This is a real-world medical entrance exam question, please give the true answer based on the question and selection. Topic name: None, Subject name: Orthopaedics
Syndesmophytes are seen in - 
Select and explain. 
A. AS, B. RA, C. OA, D. All
A: AS
Answer: A: AS 
Explanation: Syndesmophytes 

Syndesmophytes are thin, slender vertical radiodense spicules bridging the vertebral bodies, giving the spine `bamboo' appearance. They are actually ossification of outer fibres of annulus fibrosus.

Syndesmophytes are seen in :

Ankylosing spondylitis
Psoriatic arthritis
Reiter's disease
Arthritis associated with Inflammatory bowel disease