Plantar pressure analysis of custom-made insoles for safety shoes

Introduction: Current regulations in many countries require workers to wear safety shoes in factory settings [1,2]. These shoes are often heavy, rigid and uncomfortable and their daily use leads to foot problems, discomfort and fatigue resulting also in loss of many working days [3]. In order to limit the extent of these ailments [4,5],we investigated the biomechanical outcome of custom insoles, designed and produced to match the foot sole and the shape of the safety shoe (CloudSME, FP7-608886). Methods: 17 workers (6 women and 11 men, age 45.1±5.2 years; BMI 26.7±4.5 kg/m2; 42±3 shoe Euro-size) from a metalworking factory (Bonfiglioli Riduttori, Italy) volunteered for the study. These were selected following careful clinical examination. Those with normal feet, or presenting severe pathologies and systemic diseases, were excluded for ethical reasons. A custom insole (CUS) was designed on the morphology of the plantar aspect of each foot, and on the internal shape of the selected safety-shoe, and was manufactured via subtractive manufacturing from an EVA block. The foot sole was 3D scanned in double leg up-right posture using an original system (3D Scan patent, Podoactiva), which included a standard scanner and an elastic membrane which helps restrain flattening of the foot on the scanner top. The foot scans were shared with the manufacturer via a cloudbased service, with an ad-hoc procedure for a real-time feedback of their quality. The CUS were assessed against the prefabricated standard insole within safety shoes (PSS) and a comfortable offthe- shelf (OTS) insole. The three insoles were blind-tested on the same shoe, and evaluated via comfort scores and plantar pressure measurements (Pedar, Novel gmbh, Germany). Data from static up-right postures, normal and fast walking, weight lifting, stair ascending and descending were analysed using ad-hoc software by dividing the footprint into three main regions of interest [6]. Results: CUS showed better pedobarographic parameters in several plantar regions and for most of the working activities. Peak pressure was the lowest in CUS at rearfoot and forefoot during normal walking. Normal and fast walking resulted the most demanding activities in terms of peak pressure (Table 1). Discussion: The baropodometric effects of different insoles in safety-shoes have been rarely investigated and reported in the literature [7]. The present study has demonstrated that the design of custom insoles for safety shoes is valuable and can be obtained successfully with modern 3D foot scanning technology, by taking into account both the foot and the shoe footbed shapes. This new technological procedure can also benefit from recently available cloud-based services, allowing remote design and production of high-quality insoles and other orthotics.