Figure 1.

Joint acoustic emission overview. (A) A healthy knee articulates smoothly due to its smooth cartilage and appropriate amount/constituency of synovial fluid. This smooth articulation creates a noise-like JAE (blue). In JIA, thickened/inflamed synovium with excessive joint effusions, cartilage loss and/or bone erosions may be observed. These changes are hypothesized to create a JAE with several large spikes (red). (B) To record the knee JAEs, two contact accelerometers were placed on each child's knees. They viewed and replicated the movements in an instructional cartoon during JAE recording such that their movement speed and range of motion was controlled. (C) The resulting JAEs were split into their approximately ten component cycles. Forty-nine features were calculated to describe these cycles. The features, subject numbers, and clinically determined disease status were fit to a feature matrix. (D) Using logistic regression and LOSO-CV, the probability of each cycle belonging to JIA were calculated. The average of those cycle probabilities is used as a “joint health score” to indicate the severity of JIA. If the majority of cycles for a given subject had a probability of JIA ≥ 0.5, that subject was classified as having JIA.