A stethoscope for the knee: Investigating joint acoustical emissions as novel biomarkers for wearable joint health assessment

Abstract

Each year, millions of Americans endure knee injuries, ranging from simple sprains to ligament tears requiring surgical intervention. Our team is investigating wearable rehabilitation assessment technologies for patients recovering from knee injuries based on the measurement and analysis of the acoustical emissions from the knees. Using miniature electret microphones combined with piezoelectric sensors placed on the surface of the skin at the knee, we measure the sounds from the joint as subjects perform basic flexion/extension exercises and standardized sit-to-stand protocols. We then analyze the consistency of the knee acoustical emissions in the context of the activity, and the angle of the joint, to quantify the health of the joint. We have found, in early pilot studies, promising results differentiating the healthy versus injured knee, and longitudinal changes progressing from acute injury and recovery following rehabilitation. We have also determined that, in healthy subjects, the pattern of acoustic emissions is consistent within several repetitions of a movement, and for multiple recordings throughout the day (r > 0.88). Knee acoustic emissions combined with angle measurements provide promising in-depth information regarding joint health and exciting new opportunities for personalized rehabilitation protocols following injury.