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Accurate internal-external rotation measurement in total knee prostheses: A magnetic solution
Arash Arami1, Jenifer Miehlbradt, Kamiar Aminian
1Ecole Polytechnique Fédérale de Lausanne, Laboratory of Movement Analysis and Measurement, Lausanne, Switzerland. arash.arami@epfl.ch
Journal of Biomechanics
|June 16, 2012
Summary
This study introduces a novel magnetic measurement system for precise internal-external (IE) knee rotation assessment in prosthetic knees, overcoming soft tissue artifact limitations. The system offers accurate IE angle measurement with low dynamic RMS error, enhancing prosthetic performance monitoring.
Area of Science:
- Biomechanics
- Biomedical Engineering
- Orthopedic Technology
Background:
- Accurate measurement of internal-external (IE) rotations is crucial for assessing prosthetic knee function.
- Soft tissue artifacts commonly impede precise IE rotation measurements in clinical settings.
- Existing methods for IE rotation measurement in prosthetics lack the desired accuracy and reliability.
Purpose of the Study:
- To develop and validate a novel magnetic measurement system for accurate in-vivo measurement of internal-external (IE) knee rotations in prosthetic knees.
- To evaluate different sensor configurations and angle estimators for optimal IE rotation measurement.
- To assess the system's performance against a gold-standard stereophotogrammetry system and analyze its sensitivity to measurement noise.
Main Methods:
- A magnetic measurement system comprising a permanent magnet and magnetic sensors was designed for implantation in knee prostheses.
- Two distinct sensor configurations (one-sensor and two-sensor) were developed.
- Five angle estimators were defined and tested using static and dynamic measurements, compared against stereophotogrammetry, and subjected to noise analysis.
Main Results:
- The one-sensor configuration achieved a dynamic RMS error of 0.49° with a noise range of ±0.53°, offering a lower power budget.
- The two-sensor configuration, despite doubling power consumption, yielded a slightly lower dynamic RMS error of 0.37° and a noise range of ±0.42°.
- The two-sensor configuration provides redundancy, enhancing system reliability in case of sensor damage.
Conclusions:
- The developed magnetic measurement system accurately measures internal-external knee rotations in prosthetics without soft tissue artifacts.
- Both one-sensor and two-sensor configurations demonstrate high accuracy, with the two-sensor system offering improved precision and reliability.
- This technology has the potential to significantly improve the monitoring and optimization of prosthetic knee function.
