Defining spinal mobility in ankylosing spondylitis (AS). The Bath AS Metrology Index.

Abstract To determine the most appropriate clinical measurements for the assessment of ankylosing spondylitis (AS) to develop the new metrology index. One hundred and ninety-three individuals with AS were studied. The patients reflected the entire spectrum of cases of AS. Metrology was performed on 327 occasions. First the metrology (20 measurements) of 43 patients was analyzed. From this, 5 simple clinical measurements were defined which most accurately reflect axial status: cervical rotation, tragus to wall distance, lateral flexion, modified Schober's, and intermalleolar distance. These measurements were assessed for reliability, speed and both inter and intraobserver variability in another 40 patients. Analysis of the first group of 43 patients and a subsequent group of 54 patients, using the 5 measurements that constitute this new Bath AS Metrology Index (BASMI), demonstrated that they accurately and reliably mirror the 20 clinical measurements assessed previously (r = 0.92, p