Mean heights along the vertebral rim of the superior vertebral endplates (ascending syndesmophytes) and of the inferior endplates (descending syndesmophytes) of the tallest syndesmophyte in each angular sector, averaged over all vertebral levels. Heights were standardised to the height of the intervertebral disc space, so that values of 0 represent no syndesmophyte and 1.0 represent bridging. A, anterior; AL, anterolateral left; AR, anterolateral right; IDS, intervertebral disc space; P, posterior; PL, posterolateral left; PR, posterolateral right.