Which of the following is a typical x-ray finding of ankylosing spondylitis?

A typical x-ray finding of ankylosing spondylitis is sacroiliitis. This condition commonly involves inflammation of the sacroiliac joints, which are located where the sacrum and pelvis meet. On imaging, sacroiliitis may be observed as changes in the joint spaces and erosions at the sacroiliac joint.

The radiographic characteristics of ankylosing spondylitis often progress from identifiable inflammation, such as sacroiliitis, to changes associated with new bone formation and fusion of the vertebrae, leading to the classic "bamboo spine" appearance. Detecting sacroiliitis is crucial since it is one of the earliest signs of ankylosing spondylitis and plays a critical role in diagnosis.

In contrast, the other choices do not typically characterize this disease. Osteophytes are usually seen in degenerative joint diseases, but not in ankylosing spondylitis. Fracture lines are indicative of trauma or severe osteoporosis rather than a chronic inflammatory condition like ankylosing spondylitis. Soft tissue swelling does not specifically correlate with the hallmark findings of this type of spondyloarthritis. Thus, recognizing the presence of sacroiliitis on x-rays is