- Email: [email protected]
Investigation of gait protocols for plantar pressure measurement of non-pathological subjects using a dynamic pedobarograph
ELSEVIER
Investigation of gait protocols for plantar pressure measurement of non-pathological subjects using a dynamic pedobarograph A.J. Harrison*.l, School
qf Podiatry,
University
J.P. Folland College
Saljord,
Salford,
UK
Received 28 November 1995: accepted 30 April 1996
Abstract There is a clear need for a consistent and representativeprotocol for the measurement of plantar pressures. The purposeof this study wasto comparethe plantar pressuresproducedby five different modesof walking: full gait control (FGC), no gait control (NGC), stride length control (SLC), stride rate control (SRC) and the first step(FS). Ten non-pathologicalsubjectsrecordedfive trials for eachprotocol in a random order. For each trial subjectswalked barefoot over a dynamic pedobarograph.Sevenareas of the foot, the heel, ali five metatarsalheads(MTH) and the great toe (GT), were interactively selectedand analysed.Two parametersof pressuremeasurementwere investigated,peak pressuresand peak pressuretime integrals,with attention to the consistencyof the data (coefficient of variation for five trials) as well as the meanvalues. This investigation found the pressure valuesof the protocols to be very similar. No significantdifferenceswere found betweenprotocols for all areasor for individual areasfor either parameter.This wasdespitethe FS protocol having a significantly longercontact time (P < 0.001)than the other protocols. Averaged acrossall areasof the foot the protocols where stride length wascontrolled (SLC and FGC) were found to be the most consistentfor both parametersand control of this variable is recommendedfor increasedconsistencyand reliability. However, the differencesbetweenprotocols werestill small.For the heelthe first stepwasnoticeably the most consistentprotocol. The central areasof the foot (heel and MTHs 2, 3 and 4) produced more consistentpressurevaluesthan the peripheral areas (MTHs 1 and 5 and the GT). 0 1997ElsevierScienceB.V. Keywords:
Plantar foot pressure:Gait protocol; Pedobarograph
1. Introduction Plantar pressure measurement is a critical parameter in the evaluation of foot function and the assessment of
a wide range of foot pathologies. An individual’s pressure distribution and pressure values may reveal valuable information. Therefore, a consistent and representative protocol for the measurement of plantar pressures is required. The consistency is clearly important for reliable quantitative analysis and, for clinical Abbreoiations: GST, glutathione S-transferase; PPAR, peroxisome proliferator activated receptor; DEHP, di-(2-ethylhexyl)phthalate; GSH, glutathione; CDNB, I-chloro-2,4-dinitrobenzene ’ Present address: Department of P.E. Sport and Exercise Sciences, University of Limerick, Plassey Park, Limerick, Republic of Ireland. Tel: + 353 61 202809; e-mail: [email protected] * Corresponding author. 0966-6362/97/$17.00 D 1997 Elsevier Science B.V. All rights reserved. PZZ 509666362(96)01095-8
application, any protocol should represent an individual’s normal walking. The most popular protocol in the collection of plantar pressures has been a single foot contact mid-gait, whilst the patient is in the middle of several steps down a walkway. Mid-gait protocols are thought more representative of the normal walking stride [I]. Some investigators have attempted to control the speed of the subject [2,3] and others have observed gait parameters but placed no control upon these variables [4]. However, most have allowed the subject to determine their own gait after a period of familiarisation [5-71. This leaves the subject to target their footstep onto the surface of the pressure measuring device, usually a small finite area. Such targeting may tend to create unnatural gait patterns and collection of one or more
representative trials typically involves experimenter selection from several attempts. Uncontrolled mid-gait collection is, therefore, time consuming, potentially unrepresentative and inconsistent. For patients with poor co-ordination and vision this protocol may not be suitable. and for those with painful pathologies the number of trials required to generate useful data may render it unacceptable. The use of a first-step protocol espoused by Cavanagh and Ulbrecht [8,9] removes many of these drawbacks but may produce pressure values unrepresentative of normal walking. The first-step protocol requires the subject to stand one pace from the pressure measurement device and, in their own time, step onto the platform and continue walking. Rodgers [IO] compared pressures recorded from both the firststep and mid-gait protocols for 60 healthy men aged between 40 and 81 years. She found that peak pressures for the heel and metatarsal heads were on average 34% and 4.7% lower, respectively, for the first-step protocol. Only two other studies have compared gait protocols for pressure measurement. Meyers-Rice et al. [I I] investigated first-step, mid-gait and an original second step protocol. They collected three trials for the right foot of ten healthy subjects, mean age 27 years. Subject’s practised until the duration of the stance phase for ten trials varied by less than 30 ms ( < 5%). This was to increase the consistency of each individual’s gait. Some investigator selection was involved in all three protocols. Under the rearfoot peak pressure values were 14% (P <: 0.05) and 1l’Y,l lower for the first-step and secondstep protocols, respectively, when compared to the midgait protocol. Forefoot peak pressures were not found significantly different but, compared to the mid-gait protocol, the first-step and second-step protocols were 13’>:, and 7% lower, respectively. Meyers-Rice et al. [1 I] concluded that the second-step protocol produced peak pressure values more representative of the traditional mid-gdlt method. Morlock and Mittlmeier [ 121 measured pressures beneath both feet of 16 healthy subjects, mean age 30.6 years. Three trials were collected for the first-step and uncontrolled mid-gait walking, although trials > 5% different to normal walking speed were rejected. They reported different absolute values for the two protocols,
but found no statistical significance. The purpose of this investigation wa< lu compare five different gait protocols and their effect upon plantar foot pressures in non-pathological subjects. Seven different areas beneath the foot were anaiysed IO examine the interaction of protocol and area.
