High plantar pressures often lead to ulcers and amputation in persons with diabetic neuropathy. Orthoses, worn with diabetic shoes, are prescribed to decrease plantar pressures. The purpose of this study was to determine the effect of Plastazote® and Aliplast®/Plastazote® orthoses in decreasing plantar pressures. Eight men and eight women (mean age, 68 ± 6 years), with diabetic neuropathy were separated into two groups of eight, matched by body mass index and history of or current foot ulceration. One group wore custom Plastazote orthoses, the other, custom Aliplast/Plastazote orthoses, for 3 months. Plantar pressures were measured during walking with and without orthoses at predetermined velocity immediately after orthosis fabrication, at 1 month, after orthosis adjustment deemed necessary by the orthotist, and after 3 months of wear. Plantar pressure variables were recorded for six plantar regions of the foot: heel, medial midfoot, lateral midfoot, metatarsal one and big toe, metatarsals two and three and corresponding toes, and metatarsals four and five and corresponding toes. Repeated measures ANOVAs identified significant differences in peak pressure, maximum mean pressure, pressure time integral, mean force, and contact area between groups and orthosis condition (with vs. without) immediately after fabrication. Separate repeated measures ANOVAs identified significant differences in the same variables for group, orthosis condition, and time between 1 and 3 months. Walking with shoes and either orthosis significantly decreased all plantar pressure variables and increased contact areas compared with walking with shoes without orthoses under the big toe and metatarsals two and three immediately after fabrication. Peak pressure under the big toe decreased 27% and that under metatarsals two and three decreased 41% when wearing orthoses. Peak pressure also significantly decreased under the heel and metatarsals four and five (25% and 35%, respectively). No variables differed between orthosis groups or with time wearing orthoses. Wearing custom-made orthoses reduced plantar pressures by increasing contact area. Plastazote alone and Aliplast/Plastazote are equally effective in decreasing pressures at time of fabrication, at 1 month after 9 of 16 pairs of orthoses were adjusted for wear, and after orthoses wear for an additional 2 months. ( J Prosthet Orthot. 2004;16:55– 63.)
Peripheral sensory neuropathy has been associated with an increased risk of foot ulceration 1–3 and secondary amputation 2,4–6 in patients with diabetes. The most commonly proposed cause of foot ulcers in individuals with diabetic sensory neuropathy is repetitive application of pressures during walking. 7,8 Individuals with insensate feet are susceptible to foot ulcers because they are not cued by pain to use compensatory protective mechanisms to avoid repetitive pressures. Therefore, the primary focus of prevention and treatment of foot ulcers is to reduce plantar pressures under susceptible regions of the foot during walking. 9
Custom-made orthoses have been shown to effectively reduce peak plantar pressures in the diabetic neuropathic foot by increasing contact area. 10–13 The combination of prescribed extra-depth diabetic shoes and customized foot orthoses is the standard approach for treating patients with diabetic sensory neuropathy. 10,11,14,15
A variety of materials are used in manufacturing orthoses. Several researchers have investigated the physical properties of various materials under laboratory conditions to determine which materials are best at reducing pressures and maintaining pressure reduction ability over repetitive applications of bench forces. 16–18 Results of these studies have been used to recommend materials for foot orthosis manufacture. Although the testing conditions in these studies provide important information about the properties of the materials, they are not identical to patient use and do not address their function as foot orthoses in persons with diabetes. Several studies have demonstrated that foot orthoses fabricated of Plastazote® (Zotefoams Inc., Walton, KY) are effective in decreasing pressures under the diabetic foot. 10,11,13,18 Foot orthoses fabricated of a combination of Plastazote and Aliplast® (Voltek, Brebbia, VA) have not been systematically examined.
Medium-density Plastazote is a lightweight, closed-cell polyethylene foam material that has been found to compress 70% on repetitive loading and 50% on sustained loading. 17 Aliplast is a cross-linked, closed-cell polyethylene foam that reduces only 40% on sustained or repetitive loading. 17 Theoretically, the addition of a layer of Aliplast to Plastazote orthoses would increase the longevity of the orthoses.
The purpose of our study was twofold: first, to determine the relative effectiveness of foot orthoses made of Plastazote and orthoses made of a combination of Aliplast and Plastazote in decreasing dynamic plantar pressures in patients with diabetic sensory neuropathy, and second, to determine the effect of 2 months of wear on the pressure-relieving abilities of these orthoses in this patient population.
Plantar pressures were measured during walking while subjects wore diabetic shoes with and without custom-made foot orthoses. Pressures were measured at the time of fitting, after wear adjustment of orthoses at 1 month, and after 3 total months of wear.
