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
[{'content': 'Least helpful for the diagnosis of spondylolisthesis - \nSelect and explain. \nA. AP x-ray of spine, B. Lateral x-ray of spine, C. MRI, D. CT', 'role': 'user'}, {'content': 'Answer: A \nExplanation: 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.\nOn the other hand lateral x-ray, CT and MRI (sagittal view) diagnose even the mildest degree of spondylolisthesis.\nIt is worth noting that spondylolysis (not spondylolisthesis) may be missed on lateral x-ray and MRI. CT scanning is more sensitive in diagnosing spondylolysis.', 'role': 'assistant'}]