurements can be clinically valuable in otherclinical entities such as rheumatoid arthritis, hallux valgus, and sports medicine.

METHODS OF MEASURING FOOT PRESSURES

Out-of-Shoe Methods

One of the earliest studies to examine foot pressures was that of Beely in 1882 (20).Subjects ambulated over a cloth-filled sack filled with plaster of Paris to produce a foot-print. Beely postulated that the plaster would capture the plantar aspect of the foot withthe highest load, representing the deepest impression. However, this primitive techniquewas limited because it represented a crude measurement the total force of the foot cre-ating the impression rather than the dynamic pressures underneath the foot during gait.Moreover, this method was strictly qualitative and therefore susceptible to both inter-and intraobserver unreliability.

In 1930, Morton (21) described a ridged, deformable rubber pad, termed the kineto-graph. This pad made contact with an inked paper placed underneath the foot as the sub-ject ambulated over the pad. The kinetograph examined the relationship between thestatic and rigid foot deformity and was the first documented attempt to measure foot

From: The Diabetic Foot, Second EditionEdited by: A. Veves, J. M. Giurini, and F. W. LoGerfo © Humana Press Inc., Totowa, NJ

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pressures rather than forces. Elftman (22) further developed a system that allowed forthe observation of dynamic changes in pressure distribution as the subject ambulated.This device was called the barograph and consisted of a rubber mat that was smoothon top yet studded with pyramidal projections on the bottom. The mat was placed ona glass plated, and as subjects ambulated over the mat, the area of contact of the pro-jections increased according to changes in the pressures under the foot. A video cam-era recorded the deformation pattern of the mat from below as the subject walked onthe mat.

Harris–Beath Mat

Similarly, in 1947, Harris and Beath (23) used a similar method to study foot prob-lems and related foot pressure changes in a large group of Canadian soldiers. Theirdevice used a multilayered inked rubber mat that allowed contact with a piece of paperbelow. When pressure was applied to the mat with ambulation, the ink escaped from it,thereby staining the paper. Thus, the density of the inked impression was dependent onthe applied pressure. By using this technique, Barrett and Mooney (24) found high load-ing under the feet of subjects with diabetes. The major problem with this device, how-ever, was that it could not be calibrated to various degrees of foot pressures and thereforethe Harris–Beath Mat would saturate at levels within the normal limits of foot pressures.Furthermore, the amount of ink placed onto the mat could not be standardized. Silvinoand associates (25), however, calibrated the Harris–Beath mat by using a contact area ofknown size and weight, thereby producing both qualitative and semiquantitative data.

Podotrack

A similar device to the Harris–Beath mat is the Podotrack system (Medical GaitTechnology, The Netherlands). The system is based on the principles of the Harris–Beath mat. However, the footprint impression is produced by a chemical reaction withcarbon paper instead of ink. The Podotrack system has a few advantages over theHarris–Beath mat. For example, there is a standard ink layer that is carbon paper.Furthermore, the system can be calibrated with a scale representing shades of colorscorresponding to foot pressures. In 1994, a study reported that the Podotrack systemprovided reproducible results in 61% of the foot pressure values when compared withthose obtained from the pedobarograph (26). Furthermore, the Podotrack and pedo-barograph systems were comparatively examined. By placing the Podotrack system ontop of the pedobarograph, one could obtain real-time data as subjects ambulated overboth systems.

In 1974, Arcan and Brull (27) described a system that had the capability of provid-ing more detailed, though semiquantitative, information regarding foot pressure distri-bution. The apparatus consisted of a rigid transparent platform with optical filters. Anoptically sensitive elastic material and reflective layer were combined together. Footpressure measurements were performed either statically or dynamically, and thechanges in motion of the foot were recorded using a video camera.

An earlier quantitative technique to measure foot pressures was described by Huttonand Drabble in 1972 (28). Their device consisted of a force plate in which 12 beams weresuspended from two load cells. These load cells were attached to several sets of wirestrain gauges that permitted the measurement of longitudinal tension. The apparatus was

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placed onto the walkway because subjects could step on and off the plate during their gaitcycle. By using this technique, Scott and colleagues (29) scrutinized the load distributionin subjects with and without pes planus (flatfeet) and hallux valgus deformities. The dis-tribution of peak loads was expressed as a percentage of body weight and the resultsdemonstrated that the load of the control subjects was low in the midfoot and high in theforefoot. However, there was considerable variation in loads across the ball of the foot.Conversely, in subjects with pes planus, an increased load was appreciated. In addition,their study reported that subjects who had greater body weight tended to have higherpeak loads on the lateral aspect of the foot.

In a later study by Stokes and associates (18), foot pressures, body weight, and footulceration in patients with diabetes were examined. Their study was remarkable in that itdemonstrated that foot ulcers occurred at sites of maximal load. Furthermore, increasedloads in patients with foot ulceration were related to their body weight when they werecompared with healthy controls and patients with diabetes without ulcerations.

Subsequently, Ctercteko and colleagues (17) developed a computer system thatmeasured vertical foot pressures of the sole on the foot in diabetic patients with andwithout ulceration and in subjects during ambulation. The system consisted of a loadsensitive device divided into 128 strain gauge load cells with a 15 × 15 mm surface areathat was built into an 8-m walkway. The foot was divided into eight areas, and the out-put from each load cell was processed and transmitted into a microcomputer. An evalu-ation of the data provided quantitative values for the sites of peak force and pressureunder the foot and duration of contact time. It demonstrated that in both groups of dia-betic subjects, with and without ulceration, a similar pattern of reduced toe loading wasnoted when compared with control subjects. This resulted in a higher loading at themetatarsophalangeal (MTP) head region, where the majority of ulcerations were pres-ent. These results confirmed that foot ulceration occurred at sites of maximal load underthe foot.

