A kinematic model of the human ankle

Area of Science:

• Biomechanics
• Human Motion Analysis
• Orthopedic Biomechanics

Background:

• Understanding the complex spatial motion of the foot relative to the shank is crucial for diagnosing gait abnormalities and designing orthopedic interventions.
• Existing models often simplify ankle joint mechanics, potentially limiting their accuracy in representing real-world foot movement.

Purpose of the Study:

• To develop and validate a biomechanical model for quantifying the spatial gross motion of the foot with respect to the shank.
• To establish a method for determining ankle rotation axes using externally visible bony landmarks in living subjects.

Main Methods:

• A mathematical model was created to represent foot-shank spatial motion as rotations around two primary ankle axes: the upper ankle (plantar flexion/dorsiflexion) and subtalar (inversion/eversion) axes.
• The positions of these rotation axes were identified using external bony landmarks on the lower leg of a living subject.
• Input data consisted of measured plantar flexion/dorsiflexion and inversion/eversion rotation angles.

Main Results:

• The model successfully generated a 4x4 transformation matrix.
• This matrix quantitatively describes the relative position and orientation of the foot coordinate system with respect to the shank coordinate system.
• The method demonstrated the ability to measure ankle axis positions in a living subject.

Conclusions:

• The developed model provides a quantitative method to describe the spatial gross motion of the foot relative to the shank.
• Utilizing externally visible bony landmarks offers a practical approach for determining ankle rotation axes in clinical and research settings.
• This biomechanical model can serve as a valuable tool for advanced gait analysis and the study of foot and ankle kinematics.