CD9 and juvenile polyposis syndrome: Thus, in patients whose abundance of CD9+ EVs is above this threshold, aseptic loosening of the endoprosthesis can be predicted with a sensitivity of 58.8%, a specificity of 100, a total misclassification rate of 20.6%, and a false negative rate of 41.2%, indicating that a substantial number of PJI cases remained undetected using CD9+ EVs alone.