Optical Pedobarograph

The optical pedobarograph is a device that measures dynamic plantar pressures. Thedevice is based on an earlier system described by Chodera in 1957. The optical pedo-barograph consists of an elevated walkway with a glass plate that is illuminated alongthe edge and covered with a thin sheet of soft plastic (30). The light is then reflectedinternally within the plate when no pressure is applied. However, when a subject standsor ambulates across the surface, light escapes from the glass at these pressure points andis scattered by the plastic sheet, producing an image of the foot that can be seen below.A monochromatic camera detects the image, and the pressure at any given point can bedetermined automatically by measuring the intensity of that image at that specific point.This system has high spatial resolution and thereby allows an accurate measurement ofhigh-foot pressures under small areas of the foot with satisfactory precision. The opti-cal barograph is used widely in the examination of high-foot pressures such as in thediabetic foot. Additionally, this system has been used for interventional trials that studythe effectiveness of offloading high-pressure areas. However, this system is limited tomeasurements of barefoot pressures and therefore does not allow the evaluation of in-shoe pressures. Moreover, this system requires substantial space and is not easilyportable.

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In-Shoe Methods

Over the past two decades, developments in computer technology have enabledmicroprocessor-like recording devices to measure in-shoe foot pressures. In 1963,Bauman and Brand (31) recognized the limitations of barefoot pressure measurementsin the insensate and deformed foot. The apparatus they devised was composed of thinpressure-sensitive transducers that were attached to suspected areas of high pressureunderneath the foot. Although this method was expensive and elaborate in design, itproved that in-shoe foot pressures were both feasible and indeed useful. In essence,Bauman and Brand laid the foundation for the design of less expensive devices tobecome available for general use.

ELECTRODYNAGRAM

The aforementioned principles were used in the mid-1970s to develop the electro-dynagram system (EDG System, Langer Biomechanics Group, Deer Park, New York).It is currently used in both clinical and research settings (32,33). This apparatus is acomputer-assisted system that uses seven small, separate sensors that adhere to the plan-tar aspect of the foot. They are attached by cable and relay information into a computerpack carried by the subject, In-shoe and out-of-shoe walking pressures can be evaluated.However, the system is limited because only peak pressures can be measured where thesensors are placed. Hence, this system cannot provide pressure information pertainingto the entire plantar aspect of the foot.

EMED SYSTEM

The EMED system is another computer-assisted and image-generating device thatcan record both in-shoe and out-of-shoe dynamic foot pressures. Its design is continu-ally updated regularly and permits the examination of the entire plantar aspect of thefoot. The system consists of a mat based on the principle that a change in the pressureon a wire causes a similar change on its electrical capacitance, thereby allowing footpressures to be measured by recording electrical flow through the mat. The deviceincorporates a sensor area 445 × 225 mm2 that has a resolution of 5 mm2 and can pro-vide measurements with satisfactory reliability. The system has a wide clinical appealand has been used to scrutinize the asymmetry of plantar pressure distribution in youngadults with adults with ankle fractures and diabetic patients with foot ulcerations orCharcot neuroarthropathy (34).

FSCAN SYSTEM

At the author’s unit, much study has been conducted using the FSCAN System. Thissystem is a high-resolution, computerized pressure, force, and gait analysis programthat was designed according to the principles described previously (35,36). The hard-ware system collects both static and dynamic plantar pressures data by using either mats(F-Mat™ or HR Mat™) or F-scan in-shoe sensor. The mats measure foot pressures asthe subject freely ambulates or stands over the mat without sensor cables that maypotentially influence an individual’s gait pattern or standing position (Fig.1A,B).

The F-Scan system uses an in-shoe sensor that is ultrathin (0.007 inch/0.15 mm) andflexible. It consists of 960 sensing locations referred to as elements that are distributed

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uniformly across the entire plantar aspect of the foot (36,37). These sensing elementsprovide the spatial resolution required for detecting differential pressures exerted overrelatively small areas. The unique F-Scan sensor can be trimmed to sizes and insertedinto the subject’s footwear. The sensor does not interfere with the subject’s foot func-tion or reduce the true pressures by accommodating to existing deformities (Fig.1C).

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Fig. 1. (A) A subject walking with the FSCAN sensor inserted in his shoes. Changes in theelectrical capacitance, which are related to the applied pressures on the sensors during walking,are transmitted via the cable to an IBM compatible computer, in which they are analyzed usingthe FSCAN software. (12). (B) The FSCAN mat, which is based on the same principles used todesign the FSCAN sensors, can be used to measure pressures of bare feet. The mat is compati-ble and is connected to the same apparatus used for in-shoe measurements (12). (C) Computer-assisted analysis of a foot step. The highest foot pressures in this subject are seen underneath theheel and the first metatarsal area (12).

The sensor plugs into a 6-ounce analog-to-digital converter cuff unit about the ankle.This is attached to one or both of the subject’s legs. A cable connects the cuff unit to thereceiver card placed in the computer for the F-Scan standard system, or to the data log-ger (receiver) around the waist of the subject. The latter is called F-scan Mobile, thenontethered system. For clinical use, the calibration method entails applying a knownload, which is commonly the subject’s weight, over the sensing cells. By using the pre-scribed calibration method, an accuracy method of ±10% may be obtained.

For research use, the scanner system uses an additional calibration technique (via theuse of a calibration bladder) called equilibration. Equilibration assigns unique calibra-tion curve factors to each sensing cell. It is used to increase the uniformity of sensingcells within a given sensor. Therefore, this dampens the effect of cell-to-cell variationwithout reducing the spatial resolution. If these additional calibration techniques are fol-lowed, the accuracy of the pressure measurement system is within 3–5%. The F-Scanin-shoe system has the capability and option to be upgraded to include a sensor mat thatcan measure out-of-shoe foot pressures.

