Reliability of capturing plantar foot geometry using a handheld 3D scanner for dose-response modeling of custom-made foot orthoses.

Abstract

Background: Efficacy of custom-made foot orthoses largely depends on geometric characterization and outcomes can be suboptimal due to insufficient quantitative insights thereof. Addressing this is crucial for understanding geometric characteristics in dosage-response modeling.

Objective: This study evaluates the reliability of digitizing traditional and advanced geometric foot features, using a handheld 3-dimensional (3D) scanning system.

Methods: Two examiners used a handheld 3D scanner to capture the foot shape of 30 healthy participants in a non-weight-bearing condition. Intra-tester, test-retest, and inter-tester reliabilities of several linear anthropometric and geometric variables were evaluated. Subsequently, the consistency of capturing the geometry of the plantar foot surface was assessed by quantifying 2 anteroposterior and 2 mediolateral curvilinear plantar surface metrics.

Results: Intraclass correlation coefficients for the linear geometric and anthropometric variables' intra- and inter-tester reliability ranged from 0.84 to 1.00. The standard error of measurement for the Z-coordinate of the proximal medial arch point and the forefoot-rearfoot angle was substantially higher compared with the standard error of measurements observed in the other metrics. A pairwise comparison of the 4 curvilinear metrics showed no statistically significant difference on intra-tester and test-retest levels for both examiners. Inter-tester analysis identified significant ( p < 0.05) differences in specific segments of the anteroposterior and mediolateral curvilinear metrics, particularly near the distal and medial ends.

Conclusions: These results demonstrated that the digitization of linear anthropometric and geometric measurements of the human foot, obtained using a handheld 3D scanning system in a non-weight-bearing condition, exhibit good to excellent reliability. Additionally, the curvilinear metrics, related to the plantar surface curvature, showed high consistency, supporting its usage to quantify plantar geometry and provide insights into the role of geometric characteristics in dosage-response modeling in custom-made foot orthoses practice.