The subjects were ten volunteers (6 women. 4 men) with a mean age of 30 I 6 years and a mean body mass of 70.1 5 10.2 kg. All subjects were pain-free and had no history of serious foot pathology or surgery. 3.2. Equipnwnt
Plantar foot pressures were obtained using a Biokinetics Dynamic Pedobarograph (DPG) which was securely mounted in a trough below floor Ievel with the plate level with the surrounding Root-. An unlimited walkway was available. The DPG was switched on at least 30 min before data collection commenced and the maximum sampling rate of 25 Hz was used. A battery operated audible/visual metronome was used to provide regular pulsed signals as required. Black tape markings of 15 mm thickness were used when stride Iength was controlled.
All trials were barefoot and of the subject’s right foot. Any trial was rejected if it failed to land entirely in the sensitive area of the plate or if there was an obvious stutter in their gait. There was no attempt to disguise the surface of the DPG. When tape marks were used to control stride length (protocols SLC, FGC and FS) they were positioned so the final footstep should fall in the centre of the DPG. No marker was placed for the measured fbotstep. Subjects were always instructed to walk beyond the plate for at least two more strides.
A.J.
52
Harrison,
J.P.
Follami
/ Gait & Posture
6 (1997j
50-55
Table 2 Consistency of peak pressures beneath seven areas of the foot for five different walking protocols (values are mean intra-subject coefficients of variation (%) over five trials for ten subjects) Protocol
Heel
I st MTH
2nd MTH
3rd
4th MTH
5th MTH
GT
Average
MTH
FGC NGC SLC SRC FS
8.1 10.3 8.7 14.5 6.0
22.1 25.8 23.8 24.7 27.2
12.7 14.8 13.3 13.5 16.4
11.3 12.5 13.3 15.0 15.7
15.9 17.8 15.7 19.8 15.1
23.0 20.8 16.9 27.2 23.9
19.3 20.4 21.2 25.2 20.1
16.1 17.5 16.1 20.0 17.8
Average
9.5
24.1
14.2
13.6
16.9
22.4
21.2
-
Trials were carried out in random order to negate any bias due to experimental procedures. Five trials were collected for each subject under each protocol. Four variations of mid-gait protocols were investigated as they are thought to be more representative of normal walking. An explanation of each protocol is given below. No gait control (NGC): subjects were asked to walk at their chosen pace and instructed to start at least six paces from the plate. This is the traditional uncontrolled ‘mid-gait protocol’. Stride rate controlled (SRC): before data collection commenced under this condition, stride rate was determined for each subject. They were instructed to walk along a straight corridor at their normal walking pace. The experimenter ascertained their stride rate by matching a flashing (no sound) metronome to the subject’s stride rate. The subject then walked at the metronome pace (sound on) and further adjustments to the rate could be made according to their feedback. During the testing under this condition, the metronomeemitted an audible bleep and the subject was asked to walk at that pace. All floor markings were removed. Stride length control (SLC): before data collection for this condition, subjects were asked to walk from a start line at their chosen pace for six paces and the distance travelled was measured. This was repeated four times and the average stride length determined. Tape marks for six strides were placed on the floor approaching the pedobarograph allowing subjects to walk at a constant stride length by placing their toe to each mark as they walked. Full gait control (FGC): under this condition, both stride rate and stride frequency were controlled. Stride rate was determined as previously described but stride length was re-determined with the addition of the metronome bleep. For data collection, subjects were required to place their toes to each of six marks on the approach to the pedobarograph whilst walking in time to the metronome. First step (FS): a tape mark was placed so that the one mid-gait stride would land the first step in the
centre of the DPG. Subjects stood with both feet on this mark and when instructed took one step forward onto the plate and continued walking. Each trial was saved and analysed later. Analysis involved specific areas of the foot being selected from the combined frames image, which displayed the highest pressure value for every point throughout the whole footstep. The resolution of the DPG enabled clear identification of anatomical areas, which were selected allowing regional pressure values to be generated. Seven specific areas of the foot were examined, the heel, five metatarsal heads (MTH) and the great toe (GT). This selection was done interactively with the placement of discrete sized areas (ellipse in shape) upon a required part of the image. Constant sized areas of 4.86 cm2 for the heel and 3.38 cm2 for the metatarsal heads and great toe were used consistently for all trials. The placing of these areas was done by the same experimenter for all the trials. Data were exported into the spreadsheet package Quattro Pro for statistical analysis. Peak pressure and peak pressure time integral (PPTI) data were extracted from each trial. Peak pressures have become the standard measure and peak pressure time integrals were investigated because very little work has been done on this potentially valuable parameter [13]. For both parameters mean, standard deviation and coefficient of variation values for each subject’s set of five trials under each protocol were produced. Consistency of the parameters was measured by the mean intra-subject coefficient of variation (COV) for five trials (COV,,). Statistical comparison of protocols and areas was done by analysis of variance.
3. Results
The peak pressure values for the five protocols are very similar (Table 1). There is a consistent order of magnitude for the protocols beneath MTHs 2, 3 and 4 with the first step producing the highest values beneath these and MTH 5. The FGC protocol gives the lowest
A.J.
Harrison.
J.P.
Foliand
I Gait & Porture
6 (19971
50 cii
5’1
Table 3 Peak pressure time integrals (KPa/s) for seven areas of the foot during five different walking protocols (values arc the rrran I.)!‘live trials for each OS ten subjects) ----_.- .._- ----___J-s-,;*: Protocol Heel 1st 2nd 3rd 4th Sth GT MTH MTH MTH MTH ‘VITH I _____ -__-___ -._--.. -...- .~. ~.--. ^--.. -_ I--m 58 79 II9 111 72 hl 93 x4 NGC 56 79 117 106 6% 65 x3 x; SL.(‘
60
73
118
110
I?
hI
76
SRC FS
58 14
70 71
hi
121 115
Ill 108
73 70
hi) 63
94 79
‘1: I2’..
