Development of three-dimensional motion measuring device for the human ankle joint by using parallel link mechanism

Area of Science:

• Biomechanics
• Medical Devices
• Rehabilitation Engineering

Background:

• Accurate measurement of ankle joint motion is crucial for diagnosing and treating lower limb conditions.
• Existing motion capture systems (MCS) are often complex, expensive, and require specialized setups.
• There is a need for accessible, accurate, and user-friendly devices for quantifying ankle kinematics.

Purpose of the Study:

• To develop and validate a novel, non-MCS-based device for measuring three-dimensional ankle joint motions.
• To assess the accuracy and validity of the developed device by comparing its measurements to those obtained from an MCS.
• To provide physical therapists with an easy-to-use tool for precise ankle motion analysis.

Main Methods:

• A parallel link mechanism with six wire-type displacement sensors was adapted to create the ankle motion measuring device.
• The device measures ankle joint motions in six degrees of freedom (six-DOF).
• Forward kinematics of the device were solved to numerically calculate the 3D position (x, y, z) and rotation angles (θ, Φ, ψ) of a foot plate attached to the sole.

Main Results:

• Performance verification experiments were conducted by comparing the device's measurements with those from an MCS.
• The maximum root mean square error for 3D position measurements was 2.6 mm.
• The maximum root mean square error for rotation angle measurements was 1.5°.

Conclusions:

• The developed ankle motion measuring device demonstrates high accuracy and validity, comparable to MCS.
• The device offers a practical and accessible solution for physical therapists to measure ankle joint motions.
• This innovation has the potential to improve the assessment and management of ankle-related musculoskeletal conditions.