Designing orthoses for the loaded foot: Current trends in estimating the medial arch

• Foot arch drops by ∼7 mm from non-weight-bearing to weight-bearing conditions. • Digital orthotic insoles showed ∼5.5 mm variation in arch height across designers. • Inter-designer reliability was high, but variation exceeded ±1 mm tolerance. • Weight-bearing scans produced significantly different arch height estimations. • Findings stress the need for design guidelines for digital custom orthotics. The human foot undergoes significant midfoot changes when bearing weight. This study examines how digital orthotic workflows estimate these deformations and whether orthotic insoles accurately accommodate them. Foot scans and digital insole designs were analysed from two cohorts: 60 healthy participants (scanned in non-weight-bearing (NWB) and weight-bearing (WB)) recruited prospectively and 180 patients with mixed foot pathology (90 in NWB and 90 in WB) from a retrospective dataset. Three orthotic designers created insole designs for both cohorts based on a standard prescription. Designers estimated expected midfoot deformation from the original scan condition (NWB/WB). Healthy feet showed an expected arch height drop of 7.15 ± 0.90 mm from NWB to WB. Corresponding insoles demonstrated excellent inter-designer reliability in estimating arch collapse, but arch height varied by ∼5.5 mm, exceeding industrial tolerance (±1 mm) with potential clinical impact. Arch collapse estimations were similar for both cohorts with NWB scans but significantly differed with WB scans. Findings highlight the need for podiatrists to consider typical inter-designer variability and WB condition of the foot scan when prescribing and requesting arch modifications in digitally designed custom insoles, especially in the absence of formal design guidelines and sufficient arch-related data available for populations with foot pathology.