peak pressure values for the heel and MTHs 2, 3, 4 and 5. Averaged across all seven areas the highest protocol (FS) is < 6% greater than the lowest protocol (FGC). The largest difference between two protocols was beneath MTH I where NGC was 20.3% higher than SRC. No significant differences were found between protocols for all areas (P = 0.97) or for individual areas (P > 0.90). Significant differences were found between areas of the foot (P < 0.001). The peak pressure values for the FGC and SLC protocols were the most consistent with a mean intrasubject COV,,, averaged across all seven areas beneath the foot, of 16.1% (Table 2). The least consistent protocol was SRC with a value of 20.0%. The different areas of the foot were more diverse in the consistency of their peak pressure values. The heel was the most consistent with a mean intra-subject COVsT, averaged across all the protocols, of 9.5%). The peak pressure values beneath the heel of the FS protocol at 6% were the most consistent of any area and protocol combination. The central three MTHs had similar consistency of their peak pressure values. The border areas of the foot (1st MTH, 5th MTH and GT) were the least consistent. more than twice as inconsistent as the heel. The different protocols PPTI values averaged across all areas of the foot were very similar, range 81-84 KPa(s (Table 3). There was no consistent pattern across the areas of the foot, and no significant differences were found between protocols for any areas (P = 0.99). No significant differences were found between protocols for individual areas (P > 0.45), although PPTI values beneath the heel were by far the most diverse. Significant differences were found for individual areas of the foot (P < 0.001). The SLC protocol produced the most consistent PPTI values with a mean intra-subject subject COV,,, averaged across all the areas beneath the foot, of 14.4% (Table 4). SRC was the most consistent with a value of 18.5% for the same measure. The most consistent areas, in terms of the mean intra-subject COV,,, averaged across all the protocols, were the 2nd and 3rd MTH with 9.7% and 9.6%, respectively. The medial and lateral border areas were again the least consistent.
The contact period for the FS protocol was significantly longer (P < 0.001) than the other protocols which were tightly grouped (Table 5). The contact period intra-subject COV,T was highest for the NGC and SRC protocols at 3.53%) and 3.52;?& respectively.
4. Discussion
The pressure values for all of rhe protocols are remarkably similar. Averaged across all the areas of the foot the difference between protocols for both parameters was < 6%. Of course it is possible that this averaging across areas fails to distinguish between the protocols which have area specific effects. However, no significant differences were found for either parameter for all areas of the foot or for individual areas. The maximum difference between any of the protocols for either of the measured parameters under any area of the foot was only 20.3%; this was peak pressure measured beneath the 1st MTH, which appears to produce the least consistent peak pressure data of all the areas of the foot. The lowest heel peak pressures were recorded for the protocols where stride frequency was controlled (SRC and FGC), possibly causing an unnatural and tentative foot placement as subjects attempted to time heel strike with the metronome beat. No pattern can be seen in the pressure data for the forefoot areas. With the precise protocol employed by this study the first-step protocol was found to be perfectly representative of normal mid-gait walking. providing virtually identical pressure values for all but one measure (PPTI beneath the heel). Given that there are no differences for the modes of walking it would appeilr that the first-step method adopted by Cavanagh et al [14] is valid for the evaluation of plantar pressures. For nor-, ma1 subjects the other specific advantage of the firs1 step method is that it simplifies data collection. The significantly longer contact period of rhe tirststep protocol (P < 0.001) would be expected as the walking velocity should be slower. but it is confusing considering the similarity of the prtysure values. The contact times in this study have limircd accuracy due to
A.J.
54
Hurrison.
J.P.
Follu~d
; Gait & Posture
6 (1997)
50-55
4 Consistency of peak pressure time integrals beneath seven areas of the foot for five different protocols (values are mean intra-subject coefficients of variation (%) over five trials for ten subjects)
Table
Protocol
Heel
1st MTH
2nd MTH
3rd MTH
4th MTH
5th MTH
CT
Average
FGC NGC SLC SRC FS
11.1 13.3 10.4 14.2 7.8
25.5 23.5 21.4 23.9 25.8
10.8 8.7 8.5 9.3 11.4
9.7 9.7 8.4 10.3 9.9
13.8 15.4 11.6 13.0 13.0
20.0 20.5 16.9 23.8 20.4
24.5 29.8 23.9 34.9 25.4
15.9 17.3 14.4 18.5 16.2
Average
11.4
23.2
9.1
9.6
13.4
20.3
21.1
the low capture rate (25 Hz, 0.04 s), although the values presented in Table 5 are a mean of 50 trials. The mean peak pressure values averaged across all ten subjects for the NGC protocol, or in fact any of the protocols, are very similar to those presented by Betts et al. [15] for uncontrolled mid-gait walking. The contact period for the NGC protocol was 0.77 + 0.06 s, which is marginally lower than the mean contact period for normal subjects also reported by Betts et al. [15]. These facts reinforce the fact that the subjects in this study were normal and non-pathological. An explanation for the similarity of the results for all protocols is that all the protocols tried to replicate normal walking. Further, as all the trials for each subject were done on one occasion and in fairly rapid succession it is possible that the subjects walked in a similar way for all trials. In particular, if motivation was low, then a lack of attention to each individual protocol could produce homogeneous pressure values. It is possible that the interactive selection of areas beneath the foot introduced a random element. However, the authors believe that there is minimal variance within or between experimenters for this variable. The similarity of all protocols, especially with regard to the first-step protocol, is in contrast to the literature. Rodgers [lo] used a large sample and found heel peak pressures to be considerably lower (340/o) for the firststep protocol compared to a mid-gait protocol. From a population sample of the same size as this study, Meyers-Rice et al. [ll] found first-step protocol peak pressures beneath the heel to be 13% lower than for a mid-gait protocol. Whilst it may be possible that samTable 5 Contact period (mean and mean intra-subject coefficients of variation for ten subjects)
Mean contact period (sec.) Mean COV,, (%)
FGC
NGC
SLC
SRC
FS
0.79
0.77
0.77
0.78
0.85
2.6
3.5
2.4
3.5
2.4
ple size had some effect on differences between protocols, a more likely explanation for the difference between this study and others lies in the exact nature of the FS protocol adopted. It is possible that the FS protocol used in this study encouraged subjects to over reach on their first step and thus heel pressures in particular were elevated above a natural (somewhat shorter) first-step. Of all the pressure values for the first-step protocol only the PPTI beneath the heel is noticeably different to the other protocols (22O/ higher). The significantly longer contact period of the FS protocol would be expected to increase the PPTI beneath all the areas of the foot (assuming all other thing remain equal). As this is not the case, it is likely that the FS protocol did cause an over-reaching and falsely elevated heel pressures compared to a natural first-step. Further research would be required to clarify these issues. The data presented in Tables 2 and 4 shows that the FGC and SLC protocols produce the most consistent pressure values on average for all seven areas beneath the foot. As SRC is the least consistent, it is clear that the controi of stride length enhances the consistency of mid-gait pressure values and metronome walking, i.e. attempting to control stride frequency, actually reduces their repeatability. Although the differences used to draw these conclusions are quite small, the average values for the whole foot are a mean of 70 values, each of which is a coefficient of variation of five trials. Furthermore, the fact that both parameters produced similar results indicates that it is not a random occurrence . The COV,, for all protocols and areas of the foot ranged from 9.5% to 24.7% for peak pressure and 9.7% and 27.7% for PPTI. Considering that these authors have found a COVsT of S- 17% for DPG measurement of peak pressures for a standard applied pressure, it is possible that the major part of the variation between trials is due to the instrument’s design. It is also worth noting that there are likely to be variations in DPG instruments, probably due to minor differences in materials and manufacture, thus compounding the difficulties of comparing the results of different studies.
