Getting the right balance: insole design alters the static balance of people with diabetes and neuropathy

Abstract

Background: Over 1 in 3 older people with diabetes sustain a fall each year. Postural instability has been identified as independent risk factor for falls within people with Diabetic Peripheral Neuropathy (DPN). People with DPN, at increased risk of falls, are routinely required to wear offloading insoles, yet the impact of these insoles on postural stability and postural control is unknown. The aim of this study was to evaluate the effect of a standard offloading insole and its constituent parts on the balance in people with DPN.

Methods: A random sample of 50 patients with DPN were observed standing for 3 × 30 s, and stepping in response to a light, under five conditions presented in a random order; as defined by a computer program; 1) no insole, 2) standard diabetic: a standard offloading insole made from EVA/poron®, and three other insoles with one design component systematically altered 3) flat: diabetic offloading insole with arch fill removed, 4) low resilient memory: diabetic offloading insole with the cover substituted with low resilience memory V9, 5) textured: diabetic offloading insole with a textured PVC surface added (Algeos Ltd). After each condition participants self-rated perceived steadiness.

Results: Insole design effected static balance and balance perception, but not stepping reaction time in people with DPN. The diabetic and memory shaped insoles (with arch fill) significantly increased centre of pressure velocity (14 %, P = 0.006), (13 %, P = 0.001), and path length (14 %, P = 0.006), (13 %, P = 001), when compared to the no insole condition. The textured shaped and flat soft insole had no effect on static balance when compared to the no insole condition (P > 0.05).

Conclusion: Insoles have an effect on static balance but not stepping reaction time. This effect is independent of neuropathy severity. The addition of a textured cover seems to counter the negative effect of an arch fill, even in participants with severe sensation loss. Static balance is unaffected by material softness or resilience. Current best practice of providing offloading insoles, with arch fill, to increase contact area and reduce peak pressure could be making people more unstable. Whilst flat, soft insoles maybe the preferable design option for those with poor balance. There is a need to develop an offloading insole that can reduce diabetic foot ulcer risk, without compromising balance.

Keywords: Diabetic; balance; insoles; neuropathy.

Fig. 1

The four insole test conditions. b Flat: diabetic offloading insole with arch fill removed; d Textured: diabetic offloading insole with a textured PVC surface added (Algeos Ltd). a Standard diabetic: A standard offloading insole made from a prefabricated 3 mm full length medium EVA contoured shell (slimflex algeos Ltd) and covered in 6 mm of poron® (c) Low resilient memory: diabetic offloading insole with the cover substituted with low resilience memory V9

Fig. 2

Estimated means +/- standard errors during static, standing eyes closed whilst wearing each insole condition. a Total COP velocity, b Medial/lateral COP velocity, c Anterior/posterior COP velocity, d Total COP path length, e Medial/lateral COP path length, f Anterior/posterior COP path length. Significant pairwise comparisons: *P < 0.05, **P < 0.001