This system is advantageous because of its simplicity, easy storage, and repro-ducibility of data. Satisfactory reproducibility has been reported in the great majority ofstudies that have used this system. No significant differences in peak pressure werefound in eight neuropathic patients with diabetes who had foot pressures measured threetimes over a short duration, whereas in another study, the coefficient of variation inhealthy subjects was 7.8% among separate studies and 2.6% among different steps dur-ing the same study (37,38).

The F-Scan sensors, however, have potential limitations. For example, the F-Mat sen-sor has decreased resolution compared with the in-shoe sensor. Furthermore, becausethe in-shoe sensor is very thin, it may fail from wrinkling and breakage and therebyyield incorrect data (35). Rose and colleagues (35) found that two insole sensors gavedifferent results when used on the same subject. Additionally, there was a decline in sen-sitivity if the sensor was used 12 times. Altering the shoe insole can also affect footpressure measurement. However, this is not a limitation but an advantage. Material type,shape, and density affect contact area, load absorption, and force vector orientation,which in return alter force patterns, pressure profiles, and peak values. The high reso-lution of the F-Scan in-shoe sensor, therefore, allows one to measure the effect of shoeinsole alterations useful in everyday clinical practice.

NATURAL HISTORY OF FOOT PRESSURE: ABNORMALITIES IN DIABETES MELLITUS

Foot pressure measurements in patients with diabetes have been attempted for over 30years. Stokes et al. (18) used a segmental force platform to study 37 feet in 22 patientswith diabetes. High loads were found at the sites of ulcers. Patients with high loads underthe feet were also heavier in weight than those with lower loads. Toe loads in patientswith ulcers were found to be reduced. A shift of maximum loads to the lateral foot in neu-ropathic patients was also reported. In a subsequent study, Ctercteko and colleagues (17)confirmed all these findings, except for the lateral shift of maximum loads. Conversely,a medial shift was discovered in their study. In another study, neither a medial nor a lat-eral shift was found. However, peak pressures under the heel occurred with a lower fre-quency in all patients with diabetes compared with patients without diabetes (9).

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This finding may suggest an early change when foot pressures start rising under theforefoot but still remain within normal limits, as in patients without neuropathy. In pre-vious studies, we have shown that in diabetic neuropathic patients, there is a transfer ofhigh pressures from the heel and the toes to the metatarsal head (9). The main reasonsfor this transfer are neuropathy and limited joint mobility (8,9). Neuropathy leads toatrophy of the intrinsic musculature of the foot and clawing of the toes, which mayresult in prominent metatarsal heads under which high pressures occur. Though we real-ize that forefoot pressures are increased in the feet of patients with diabetic neuropathy,it has also been demonstrated that rearfoot pressures also increase as well especially inmoderate-to-severe neuropathy (39). Moreover, a transfer of peak pressures from therearfoot to the metatarsal heads was noted in patients with diabetic neuropathy (13).Accordingly, it has been demonstrated that the ratio of forefoot to rearfoot pressures isindeed increased in severe diabetic neuropathy (39). This further indicates the inabilityof the neuropathic foot to distribute foot pressure and avoid the development of high-foot pressures. Additionally, limited joint mobility impairs the ability of the foot toabsorb and redistribute the forces related to impact on the ground while walking. Itseffects on the foot appear to be global in nature and include reduced motion at the ankle,subtalar, and first metatarsophalangeal joints (MTPJ) (40). Vital musculoskeletal struc-tures such as the Achilles tendon and plantar fascia may also be involved with changessuch as shortening and thickening of both structures (41). The foot becomes stiff, rigid,and less able to dampen pressure. Consequently, this contributes to the development ofhigh foot pressures and subsequent ulceration (9,14). Additionally, patients with dia-betes mellitus may also have reduced plantar soft tissue thickness (42,43), which fur-ther reduces the ability of the foot to mitigate foot pressures. An inverse relationshipexists between reduced plantar tissue thickness and elevated foot pressures in somepatients with diabetes mellitus (44).

FOOT PRESSURES AND FOOT ULCERATION

Foot ulceration is a significant cause of morbidity in patients with diabetes mellitusand can lead to prolonged lengths of hospital stay. Numerous risk factors for foot ulcer-ation in diabetes have been confirmed. These include limited joint mobility, peripheralneuropathy, vascular disease, and high plantar pressures have been implicated as sig-nificant predisposing factors leading to ulceration in population-based and clinical stud-ies seeking to quantify such relationships.

Boulton and associates (5) were the first group to employ the optical pedobarographfor research purposes to examine the relationship between high-foot pressures andulceration. In their study, diabetic patients with and without neuropathy and individualswithout diabetes were examined to evaluate the relationships among foot pressures,neuropathy, and foot ulceration. Their results demonstrated that a significantly largernumber of patients with diabetic neuropathy had abnormally high-foot pressures com-pared with controls. Furthermore, patients with a previous history of foot ulceration hadhigh pressures at ulceration sites. Because ulceration occurred at sites of high plantarfoot pressures, foot pressure reduction, therefore should lead to a reduced incidence offoot ulceration in neuropathic patients with diabetes.

In a subsequent study performed by the same group, sorbothane shoe inserts wereemployed in an attempt to evaluate pressure reduction in patients with diabetes (45).

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Abnormally high-foot pressures were measured in 33% of feet without insoles and in6% of feet when using the insoles, thereby indicating that special accommodativeinsoles may help reduce plantar foot pressures in diabetic neuropathic patients.

In a prospective study that lasted 3 year and comprised diabetic patients with long-standing diabetes and neuropathy, Kelly and Coventry (46) also examined the long-termchanges in plantar foot pressure. Their results demonstrated that important alterationsof foot pressure distribution had occurred in a significant number of these subjects,some of whom had developed recurrent ulcerations at these sites of high pressure.Moreover, it was again confirmed that patients with neuropathy and the characteristicintrinsic-minus foot had abnormally high-foot pressures measured at the metatarsalheads (15).

