The signed helical angle: A technique for characterizing midfoot motion during gait.

Area of Science:

• Biomechanics
• Orthopedics
• Kinesiology

Background:

• Quantifying midfoot motion is crucial for understanding gait and biomechanical function.
• Existing motion capture techniques struggle to accurately represent the non-planar nature of midfoot articulations.

Purpose of the Study:

• To develop and validate a novel Signed Helical Angle (SHA) method for quantifying midfoot angular displacement.
• To compare the SHA method's results with traditional planar analyses of midfoot motion.

Main Methods:

• Utilized motion capture data from 40 healthy subjects walking at a controlled speed.
• Calculated finite helical axes and angles using a two-segment foot model.
• Classified axes as pronation or supination, assigning a sign to quantify angular displacement.

Main Results:

• Pronation and supination axes showed distinct clustering in the transverse plane when excluding transitions.
• The SHA method demonstrated a greater range of motion (39% pronation, 25% supination) compared to sagittal plane analyses.
• SHA directly measures the motion path, capturing the influence of multiple planes on midfoot movement.

Conclusions:

• The Signed Helical Angle (SHA) method offers an intuitive and effective approach for analyzing midfoot motion.
• SHA is particularly valuable for detecting subtle changes in motion, often missed by planar analyses, in clinical and research applications.