Syndesmophytes are seen in -: (A) AS, (B) RA, (C) OA, (D) All
Answer is A. 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