22nd June 2023

An 82-year-old gentleman presents with a three-week history of lumbar back pain to the emergency department.

An 82-year-old gentleman presents with a three-week history of lumbar back pain to the emergency department. He is now using a walking stick, having previously been ambulant fully unaided. He has a history of prostate cancer, treated with radical radiotherapy 12 years ago, ischaemic heart disease, hypertension, and type 2 diabetes mellitus. He has bilateral lower limb weakness (power 4/5) and a palpable bladder. What is the most important investigation?