- Email: [email protected]
A study of the effect of wear on the pressure-relieving properties of foot orthosis
A study of the effect of wear on the pressure-relieving properties of foot orthosis J. Barrow, J. Hughes, P. Clark, L. Kienerman Northwick Park Hospital, Middlesex, UK and Royal Liverpool Hospital, Liverpool, UK SUMMA R Y. There is little comparative data available to assist choice of materials for the manufacture of orthoses, and there have been few objective studies comparing insole designs. This study has compared two materials, PPT and SPENCO, and assessed one design of insole together with a commonly used variation of that design. Both materials and designs have been tested for effectiveness against each other and against themselves following a period of continuous wear. The pedobarograph was used to measure the changes in pressure. Seven subjects, with a high pressure pattern under the second metatarsal head of one foot, wore a series of four insoles in random order for 1 month each. The four insoles were made to the same pattern for each patient, two of PPT and two of SPENCO, each with a U’d plantar metatarsal pad. In one insole of each material, the U-shaped cut-out was filled with sponge. Pedobarograph recordings were taken, barefoot and with the insole taped to the foot, at issue and after 1 month of wear for each insole. Results show that all the insoles were effective in reducing pressure and force under the areas measured (P
the areas on either side of the lesions were affected by the insole.
The range of materials available for the manufacture of orthosis is increasing continuously, but little data is available to assist choice in terms of effectiveness over a period of wear, and thus cost-effectiveness. Most of the materials used are not manufactured specifically for the orthosis market, and manufacturers, therefore, do not test their materials in an appropriate way. Research within the chiropodial and orthotic professions has tested various materials for their pressure-relieving properties under varying conditions, and in most of these trials, PPT and SPENCO have been found to be among the best as pressure relievers. However, there is little data available on the effect of wear.‘-3 The pedobarograph has been shown to be capable of measuring the effectiveness of orthosis at reducing pressure and force.4 This study was performed using the pedobarograph to examine changes in the pressure-reducing properties of PPT and SPENCO after 1 month of wear, and with two different insole designs.
METHOD Seven patients, each with a high pressure point under the second metatarsal head took part in the study. A high pressure point was defined as one in which the second metatarsal registered a higher pressure than the adjacent areas by at least 0.5 kg/cm or 49.05 kPa. Figure 1 shows a black and white illustration of the combined frames picture of a typical pedobarograph recording. The area of highest press-
AIMS The objectives of the study were much pressure relief was obtained wearing made-to-measure insoles assess the effect on peak pressure of the addition of a sponge button highest pressure; and to discover
to discover how by patients after for I month; to and contact time under the area of if the pressure in
Fig. 1-A black and white illustration of the combined frames picture of a typical pedobarograph recording. The areas of highest pressure appear as the lightest areas. 195
196
The Foot
ure is the lightest area, and is under the second metatarsal head in this recording. One foot only from each patient was studied, and in those with bilateral high pressure under the second metatarsal head, the foot to be studied was randomly chosen. A single insole identical to the first insole supplied was provided for the other foot. The study took the form of a controlled crossover trial, in which each patient was given one of four different insoles at monthly intervals. The patients’ pressures were measured on the pedobarograph, barefoot and with the insole at the time of issue. Patients returned at l-month intervals, at which time the pressure measurements were repeated. They were then given another insole, and the measurements repeated with this one. The order of fitting the different types of insole was randomly determined. To measure the pressure with the insole it was attached to the foot using Micropore dressing tape. Each pressure recording was made 3 times at each visit. The patients wore their normal shoes, which in some cases were NU-Style shoes provided by the National Health Service. All other shoes