What is the most likely diagnosis for a patient with a history of SI joint pain and "bamboo spine" on X-ray?

• A. Osteoarthritis
• B. Rheumatoid arthritis
• C. Ankylosing spondylitis
• D. Herniated nucleus pulposus

Answer: (C)

The most likely diagnosis for a patient with a history of sacroiliac joint pain and "bamboo spine" observed on X-ray is ankylosing spondylitis. This condition is characterized by chronic inflammation of the spine and the sacroiliac joints, leading to progressive stiffness and eventual fusion of the vertebrae, which is visually represented by the "bamboo spine" appearance on imaging studies.

Ankylosing spondylitis typically affects younger individuals, often in their late teens to thirties, and is associated with the HLA-B27 antigen. The SI joint pain is an early symptom, and over time, as inflammation persists, it can lead to significant postural changes and loss of motion. "Bamboo spine" describes the radiological finding of fused vertebrae resembling the appearance of bamboo, which is a hallmark of chronic inflammatory changes in the spine associated with this condition.

In contrast, osteoarthritis primarily affects weight-bearing joints and presents with different radiological features. Rheumatoid arthritis is more systemic and usually affects multiple joints symmetrically, including the hands and feet, and does not typically cause the bamboo spine appearance. A herniated nucleus pulposus would present with different symptoms such as rad