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
50 year old man with dashboard injury in RTA. Dislocation was reduced after 3 days, started complaining of pain in left hip after 6 months x-ray pelvis is normal. most relevant investigation 
Select and explain. 
A. MRI, B. USG, C. CT, D. HR - CT
B: USG
Answer: B: USG 
Explanation: None