Discovering Associations between Acoustic Emission and Magnetic Resonance Imaging Biomarkers from 10 Osteoarthritic Knees

Abstract

Objective: Acoustic emission (AE) sensed from knee joints during weight-bearing movements greatly increases with joint deterioration, but the relationship between AE patterns and specific anatomical damage, as seen for example in magnetic resonance imaging (MRI), is unknown. This knowledge is essential to validate AE biomarkers for the evaluation of knee joints, and forms the objective of this exploratory work to associate knee AE and MRI. Methods: A novel processing framework is proposed to enable direct correlation between static 3D MRI of knees and their dynamic 1D AE during sit-stand-sit movements. It comprises a method to estimate articular cartilage thickness according to joint angle from knee MRI, and a method to derive statistically representative waveform features according to joint angle from movement and load-dependent knee AE. Results: In 10 subjects diagnosed with knee osteoarthritis, age 55 similar to 79 years and body mass index 25 similar to 35 kg/m(2), a strong inverse relationship between knee AE and cartilage thickness in the medial tibiofemoral compartment around the fully standing position was observed. Knees with thinner articular cartilage generated more AE with higher amplitude, greater energy, longer duration, and higher frequencies, in agreement with the assumption of more intense articulation friction under full body weight. Conclusion: AE provides promising quantitative biomarkers in knee joint disease. Significance: These findings provide impetus for the further development of AE as a low-cost non-invasive biomarker modality to improve the management of knee joint disease.