The orthoses affected specific regions of the foot differently, and more significant differences were seen for the right foot than the left foot.
The orthoses increased contact area under the heel, medial midfoot, second and third metatarsal heads and toes and the big toe (Tables 2 and 3). Increases in contact area averaged 2.3 cm2 during orthosis wear except for the medial midfoot, which increased 7.7 cm2 with orthosis. However, the orthoses did not significantly affect contact area under the lateral midfoot or lateral two metatarsal heads and toes.
Mean force under the medial midfoot increased 16.9 N with orthosis wear. Mean force was not significantly affected by orthosis wear for any other region.
The increases in contact area for the medial metatarsals, heel, and big toe without changes in mean force during orthosis wear resulted in decreases in peak pressure, maximum mean pressure, and pressure time integral. Peak pressure decreased 8.3 to 9.3 N/cm2, maximum mean pressure 3.1 to 3.9 N/cm2, and pressure time integral 2.5 to 3.3 (N/cm2)/second. Although orthosis wear did not significantly affect contact area or mean force of the fourth and fifth metatarsal heads and toes, peak pressure decreased 6.2 N/cm2, maximum mean pressure decreased 2.6 N/cm2, and pressure time integral decreased 2.0 (N/cm2)/second.
The increases in both contact area and mean force under the medial midfoot resulted in no change in peak pressure, maximum mean pressure, or pressure time integral because of orthosis wear. The only significant change in pressures for the lateral midfoot was a 3.9 N/cm2 decrease in peak pressure with orthosis wear.
The orthoses had a similar but lesser effect on the left foot. The effect was significant for all changes mentioned, except that the smaller differences between wearing and not wearing orthoses did not reach statistical significance for left big toe contact area and maximum mean pressure, heel maximum mean pressure and pressure time integral, and lateral mid-foot peak pressure and maximum mean pressure.
EFFECT OF ORTHOSES ADJUSTED FOR WEAR
Orthoses adjusted for 1 month of wear by the addition of a layer of material and/or metatarsal pads or heel wedge affected pressure variables in a manner similar to that seen with new orthoses. This effect of the adjusted orthoses did not differ between month 1, when alterations were first made and month 3, after 2 additional months of wear.
As was seen with the wearing of new orthoses, walking with orthoses adjusted for wear increased total foot contact area and decreased pressures bilaterally compared with walking without orthoses (Table 3). Values at 1 and 3 months were similar to those found for new orthoses (Tables 3 and 4). Wearing the adjusted orthoses increased contact area 20.2 cm2 and decreased peak pressure 10.5 N/cm2, maximum mean pressure 5.2 N/cm2, and pressure time integral 5.9 N/cm2 /second on average compared with walking shod without orthoses. Mean force was not affected by orthoses wear, averaging 622.7 N.
As was seen with the wearing of new orthoses, walking with orthoses adjusted for wear affected specific regions of the foot differently. The differences were similar to those seen for the new orthoses, but fewer differences met the rigor of the < .0083 significance when the number of pairs of subjects dropped to five in the 1- to 3-month analyses.
Unlike the results seen with the wearing of new orthoses, the contact area for isolated areas of the foot was not significantly affected by the wearing of adjusted orthoses, although trends were similar to those seen with new orthoses. As with new orthoses, orthoses adjusted for wear increased mean force only under the medial midfoot and decreased peak pressure and maximum mean pressure under the heel and big toe compared with walking without orthoses. In contrast to new orthoses, orthoses adjusted for wear significantly decreased maximum mean pressure only under the second and third metatarsal heads and toes and peak pressure only under the fourth and fifth metatarsal heads and toes. The pressure time integral was significantly decreased under the heel, second and third metatarsal heads and toes, and fourth and fifth metatarsal heads and toes when walking with orthoses adjusted for wear compared with walking without orthoses.
Contact area was significantly increased when wearing orthoses adjusted for wear only under the medial midfoot and second and third metatarsal heads and toes. Medial midfoot mean force was not significantly increased, unlike that seen with new orthoses. Peak pressure, maximum mean pressure, and pressure time integral were all decreased under the heel, big toe and second and third metatarsal heads and toes of the left foot, whereas the medial midfoot, lateral midfoot, and fourth and fifth metatarsal heads and toes were not significantly affected by the adjusted orthoses.
