Functional calibration procedure for 3D knee joint angle description using inertial sensors.

Area of Science:

• Biomechanics
• Kinesiology
• Medical Instrumentation

Background:

• Accurate 3D knee joint angle measurement is crucial for clinical evaluation and treatment comparison.
• Existing motion capture systems are often lab-bound, necessitating ambulatory solutions for routine practice.
• Inertial Measurement Units (IMUs) show potential for unconstrained knee joint orientation tracking.

Purpose of the Study:

• To develop and validate a novel calibration procedure for IMU-based 3D knee joint angle measurement.
• To adapt the calibration for the joint coordinate system (JCS) using only IMU data.
• To assess the repeatability and accuracy of the proposed method during gait.

Main Methods:

• A new functional calibration procedure utilizing active and passive movements was developed.
• Eight healthy subjects participated in the study.
• The system's performance was evaluated against a reference system during gait, assessing repeatability and measurement errors.

Main Results:

• The calibration procedure demonstrated high repeatability (offset < 1°, SD < 0.3°, CMC > 0.9).
• The system achieved high precision (SD < 2°, CC > 0.75) and moderate accuracy (4.0°–8.1°) for 3D knee angles compared to the reference.
• The IMU-based system combined with the functional calibration is a promising tool for ambulatory knee motion analysis.

Conclusions:

• The proposed IMU-based system and functional calibration offer a reliable method for measuring 3D knee joint angles in ambulatory settings.
• This approach provides a practical tool for clinical examination and monitoring therapeutic interventions.
• The methodology is adaptable for assessing other complex joints like the ankle and elbow.