Sixteen subjects older than 60 years (mean age, 68 ± 6 years) with type II diabetes mellitus and peripheral sensory neuropathy were recruited from clients of Fountain Valley Orthotics and Prosthetics, Inc. (Fountain Valley, CA). Peripheral neuropathy was determined based on the subject's ability to detect the touch of a Semmes-Weinstein (Medical Monofilament Manufacturing, Plymouth, MA) 10-gram monofilament on the plantar surface of the foot. Subjects were matched into two groups (Plastazote or Aliplast/Plastazote) of eight according to body mass index (BMI) and history and/or presence of plantar foot ulcerations. BMI matching was based on the categories of "obese" (BMI greater than or equal to 30), "overweight" (BMI = 25 to 29) or "normal-weight" (BMI less than or equal to 24). 19 History and/or presence of plantar ulcers were determined by questionnaire and skin inspection. All subjects signed an informed consent approved by the Institutional Review Board of California State University, Long Beach. No significant differences were found in height, body weight, BMI, age, or years since diagnosis of diabetes among subjects in the Plastazote and Aliplast/Plastazote groups ( Table 1 ).
The Pedar® in-shoe pressure measurement system (Novel Electronics Inc., Minneapolis, MN) measured pressures on the plantar surface of the foot inside the shoes with and without custom-made orthoses. Each pressure insole consists of a 2.5-mm thick array of 99 capacitive pressure sensors (approximately 0.391 cm 2 /sensor). These pressure sensors were sampled at a rate of 50 Hz. Before data collection, the insoles were calibrated according to the manufacturer's directions. Data were collected as subjects traversed a ninemeter walkway.
Before data collection, age, height, weight, BMI, sensitivity to a 10-gram monofilament, answers to a history questionnaire, and presence of ulcerations were recorded. Subjects were matched consecutively as they volunteered for the study. The first subject tested was randomly (via a coin toss) placed in one of two treatment groups, and the next volunteer who matched BMI and history or presence of ulcers was placed in the other treatment group. Subsequent unmatched volunteers were randomly placed into one of the treatment groups by coin toss, and the next matching volunteer was placed in the other treatment group. One treatment group then was fitted with foot orthoses comprised of medium-density Plastazote only, and the second treatment group was fitted with foot orthoses comprised of a combination of medium-density Plastazote and Aliplast. We chose these materials for the orthoses to compare a relatively compressible material (medium- density Plastazote), which has been shown to decrease in thickness during 3 months of orthosis wear,20 with Plastazote supported by an additional layer of less compressible material, Aliplast. 17 All foot orthoses were custom manufactured for each participant by the same orthotist during the subject's initial session.
Each subject was fitted with the most appropriate pair of Pedar insoles. Subjects wore prescribed deep-fitting diabetic shoes and thin socks and were tested under two conditions, first without the foot orthoses and then with the foot orthoses. Before each trial, subjects unloaded each of the insoles by sequentially lifting each foot off the floor while a baseline measurement was recorded.
Subjects then walked a distance of nine meters at a velocity between 69 and 79 meters per minute for each trial, but only steps within the middle six meters were analyzed. This velocity is within one standard deviation of normative values reported by Perry 21 for freely chosen comfortable walking speeds in adults older than 60 years. Each subject had two practice trials before data recording for each condition to adjust to the Pedar insoles and to practice maintaining a specific walking speed. Time taken to traverse the designated 6 meters was measured during data collection by an investigator with a stopwatch. This time duration was compared with a previously made velocity conversion chart to determine if the subject walked within the appropriate predetermined velocity range. If the subject did not walk at the appropriate velocity, the subject repeated the trial walking either more quickly or more slowly, as appropriate. Two walking trials with and two trials without orthoses were recorded and used for analyses. Subjects were allowed to rest between trials.
Pressure measurements were recorded at three separate sessions: initial visit, after 1 month, and after 3 months. The same procedure was followed at each of the three recording sessions. Before data collection at the 1-month session, the orthotist made modifications to any insoles that, based on his clinical opinion, were worn or "bottomed out." As a result, metatarsal pads extending from the second to fourth metatarsals were added to two Plastazote and six Aliplast/Plastazote orthoses. An additional layer of Plastazote was added to one of the Plastazote foot orthoses with the metatarsal pad and to another Aliplast/Plastazote foot orthosis, and a lateral heel wedge was added to one Aliplast/Plastazote orthosis with a metatarsal pad. A total of three Plastazote and six Aliplast/ Plastazote foot orthoses were modified.
All 16 subjects completed the pretrial session. Data from two subjects wearing Plastazote orthoses were lost at the 1-month session. One subject had measurements on one foot only at 1 month because a sore on the dorsum of her fourth toe prevented her from wearing the orthosis on that side. Another subject's 1-month orthosis trial was lost because of a recording error. The other orthosis trial, rather than the mean of two walks, was used for this subject. Three subjects wearing Aliplast/Plastazote orthoses were lost to 3-month testing. Two refused testing, and one could not be contacted. As a result, only five pairs of subjects were available for analysis between 1 and 3 months.
Raw data were examined immediately after data collection for each trial to ensure that a minimum of six steps per foot was detected and to check for any gross errors in data. Trials with fewer than six steps per foot or with recording errors were repeated. The plantar surface of the foot was divided into six regions (masks) for data analysis: heel, medial midfoot, lateral midfoot, first metatarsal head and great toe, second and third metatarsal heads and toes, and fourth and fifth metatarsal heads and toes ( Figure 1 ).