were of a sensible, low-heeled leather design, usually with a lace. The insoles were made to a cardboard template of the patient’s shoe. The positions of bony prominences were transferred to the card by marking the foot with felt-tip pen and spraying the cardboard in the shoe with spirit. The patient then walked barefoot in the shoe, and the marks transferred from the foot to the template. This is a standard technique used in chiropody for this type of insole, which allows U’s to be cut out for a particular site, and to be placed accurately on the insole. The four insoles were designated A, B, C and D and were manufactured as follows: Insole A: regenerated leather board base, PPT 3 mm plantar pad with a U for the second metatarsal, PPT 3 mm with nylon cover as a cover over the full length. Insole B: regenerated leather board base, 3 mm SPENCO plantar pad with U for the second metatarsal. 3 mm SPENCO with nylon cover as a cover over the full length; Insole C: as insole A. but with a grey latex sponge button in the U for the second metatarsal head; Insole D: as insole B, with a sponge button. Precovered PPT and SPENCO were used to eliminate any differences in thickness which could occur if leather covers had been used. The pedobarograph results were analyzed by examining the pressure and force over time in each of the chosen areas. The areas were the same size at each site. Site 1 covered the first metatarsal head; site 2, the second metatarsal head and site 3 covered the third and fourth metatarsal heads. To maintain a
uniform choice of site, at the first session an outline of the picture of the foot on the monitor was drawn on acetate sheet, with the areas for analysis marked in, and this was fitted over the picture of all subsequent walks so that the same areas were analyzed each time. Statistical methods To assess the effect of the insoles, the difference between the barefoot data and the measurements with the insoles in place on the same visit were calculated. These differences were used as the dependent variable in analysis of variance. The insole types, PPT and SPENCO, use or not of buttons, sites 1, 2 or 3 and the condition of the insole, i.e. new or old, were used as within-subject factors. Comparisons of individual group means was carried out using ‘Tukey (a)’ method.5
RESULTS Peak pressure Force and pressure were analyzed separately, but the results did not differ, and only pressure results are presented here. All insoles reduced pressure. There was no difference between the new and the old insoles in pressure reduction, (77 kPa and 74 kPa respectively, P=O.51), nor did this vary according to site, insole or the combination of site and insole. The table shows the mean reduction in peak pressure for all types of insoles at all sites. Figure 2 shows the mean reduction in peak pressure, under the second metatarsal head, for all patients with each insole, averaged over both new and old insoles. If any pattern can be discerned it is that, for PPT, peak pressure relief is lower with the button than without it. Five patients show a reduction, and 2 an increase, whereas for SPENCO there is no difference, 3 showing a reduction, 3 showing an increase, and 1 showing no change at all. The patient with the highest pressure when barefoot (closed diamond symbol in Fig. 2) achieved the greatest reduction in peak pressure. Figure 3 shows the mean reduction in peak pressure for each insole type and each site, together with the 95% confidence intervals. Where the confidence interval bars overlap here and in Figures 4 and 5, this Table l-Mean reduction in peak pressure (kPa) for all sites and all insoles. Range of peak pressure reduction shown in parentheses. PPT No button
Button
SPENCO No button
Site 1 Site 2
55 (41-69) 99 (85-I 13)
82 (68-97) 79 (65-93)
76 (62-91) 105 (91-119)
Site 3
55 (40-69)
48 (34-63)
41 (27-55)
Button 81 (67-96) 119 (1044133) 66 (52-81)
.4 study of the effect of wear on the pressure-relieving
O-
the mean pressure
reduction
under
197
With button
the second
D
B
C
A showing
of foot orthosis
Spenco
PPT With button
Fig. Z-Graphs
properties
metatarsal
head for all insoles. for all patients.
20-
Spenco
PPT
0”
With button
With button A
C
B
D
Fig. X-Graph of the mean reduction
in pressure and 95% confidence interval for all insoles in all sites. The secondmetatarsalhead by the open circles joined with the solid lines, the first metatarsal head (site I) by the solid circles joined with the lines. and the third and fourth metatarsal heads, (site 3) the solid squares joined with the dotted and dashed lines.