Definite proof that abnormally high pressures in patients with diabetes were relatedto the development of plantar foot ulceration can be derived from a pivotal prospectivestudy that followed a large number of patients for a mean period of 30 months (15).During this study, plantar ulcers developed in 17% of all feet and in 45% of feet withdiabetic neuropathy. All of these ulcerations occurred in patients with high foot pres-sures at baseline, thereby suggesting that high-foot pressures, especially in neuropathicpatients, are predictive for the development of foot ulceration and may be useful foridentifying at-risk patients (Fig. 2).

Given the correlation between foot pressures and foot ulceration, a study to evaluatethe role between joint mobility and racial affinity in the development of high-foot pres-sures was performed. This study demonstrated that black subjects without diabetes andpatients with diabetes have increased joint mobility compared to Caucasian healthy sub-jects and patients with diabetes (16). An increase in joint mobility results in lower peakplantar pressures and therefore a lower risk of foot ulceration.

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Fig. 2. Histogram demonstrating the distribution of peak pressures under the foot of healthysubjects (black columns), diabetic nonneuropathic patients (gray columns) and neuropathicpatients with diabetes (white columns). Peak pressures were more often under the metatarsalheads of the neuropathic patients, whereas they were less often under the heel and great toe. Itis also of interest that peak pressures under the heel were less frequent in the nonneuropathicpatients (*p < 0.05) (15).

Similarly, the role of neuropathy and high-foot pressures in diabetic foot ulcerationwas evaluated (47). In a cross-sectional multicenter study, the magnitude of associationof several different risk factors for foot ulceration in patients with diabetes mellitus wasdetermined. A cross-sectional group of 251 subjects consisting of Caucasian, Black, andHispanic races were studied. There was equal distribution of men and women across theentire study population. All patients underwent a complete medical history and lowerextremity evaluation for neuropathy and foot pressures. Neuropathic factors weredichotomized (0/1) into 2 high-risk variables: a high vibration perception threshold(hiVPT) >25 V and unable to feel a 5.07 or smaller Semmes–Weinstein monofilament(Hi SWF). The mean dynamic foot pressures of three footsteps were measured using theFSCAN mat system with patients walking in stockings but without shoewear.Maximum plantar pressures were dichotomized into a high pressure variable (Pmax6)indicating those subjects with pressures ≥6 kg/cm2 (n = 96). The total of 99 patients hada current or prior history of ulceration at baseline.

The sensor was used in a floor mat system designed to measure barefoot or stocking-foot dynamic pressures. Maximum peak pressures for the entire foot were obtainedwithout regard for specific location by averaging those obtained for three midgait footsteps and were then dichotomized into a high pressure variable indicating those subjectswith pressures ≥6 kg/cm2.

With a specific focus on plantar foot pressures, joint mobility and neuropathic para-meters consistent with ulceration, this study demonstrated that patients with foot pres-sures ≥6 kg/cm2 were twice as likely to have ulcerations than those without highpressures, even after adjustment for age, gender, diabetes duration, and racial affinity.In the black and Hispanic groups, significantly lower plantar pressures were demon-strated compared with the Caucasian group. High plantar pressures were relativelyinfrequent and were not found to be significant predictors of ulceration. Foot pressures≥6 kg/cm2 were independently associated with ulceration, but to a lesser extent than theneuropathy variables (Tables 1 and 2).

This study demonstrated that the association of high-foot pressures, high vibrationperception threshold, and insensitivity to a 5.07 monofilament contributed to the devel-opment of foot ulceration. Furthermore, their group demonstrated significant racial dif-ference in joint mobility, associated foot pressures, and the prevalence of ulcerationamong Caucasian, black, and Hispanic patients. These findings have guided efforts atdetecting patients with diabetes at risk of ulceration by incorporating such parametersinto screening programs. Foot pressures should be evaluated to detect those neuropathicindividuals at risk of ulceration from excessive callus formation or repetitive stress(9,10). Although the two measures of neuropathy have the greater magnitude of effect,foot pressures can still be evaluated to detect those neuropathic individuals at risk ofulceration from excessive plantar callus formation or repetitive stress.

THE ROLE OF FOOT PRESSURES: AS A SCREENING METHOD TO IDENTIFY AT-RISK PATIENTS

Because diabetic foot ulceration is a preventable long-term complication of diabetesmellitus, screening techniques to identify the at-risk patient are probably the mostimportant step in reducing the rate of foot ulceration and lower limb amputation. To this

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end, various screening techniques have been proposed and are currently in use. Theseinclude the evaluation of vibration perception threshold (VPT), foot pressure measure-ments, joint mobility, and SWF 5.07 testing. Furthermore, a history of previous footulceration, Tc PO2 level of <30 mmHg and the existence of foot deformities have beenshown to be risk factors for the development of diabetic foot ulceration. In our unit, a

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Table 2Multivariate Logistic Regression for Ulceration by Race, Controlling for Age, Sex, and Diabetes Duration

Odds ratio (O.R.) 95% Confidence interval p value

CaucasianPmax6 7.7 2.07–28.4 0.002HiVPT 7.4 2.4–22.9 0.001HiSWF 3.7 1.3–10.3 0.013

BlackPmax6 0.53 0.05–5.8 0.608HiVPT 7.2 1.2–43.7 0.032HiSWF 19.8 1.1–344.2 0.041

HispanicPmax6 2.1 0.38–11.5 0.395HiVPT 6.6 2.3–18.5 0.000HiSWFa – – –a Dropped due to perfect prediction of outcome.