Any random variance in the instrumentation could also account for the similarity of the protocols. Boulton et ai. [6] f.ound peak pressure coefficients variation to range from 7 to 14%. This was from multiple studies of uncontrolled mid-gait walking for several subjects over a week. The NGC protocol of this study found only two areas of the foot (i.e. the heel and 3rd MTH) had (XIV,,- which fell within these limits. Of the anatomical areas beneath the foot the heel predictably records the most consistent pressure values for all the protocols. After all, it is a large stable centrally situated area, which usually bears the entire body weight on a relatively constant area. The central MTHs (2. 3 and 4) are more tightly bound together [ 161. perhaps explaming their noticeably more consistent pressure values compared to the peripheral areas (MTHs I and 5). To conclude. whilst no statistically significant differences in protocols were found, the authors recommend, where possible. the stride length controlled protocol (SK) as the most consistent for forefoot plantar pressure investigations. The first-step protocol (FS) also provided consistent data, particularly for the heel and is desirable due to its ease of administration with pathological subjects. However, some care is advised in determining the exact methodology employed in the FS protocol, since it is believed that this protocol may be sensitive to variations in the length of the first step.
[3] Holmes ations IO5 [4] i5]
[II
pressure 1991:1:1O7
Kirsche
D, Frey
S. Schuh Akt
unter Endokrin
121 Holmes GB, Timmesman effect of metatarsal pads I lii):l4i
145.
D, Haring
L. on
H, Mehnert
H. Dynamische
dem Fuss an patienten Stoffw 1985;6:133-142.
A quantitative plantar pressures.
assessment Foot Ankle
mit of
diathe 1990:
PK.
Quantitative mity and Foot and
RP.
Franks
C’I.
Wiird
under
Ulbrecht
rhe
weight
~~CI~III~
JS. Biomtchamci
!)t’ihr
approach to the assessmcn~ plantar pressure. In: Jahsb M Ankle. Philadelphia: Saunders.
of
three
pdthOtOgicdt
[I21
Morlock
[13]
533. Alexander dynamic
methods subjects.
MM.
method-results
of J Am
T‘~I< pattern f~)rcli~<)t.
Mittlmeier
tit. I:OI>I
cilabctic
l~.~~t: .4 dcfclp o! tht~
III II?C riiab~uc I’hiia&iphia:
State i fntvrrsity. T. Co.~nwdl MW.
t:)or. i..~r during PhD
198.5. Compare-
obtaining plantar pressures in nonPod Med Asioc i9%;84ti~)):499. T. First :+lep method ~5. t’tt.11 gait
of a comparison.
Fur
J Ph!,\
%11pd Kebab
199X!:
1.l. Chao EYS. Johnson KA I‘hc ahsexsment oi fool to ground contact forces :lnd plantar pressure
distribution: a review clinical applications. Cavanagh predIctor
Pennsylvania L. McPhoil
1.
m neuropathlc
MM. Plantar pressure distrthuiiijr; mcdsurcment walking: Normal values and prt:t.!tt.itve equations.
Diss. L’niverslty Park, [I 11 Meyers-Rice B. Sugars bon
Duckworth
:~j_ nruropa~h~. l-1 ~3. Dzs)rtlcr\ ‘N!
[4] C
JD.
of foot pressure abnormalities Diabetes Res 1987:5.Y t 7: P. Jagoe JR. KIcncrm,~;l i.
distribution -10X.
[K] CaLanagh
[lo]
considrr1091;12(2).
Pressure under thr :srcioot !n rheumatoid Res 1983:187:2 33 .?4_’ M, Hutton WC’. c.‘orhetr 11. (.‘hange\ 111 rheumatoid I~cI! Al::! K!wIr~l 1 fh 1W),3P:
Betts
The natural history diabetic subjects. [7] Hughes .I, Clark
fare
Druckverteilungsmessung betischen ulcera.
MH. Pciciical T:~IIII ,412kle
108.
Minns RJ. Craxford. arthritis. Clin Orthop Sharma M. Dhanedran load bearing in the
549 552. [6] Boulton AJM.
