<prompt> Least helpful for the diagnosis of spondylolisthesis -AP x-ray of spineLateral x-ray of spineMRICT  <response>: All the given radiological investigations are used for spondylolisthesis. However, AP x-ray of spine is least helpful as in low grades of spondylolisthesis it may be normal.On the other hand lateral x-ray, CT and MRI sagittal view diagnose even the mildest degree of spondylolisthesis.It is worth noting that spondylolysis not spondylolisthesis may be missed on lateral x-ray and MRI. CT scanning is more sensitive in diagnosing spondylolysis. 