The Heidelberg Functional Foot Model-Application to Cavovarus and Equinovarus Feet

Area of Science:

• Biomechanics
• Orthopedics
• Gait Analysis

Background:

• Multisegment foot models are crucial for biomechanical research and gait analysis.
• Existing models often lack functional verification for joint positions, relying on simplified methods.
• Phenomenological angles offer sensitive, radiologically aligned indicators of foot mechanics, bypassing joint center calculations.

Purpose of the Study:

• To introduce the Heidelberg functional foot model (HFFM), integrating functionally verified joint positions with clinical measures.
• To enhance the clinical interpretability of gait analysis through a novel foot modeling approach.
• To assess the HFFM's sensitivity in analyzing foot deformities like cavovarus and equinovarus.

Main Methods:

• Developed a four-segment foot model (shank, hindfoot, forefoot, hallux) based on the Heidelberg foot measurement method (HFMM).
• Established anatomical coordinate systems using regression formulas derived from functional joint parameter determination.
• Integrated six clinically relevant angles from the HFMM into the HFFM and compared kinematic angles with radiological measures.

Main Results:

• Equinovarus (EV) feet demonstrated more pronounced hindfoot varus and forefoot adduction compared to cavovarus (CV) and typically developed (TD) feet.
• EV feet exhibited increased subtalar inversion and a stronger medial arch than CV feet within the HFMM parameters.
• Significant correlations were found between hindfoot/shank flexion, forefoot/hindfoot flexion, and medial arch/radiological angles.

Conclusions:

• The HFFM provides a sensitive method for analyzing equinovarus and cavovarus deformities without static offsets, due to its functional approach.
• The model enhances the understanding of foot deformity biomechanics by enabling kinetic calculations.
• The HFFM improves clinical interpretability in gait analysis for various foot conditions.