[14]
References
GB, Timmerman L. Wrllita the use of the pedobarorraph
for
of the evolution of current Foot Ankle 1990;711 l.‘2-
PR. Sims DS. of peak plantai’ 199l;l4(8i:7SF1--7S5
Saunders: prcssurc
techniques ib?
l.J. C~ci~l?. maxs !I? di.3 i~‘lii mi’~
i*
and ;I )Tpor fktbc"t2s
Investigation of gait protocols for plantar pressure measurement of non-pathological subjects using a dynamic pedobarograph A.J. Harrison*.l, School
qf Podiatry,
University
J.P. Folland College
Saljord,
Salford,
UK
Received 28 November 1995: accepted 30 April 1996
Abstract There is a clear need for a consistent and representativeprotocol for the measurement of plantar pressures. The purposeof this study wasto comparethe plantar pressuresproducedby five different modesof walking: full gait control (FGC), no gait control (NGC), stride length control (SLC), stride rate control (SRC) and the first step(FS). Ten non-pathologicalsubjectsrecordedfive trials for eachprotocol in a random order. For each trial subjectswalked barefoot over a dynamic pedobarograph.Sevenareas of the foot, the heel, ali five metatarsalheads(MTH) and the great toe (GT), were interactively selectedand analysed.Two parametersof pressuremeasurementwere investigated,peak pressuresand peak pressuretime integrals,with attention to the consistencyof the data (coefficient of variation for five trials) as well as the meanvalues. This investigation found the pressure valuesof the protocols to be very similar. No significantdifferenceswere found betweenprotocols for all areasor for individual areasfor either parameter.This wasdespitethe FS protocol having a significantly longercontact time (P < 0.001)than the other protocols. Averaged acrossall areasof the foot the protocols where stride length wascontrolled (SLC and FGC) were found to be the most consistentfor both parametersand control of this variable is recommendedfor increasedconsistencyand reliability. However, the differencesbetweenprotocols werestill small.For the heelthe first stepwasnoticeably the most consistentprotocol. The central areasof the foot (heel and MTHs 2, 3 and 4) produced more consistentpressurevaluesthan the peripheral areas (MTHs 1 and 5 and the GT). 0 1997ElsevierScienceB.V. Keywords:
Plantar foot pressure:Gait protocol; Pedobarograph
1. Introduction Plantar pressure measurement is a critical parameter in the evaluation of foot function and the assessment of
a wide range of foot pathologies. An individual’s pressure distribution and pressure values may reveal valuable information. Therefore, a consistent and representative protocol for the measurement of plantar pressures is required. The consistency is clearly important for reliable quantitative analysis and, for clinical Abbreoiations: GST, glutathione S-transferase; PPAR, peroxisome proliferator activated receptor; DEHP, di-(2-ethylhexyl)phthalate; GSH, glutathione; CDNB, I-chloro-2,4-dinitrobenzene ’ Present address: Department of P.E. Sport and Exercise Sciences, University of Limerick, Plassey Park, Limerick, Republic of Ireland. Tel: + 353 61 202809; e-mail: [email protected] * Corresponding author. 0966-6362/97/$17.00 D 1997 Elsevier Science B.V. All rights reserved. PZZ 509666362(96)01095-8
application, any protocol should represent an individual’s normal walking. The most popular protocol in the collection of plantar pressures has been a single foot contact mid-gait, whilst the patient is in the middle of several steps down a walkway. Mid-gait protocols are thought more representative of the normal walking stride [I]. Some investigators have attempted to control the speed of the subject [2,3] and others have observed gait parameters but placed no control upon these variables [4]. However, most have allowed the subject to determine their own gait after a period of familiarisation [5-71. This leaves the subject to target their footstep onto the surface of the pressure measuring device, usually a small finite area. Such targeting may tend to create unnatural gait patterns and collection of one or more
representative trials typically involves experimenter selection from several attempts. Uncontrolled mid-gait collection is, therefore, time consuming, potentially unrepresentative and inconsistent. For patients with poor co-ordination and vision this protocol may not be suitable. and for those with painful pathologies the number of trials required to generate useful data may render it unacceptable. The use of a first-step protocol espoused by Cavanagh and Ulbrecht [8,9] removes many of these drawbacks but may produce pressure values unrepresentative of normal walking. The first-step protocol requires the subject to stand one pace from the pressure measurement device and, in their own time, step onto the platform and continue walking. Rodgers [IO] compared pressures recorded from both the firststep and mid-gait protocols for 60 healthy men aged between 40 and 81 years. She found that peak pressures for the heel and metatarsal heads were on average 34% and 4.7% lower, respectively, for the first-step protocol. Only two other studies have compared gait protocols for pressure measurement. Meyers-Rice et al. [I I] investigated first-step, mid-gait and an original second step protocol. They collected three trials for the right foot of ten healthy subjects, mean age 27 years. Subject’s practised until the duration of the stance phase for ten trials varied by less than 30 ms ( < 5%). This was to increase the consistency of each individual’s gait. Some investigator selection was involved in all three protocols. Under the rearfoot peak pressure values were 14% (P <: 0.05) and 1l’Y,l lower for the first-step and secondstep protocols, respectively, when compared to the midgait protocol. Forefoot peak pressures were not found significantly different but, compared to the mid-gait protocol, the first-step and second-step protocols were 13’>:, and 7% lower, respectively. Meyers-Rice et al. [1 I] concluded that the second-step protocol produced peak pressure values more representative of the traditional mid-gdlt method. Morlock and Mittlmeier [ 121 measured pressures beneath both feet of 16 healthy subjects, mean age 30.6 years. Three trials were collected for the first-step and uncontrolled mid-gait walking, although trials > 5% different to normal walking speed were rejected. They reported different absolute values for the two protocols,
but found no statistical significance. The purpose of this investigation wa< lu compare five different gait protocols and their effect upon plantar foot pressures in non-pathological subjects. Seven different areas beneath the foot were anaiysed IO examine the interaction of protocol and area.