Table 1Logistic Regression Results for Risk of Ulceration

Odds ratio (O.R.) 95% Confidence interval p value

Univariate resultsAgea 1.02 1.00–1.03 0.019Sexb 0.26 0.18–0.38 0.000BMI 0.97 0.94–0.99 0.048Diabetes durationa 1.04 1.02–1.06 0.000Pulses 0.31 0.18–0.52 0.000Pmax6 3.9 2.6–5.7 0.000HiVPT 11.7 7.4–18.4 0.000HiSWF 9.6 5.02–18.5 0.000HiRisk 7.4 4.8–11.6 0.000

Multivariate results (Controlling for age, sex, duration, race)Pmax6 2.1 1.32–3.39 0.002HiVPT 4.4 2.58–7.54 0.000HiSWF 4.1 1.89–8.87 0.000HiRiskc 4.1 2.48–6.63 0.000a Indicates O.R. per year of increase.b Indicates reduced risk of ulceration in females relative to males.c Indicates multivariate O.R. for interaction term without other neuropathic or pressure variables in

model.

study evaluated plantar pressures and screening techniques to identify people at highrisk for diabetic foot ulceration (48). The objective of this study was to compare thespecificity, sensitivity, and prospective predictive value of the most commonly usedscreening techniques for the identification of high risk for foot ulceration in a prospec-tive multicenter fashion. Furthermore, this study aimed to identify as many risk factorsas possible and to develop a screening strategy that, by combining the detection of twoor more risk factors, would provide the best tool for identifying the at-risk patient.

Two hundred and forty-eight patients from three large diabetic foot centers includingour own unit were evaluated in a prospective study. Neuropathy symptom score, neu-ropathy disability score (NDS), VPT, SWF, joint mobility, peak plantar pressures, andvascular status were evaluated in each of the subjects. Patients were followed up every6 months for a mean period of 30 months, and all new foot ulcers were recorded. Thesensitivity, specificity, and positive predictive value of each risk factor were evaluated.

Foot ulcers developed in 73 patients during the study. Patients who developed footulcers were frequently men, had diabetes for a longer duration, and had an inability todetect a 5.07 monofilament. NDS alone had the best sensitivity, whereas the combina-tion of the NDS and the inability to detect a 5.07 monofilament reached a sensitivity of99%. However, foot pressures had the best specificity, and the best combination wasthat of NDS and foot pressures.

This study prospectively evaluated the association of several risk factors for footulceration. The results demonstrated that a high NDS obtained during a simple stratifiedclinical examination provided the best sensitivity in identifying patients at risk for footulceration, whereas high VPT, the inability to feel a SWF 5.07and high-foot pressureswere independent factors. Furthermore, the combination of NDS and a SWF 5.07 (10 g)could identify all but 1 of 95 ulcerated feet. The use of these two simple methods in clin-ical practice can assist in identifying the at-risk patient, which is the first step in the pre-vention of foot ulceration. Foot pressures are often elevated in patients with diabeticneuropathy. However, as an initial tool by itself, the measurement of foot pressures isnot very helpful in predicting the development of foot ulceration. This was demon-strated in this study and confirmed in a subsequent study (49). In terms of predictingulceration, foot pressure measurements are only useful when combined with othermodalities making them not very practical as an initial tool. They may be used as a valu-able postscreening test in conjunction with assessing the effectiveness of offloading byappropriate footwear.

Although several studies exist evaluating whole foot pressures, there is a paucity ofresearch examining forefoot and rearfoot plantar pressures. In our unit, we measuredforefoot and rearfoot pressures separately and examined their validity in predicting footulceration (13). Ninety patients with diabetes mellitus were examined, and peak pres-sures under the rearfoot and forefoot were evaluated using the FSCAN mat system withsubjects ambulating without foot wear (13). Significant correlations were foundbetween forefoot peak pressures and age, height, neuropathy disability score, VPT, andforce applied on the ground while walking. In contrast, reverse correlations were foundbetween rearfoot peak pressures and measurements of neuropathic severity.

Binary regression analysis demonstrated a higher risk of foot ulceration in patientswith high foot pressures. However, no association was found for rearfoot pressure.Thus, peak foot pressure measurements of the forefoot, but not the rearfoot correlate

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with neuropathy measurements can also predict foot ulceration over 36 months.Moreover, forefoot pressure correlated with the severity of diabetic neuropathy and lim-ited joint mobility. It is also of interest that a negative correlation was found betweenrearfoot and forefoot pressures. This finding confirms that there is a transfer of peakpressures from the rearfoot to the metatarsal heads in diabetic neuropathy. Additionally,it indicates an inability of the neuropathic foot to distribute pressure and avoid thedevelopment of high pressures that eventually leads to the production of foot ulcerationunder these areas. Therefore, measurement of forefoot peak pressures rather than thewhole foot may be more useful for identifying at-risk patients when designing a screen-ing protocol (13).

OFFLOADING THE DIABETIC FOOT: THE ROLE OF FOOTWEAR

Given the high rate of foot ulceration in at-risk patients with diabetes, the need forbetter preventative methods to offload the foot cannot be more apparent. The effective-ness of footwear in reducing high plantar pressures has been scrutinized using the opti-cal pedobarograph (5,50–52). Several foot pressure studies have examined hosiery andinsole materials in the diabetic at-risk population and in patients with rheumatoid arthri-tis and neuropathy (12,15,16,50–52). Currently available footwear products are con-stantly evolving. Thus, the lack of uniform data makes the interpretation of pressurereduction studies challenging in both clinical and research settings.

Hosiery

The use of padded hosiery to reduce foot pressures has been evaluated in the litera-ture (45,51–53). In an initial study, the pressure-relieving capacity of specially designedhosiery with padding at the heel and forefoot was tested (51). A significant reduction inpeak plantar pressure, up to 30%, was obtained from patients with diabetes who wereat risk for ulceration. In a subsequent study, commercially available hosiery, experi-mental hosiery, and padded socks were evaluated for foot pressure reduction (52). Tenpatients who wore experimental padded hosiery for 6 months were tested with an opti-cal pedobarograph. The experimental hosiery continued to provide a significant reduc-tion in forefoot pressures at 3 and 6 months, although the level of reduction was lessthan that seen at baseline.

