The characteristic X-ray manifestation of ankylosing spondylitis is sacroiliac arthritis, which manifests as worm-like destruction of the sacroiliac joint area, like a worm bite, one nest at a time. This can lead to a narrowing of the sacroiliac joint space and eventually to a complete fusion of the sacroiliac joint without a single gap. Therefore, the manifestation of ankylosing spondylitis X-ray can be roughly divided into 4 stages: stage I partial worm-like changes, stage II most of the worm-like changes, stage III worm-like changes of the entire joint, combined with the narrowing of the joint space, and stage IV complete fusion of the sacroiliac joint.