The subjects were ten volunteers (6 women. 4 men) with a mean age of 30 I 6 years and a mean body mass of 70.1 5 10.2 kg. All subjects were pain-free and had no history of serious foot pathology or surgery. 3.2. Equipnwnt
Plantar foot pressures were obtained using a Biokinetics Dynamic Pedobarograph (DPG) which was securely mounted in a trough below floor Ievel with the plate level with the surrounding Root-. An unlimited walkway was available. The DPG was switched on at least 30 min before data collection commenced and the maximum sampling rate of 25 Hz was used. A battery operated audible/visual metronome was used to provide regular pulsed signals as required. Black tape markings of 15 mm thickness were used when stride Iength was controlled.
All trials were barefoot and of the subject’s right foot. Any trial was rejected if it failed to land entirely in the sensitive area of the plate or if there was an obvious stutter in their gait. There was no attempt to disguise the surface of the DPG. When tape marks were used to control stride length (protocols SLC, FGC and FS) they were positioned so the final footstep should fall in the centre of the DPG. No marker was placed for the measured fbotstep. Subjects were always instructed to walk beyond the plate for at least two more strides.
A.J.
52
Harrison,
J.P.
Follami
/ Gait & Posture
6 (1997j
50-55
Table 2 Consistency of peak pressures beneath seven areas of the foot for five different walking protocols (values are mean intra-subject coefficients of variation (%) over five trials for ten subjects) Protocol
Heel
I st MTH
2nd MTH
3rd
4th MTH
5th MTH
GT
Average
MTH
FGC NGC SLC SRC FS
8.1 10.3 8.7 14.5 6.0
22.1 25.8 23.8 24.7 27.2
12.7 14.8 13.3 13.5 16.4
11.3 12.5 13.3 15.0 15.7
15.9 17.8 15.7 19.8 15.1
23.0 20.8 16.9 27.2 23.9
19.3 20.4 21.2 25.2 20.1
16.1 17.5 16.1 20.0 17.8
Average
9.5
24.1
14.2
13.6
16.9
22.4
21.2
-
Trials were carried out in random order to negate any bias due to experimental procedures. Five trials were collected for each subject under each protocol. Four variations of mid-gait protocols were investigated as they are thought to be more representative of normal walking. An explanation of each protocol is given below. No gait control (NGC): subjects were asked to walk at their chosen pace and instructed to start at least six paces from the plate. This is the traditional uncontrolled ‘mid-gait protocol’. Stride rate controlled (SRC): before data collection commenced under this condition, stride rate was determined for each subject. They were instructed to walk along a straight corridor at their normal walking pace. The experimenter ascertained their stride rate by matching a flashing (no sound) metronome to the subject’s stride rate. The subject then walked at the metronome pace (sound on) and further adjustments to the rate could be made according to their feedback. During the testing under this condition, the metronomeemitted an audible bleep and the subject was asked to walk at that pace. All floor markings were removed. Stride length control (SLC): before data collection for this condition, subjects were asked to walk from a start line at their chosen pace for six paces and the distance travelled was measured. This was repeated four times and the average stride length determined. Tape marks for six strides were placed on the floor approaching the pedobarograph allowing subjects to walk at a constant stride length by placing their toe to each mark as they walked. Full gait control (FGC): under this condition, both stride rate and stride frequency were controlled. Stride rate was determined as previously described but stride length was re-determined with the addition of the metronome bleep. For data collection, subjects were required to place their toes to each of six marks on the approach to the pedobarograph whilst walking in time to the metronome. First step (FS): a tape mark was placed so that the one mid-gait stride would land the first step in the
centre of the DPG. Subjects stood with both feet on this mark and when instructed took one step forward onto the plate and continued walking. Each trial was saved and analysed later. Analysis involved specific areas of the foot being selected from the combined frames image, which displayed the highest pressure value for every point throughout the whole footstep. The resolution of the DPG enabled clear identification of anatomical areas, which were selected allowing regional pressure values to be generated. Seven specific areas of the foot were examined, the heel, five metatarsal heads (MTH) and the great toe (GT). This selection was done interactively with the placement of discrete sized areas (ellipse in shape) upon a required part of the image. Constant sized areas of 4.86 cm2 for the heel and 3.38 cm2 for the metatarsal heads and great toe were used consistently for all trials. The placing of these areas was done by the same experimenter for all the trials. Data were exported into the spreadsheet package Quattro Pro for statistical analysis. Peak pressure and peak pressure time integral (PPTI) data were extracted from each trial. Peak pressures have become the standard measure and peak pressure time integrals were investigated because very little work has been done on this potentially valuable parameter [13]. For both parameters mean, standard deviation and coefficient of variation values for each subject’s set of five trials under each protocol were produced. Consistency of the parameters was measured by the mean intra-subject coefficient of variation (COV) for five trials (COV,,). Statistical comparison of protocols and areas was done by analysis of variance.
3. Results
The peak pressure values for the five protocols are very similar (Table 1). There is a consistent order of magnitude for the protocols beneath MTHs 2, 3 and 4 with the first step producing the highest values beneath these and MTH 5. The FGC protocol gives the lowest
A.J.
Harrison.
J.P.
Foliand
I Gait & Porture
6 (19971
50 cii
5’1
Table 3 Peak pressure time integrals (KPa/s) for seven areas of the foot during five different walking protocols (values arc the rrran I.)!‘live trials for each OS ten subjects) ----_.- .._- ----___J-s-,;*: Protocol Heel 1st 2nd 3rd 4th Sth GT MTH MTH MTH MTH ‘VITH I _____ -__-___ -._--.. -...- .~. ~.--. ^--.. -_ I--m 58 79 II9 111 72 hl 93 x4 NGC 56 79 117 106 6% 65 x3 x; SL.(‘
60
73
118
110
I?
hI
76
SRC FS
58 14
70 71
hi
121 115
Ill 108
73 70
hi) 63
94 79
‘1: I2’..
