Proposal and Validation of a Knee Measurement System for Patients With Osteoarthritis

Objective: Currently most measurements of knee joint function are obtained through observation and patient-reported outcomes. This paper proposes an implementation and validation of a knee monitor to measure quantitative joint data in multiple degrees of freedom. The proposed system is configurable with minimal patient interaction and no frame-alignment calibration procedure is required for measurement after visually placing/replacing sensors on patients. Methods: A mobile software system was developed using a method of extracting clinical knee angles based on attitude estimations from independent wearable sensors. Validation was performed using a robot phantom and results were compared with a gold standard motion capture system. Two instrumentation placements (lateral and posterior) were examined. Results: A posterior sensor placement was determined to provide the most repeatable results through multiple degrees of freedom and measurement accuracy approached a gold standard motion capture technology with low root-mean-square error (flexion: 3.34°, internal/external rotation: 2.18°, and varus/valgus: 1.44°). Conclusion: The proposed system is simple to use and convenient for use in ambulatory or unsupervised environments for joint measurement; however, it was shown that accuracy can be sensitive to sensor placement. Significance: This system would be beneficial for obtaining quantitative patient data or tracking functional activity in variable environments, providing clinicians with indications of how patients' knees function during activity, potentially permitting more individualized care and recommendations.