Radiologic changes of ischial tuberosity in ankylosing spondylitis.

The objective of the paper was to emphasize the meaning of involvement of ischial tuberosity in ankylosing spondylitis, enriching the clinical picture of the disease and pointing to ankylosing spondylitis, especially when sacroiliitis is absent or less developed. Radiologic examination of ischial tuberosity was performed in 68 patients with different developmental stages of ankylosing spondylitis. There were 66 (97%) men and two (3%) women, aged 30 to 56 years. Anteroposterior radiographs of the pelvis were performed in all patients and independently assessed by two radiologists. The radiologic changes of ischial tuberosity were classified into four stages: 1) stage of minimal changes, 2) stage of destructive changes, 3) stage of reconstructive changes, and 4) stage of ossification of tendon fibers in the form of rumpled tufts. Radiologic changes of enthesitis were found on ischial tuberosity in 31 patients (45.5%, p < 0.01). Stage 1 or minimal changes were found in two (6.5%); stage 2 or destructive changes in 13 (42.0%); stage 3 or reconstructive changes in 11 (35.5%) and stage 4 or "tufts phenomenon" in five (16.0%) patients. The classification of changes is useful for the assessment of disease range and progression as well as for the diagnosis when sacroiliitis is obscurely developed and other radiologic signs are not present.