(site 2) is shown dotted
indicates no significant difference between the means, whereas where there is a large gap there is a significant difference (PcO.05). Where the overlap is small this means that the result is inconclusive. There is a significant difference between the sites, (P = 0.012) as would be expected. There is a marginal interaction between the button and the site, (P= 0.055) and a significant interaction between buttons, insole type and site (P= 0.017). All the insoles produced a significant reduction in peak pressure, which can be confirmed from Figure 3, where it can be seen that none of the confidence intervals contain 0. For
PPT the second metatarsal head (site 2) shows a significantly greater pressure relief than the other two sites. However, with the button, this pressure relief is reduced in site 2 and increased under the first metatarsal head, site 1, so it appears that the button transfers the pressure relief from site 2 to site 1. For SPENCO insoles without the button, again the greatest pressure relief is under the second metatarsal head, (site 2) and, with the button this relief is marginally improved and there is no transfer of pressure relief away to another site. The other two sites, the first and the third and fourth metatarsal
198
The Foot
0.02
T
0.01
0
-----
$ _? -0.01
-0.02
v
Spenco
PPT
-0.03!
With button
With button
Fig. 4-Graph showing the changes in contact insoles and the dotted lines the old insoles.
time for the two materials
No button
Button
No button
1st met head
averaged
over all areas. The solid lines represent
Button
2nd met head
Fig. S-Graph showing the change in contact time under the three sites for an average without. The solid lines represent the new insoles and the dotted lines the old insoles.
heads, also show marginal increases in pressure relief. This suggests that using the button with PPT interferes with its intended pressure relief, whereas with SPENCO it makes a marginal improvement. Without the button there is no great difference between PPT and SPENCO. Contact time There was a significant difference between the sites, (P=O.O13) as expected. There were also significant interactions between button and condition of old versus new, (P=O.O08), button type and condition,
No button
the new
Button
3rd’4thmet head of both materials
with the button
and both
(P=O.O21), and button, site and condition (P= 0.013). Figure 4 shows that for new insoles the button produces a reduction in contact time, whereas when it is old there is an increase in contact time. These differences are small for PPT insoles but very large for SPENCO insoles. Figure 5 shows that for the second metatarsal head there is a reduction in contact time without the button, which disappears with the button. This applies to both new and old insoles. For the adjacent areas the button appears to reduce contact time for new insoles, but increases it for old insoles. This is
A study of the effect of wear on the pressure-relieving
more marked under the first than the metatarsal heads.
third
and
fourth
DISCUSSION The results presented are based on a study of 7 patients, all with a very similar lesion. We have looked at only one insole design. To confirm these findings a larger group of patients should be examined, and a greater variety of lesions and insole designs studied. There is no statistically significant difference in the wear properties of SPENCO and PPT, with both materials being as effective after 1 month of continuous wear as they are when new. There is little to choose between PPT and SPENCO as insole materials in terms of pressure relief when new and after 1 month of wear without the sponge buttons. Using sponge buttons makes a marginal improvement in pressure reduction for SPENCO insoles, but appears to transfer some pressure reduction away from the second metatarsal head for PPT. There are significant interactions involving all four factors regarding contact time, and this makes interpretation of the change in contact time difficult. The button removes the reduction in contact time under the second metatarsal head for old and new insoles. For the other two sites the button reduces contact time when new. but increases it when old. This latter pattern applies to both types, but more to SPENCO than PPT. These results suggest that a button does not help with contact time reduction, and that its effects are more exaggerated for SPENCO.
CONCLUSIONS This study has shown that both insole materials reduce peak pressure under the foot, and neither
properties
of foot orthosis
199
showed a wear effect. There is no advantage in putting a sponge button in either type of insole made to this design, and there is possibly a disadvantage for PPT insoles.
References 1. Campbell G J, McLure M. Newell E N. Compressive behaviour after simulated service conditions of some foamed materials intended as orthotic shoe insoles. J Rehabil Res Dev 1984: 21(2): 57-65. 2. Campbell G J. McLure M, Newell E N. Compression testing of foamed plastics and rubbers for use as orthotic shoe insoles. Prosthet Orthot Int 1982: 6: 48-52. of shoe insole 3. Leber C, Evanski P M. A comparison materials in plantar pressure relief. Prosthet Orthot Int 1986; 10: 1355138. 4. Hughes J. Klenerman L. Foulston J. The use of the pedobarograph in assessment of the elTectiveness of foot orthosis. Biomechan Orthot Management Foot I 5.
