Least helpful investigation in the diagnosis of spondylolisthesis?
A. AP view X-ray
B. Lateral view X-ray
C. MRI scan
D. CT scan
Correct answer : A. AP view X-ray
Diagnosis of spondylosisthesis is obtained on lateral plain films of the lumbar spine performed in upright positin, CT with sagittal reformations or sagittal MR imaging of the lumbar spine.
Ref: Spondylolysis, spondylolisthesis, and degenerative spondylolisthesis By Robert Gunzburg, Marek Szpalski (via google books)
Use of AP view X-ray in spondylolisthesis:
The inverted Napoleon hat sign is seen on the AP radiograph of the spine at the level of the fifth lumbar vertebra and the sacrum in severe high grade spondylolisthesis and / or severe lumbar lordosis.