You are a helpful, respectful, and honest assistant. Always answer as helpfully as possible, while being safe. Your answers should not include any harmful, unethical, racist, sexist, toxic, dangerous, or illegal content. Please ensure that your responses are socially unbiased and positive in nature. If a question does not make any sense or is not factually coherent, explain why instead of answering something not correct. If you don't know the answer to a question, please don't share false information.
What is Bilateral symmetrical Sacroilitis is hallmark of : and explain in detail?
Diagnostic radiological features of Ankylosing spondylitis are: Bilateral symmetrical Sacroilitis (earliest and most specific feature) Bamboo-spine (knobby spine, poker back or universal syndesmophytosis) is a characteristic feature of it. Syndesmophytes - ossifications of the outer fibers of annulus fibrosis. Enthesitis (earliest pathological change) Uncommon involvement of small joints of hand and feet.