Effects of heel apex position, apex angle and rocker radius on plantar pressure in the heel region

Abstract

Introduction: Rocker shoes and insoles are used to prevent diabetic foot ulcers in persons with diabetes mellitus and loss of protective sensation, by reducing the plantar pressure in regions with high pressure values (>200 kPa) (e.g., hallux, metatarsal heads and heel). However, forefoot rocker shoes that reduce pressure in the forefoot inadvertently increase pressure in the heel. No studies focused on mitigating the negative effects on heel pressure by optimizing the heel rocker midsole, yet. Therefore, we analyze the effect of different heel rocker parameters on the heel plantar pressure.

Methods: In-shoe pressure was measured, while 10 healthy participants walked with control shoe and 10 different heel rocker settings. Peak pressure was determined in 7 heel masks, for all shoes. Generalized estimating equations was performed to test the effect of the different shoes on the peak pressure in the different heel masks.

Results: In the proximal heel, a rocker shoe with distal apex position, small rocker radius and large apex angle (100°), shows the largest significant decrease in peak pressure compared to rocker shoes with more proximally located apex positions. In the midheel and distal heel, the same rocker shoes or any other rocker shoes, analyzed in this study, do not reduce the PP more than 2 % compared to the control shoe. For the midheel and distal heel region with high pressure values (>200 kPa), rocker shoes alone are not the correct option to reduce the pressure to below 200 kPa.

Conclusion: When using rocker shoes to reduce the pressure in the forefoot, a heel rocker midsole with a distal apex position, small rocker radius and apex angle of 100°, mitigates the negative effects on proximal heel pressure. For the midheel and distal heel, other footwear options as an addition or instead of rocker shoes are needed to reduce the pressure.

Keywords: Diabetes mellitus; Diabetic foot; Diabetic foot ulcer; Footwear; Heel pressure; Plantar pressure; Prevention; Rocker shoe.

Fig. 1

Heel rocker parameters for the rocker shoe. A: apex position and apex angle. B: rocker radius at the apex position.

Fig. 2

The different heel apex angles are represented by the dotted lines in figure A: the red dotted line: apex angle of 100°, the black dotted line: apex angle of 90° and blue dotted line: apex angle of 80°. The distal (20 % of shoe length, referenced to the heel), mid (11 % of shoe length, referenced to the heel) and proximal (6 % of shoe length, referenced to the heel) heel apex positions are also shown in figure A. Figure B illustrates the rocker shoe with the large heel radius, 22 % of shoe length with an apex position of 20 % of shoe length (purple circle). The same figure shows the small heel radii, 14 % with an apex position of 20 % (pink circle), 10 % with an apex position of 11 % (yellow circle) and 6 % with an apex position of 6 % of shoe length (red circle). Figure C represents the real image of the control shoe and figure D (purple circle in figure B), E (pink circle), F (yellow circle), and G (red circle) represent the heel rocker shoes that are schematically represented in figure B.

Fig. 3

Heel masks of the Pedar-X insole. The numbers represent the following masks, 1: proximal central heel region, 2: medial side of proximal heel region, 3: lateral side of proximal heel region, 4: medial side of midheel region, 5: lateral side of midheel region, 6: medial side of distal heel region, 7: lateral side of distal heel region.

Fig. 4

Relative changes in peak pressure (compared to the control condition) for different conditions based on the combination of different heel apex positions (20 %, 11 % and 6 %), apex angles (100°, 90° and 80°) and rocker radii (small: 14 %, 10 %, 6 % and large: 22 %), with the following abbreviations for the different conditions: AP20A100_C1, AP11A100_C2, AP6A100_C3, AP20A90RSmall_C4, AP20A90RLarge_C5, AP11A90_C6, AP6A90_C7, AP20A80_C8, AP11A80_C9 and AP6A80_C10. Negative percentages indicate a decrease in peak pressure compared to the control condition, while positive percentages show an increase. #: Significant difference compared to control (P < 0.001). *: Significant difference between conditions (P < 0.001).