peak pressure values for the heel and MTHs 2, 3, 4 and 5. Averaged across all seven areas the highest protocol (FS) is < 6% greater than the lowest protocol (FGC). The largest difference between two protocols was beneath MTH I where NGC was 20.3% higher than SRC. No significant differences were found between protocols for all areas (P = 0.97) or for individual areas (P > 0.90). Significant differences were found between areas of the foot (P < 0.001). The peak pressure values for the FGC and SLC protocols were the most consistent with a mean intrasubject COV,,, averaged across all seven areas beneath the foot, of 16.1% (Table 2). The least consistent protocol was SRC with a value of 20.0%. The different areas of the foot were more diverse in the consistency of their peak pressure values. The heel was the most consistent with a mean intra-subject COVsT, averaged across all the protocols, of 9.5%). The peak pressure values beneath the heel of the FS protocol at 6% were the most consistent of any area and protocol combination. The central three MTHs had similar consistency of their peak pressure values. The border areas of the foot (1st MTH, 5th MTH and GT) were the least consistent. more than twice as inconsistent as the heel. The different protocols PPTI values averaged across all areas of the foot were very similar, range 81-84 KPa(s (Table 3). There was no consistent pattern across the areas of the foot, and no significant differences were found between protocols for any areas (P = 0.99). No significant differences were found between protocols for individual areas (P > 0.45), although PPTI values beneath the heel were by far the most diverse. Significant differences were found for individual areas of the foot (P < 0.001). The SLC protocol produced the most consistent PPTI values with a mean intra-subject subject COV,,, averaged across all the areas beneath the foot, of 14.4% (Table 4). SRC was the most consistent with a value of 18.5% for the same measure. The most consistent areas, in terms of the mean intra-subject COV,,, averaged across all the protocols, were the 2nd and 3rd MTH with 9.7% and 9.6%, respectively. The medial and lateral border areas were again the least consistent.
The contact period for the FS protocol was significantly longer (P < 0.001) than the other protocols which were tightly grouped (Table 5). The contact period intra-subject COV,T was highest for the NGC and SRC protocols at 3.53%) and 3.52;?& respectively.
4. Discussion
The pressure values for all of rhe protocols are remarkably similar. Averaged across all the areas of the foot the difference between protocols for both parameters was < 6%. Of course it is possible that this averaging across areas fails to distinguish between the protocols which have area specific effects. However, no significant differences were found for either parameter for all areas of the foot or for individual areas. The maximum difference between any of the protocols for either of the measured parameters under any area of the foot was only 20.3%; this was peak pressure measured beneath the 1st MTH, which appears to produce the least consistent peak pressure data of all the areas of the foot. The lowest heel peak pressures were recorded for the protocols where stride frequency was controlled (SRC and FGC), possibly causing an unnatural and tentative foot placement as subjects attempted to time heel strike with the metronome beat. No pattern can be seen in the pressure data for the forefoot areas. With the precise protocol employed by this study the first-step protocol was found to be perfectly representative of normal mid-gait walking. providing virtually identical pressure values for all but one measure (PPTI beneath the heel). Given that there are no differences for the modes of walking it would appeilr that the first-step method adopted by Cavanagh et al [14] is valid for the evaluation of plantar pressures. For nor-, ma1 subjects the other specific advantage of the firs1 step method is that it simplifies data collection. The significantly longer contact period of rhe tirststep protocol (P < 0.001) would be expected as the walking velocity should be slower. but it is confusing considering the similarity of the prtysure values. The contact times in this study have limircd accuracy due to
A.J.
54
Hurrison.
J.P.
Follu~d
; Gait & Posture
6 (1997)
50-55
4 Consistency of peak pressure time integrals beneath seven areas of the foot for five different protocols (values are mean intra-subject coefficients of variation (%) over five trials for ten subjects)
Table
Protocol
Heel
1st MTH
2nd MTH
3rd MTH
4th MTH
5th MTH
CT
Average
FGC NGC SLC SRC FS
11.1 13.3 10.4 14.2 7.8
25.5 23.5 21.4 23.9 25.8
10.8 8.7 8.5 9.3 11.4
9.7 9.7 8.4 10.3 9.9
13.8 15.4 11.6 13.0 13.0
20.0 20.5 16.9 23.8 20.4
24.5 29.8 23.9 34.9 25.4
15.9 17.3 14.4 18.5 16.2
Average
11.4
23.2
9.1
9.6
13.4
20.3
21.1
the low capture rate (25 Hz, 0.04 s), although the values presented in Table 5 are a mean of 50 trials. The mean peak pressure values averaged across all ten subjects for the NGC protocol, or in fact any of the protocols, are very similar to those presented by Betts et al. [15] for uncontrolled mid-gait walking. The contact period for the NGC protocol was 0.77 + 0.06 s, which is marginally lower than the mean contact period for normal subjects also reported by Betts et al. [15]. These facts reinforce the fact that the subjects in this study were normal and non-pathological. An explanation for the similarity of the results for all protocols is that all the protocols tried to replicate normal walking. Further, as all the trials for each subject were done on one occasion and in fairly rapid succession it is possible that the subjects walked in a similar way for all trials. In particular, if motivation was low, then a lack of attention to each individual protocol could produce homogeneous pressure values. It is possible that the interactive selection of areas beneath the foot introduced a random element. However, the authors believe that there is minimal variance within or between experimenters for this variable. The similarity of all protocols, especially with regard to the first-step protocol, is in contrast to the literature. Rodgers [lo] used a large sample and found heel peak pressures to be considerably lower (340/o) for the firststep protocol compared to a mid-gait protocol. From a population sample of the same size as this study, Meyers-Rice et al. [ll] found first-step protocol peak pressures beneath the heel to be 13% lower than for a mid-gait protocol. Whilst it may be possible that samTable 5 Contact period (mean and mean intra-subject coefficients of variation for ten subjects)
Mean contact period (sec.) Mean COV,, (%)
FGC
NGC
SLC
SRC
FS
0.79
0.77
0.77
0.78
0.85
2.6
3.5
2.4
3.5
2.4
ple size had some effect on differences between protocols, a more likely explanation for the difference between this study and others lies in the exact nature of the FS protocol adopted. It is possible that the FS protocol used in this study encouraged subjects to over reach on their first step and thus heel pressures in particular were elevated above a natural (somewhat shorter) first-step. Of all the pressure values for the first-step protocol only the PPTI beneath the heel is noticeably different to the other protocols (22O/ higher). The significantly longer contact period of the FS protocol would be expected to increase the PPTI beneath all the areas of the foot (assuming all other thing remain equal). As this is not the case, it is likely that the FS protocol did cause an over-reaching and falsely elevated heel pressures compared to a natural first-step. Further research would be required to clarify these issues. The data presented in Tables 2 and 4 shows that the FGC and SLC protocols produce the most consistent pressure values on average for all seven areas beneath the foot. As SRC is the least consistent, it is clear that the controi of stride length enhances the consistency of mid-gait pressure values and metronome walking, i.e. attempting to control stride frequency, actually reduces their repeatability. Although the differences used to draw these conclusions are quite small, the average values for the whole foot are a mean of 70 values, each of which is a coefficient of variation of five trials. Furthermore, the fact that both parameters produced similar results indicates that it is not a random occurrence . The COV,, for all protocols and areas of the foot ranged from 9.5% to 24.7% for peak pressure and 9.7% and 27.7% for PPTI. Considering that these authors have found a COVsT of S- 17% for DPG measurement of peak pressures for a standard applied pressure, it is possible that the major part of the variation between trials is due to the instrument’s design. It is also worth noting that there are likely to be variations in DPG instruments, probably due to minor differences in materials and manufacture, thus compounding the difficulties of comparing the results of different studies.