B J. Statistical principles d ed. McGraw Hill, 1971.
in experimental
The Authors J. Barrow BSc(Hons), DPodM Chiropody Department J. Hughes BA, MPhil, MCSP Section of Molecular Rheumatology Clinical Research Centre P. Clarke BSc Section of Medical Statistics Clinical Research Centre Northwick Park Hospital Watford Road Harrow Middlesex HAI 3U.l UK Professor L. Klenerman ChM, FRCS University Department of Orthopaedic Royal Liverpool Hospital Prescott Street Liverpool L69 3BX UK Correspondence
to Professor
Surgery
L. Klenerman.
design.
the areas on either side of the lesions were affected by the insole.
The range of materials available for the manufacture of orthosis is increasing continuously, but little data is available to assist choice in terms of effectiveness over a period of wear, and thus cost-effectiveness. Most of the materials used are not manufactured specifically for the orthosis market, and manufacturers, therefore, do not test their materials in an appropriate way. Research within the chiropodial and orthotic professions has tested various materials for their pressure-relieving properties under varying conditions, and in most of these trials, PPT and SPENCO have been found to be among the best as pressure relievers. However, there is little data available on the effect of wear.‘-3 The pedobarograph has been shown to be capable of measuring the effectiveness of orthosis at reducing pressure and force.4 This study was performed using the pedobarograph to examine changes in the pressure-reducing properties of PPT and SPENCO after 1 month of wear, and with two different insole designs.
METHOD Seven patients, each with a high pressure point under the second metatarsal head took part in the study. A high pressure point was defined as one in which the second metatarsal registered a higher pressure than the adjacent areas by at least 0.5 kg/cm or 49.05 kPa. Figure 1 shows a black and white illustration of the combined frames picture of a typical pedobarograph recording. The area of highest press-
AIMS The objectives of the study were much pressure relief was obtained wearing made-to-measure insoles assess the effect on peak pressure of the addition of a sponge button highest pressure; and to discover
to discover how by patients after for I month; to and contact time under the area of if the pressure in
Fig. 1-A black and white illustration of the combined frames picture of a typical pedobarograph recording. The areas of highest pressure appear as the lightest areas. 195
196
The Foot
ure is the lightest area, and is under the second metatarsal head in this recording. One foot only from each patient was studied, and in those with bilateral high pressure under the second metatarsal head, the foot to be studied was randomly chosen. A single insole identical to the first insole supplied was provided for the other foot. The study took the form of a controlled crossover trial, in which each patient was given one of four different insoles at monthly intervals. The patients’ pressures were measured on the pedobarograph, barefoot and with the insole at the time of issue. Patients returned at l-month intervals, at which time the pressure measurements were repeated. They were then given another insole, and the measurements repeated with this one. The order of fitting the different types of insole was randomly determined. To measure the pressure with the insole it was attached to the foot using Micropore dressing tape. Each pressure recording was made 3 times at each visit. The patients wore their normal shoes, which in some cases were NU-Style shoes provided by the National Health Service. All other shoes were of a sensible, low-heeled leather design, usually with a lace. The insoles were made to a cardboard template of the patient’s shoe. The positions of bony prominences were transferred to the card by marking the foot with felt-tip pen and spraying the cardboard in the shoe with spirit. The patient then walked barefoot in the shoe, and the marks transferred from the foot to the template. This is a standard technique used in chiropody for this type of insole, which allows U’s to be cut out for a particular site, and to be placed accurately on the insole. The four insoles were designated A, B, C and D and were manufactured as follows: Insole A: regenerated leather board base, PPT 3 mm plantar pad with a U for the second metatarsal, PPT 3 mm with nylon cover as a cover over the full length. Insole B: regenerated leather board base, 3 mm SPENCO plantar pad with U for the second metatarsal. 3 mm SPENCO with nylon cover as a cover over the full length; Insole C: as insole A. but with a grey latex sponge button in the U for the second metatarsal head; Insole D: as insole B, with a sponge button. Precovered PPT and SPENCO were used to eliminate any differences in thickness which could occur if leather covers had been used. The pedobarograph results were analyzed by examining the pressure and force over time in each of the chosen areas. The areas were the same size at each site. Site 1 covered the first metatarsal head; site 2, the second metatarsal head and site 3 covered the third and fourth metatarsal heads. To maintain a