Furthermore, commercial hosiery designed as sportswear was examined and com-pared with experimental hosiery. Although these socks (medium or high-densitypadding) provided a substantial pressure reduction vs barefoot (10.4% and 17.4%,respectively), this was not as great as that seen with experimental hosiery (27%) (52).Thus, the use of socks designed to reduce pressures on diabetic neuropathic feet may bean effective adjunctive measure for the reduction of foot pressures. Although develop-ment of fiber technology and padding distribution continues, the currently available high-density socks are perhaps the best choice of hosiery for protection of the insensate foot.

In another study, in-shoe foot pressures of patients with at-risk feet were compared withhealthy subject foot pressures without shoes using the FSCAN system (14). Foot pressureswere measured under three conditions in each subject. First, subjects were placed directlyin the shoes (S) to measure the pressure between the footwear and the sock. Second, thesensor was taped directly to the barefoot (B), and the subject ambulated wearing both

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footwear and socks. Finally, the footwear was removed, and each subject ambulated wear-ing only socks (H). The total force and peak pressure under each foot was measured foreach condition.

The results demonstrated that the diabetic group had greater peak pressures com-pared with the controls and that in both groups a significant pressure reduction wasfound when subjects ambulated with footwear (14). The study concluded that footwearcan offer a cushioning effect and that this property may be further incorporated todesign shoewear that can protect against the development of high-foot pressures andfoot ulceration (Fig. 3).

Following this study, the authors prospectively examined the effect of using speciallypadded hosiery in combination with specially fit footwear on providing in-shoe pressurerelief (53). Fifty patients at risk for foot ulceration were recruited for the study. All ofthe patients were provided with three pairs of specially padded hosiery and with twopairs of extra-depth footwear or extra-width running shoes. Dynamic foot pressureswere measured at baseline with the patients wearing their regular socks alone, regularfootwear and socks, the padded socks, and the new footwear and padded socks. Footpressures were measured at baseline and subsequent visits over a period of 30 months(Fig. 4).

As initial pressure relief was provided by the new footwear at baseline comparedwith the patients’ own footwear, yet very few differences in peak forces were foundamong the baseline, interim, and final visits. Moreover, no significant changes in footpressures were found over a period of 6 months of continuous usage using specificallydesigned footwear in a group of patients with diabetes at risk for foot ulceration. This alsoillustrates the importance of making simple recommendations of appropriate footwear

Foot Pressure Abnormalities in the Diabetic Foot 175

Fig. 3. Foot pressure measurement in healthy control subjects and patients with diabetes whilewearing either their socks alone (black column) or both shoes and socks (white columns). Footpressures with socks alone were significantly lower to the ones measured when ambulating withboth shoes and socks in both subjects with diabetes and healthy subjects (*, ¶: p < 0.02) (14).

in patients at risk for foot ulceration in an effort to provide the most suitable environ-ment for such a foot.

Shoewear

Given the potential of shoes and associated modalities to reduce foot pressures inneuropathic feet and healthy subjects, a discussion of the associated offloading capabil-ities is warranted. It is anticipated that the use of modern technology may be useful indesigning shoes and insoles that will redistribute and reduce foot pressures from areasprone to ulceration.

Shoes are an important consideration for patients at risk for ulceration. They provideprotection as a covering for the feet and function as a barrier against toxic substancesand thermal extremes. Shoes can also function to decrease plantar foot pressures. Forexample, noncustom footwear worn by healthy subjects without diabetes decreased footpressures by 30–35% (18). Moreover, greater foot pressure reductions may be observedin patients with elevated foot pressures wearing shoes compared to walking barefoot.

Healing sandals have been employed to decrease plantar pressures in the diabeticfoot (54). These sandals consist of a postoperative shoe with a thick, soft insole that canbe further modified by making the sole rigid with a rocker bottom. The rocker sole isimportant for the reduction of plantar pressures underneath the forefoot (2,55). The softsole allows for greater pressure distribution beneath the metatarsal heads, whereas therocker sole alters the mechanics of the forefoot just prior to toe-off, both of which leadto reduced forefoot pressures (55).

The postoperative shoe is another modality used in the treatment of plantar footulcerations. This shoe is used quite frequently because of its availability; it provides thepatient with a gait modifying device. Although it does decrease foot pressures, the post-operative shoe is only minimally effective in the treatment of foot ulcerations compared

176 Lyons et al.

Fig. 4. Changes in the peak foot pressures in neuropathic and nonneuropathic patients over aperiod of 30 months. The pressures at the end of the study (white columns) were higher com-pared to the baseline measurements (black columns) in both the neuropathic and nonneuropathicpatients (15).

with other modalities (54) and is slightly more effective than a canvas shoe (56).Modifications to the sole and insole may further enhance the effectiveness of the post-operative shoe.

Additionally, half-shoes have been used with success for plantar pressure reduction(54–56). These shoes consist of a postoperative shoe with a large wedge heel thatextends just behind the forefoot. The forefoot in the postoperative shoe with a heel ofthis configuration is kept off the ground. Pressure reduction can be as high as 66% com-pared with pressures in a baseline canvas shoe (56). Because of the configuration of theheel which is high and wedged in dorsiflexion, instability when ambulating can be aproblem. This instability is even more significant with neuropathic patients. Therefore,an ambulatory aid such as a cane or crutches may assist in walking.