Any random variance in the instrumentation could also account for the similarity of the protocols. Boulton et ai. [6] f.ound peak pressure coefficients variation to range from 7 to 14%. This was from multiple studies of uncontrolled mid-gait walking for several subjects over a week. The NGC protocol of this study found only two areas of the foot (i.e. the heel and 3rd MTH) had (XIV,,- which fell within these limits. Of the anatomical areas beneath the foot the heel predictably records the most consistent pressure values for all the protocols. After all, it is a large stable centrally situated area, which usually bears the entire body weight on a relatively constant area. The central MTHs (2. 3 and 4) are more tightly bound together [ 161. perhaps explaming their noticeably more consistent pressure values compared to the peripheral areas (MTHs I and 5). To conclude. whilst no statistically significant differences in protocols were found, the authors recommend, where possible. the stride length controlled protocol (SK) as the most consistent for forefoot plantar pressure investigations. The first-step protocol (FS) also provided consistent data, particularly for the heel and is desirable due to its ease of administration with pathological subjects. However, some care is advised in determining the exact methodology employed in the FS protocol, since it is believed that this protocol may be sensitive to variations in the length of the first step.
[3] Holmes ations IO5 [4] i5]
[II
pressure 1991:1:1O7
Kirsche
D, Frey
S. Schuh Akt
unter Endokrin
121 Holmes GB, Timmesman effect of metatarsal pads I lii):l4i
145.
D, Haring
L. on
H, Mehnert
H. Dynamische
dem Fuss an patienten Stoffw 1985;6:133-142.
A quantitative plantar pressures.
assessment Foot Ankle
mit of
diathe 1990:
PK.
Quantitative mity and Foot and
RP.
Franks
C’I.
Wiird
under
Ulbrecht
rhe
weight
~~CI~III~
JS. Biomtchamci
!)t’ihr
approach to the assessmcn~ plantar pressure. In: Jahsb M Ankle. Philadelphia: Saunders.
of
three
pdthOtOgicdt
[I21
Morlock
[13]
533. Alexander dynamic
methods subjects.
MM.
method-results
of J Am
T‘~I< pattern f~)rcli~<)t.
Mittlmeier
tit. I:OI>I
cilabctic
l~.~~t: .4 dcfclp o! tht~
III II?C riiab~uc I’hiia&iphia:
State i fntvrrsity. T. Co.~nwdl MW.
t:)or. i..~r during PhD
198.5. Compare-
obtaining plantar pressures in nonPod Med Asioc i9%;84ti~)):499. T. First :+lep method ~5. t’tt.11 gait
of a comparison.
Fur
J Ph!,\
%11pd Kebab
199X!:
1.l. Chao EYS. Johnson KA I‘hc ahsexsment oi fool to ground contact forces :lnd plantar pressure
distribution: a review clinical applications. Cavanagh predIctor
Pennsylvania L. McPhoil
1.
m neuropathlc
MM. Plantar pressure distrthuiiijr; mcdsurcment walking: Normal values and prt:t.!tt.itve equations.
Diss. L’niverslty Park, [I 11 Meyers-Rice B. Sugars bon
Duckworth
:~j_ nruropa~h~. l-1 ~3. Dzs)rtlcr\ ‘N!
[4] C
JD.
of foot pressure abnormalities Diabetes Res 1987:5.Y t 7: P. Jagoe JR. KIcncrm,~;l i.
distribution -10X.
[K] CaLanagh
[lo]
considrr1091;12(2).
Pressure under thr :srcioot !n rheumatoid Res 1983:187:2 33 .?4_’ M, Hutton WC’. c.‘orhetr 11. (.‘hange\ 111 rheumatoid I~cI! Al::! K!wIr~l 1 fh 1W),3P:
Betts
The natural history diabetic subjects. [7] Hughes .I, Clark
fare
Druckverteilungsmessung betischen ulcera.
MH. Pciciical T:~IIII ,412kle
108.
Minns RJ. Craxford. arthritis. Clin Orthop Sharma M. Dhanedran load bearing in the
549 552. [6] Boulton AJM.
[14]
References
GB, Timmerman L. Wrllita the use of the pedobarorraph
for
of the evolution of current Foot Ankle 1990;711 l.‘2-
PR. Sims DS. of peak plantai’ 199l;l4(8i:7SF1--7S5
Saunders: prcssurc
techniques ib?
l.J. C~ci~l?. maxs !I? di.3 i~‘lii mi’~
i*
and ;I )Tpor fktbc"t2s