We used the mean of all steps within the center six meters of each nine-meter walk for statistical analysis. The following variables were calculated for the whole foot and each mask: peak pressure, maximum mean pressure, pressure time integral, contact area, and mean force. Intraclass correlation coefficients (ICCs) were calculated for each of the five variables of the six regions of each foot and the whole foot between the two trials of each condition (with and without the orthoses) for before the test and at 1 month and 3 months. The 420 ICCs ranged from 0.04 to 1.00. Because 12% of the 420 ICCs below 0.8 showed no specific pattern across the variables or regions of the foot, we chose to use the mean of the two trials for additional statistical analysis.
A repeated measures ANOVA across the six regions of the foot was used to identify significant differences attributable to wearing new custom-made orthoses (orthosis vs. no orthosis) and to orthosis material (Plastazote vs. Aliplast/Plastazote) for each variable. A repeated measures ANOVA also was used to identify significant differences in each variable across the regions of the foot at 1 and 3 months because of orthosis, orthosis material, and time (1 vs. 3 months). Because the six regions of the foot are interrelated, we accepted an alpha level of .0083 (.05/6). The Statistical Programs for Social Sciences SPSS, version 11.5) was used for all data analysis.
Wearing foot orthoses affected all pressure variables for most of the regions of the foot. Neither the orthosis material nor time wearing the orthoses affected any variables for the whole foot or any specific region of the foot.
Contact area on the plantar surface of the entire foot increased 21.2 cm 2 on average when walking shod with custom-made orthoses compared with walking shod without orthoses. However, the mean force was not significantly changed by wearing the custom-made orthoses, averaging 620.0 N. As a result, walking with orthoses significantly decreased peak pressure 12.0 N/cm 2 , maximum mean pressure 4.9 N/cm 2 , and pressure time integral 5.6 (N/cm 2 )/second compared with walking without orthoses ( Table 2 , Table 3R for right foot and Table 3L for left foot).
The orthoses affected specific regions of the foot differently, and more significant differences were seen for the right foot than the left foot.
Contact area. The orthoses increased contact area under the heel, medial midfoot, second and third metatarsal heads and toes and the big toe ( Table 2 , Table 3R for right foot and Table 3L for left foot). Increases in contact area averaged 2.3 cm 2 during orthosis wear except for the medial midfoot, which increased 7.7 cm 2 with orthosis. However, the orthoses did not significantly affect contact area under the lateral midfoot or lateral two metatarsal heads and toes.
Mean force. 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.
Pressure variables. 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/cm 2 , maximum mean pressure 3.1 to 3.9 N/cm 2 , and pressure time integral 2.5 to 3.3 (N/cm 2 )/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/cm 2 , maximum mean pressure decreased 2.6 N/cm 2 , and pressure time integral decreased 2.0 (N/cm 2 )/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/cm 2 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 midfoot peak pressure and maximum mean pressure.
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 3R for right foot and Table 3L for left foot). Values at 1 and 3 months were similar to those found for new orthoses ( Table 3R for right foot, Table 3L for left foot, and Table 4 ). Wearing the adjusted orthoses increased contact area 20.2 cm 2 and decreased peak pressure 10.5 N/cm 2 , maximum mean pressure 5.2 N/cm 2 , and pressure time integral 5.9 N/cm 2 /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/cm 2 , was lower than that reported by Bryant et al. 22 (35.0 ± 7.8 N/cm 2 ) and lower than the results reported by Ashry et al. 11 (38.0 ± 1.6 N/cm 2 ; converted from g/cm 2 ) 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/cm 2 ), compared with our subjects' big toe peak pressure of 30.9 ± 11.4 N/cm 2 . 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-vinylacetate, 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/cm 2 , compared with our decrease of 7.5 N/cm 2 , and under the first metatarsal head on the sound side by 11.2 N/cm 2 , compared with our decrease under the big toe, including the first metatarsal head, of 8.5 N/cm 2 .
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.
Correspondence to: Olfat Mohamed, PhD, PT, California State University, Long Beach, 1250 Bellflower Boulevard, Long Beach, CA 90840–5603; e-mail: firstname.lastname@example.org
OLFAT MOHAMED, PhD, PT, is affiliated with the Department of Physical Therapy, California State University, Long Beach, California.
KAY CERNY, PhD, PT, is affiliated with the Department of Physical Therapy, California State University, Long Beach, California.
LOREN ROJEK, CPO, is affiliated with the Department of Physical Therapy, California State University, Long Beach, California.
KRISTA HERBERT, BS, is affiliated with the Department of Physical Therapy, California State University, Long Beach, California.
REBECCA TURNER, BS, is affiliated with the Department of Physical Therapy, California State University, Long Beach, California.
SEAN WAISTELL, BS, is affiliated with the Department of Physical Therapy, California State University, Long Beach, California.