Flatfoot vs Pronation: Structural and Functional Dissociation Between Foot Posture and Foot Physiology

Area of Science:

• Biomechanics
• Podiatry
• Orthopedics

Background:

• Static foot posture assessment, using tools like the Foot Posture Index-6 (FPI-6), is commonly used in clinical practice to infer foot structure and function.
• The FPI-6 is often employed to identify flatfoot and abnormal dynamic loading, but its accuracy in reflecting underlying structural collapse and functional plantar loading is not well-established.

Purpose of the Study:

• To investigate the concordance between static foot posture (FPI-6), structural flatfoot (Arch Index - AI), and dynamic plantar loading during gait in healthy adults.
• To determine if static pronation measurements accurately represent structural arch collapse and functional plantar pressure distribution.

Main Methods:

• A secondary analysis of a cross-sectional dataset involving 100 healthy adults (200 feet).
• Static foot posture was assessed using the FPI-6 (pronated if ≥ +6).
• Structural flatfoot was determined by the Arch Index (AI) (flatfoot if ≥ 0.26).
• Dynamic plantar pressures and forces during walking were measured using a pressure platform, analyzing regional data (hallux, metatarsals, midfoot, heel).
• Statistical analyses included Spearman correlations and chi-squared tests to explore associations between static and dynamic measures.

Main Results:

• A significant portion of feet were classified as pronated by FPI-6 (43.2%), but fewer met structural flatfoot criteria by AI (19%).
• Limited overlap was observed between FPI-6 pronation and AI flatfoot classifications (16.3%).
• No significant association was found between FPI-6 and AI (ρ = -0.05, P = .445).
• Distinct dynamic loading patterns were associated with FPI-6 (increased hallux loading, reduced fifth metatarsal loading) and AI (greater central/lateral forefoot loading), indicating poor concordance.

Conclusions:

• In this cohort of asymptomatic adults, static pronation measured by FPI-6 was not significantly associated with structural flatfoot (AI) and showed limited correlation with dynamic plantar loading.
• These findings suggest that static foot posture may not be a reliable indicator of underlying foot structure or dynamic function.
• A multidimensional approach integrating static, structural, and dynamic assessments is recommended for a more comprehensive clinical evaluation of foot posture and function.