Table 4 Description of insole features designed to reduce neuropathic forefoot plantar ulcer occurrence found in the literature

Fully custom-made insoles with multi-density and multi-layered materials, an open-cell or cross cell material top cover.

Modification: Local removal of material on the insole, local softening, adding metatarsal, hallux pad or bar on the insole, replacement of the top cover

Bus et al. 2011 [30]

Custom made insole made from multilayered materials with cork base added with micro cork, a mid-layer of EVA base multiform. Additional metatarsal pad or bar with extra arch support.

Bus et al. 2013 [57]

Insole made of 12 mm microcellular rubber (MCR), shore value 20⁰

Charanya et al. 2004 [41]

Metatarsal dome, arch supports, and extra arch supports

Insoles made of 5 mm Lunalastic as the top layer, 8 mm Lunasoft SL as the bottom layer, 1.1 mm Rhenoflex 3208® as internal reinforcement. Every layer of arch support has 5 mm thickness of Lunalastic material.

Guldemond et al. 2007 [42]

3 mm Shore A 35⁰ EVA as 1st layer, 2 mm Velcro and velvet in 2nd layer and 6 mm Shore A 50⁰ Poron in the third layer

Lin et al. 2013 [64]

Multilayered with 40° shore hardness EVA base and Poron top cover, cut-out in the affected metatarsal head.

López-Moral et al. 2019 [60]

Insole base with 5 mm 50⁰ Shore A EVA with three different metatarsal bar (MB) positioning out of two different types materials: 20⁰ Shore A EVA, 20⁰ Shore A Poron

Martinez-Santos et al. 2019 [47]

1.27 cm thick number 2 plastazote with shore value approx. 35, metatarsal pad (MP), positioned proximal to metatarsal heads

Mueller et al. 2006 [48]

Full length 3 mm blue medium density Ethylene Vinyl Acetate (EVA) shell and 6 mm grey Poron top cover

Paton et al. 2012 [50]

SM-2, 3 & 4: ¾ custom insoles with EVA base and 3 mm PPT full-length top cover

SM-5 & 6: Custom insoles with EVA base and 3 mm PPT full-length top cover

Praet et al. 2003 [51]

Insoles from the static footprint and foam box impression, configured with arch support, metatarsal bar, soft fillers. Insole materials: PPT, Duuroterm, Alcaform

Rizzo et al. 2012 [61]

Custom insoles: 35 & 55⁰ Shore A hardness EVA (14 mm thickness) for custom made insoles manufactured from positive plaster moulds, metatarsal bars proximal to II-IV MTH’s.

Prefabricated insole: Hardcore EVA base, 12⁰ Shore hardness microfiber top layer (GloboTec® comfort 312,750,501,400)

Tang et al. 2014 [53]