uniform choice of site, at the first session an outline of the picture of the foot on the monitor was drawn on acetate sheet, with the areas for analysis marked in, and this was fitted over the picture of all subsequent walks so that the same areas were analyzed each time. Statistical methods To assess the effect of the insoles, the difference between the barefoot data and the measurements with the insoles in place on the same visit were calculated. These differences were used as the dependent variable in analysis of variance. The insole types, PPT and SPENCO, use or not of buttons, sites 1, 2 or 3 and the condition of the insole, i.e. new or old, were used as within-subject factors. Comparisons of individual group means was carried out using ‘Tukey (a)’ method.5
RESULTS Peak pressure Force and pressure were analyzed separately, but the results did not differ, and only pressure results are presented here. All insoles reduced pressure. There was no difference between the new and the old insoles in pressure reduction, (77 kPa and 74 kPa respectively, P=O.51), nor did this vary according to site, insole or the combination of site and insole. The table shows the mean reduction in peak pressure for all types of insoles at all sites. Figure 2 shows the mean reduction in peak pressure, under the second metatarsal head, for all patients with each insole, averaged over both new and old insoles. If any pattern can be discerned it is that, for PPT, peak pressure relief is lower with the button than without it. Five patients show a reduction, and 2 an increase, whereas for SPENCO there is no difference, 3 showing a reduction, 3 showing an increase, and 1 showing no change at all. The patient with the highest pressure when barefoot (closed diamond symbol in Fig. 2) achieved the greatest reduction in peak pressure. Figure 3 shows the mean reduction in peak pressure for each insole type and each site, together with the 95% confidence intervals. Where the confidence interval bars overlap here and in Figures 4 and 5, this Table l-Mean reduction in peak pressure (kPa) for all sites and all insoles. Range of peak pressure reduction shown in parentheses. PPT No button
Button
SPENCO No button
Site 1 Site 2
55 (41-69) 99 (85-I 13)
82 (68-97) 79 (65-93)
76 (62-91) 105 (91-119)
Site 3
55 (40-69)
48 (34-63)
41 (27-55)
Button 81 (67-96) 119 (1044133) 66 (52-81)
.4 study of the effect of wear on the pressure-relieving
O-
the mean pressure
reduction
under
197
With button
the second
D
B
C
A showing
of foot orthosis
Spenco
PPT With button
Fig. Z-Graphs
properties
metatarsal
head for all insoles. for all patients.
20-
Spenco
PPT
0”
With button
With button A
C
B
D
Fig. X-Graph of the mean reduction
in pressure and 95% confidence interval for all insoles in all sites. The secondmetatarsalhead by the open circles joined with the solid lines, the first metatarsal head (site I) by the solid circles joined with the lines. and the third and fourth metatarsal heads, (site 3) the solid squares joined with the dotted and dashed lines.
(site 2) is shown dotted
indicates no significant difference between the means, whereas where there is a large gap there is a significant difference (PcO.05). Where the overlap is small this means that the result is inconclusive. There is a significant difference between the sites, (P = 0.012) as would be expected. There is a marginal interaction between the button and the site, (P= 0.055) and a significant interaction between buttons, insole type and site (P= 0.017). All the insoles produced a significant reduction in peak pressure, which can be confirmed from Figure 3, where it can be seen that none of the confidence intervals contain 0. For
PPT the second metatarsal head (site 2) shows a significantly greater pressure relief than the other two sites. However, with the button, this pressure relief is reduced in site 2 and increased under the first metatarsal head, site 1, so it appears that the button transfers the pressure relief from site 2 to site 1. For SPENCO insoles without the button, again the greatest pressure relief is under the second metatarsal head, (site 2) and, with the button this relief is marginally improved and there is no transfer of pressure relief away to another site. The other two sites, the first and the third and fourth metatarsal
198
The Foot
0.02
T
0.01
0
-----
$ _? -0.01
-0.02
v
Spenco
PPT
-0.03!