Force under the whole foot was not statistically different between walking with or without orthoses, between Plastazote and Aliplast/Plastazote orthosis groups, or between 1-and 3-month testing. By limiting velocity to specific ranges, we were successful in removing the confounding factor of speed on our force measurements.
The peak pressure under the heel, lateral midfoot, and big toe when subjects walked without orthoses in this study were within one standard deviation of those found in our 20 younger subjects without diabetes who walked in athletic shoes over concrete (unpublished data). Our peak pressures without orthoses also were within one standard deviation of the results reported by Bryant et al. 22 and Bennett and Duplock 23 of subjects without diabetic neuropathy for the big toe. We cannot compare metatarsal regions between our two studies or between this study and studies reported in the literature because the metatarsal regions were divided differently in all of the studies. However, our heel peak pressure, averaging 25.6 ± 7.1 N/cm2, was lower than that reported by Bryant et al. 22 (35.0 ± 7.8 N/cm2) and lower than the results reported by Ashry et al. 11 (38.0 ± 1.6 N/cm2; converted from g/cm2) for 11 patients with diabetic neuropathy walking in extra-depth shoes. Peak pressure under the first metatarsal head also was higher in the study by Ashry et al. 11 (51.4 ± 23.1 N/cm2), compared with our subjects’ big toe peak pressure of 30.9 ± 11.4 N/cm2. Differences in pressures between this study and those reported in the literature may reflect the differences in percent of the foot used to define the specific foot regions or differences in measurement systems used in the studies. For example, our big toe region includes both the first metatarsal head and the great toe, whereas Ashry et al. 11 used a separate region for the first metatarsal head alone. Bryant et al. 22 used the EMED force plate (Novel Electronics, Munich, Germany), which records only one footfall per walk; Bennett and Duplock 23 used the Musgrave Footprint force plate (Preston Communications, Ltd., Dublin, Ireland); and Ashry et al. 11 used the F-Scan (Tekscan, Boston, MA) insole measurement system.
The purpose of custom-made orthoses for persons with diabetic neuropathy is to decrease pressures under areas of the foot susceptible to ulceration. Mechanisms used are increasing plantar surface contact area and decreasing forces under susceptible surfaces. Custom-made foot orthoses made of graphite with a Naugahyde cover, 10 polyurethane, 14 Plastazote with and without metatarsal pads and medial arch supports, 11 Plastazote and urethane, 24 and ethylene-vinyl-acetate, polyethylene foam, elastomere and silicone 12 have been shown to reduce peak pressure and increase contact area in persons with diabetic neuropathy. The custom-made Plastazote and Aliplast/Plastazote orthoses used in this study also reduced peak pressure under the whole foot, heel, and second and third metatarsal heads and toes by increasing contact area. Maximum mean pressure and pressure time integral also were decreased under the whole foot and under the second and third metatarsal heads and toes by increasing contact area. The orthoses increased both contact area and mean force under the medial midfoot, resulting in no change in medial midfoot pressures. Thus, the custom-made orthoses relieved pressure under ulcer-susceptible areas of the foot by shifting load, but not pressures, to the medial midfoot. The effect of orthoses was more pronounced for the right foot, but similar trends were seen for the left foot. Had we studied a larger sample, the effect of orthoses may have been as significant for the left foot.
Ashry et al. 11 compared peak pressures in patients with diabetic neuropathy and unilateral amputation of the great toe and first metatarsal under five conditions: 1) extra-depth shoe alone and extra-depth shoe with 2) custom-made Plastazote insoles, 3) insoles with a metatarsal pad, 4) insoles with medial arch support, and 5) insoles with both metatarsal pad and medial arch support. They also showed a reduction in peak pressure under the heel and metatarsal heads bilaterally and the great toe on the nonamputated side with orthoses wear. 11 Their insoles decreased peak pressure under the heel by an average of 12.7 N/cm2, compared with our decrease of 7.5 N/cm2, and under the first metatarsal head on the sound side by 11.2 N/cm2, compared with our decrease under the big toe, including the first metatarsal head, of 8.5 N/cm2.
