Performance of ultrasounds compared with radiographs to detect chronic enthesitis signs in patients with ankylosing spondylitis.

To assess the performance of ultrasound in detecting erosion, swelling, and new bone comparing to radiographs in five lower limb entheses in patients with ankylosing spondylitis (AS). Prospective study of 60 patients meeting modified New York criteria for AS. Lateral radiographs of both knees and ankles followed by a high-resolution Doppler ultrasound examination with a high-frequency (15 MHz) linear probe were performed. Ultrasound had an excellent sensitivity, but specificity was very weak compared to radiographs for erosion, swelling, and new bone formation. Negative and positive predictive values were good only for erosion. Ultrasound seems to be a performant instrument in detecting signs of chronic enthesitis particularly when radiograph is normal.