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Table 1 Characteristics of the selected studies that used pressure reduction as the primary outcome measure

From: Footwear and insole design features that reduce neuropathic plantar forefoot ulcer risk in people with diabetes: a systematic literature review

Author, date Location Study design Follow up period Sample size Sample characteristics Intervention & Comparison Outcome measures Result
Arts et al. 2012 [38] Netherlands Repeated measures Same day 171 (336 ft) Diabetic neuropathy
Previous plantar ulcer
Custom-made footwear
Semi-customised footwear
Barefoot
Peak plantar pressure (PPP) of < 200 kPa considered successful Custom-made footwear is least effective in pressure reduction (< 200 KPa) at forefoot compared to midfoot and known ulcer locations (29% vs 81 and 62%)
Arts et al. 2015 [39] Netherlands Repeated measures Same day 85 Diabetic neuropathy Previous plantar foot ulcer Various footwear modifications to custom or semi-custom footwear
Footwear before modification
% plantar pressure reduction MP, local cushion and plastazote top cover reduce PP respectively by15.9, 15, 14.2% and combinedly 24 and 22% at the forefoot.
Bus et al. 2011 [30] Netherlands Repeated measures Not reported 23 Diabetic
Neuropathy,
Foot deformity
Foot ulcer
Fully custom-made footwear and insoles In-shoe plantar pressure reduction by more than 25% (Criteria A) or below the absolute value of 200 kPa (Criteria B) MB or MP, replacing the top cover, early rocker can reduce pressure at hallux and metatarsal area ranging from 10.1 to18.6% as an individual modification.
Bus et al. 2004 [40] Netherlands Repeated measure Not reported 20 Diabetic
Neuropathy,
History of healed plantar foot ulcers
Foot deformity
Insoles; 9.5 mm thick flat PPT insole and custom-made insoles out of open-cell urethane foams of hardness 60–80. Custom-made insoles were made by CADCAM process. Plantar pressure reduction
FTI
Custom-made insoles reduce plantar pressure and FTI significantly at medial and lateral heal, MTH1 and FTI at lateral MTHs when compared with flat PPT insoles.
Charanya et al. 2004 [41] India Case-control study 6 months 25 Diabetic
Neuropathy
History of active and healed plantar ulcers
Non-diabetic (Control)
Footwear with an insole made of 12 mm MCR, shore value 200, Toughened rocker profile rubber outsole Foot sole hardness reduced close to normal, shore value 200 Plantar ulcers healed in three-four weeks, foot sole skin hardness reduced to 25–30 from 45 to 50 shore values.
Guldemond et al. 2007 [42, 43] Netherlands Repeated measures Not reported 17 Diabetic
Neuropathy
Higher barefoot plantar pressure (≥700 kPa)
Insole with various height arch supports and with and without a metatarsal dome In-shoe plantar pressure reduction (36% & 39%),
Walking convenience on a 10-point rating scale
Extra arch support and MD are respectively effective in 39% & 36% pressure reduction in central and medial regions of the forefoot
Hastings et al. 2007 [44] USA Repeated measure 22 months 20 Diabetic
Neuropathy History of plantar foot ulcers
No active foot ulcers
No Charcot neuropathy
Three footwear conditions; extra depth footwear with 1) Total Contact Insoles (TCI), 2) TCI with proximal Metatarsal Pad (MP), 3) TCI with distal MP,
CT Scan
PPP
CT Scan for positioning of MP against MTHs
Highest (57%) PPP reduction occurred at 2nd MTH when MP placed at 10.6 mm proximal to MTH line. Variable PPP under the 2nd MTH varied between 32 ± 16% when positioning of MP varies between 6.1 mm to 10.6 mm proximal to MTH line.
Lin et al. 2013 [45] China Repeated measure Not reported 26 Diabetic
Neuropathy
Insole with pre-plug removal, post-plug removal, and post-plug removal + arch support Mean peak pressure (MPP), maximum force, contact area Removing insole plug is effective in offloading MPP by 32.3% and adding arch support reduces further 9.5% at the forefoot
Lott et al. 2006 [46] USA Repeated measure Not reported 20 Diabetic
Neuropathy History of midfoot or forefoot plantar ulcers
Four different conditions; 1) Barefoot, 2) Footwear, 3) Footwear + TCI, 4) Footwear + TCI + MP Plantar pressure reduction
Soft tissue thickness (STT)
PP & ST strain under 2nd MTH are highest at the barefoot condition and lowest at footwear + TCI + MP condition. Mean PP for all four conditions under 2nd MTH is 272 kPa, 173 kPa, 140 kPa and 98 kPa.
