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A comparison of intersegmental joint dynamics to isokinetic dynamometer measurements
K R Kaufman1, K N An, E Y Chao
1Motion Analysis Laboratory, Children's Hospital, San Diego, CA 92123, USA.
Journal of Biomechanics
|October 1, 1995
Summary
This study found significant errors in isokinetic dynamometer measurements for knee motion and moment. These devices may not accurately capture knee joint dynamics during testing.
Area of Science:
- Biomechanics
- Kinetics and Kinematics
- Human Movement Analysis
Background:
- Isokinetic dynamometers are widely used for assessing knee joint function.
- Accurate measurement of knee motion and joint moments is crucial for clinical evaluation and research.
- Potential errors in dynamometer measurements can impact diagnostic and therapeutic outcomes.
Purpose of the Study:
- To quantify measurement errors of an isokinetic dynamometer for knee evaluation at different angular velocities (60°/s and 180°/s).
- To compare dynamometer-derived kinematics and kinetics with those calculated using inverse dynamics.
Main Methods:
- Five healthy subjects performed knee flexion and extension exercises on an isokinetic dynamometer.
- Kinematics were measured using a triaxial electrogoniometer.
- Reaction forces were measured with a custom load cell, and inverse dynamics were applied to calculate knee joint intersegmental dynamics.
Main Results:
- Isokinetic dynamometer underestimated knee flexion by 7-9° and overestimated extension by 10-13°.
- Knee moment errors were 5 Nm during flexion and 25-29 Nm during extension.
- Gravity correction improved extension moment accuracy but worsened flexion moment accuracy.
Conclusions:
- Isokinetic dynamometers exhibit notable errors in measuring knee motion and joint moments.
- These inaccuracies may affect the reliability of assessments, particularly during extension.
- Further research is needed to refine measurement techniques and improve the accuracy of isokinetic testing.