Not all shoes relieve foot pressures equally; however, employing materials that sig-nificantly reduce foot pressures may prevent the recurrence of ulceration in patientswith a prior history of ulceration (56). Shoes that provide a cushion effect reduce plan-tar pressures (54,56). Leather oxford shoes may decrease plantar pressures in someareas and yet increase pressures in other regions, particularly underneath the lateralmetatarsal heads and great toe (56). Therefore, when purchasing a dress shoe, patientsshould select a softer sole as opposed to a harder sole, which may not afford as muchpressure relief. A dress shoe with a rigid sole can be replaced with a softer sole withoutdramatically altering the appearance of the shoe. Also, selection of a shoe with a remov-able insole allows for frequent replacement of worn insoles with a new insole andresults in a greater cushioning effect.

Running shoes are an option for patients with elevated foot pressures and at-risk feet(56–58) (Fig. 5). Also, running shoes are less expensive than extra-depth and customfootwear. They provide a readily available option for obtaining protective shoewear forpatients with a reasonably straight foot. Moreover, running shoes may provide a morecosmetically acceptable alternative to extra-depth or custom shoes. Significant pressurereduction can be expected with running shoes. Thirty-nine subjects were studied to eval-uate the pressure-reducing effects of running shoewear (58). Three groups of 13 sub-jects were categorized as having diabetes with neuropathy, diabetes without neuropathy,and those with neither diabetes nor neuropathy. Foot pressures were evaluated whilesubjects were wearing thin socks and compared with those of subjects wearing leatheroxfords and running shoes. A mean decrease in foot pressures of 31% was noted for allthree groups while wearing running shoes compared with wearing the socks alone (58).

In another study, 13 patients with diabetes and neuropathy were evaluated in varioustypes of footwear, including the patients’ own leather oxfords and extra-depth and run-ning shoes (59). Running shoes were found to decrease mean plantar foot pressures incomparison with the patients’ own leather oxfords by 47% at the second and third MTPJ,29% at the first MTPJ, and 32% at the great toe (59). Running shoes are therefore aviable option for patients at risk for ulceration. For patients with significant foot defor-mities and prominences other options such as custom footwear must be considered.

Different types of shoes provide various levels of plantar pressure relief. A recentstudy using a running shoe product found a decrease of between 27% and 38% in plan-tar pressures compared with a leather oxford product (60). Similarly, another studyemploying a running shoe demonstrated a reduction of between 29% and 47% in footpressures compared with leather oxford footwear (61).

Foot Pressure Abnormalities in the Diabetic Foot 177

Note that athletic shoes may not provide the same pressure relief compared with run-ning shoes. For example, cross-trainer-style footwear may not decrease foot pressurescompared with running shoes (38). Foot pressures in 32 diabetic patients with neuropa-thy and histories of recently healed ulcerations were examined. Foot pressures weremeasured in a canvas oxford and compared with those using an extra-depth shoe, an SAScomfort shoe, and athletic cross-trainer shoes. Measurements were obtained with themanufacturers’ insole and with a visco-elastic insole for each shoe type. For patients witha history of ulcerations underneath the metatarsal heads, pressure reduction in all threeshoe types were relatively similar as compared to foot pressures in canvas shoe (38).

However, for those patients with a history of great toe ulcers, the extra-depth andcomfort SAS shoes decreased foot pressures under the great toe, whereas the cross-trainer shoewear actually increased foot pressures in this area as compared to the can-vas oxfords. One may surmise that foot pressure reduction between running shoes andcross-training shoes may be different particularly underneath the great toe. Therefore,patient counseling on the selection and purchase of specific footwear is vital; especiallyin the marketplace where the vast choices of footwear available may easily overwhelma patient not familiar with athletic shoes (38).

Extra-depth footwear is another option for the patient with at-risk feet. The extraspace in the toe box is particularly useful for patients with forefoot deformities. Extra-depth footwear also decreases foot pressures significantly (56–58). The pressure reduc-tion ability of extra-depth shoewear can be further augmented with the use of speciallypadded socks as discussed previously (59,60) and insoles (58). It is the authors’ experi-ence that many extra-depth shoes contain a flat insole with minimal cushioning quality.

178 Lyons et al.

Fig. 5. Running shoes can reduce foot pressures. They are readily available, lightweight, andaffordable. The material of the shoe upper is soft and padded on the inside where it interfaceswith the foot. A soft sole will reduce foot pressures along with a soft insole that should be remov-able to allow for frequent replacement.

A study evaluating extra-depth shoes demonstrated pressure reduction with the factoryinsole 16%, 27%, 19%, and 34% at the great toe, first MTPJ, second MTPJ, third MTPJand heel, respectively (54). With a custom accommodative insole, the pressure reduc-tion was increased to 33, 50, 48, and 49%, respectively (55). In a subsequent study, 32patients with diabetes and a history of ulceration noted a significant reduction in footpressures using extra-depth shoes when compared with a baseline of the patient’s owncanvas oxford. When the factory-constructed insole was replaced with a commerciallyavailable insole, a further pressure reduction of 4–15% was observed. Therefore, pres-sure reduction using extra-depth shoes can easily be augmented with the use of a read-ily available insole. The pressure reducing ability of extra-depth footwear can be furtheraugmented with specially padded socks (47).

In another study, patients with diabetes who exercised and those who did not were eval-uated to determine what effect aerobic exercise might have on foot pressures with andwithout shoes (60). When participants ambulated without their shoes, the peak pressureswere highest in group DNE (diabetic nonexercisers). Foot pressures were also higher ingroups CE (healthy exercisers), CS (healthy nonexercisers), and DE (exercisers with dia-betes); probably a result of the increased stress of the foot skin and the subsequent callusformation.

However, when foot pressures were measured wearing shoes a different pictureemerged. The foot pressures were highest in groups CS and DS, intermediate in groupDNE, and lowest in groups CE and DE (Fig. 6). Those who consistently exercisedachieved the highest pressure relief. These differences may reflect the ability of regu-larly exercising individuals to choose comfortable and good quality shoewear. In sum-mary, these results indicate that proper selection of footwear can result in considerablepressure relief.

