"Bamboo spine" is seen in

Ans. a (Ankylosing spondylitis). (Ref. Sutton Textbook of Radiology, 6th ed., 1220)RADIOGRAPHIC FINDINGS OF ANKYLOSING SPONDYLITIS# Radiographically demonstrable sacroiliitis is usually present in AS.# The earliest changes by standard radiography are blurring of the cortical margins of the subchondral bone, followed by erosions and sclerosis.# Progression of the erosions leads to "pseudowidening" of the joint space; as fibrous and then bony ankyloses supervene, the joints may become obliterated.# The changes and progression of the lesions are usually symmetric.# In the lumbar spine, progression of the disease leads to straightening, caused by loss of lordosis, and reactive sclerosis, caused by osteitis of the anterior corners of the vertebral bodies with subsequent erosion, leading to "squaring" of the vertebral bodies. (The Anderson & Romano's lesions)# Progressive ossification leads to eventual formation of marginal syndesmophytes, visible on plain films as bony bridges connecting successive vertebral bodies anteriorly and laterally - 'the bamboo-spine' appearance.# In mild cases, years may elapse before unequivocal sacroiliac abnormalities are evident on plain radiographs. Dynamic MRI is the procedure of choice for establishing a diagnosis of sacroiliitis.MRI is highly sensitive and specific for identifying early intra-articular inflammation, cartilage changes, and underlying bone marrow edema in sacroiliitis.