Comparison of plantar pressure in three types of insole given to patients with diabetes at risk of developing foot ulcers - A two-year, randomized trial

Ulla Hellstrand Tang, Roland Zügner, Vera Lisovskaja, Jon Karlsson, Kerstin Hagberg, Roy Tranberg, Ulla Hellstrand Tang, Roland Zügner, Vera Lisovskaja, Jon Karlsson, Kerstin Hagberg, Roy Tranberg

Abstract

Background: Special insoles and shoes designed to prevent foot ulcers caused by repetitive high pressures are recommended for patients with diabetes who have any of the following risk factors: neuropathy; peripheral vascular disease; foot deformities; previous ulcers; amputation; and skin pathologies. However, there is a need for increased knowledge regarding: a) differences in the peak pressure (PP) and pressure time integral (PTI) for different types of insoles; and b) the properties of the pressure distribution for insoles used over a period of several months. We present the results of a randomized trial to compare the plantar pressures of three commonly used insoles.

Objectives: The primary objective was to compare the PP and PTI between three types of insoles. The secondary objective was to explore the long-term pattern of peak plantar pressure distribution and variations in specific regions of interest (ROI). The tertiary objective was to investigate the impacts of insole adjustments, how much the insoles were used, and the levels of patient satisfaction.

Methods: In a 2-year trial, 114 patients with type 1 (N = 31) or type 2 (N = 83) diabetes (62 men and 52 women; mean age, 57.7 ± 15.4 years; duration of diabetes, 12.3 ± 11.2 years; neuropathy, 38%), were randomized to be supplied with one of three different insoles. The ethylene vinyl acetate (EVA) insoles were used in outdoor walking shoes. The 35 EVA group (N = 39) received soft custom-made insoles composed of EVA of 35 shore A hardness, the 55 EVA group (N = 37) received custom-made insoles composed of EVA of 55 shore hardness, and the control group (N = 38) received prefabricated insoles composed of a hard core with a top layer of soft 12 shore hardness microfiber. Using F-Scan®, the in-shoe plantar pressures were measured at seven ROI (hallux, metatarsal head 1, metatarsal head 2, metatarsal head 4, metatarsal head 5, lateral aspect of the mid-foot, heel) on five occasions during the study period. The plantar-pressure variables used were PP (main outcome) and PTI. The plantar patterns of load were explored, satisfaction and usage of the insoles were rated by the participants, and insole adjustments were recorded.

Results: A mixed model analysis estimated lower PP values in the heel regions for the 35 EVA and 55 EVA insoles (171 ± 13 and 161 ± 13 kPa, respectively) than for the prefabricated insoles (234 ± 10 kPa) (p < 0.001). Also for some of the other six ROI indications of difference in PP or PTI could be observed. The redistribution of peak plantar pressure for all of the insoles, was stable at the mid-foot, while the proportion of load on the distal area changed during the study period According to the self-reported answers (scale, 0-100), the average usage of the insoles was rated as 79 and satisfaction was rated as 85 (N = 75). Thirty-two percent of the subjects had not received foot care. Fourteen adjustments to insoles were made during the study period, and 86 pairs of insoles were exchanged due to wear, with 49% being exchanged in the 35 EVA group.

Conclusions: Custom-made insoles used in combination with stable walking shoes gave lower pressures at the heel region. The variation makes it difficult to detect a systematic difference in plantar pressure for the 6 ROI, if such a difference indeed exists. The levels of satisfaction and usage for all the insoles tested were high. The insoles maintained their pressure redistribution properties over long periods, and few adjustments were needed.

Keywords: 35 EVA, 35 shore EVA insoles; 55 EVA, 55 shore EVA insoles; Clinical trial; Diabetes; EVA, ethylene vinyl acetate; Foot ulcer; Insoles; MTH1, metatarsal head 1; MTH2, metatarsal head 2; MTH4, metatarsal head 4; MTH5, metatarsal head 5; Offloading; PP, peak pressure; PTI, pressure time integral; Prevention; ROI, region of interest.

Figures

Figure 1
Figure 1
Insoles and shoes. A) The contours of the custom-made insoles composed of ethylene vinyl acetate (EVA) with a standardized metatarsal bar. B) Prefabricated insole GloboTec® Comfort 312750501400 (GloboTec, Bauerfeind, Germany), with support of the medial arch and a metatarsal pad in the forefoot in a material with a core (reinforcement element) that consists of a mixture of thermoplastic, polyurethane, polyester, and polycarbonate. The cushioning material is foam that belongs to the chemical family of urethane polymers with a shore density of about 12 shore A. The cover is a 2-mm layer of microfiber, consisting of polyester and polyurethane. C) Photograph of a representative walking shoe used in the study (Opara Deluxe men 809159, ladies 8807159; Erimed, Stockholm, Sweden). The shoe has a semi-rigid outer sole, a stable heel counter, and adjustable lacing. The maximum height of the toe box is 40 mm vs. 43 mm for EUR size 38/Women last vs 45/Men last. D) An example of a custom-made insole that is ready to be exchanged due to the presence of cracks and breakdown areas.
Figure 2
Figure 2
Flow chart for the participants in the study and the reasons for study drop-outs. The “measurement time point” reflects the time interval and is reported as a range (minimum to maximum). The numbers of participants are presented in parentheses. Reasons for dropping out are explained as follows: *participant drop-out for personal reasons; †other disease made participation impossible; ‡ participant wanted to change material of the insoles or the participant was prescribed another insole material.
Figure 3
Figure 3
Peak pressure in seven regions of interests A-G. For each region of interest, the peak pressures for three types of insoles are presented as a box plot. Gray boxes represent the 35 EVA insoles, black boxes the 55 EVA insoles, and white boxes the prefabricated insoles. The outliers (circles) represent high pressure levels and give evidence as to the significant inter-individual variation. For the heels, the pressures in the prefabricated insoles are higher than those in the custom-made 35 EVA and 55 EVA insoles at each follow-up (p < 0.001) H. Schematic of the seven regions of interests displayed in the F-Scan.
Figure 4
Figure 4
Proportion of peak pressure during the study period Patients with diabetes who were at risk of developing foot ulcers (N = 114) took part in an intervention with three types of insole: A, 35 shore EVA insoles; B, 55 shore EVA insoles; C, prefabricated insoles. The distributions and changes over time of the plantar peak pressures are presented as the proportion of load for each region of interests. The proportional loads are highest at metatarsal head 2 and the hallux. MTH1, metatarsal head 1; MTH2, metatarsal head 2; MTH4, metatarsal head 4; MTH5, metatarsal head 5.

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Source: PubMed

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