Foot Pressure Abnormalities in the Diabetic Foot 179

Fig. 6. Percentage of foot pressure relief achieved by the athletic shoes in healthy controlswho exercised regularly (CE group), type 1 nonneuropathic diabetic patients who exercisedregularly (DE), type 1 diabetic neuropathic patients who exercised regularly (DNE), healthy con-trols who did not exercise regularly (CS) and patients with diabetes who did not exercise regu-larly (DS). The highest pressure relief was achieved in the three first groups who consisted ofregularly exercising subjects. These data indicate that proper selection of footwear can result toconsiderable pressure relief (55).

Insoles and Orthotics

Insoles and orthotics are recommended for the prevention of ulcerations in at-riskfeet. (38,61–64). The addition of a material to cushion the plantar aspect of the foot candecrease foot pressures significantly (5). By using a 5-mm thick visco-elastic polymerinsole, foot pressure reduction has been reported (45). In another study, 4-mm thickvisco-elastic insoles were noted to decrease foot pressures from 5–20% above what wasobserved with stock insoles of extra-depth, comfort, and athletic shoes (30).

Custom orthotics of both the soft and rigid variety are used to decrease foot pres-sures (38,61–64). Heat-pressed Plastizote™ insoles decrease foot pressures for diabeticpatients by 40–50% (62). Modifications to these insoles by adding arch or metatarsalpads do not increase the pressure reduction significantly (62). However, rigid materialssuch as polyurethane foot orthoses may reduce plantar pressures by approx 50% (63).Rigid orthotics composed of graphite materials decrease pressures underneath the firstmetatarsal head and medial heel by approx 30–40% (63,64).

The FSCAN system was employed to measure dynamic pressures at the shoe–footinterface during normal walking with different orthotics (65). This study evaluated theefficacy of pressure redistribution with a Plastizote, Spenco, cork, and plastic footorthosis as compared with a control (no orthotic). Measurements varied upwards to 18%between sensors and changes in stance time of up to 5% occurred between the orthoticsand the control conditions. These results demonstrated the inherent measurement vari-ances of the FSCAN system using numerous orthoses.

Although these variances hindered reliability among the orthoses, statistically sig-nificant differences in peak pressure between the orthotics were noted. Plastizote, cork,and plastic foot orthoses were beneficial for decreasing pressure in the forefoot, heel,and second through fifth metatarsal regions. However, these orthotics had the potentialto increase the plantar pressures in the midfoot region. In conclusion, the results demon-strated that using an orthotic to relieve pressures in one region of the shoe–foot inter-face may increase pressures over another region of the plantar surface (65).

Viswanathan et al. also evaluated the effectiveness of different insoles in therapeuticfootwear. They evaluated neuropathic patients with diabetes stratified into four groups.Three of the four groups consisted of patients with therapeutic shoes with insoles, eachgroup differing in the composition of the insole. They were compared with a fourthgroup of similar neuropathic diabetic patients with nontherapeutic footwear. Foot pres-sures were measured initially and 9 months later and were noted to be significantlyreduced along with the rate of development of new ulcerations as compared to the groupwearing the nontherapeutic footwear (66).

Interestingly, not all studies support the use of therapeutic footwear in the preven-tion of foot ulcerations in those patients at risk. A recent study by Reiber et al. (67)has demonstrated that therapeutic footwear did not prevent ulceration in their study ofdiabetic individuals without severe foot deformity. In this study, patients with customfoot insoles fared no better than patients with prefabricated foot insoles and controlpatients with their usual footwear. All three groups had a similar rate of ulceration. Itis important to understand that this does not indicate that therapeutic footwear has lessimportance than previously thought. It may play just as an important role as ever inpatients with severe deformities. It may also mean that the custom insoles in the study

180 Lyons et al.

were not offloading the sites of increased pressure any better than prefabricateddevices or usual footwear but this is difficult to ascertain as pressure measurementsbetween groups was not carried out. Perhaps future studies may investigate the abil-ity of widely dispensed therapeutic footwear to decrease foot pressures by actuallymeasuring foot pressure reduction and correlating this to the ability to decrease riskof ulceration.

SUMMARY

Several methods of measuring and reducing foot pressures including their advantagesand limitations have been discussed. Extra-depth footwear, jogging shoes, hosiery,insoles, and orthoses have been shown to decrease plantar foot pressures. Furthermore,these devices can prevent the occurrence and recurrence of foot ulceration. However,when using orthoses or other inserts care must be taken not to increase pressures overanother region of the foot.

In the last two decades, the development of intricate computerized systems has rev-olutionized diabetic foot pressure measurements and made their application possible fordaily clinical practice. Foot pressure measurements obtained from out-of-shoe and in-shoe methods may have far-reaching consequences for both research and clinical appli-cations. Moreover, these systems can potentially identify at-risk patients and provide abasis for the implementation of either footwear modifications or surgical intervention.Foot pressure measurement systems are still being developed. Currently, research is inthe initial phase of developing methods of measuring in-shoe shear forces. Piezoelectrictransducers are currently being evaluated which may be able to measure both verticaland shear forces (68). In the future, computer systems will hopefully become morewidely available and may be employed routinely for diabetic foot management and avariety of foot conditions.

SUGGESTED READING

1. Welton EA. The Harris and Beath footprint: interpretation and clinical value. Foot Ankle1992;13:462–468.

2. van Schie CH, Abbott CA, Vileikyte L, et al. A comparative study of Podotrack, a simplesemiquantitative plantar pressure measuring device and the optical pedobarograph on theassessment of pressure under the diabetic foot. Diabet Med 1999;16:154–159.

3. van Ijzer M. The Podotrack, a new generation Harris mat. Podopost, 1993;39–41.

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