Ashry et al. 11 found no differences in peak pressure between orthoses with and without adaptations. Their adaptations to the orthoses, in contrast to ours, were applied to new Plastazote orthoses. In our study, the adaptations were made after 1 month of use. When our orthoses were adjusted for wear with the addition of a metatarsal pad, heel wedge, or added thickness to the material, they also were effective in relieving plantar pressures. The fewer significant results found with the wear-adjusted orthoses, compared with the new orthoses, probably are attributable to the smaller sample when studying the wear-adjusted orthoses. Only five of the eight pairs of subjects were available for 1- to 3-month comparisons with the wear-adjusted orthoses.
Our wear-adjusted foot orthoses maintained their pressure-relieving ability for at least 2 months. The numeric differences in pressure variables and contact area with and without orthoses were as large after 2 months of wear as they were just after alteration for wear at 1 month. We had not asked our subjects to record the number of hours each wore the orthoses. We suspect that some subjects may not have worn their orthoses daily, as evidenced by the condition of the orthoses and the forgetfulness of one subject to bring the orthoses to 3-month testing. Lack of wear could have contributed to the preservation of the orthosis material during the 2-month period. To more strongly substantiate the longevity of wear-adjusted Plastazote and Aliplast/Plastazote orthoses to decrease pressures, additional studies should have subjects keep a log of time that they walked while wearing their orthoses. Whether Plastazote or Aliplast/Plastazote orthoses without adjustment for wear would have continued to reduce pressures over time also is not known. Common clinical practice and ethics prevented us from studying this effect. Additional studies should include a larger number of subjects, and plantar pressures should be measured after 1 month of wear but before orthoses are altered.
Lobmann et al. 12 studied the effect of orthoses made of a combination of ethylene-vinyl-acetate, polyethylene foam, elastomere and silicone during the period of 1 year. Orthoses in patients with diabetic neuropathy deemed at high risk for ulceration (whole foot peak pressure > 400 kPa) were effective in reducing pressures under the whole foot, heel and heads of the first through third metatarsals to 6 months but not for 1 year. Whether wear-adjusted Plastazote or Aliplast/ Plastazote orthoses continue to reduce pressures for 6 months is not known.
Sanfilippo et al., 18 using 10 subjects without diabetic neuropathy, studied pressure reduction in five different insole materials, including firm density Plastazote. Force and peak pressure reduction with Plastazote did not differ from that seen with Spenco (Spenco Medical Corp., Waco, TX), PPT (Alimed, Dedham, MA), Nickelplast (Alimed), or Pelite (Durr-Fillauer, Birmingham, AL). However, contact area with Plastazote was greater than that with Pelite and Nickelplast but equal to that with Spenco and PPT. Failure to find significant differences between orthoses made of Plastazote alone and orthoses made with the combination of Plastazote and Aliplast in our study suggests that neither orthosis is more beneficial than the other in decreasing plantar pressures during a period of 3 months in persons with diabetic neuropathy. No trends were seen that would suggest that, with a larger number of subjects, true differences would be seen between orthoses made of the two different materials. For example, at the initial test, differences in maximum mean pressure and peak pressure between orthosis groups when walking with orthoses paralleled the differences in peak pressures between groups when walking without the orthoses. However, fewer Plastazote orthoses were altered at 1 month than were Aliplast/Plastazote orthoses. Three Plastazote and six Aliplast/Plastazote orthoses were altered. The added expense of adding Aliplast to custom-made Plastazote orthoses is not supported by this study.
Our results support common clinical practice of using custom-made orthoses to increase contact area and reduce plantar pressures under susceptible regions of the foot in persons with diabetic peripheral neuropathy. The added expense of adding Aliplast to custom-made Plastazote orthoses is not supported by the data of this study. Orthoses adjusted for 1 month of wear continue to be effective in relieving plantar pressures for an additional 2 months in persons with diabetic neuropathy.
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Keywords:© 2004 American Academy of Orthotists & Prosthetists
diabetes; foot; insoles; orthosis; pressure; ulceration