With button
With button
Fig. 4-Graph showing the changes in contact insoles and the dotted lines the old insoles.
time for the two materials
No button
Button
No button
1st met head
averaged
over all areas. The solid lines represent
Button
2nd met head
Fig. S-Graph showing the change in contact time under the three sites for an average without. The solid lines represent the new insoles and the dotted lines the old insoles.
heads, also show marginal increases in pressure relief. This suggests that using the button with PPT interferes with its intended pressure relief, whereas with SPENCO it makes a marginal improvement. Without the button there is no great difference between PPT and SPENCO. Contact time There was a significant difference between the sites, (P=O.O13) as expected. There were also significant interactions between button and condition of old versus new, (P=O.O08), button type and condition,
No button
the new
Button
3rd’4thmet head of both materials
with the button
and both
(P=O.O21), and button, site and condition (P= 0.013). Figure 4 shows that for new insoles the button produces a reduction in contact time, whereas when it is old there is an increase in contact time. These differences are small for PPT insoles but very large for SPENCO insoles. Figure 5 shows that for the second metatarsal head there is a reduction in contact time without the button, which disappears with the button. This applies to both new and old insoles. For the adjacent areas the button appears to reduce contact time for new insoles, but increases it for old insoles. This is
A study of the effect of wear on the pressure-relieving
more marked under the first than the metatarsal heads.
third
and
fourth
DISCUSSION The results presented are based on a study of 7 patients, all with a very similar lesion. We have looked at only one insole design. To confirm these findings a larger group of patients should be examined, and a greater variety of lesions and insole designs studied. There is no statistically significant difference in the wear properties of SPENCO and PPT, with both materials being as effective after 1 month of continuous wear as they are when new. There is little to choose between PPT and SPENCO as insole materials in terms of pressure relief when new and after 1 month of wear without the sponge buttons. Using sponge buttons makes a marginal improvement in pressure reduction for SPENCO insoles, but appears to transfer some pressure reduction away from the second metatarsal head for PPT. There are significant interactions involving all four factors regarding contact time, and this makes interpretation of the change in contact time difficult. The button removes the reduction in contact time under the second metatarsal head for old and new insoles. For the other two sites the button reduces contact time when new. but increases it when old. This latter pattern applies to both types, but more to SPENCO than PPT. These results suggest that a button does not help with contact time reduction, and that its effects are more exaggerated for SPENCO.
CONCLUSIONS This study has shown that both insole materials reduce peak pressure under the foot, and neither
properties
of foot orthosis
199
showed a wear effect. There is no advantage in putting a sponge button in either type of insole made to this design, and there is possibly a disadvantage for PPT insoles.
References 1. Campbell G J, McLure M. Newell E N. Compressive behaviour after simulated service conditions of some foamed materials intended as orthotic shoe insoles. J Rehabil Res Dev 1984: 21(2): 57-65. 2. Campbell G J. McLure M, Newell E N. Compression testing of foamed plastics and rubbers for use as orthotic shoe insoles. Prosthet Orthot Int 1982: 6: 48-52. of shoe insole 3. Leber C, Evanski P M. A comparison materials in plantar pressure relief. Prosthet Orthot Int 1986; 10: 1355138. 4. Hughes J. Klenerman L. Foulston J. The use of the pedobarograph in assessment of the elTectiveness of foot orthosis. Biomechan Orthot Management Foot I 5.
B J. Statistical principles d ed. McGraw Hill, 1971.
in experimental
The Authors J. Barrow BSc(Hons), DPodM Chiropody Department J. Hughes BA, MPhil, MCSP Section of Molecular Rheumatology Clinical Research Centre P. Clarke BSc Section of Medical Statistics Clinical Research Centre Northwick Park Hospital Watford Road Harrow Middlesex HAI 3U.l UK Professor L. Klenerman ChM, FRCS University Department of Orthopaedic Royal Liverpool Hospital Prescott Street Liverpool L69 3BX UK Correspondence
to Professor
Surgery
L. Klenerman.
design.