Martinez-Santos et al. 2019 [47] UK Repeated measure Not reported 60 Diabetic
Neuropathy
No previous ulcers
Insole with three different metatarsal bar (MB) positioning, two different types of materials PPP Maximum pressure reduction can be achieved by positioning metatarsal bar at 72% length of insole, irrespective of material type
Mueller et al. 2006 [48] USA Repeated measure Not reported 20 Diabetic
Neuropathy history of plantar ulcers
Three footwear conditions: 1) Footwear, 2) Footwear with TCI, and 3) Footwear with TCI + MP PPP
PTI
STT
TCI and metatarsal pad caused reductions of pressure under the metatarsal heads
Owings et al. 2008 [49] USA Repeated measure Not reported 20 Diabetic
Neuropathy
Higher (> 750 kPa) barefoot plantar pressure at MTH region
Three different type custom-made insoles (X, Y from shape-based and Z combined foot shape with plantar pressure data). Footwear with rigid rocker sole and flexible sole Peak pressure
FTI
Shape and pressure-based insoles (Z) showed improved offloading by 32 and 21%, PTI reduction 40 and 34% when compared to shape-only-based insoles (X-Polypropylene base, Y- EVA base). A similar trend was observed in flexible and rocker bottom shoes for the same insoles.
Paton et al. 2012 [50] UK RCT 18 months 119 Neuropathic diabetic foot ulceration Prefabricated and custom-made insole In-shoe pressure reduction, PTI, forefoot rate of load, total contact area Prefab versus custom insoles, PPP ≥ 6%,
Praet et al. 2003 [51] Netherlands Repeated measure Not reported 10 Diabetic
Neuropathy
No active ulcer, No major foot deformities
Three different types of footwear designs Peak pressure reduction at multiple areas under the foot Rocker sole can offload the forefoot area by 65%
Preece et al. 2017 [52] UK Case-control Not reported 168 Diabetic
Neuropathy (n = 17)
Healthy control (N = 66)
Eight types of rocker sole design Pressure reduction threshold of ≤200 kPa Rocker apex position at 52%, 200 rocker angle, 950 apex angle yields effective offloading at most
Tang et al. 2014 [53] Sweden RCT Two years 114 Diabetic neuropathy
Angiopathy
Foot deformities
Previous ulcers or amputation
Three types of insoles, custom made (35 & 55° shore hardness EVA) vs prefab insoles with hardcore EVA + soft microfiber top cover (Control) PPP
PTI
The overall PPP for the insoles was between 180 kPa to 211 kPa, PTI differences 14 kPa/sec & 20 kPa/sec with Control.
Teffler et al. 2017 [54] UK Randomised crossover Not reported 20 Diabetic neuropathy
Increased forefoot plantar pressure
No Charcot foot or partial amputation
Three types of insoles 1) Standard (Shape-based), milled insoles, 2) Milled, virtually optimised insoles and 3) 3D printed virtually optimised insoles PPP Virtually optimised insole reduced PPP by a mean of 41.3 kPa for milled and 40.5 kPa for 3D printed insoles in the same participants’ group.
Tsung et al. 2004 [55] China Case-control Not reported 14 Diabetic neuropathy
No Charcot foot or partial amputation
Control: no foot deformity
Five support conditions including footwear-only, flat insoles; and three custom-made insoles with three weight-bearing conditions; 1) Full weight-bearing (FWB), 2) Semi-weight-bearing (SWB) and 3) Non-weight-bearing (NWB) MPP
PTI
Mean contact area
For 2–3 MTH regions, SWB insoles yield maximum offloading comparing to two other insoles type. For MTH1, NWB insoles provide maximum offloading. FWB insoles show maximum PTI comparing to NWB & SWB conditions. NWB insoles provide maximum arch support and contoured shaped insoles.